NBS

Reference PubnNATL INST. OF STAND & TECH CatJOOS

AlllDS Tfi333M

\ NBS TECHNICAL NOTE 1043

'"ffAU Ot *

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

100

U5753

NO. 1043

1981
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act ot Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity m

trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

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agencies; develops, produces, and distributes Standard Reference Materials; and provides

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THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

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'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. 'Some divisions within the center are located at Boulder, CO 80303.
MATIONAI^ BUREAU

or STAMDAKDa

UBBART

AUG 1 1981

The Characterization of a°:r

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Optical Fiber Waveguides

A Bibliography with Abstracts, 1970 - 1980

no. 10^1

Edited by

G.W. Day

Electromagnetic Technology Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

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U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued June 1981
NATIONAL BUREAU OF STANDARDS TECHNICAL NOTE 1043

Nat. Bur. Stand. (U.S.), Tech. Note 1043, 72 pages (June 1981)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON 1981

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

Price $4.25 (Add 25 percent for other than U.S. mailing)
CONTENTS

Page INTRODUCTION 1

1

.

GENERAL TOP ICS 3 1.1 Review Papers 3 1.2 Multiple Parameters 3

2. ATTENUATION MEASUREMENTS 10

2 .

1

General 10 2.2 Di rect Methods 11 2.3 OTDR Methods (See also 5.3) 14 2.4 Other Methods 18

3. BANDWIDTH/DISTORTION MEASUREMENTS 21

3 .

1

General 21 3.2 Time Domain Methods 23 3.3 Frequency Domain Methods 30 3.4 Other Methods 34

4. INDEX PROFILE MEASUREMENTS (FIBERS AND PREFORMS) 36 4.1 General 36 4.2 Interferometric Methods (Longitudinal) 37 4.3 Interferometric Methods (Transverse) 39 4.4 Other Transverse Methods 41 4.5 Near-Field Methods 45 4.6 Reflection Methods (Longitudinal) 47 4.7 Other Methods 48

5. CHARACTERIZATION OF DISCONTINUITIES

(JOINTS, SPLICES, CONNECTORS, COUPLERS, DEFECTS) 49

5 .

1

General 49 5.2 Insertion Methods 50 5.3 OTDR Methods (See also 2.3) 51

6. MODAL CHARACTERIZATION OF MULTIMODE FIBERS 53

7. GEOMETRIC MEASUREMENTS 56

8. FIELD MEASUREMENTS 61

9. SINGLE MODE FIBER CHARACTERIZATION 62

The Characterization of Optical Fiber Waveguides

A Bibliography with Abstracts, 1970 - 1980

Edited by

G. W. Day

National Bureau of Standards

Boulder, CO 80303

This bibliography contains approximately 450 citations of papers concerning the characterization of optical fiber waveguides. Papers from scientific journals, trade journals and conferences

are included along with book chapters. The citations are organized by parameter measured and mea- surement method. Where published abstracts are available they are included.

Key words: Bibliography, measurements, optical fibers, optical communications.

INTRODUCTION

Since the theoretical work of the mid-sixties

and the experimental break-through of a decade ago, the literature of optical fiber communications has grown at an accelerating rate and is now vast. Examination of the 1980 subject index of the journal

Applied Optics , for example, shows that "Fiber

Optics" is by far the largest subject category and comprises several percent of the total content of the volume.

Specialists in optical communciations generally

recognize that the characterization of the transmission medium, the fiber itself, is among the more challenging and important problems in the field. The published literature reflects an emphasis in this area as does the level of participation and attendance at conferences devoted specifically to the topic* The growing interest in measurement

standards observed by several national and international standards groups is another indication of the importance of the problem.

There are as yet no comprehensive books treating the subject of fiber measurements; neither are there many extended review articles. This places newcomers to the field, especially those who must

quickly learn to specify components and design sys- tems, at a particular disadvantage. The main purpose of this bibliography is to assist such individuals to identify and organize the published

literature. It should also be useful as a guide and reference document to those more experienced.

The scope of this bibliography is limited to the optical properties of fiber and connecting

devices. Mechanical characterizations are excluded

except for the geometric parameters of the core and cladding because of their intimate relation to optical properties. Most of the papers deal rather spe- cifically with measurement techniques. Some theoretical and analytical papers that directly support measurement techniques are also included.

The listings were compiled from several sources. The Engineering Index and Physics Ab- stracts were consulted as were the annual indices of journals in which papers on fiber measurements fre- quently appear. Lists of references from the more extensive review articles were another source. Papers from conferences are included whenever they

contain substantial technical information and when

the digest or proceedings is, in the editor's judgment, readily available.

The final product is a comprehensive but not exhaustive compilation of the literature. Numerous

papers, some of which may be very important, have undoubtedly been overlooked. The editor begs the forgiveness of both the authors of those papers and

the reader who may thus miss useful information.

*To date three such topical meetings have been held in different countries. They are as follows: Symposium on Optical Fiber Measurements - 1980, Boulder, Digest published as NBS-SP-597 by the U.S. Govt. Printing Office. Messtechnik in der optischen Nachrichtentechnik, Berlin, 1980, Digest published by VDE-Verlag GmgH.

Colloquium on Measurement Techniques for Optical Fibre Systems, London, 1979, Digest published by lEE.
The basic organization is by measurement para- meter. When those categories are large they are subdivided by measurement method. Entries are in inverse chronological order by year and alphabetical order by author within a given year. There are no duplicate entries. The reader is therefore cau- tioned to look for specific material in all of the appropriate sections. Useful material on OTDR techniques, for example, could appear in sections 1.1,

1.2, 2.1, 2.3, and 5.3.

The citation format for journal articles

follows fairly closely the ANSI standard using journal abbreviations recommended by the AIP: Journal Abbreviation vol. #: inclusive pg. #s; year

Conference publications take the form:

Type of pub., Conf. Name, Location: inclusive

pg. #s; year, Publisher

Book chapters take the form:

In "Book Title", Author or Editor, Publisher, year

Papers in languages other than English are indicated

by the original language title followed by the translated title. English abstracts are included where available.

The editor is greatly indebted to Thinh Q. Sam

for assuming much of the routine work of compiling

this bibliography and to Victoria R. Schneller of

the National Oceanic and Atmospheric Administration

Library, Boulder, for assistance in the literature

search.
1. GENERAL TOPICS

1.1 Review Papers

B. Costa and B. Sordo

Fibre characterization

In "Optical fibre communications". Technical Staff

of CSELT, McGraw Hill, 1980

P. L. Chu

Measurements in optical fibres

Proc. TREE Aust. 40:102-114; 1979

Various measurements of optical fibre characteristics are reviewed. These include measurements of attenuation, pulse distortion, fibre bandwidth, mode dependent attenuation, refractive index profile and fibre diameter. Emphasis is given to those methods

which have not been reported in great detail in other review papers on similar topics.

Leonard G. Cohen, Peter Kaiser, Paul D. Lazay, and Herman M. Presby

Fiber characterization

In "Optical fiber telecommunications", S. E. Miller

and A. G. Chynoweth, eds.. Academic Press, 1979

Felix P. Kapron, K. Scott Gordon, and Francis M. E. Sladen

Measurement techniques for passive optical components

Conf. Rec, Int. Conf. Conmun. 36.5.1-36.5.6; 1979, IEEE Boston,

Passive optical components in fiber communications

systems include source-to-fiber couplers, the fiber,

fiber-to-fiber joints, directional couplers, and wavelength-selective devices. This paper will con- sider the component specifications necessary for accurate systems design. Attenuation alone is in- sufficient to predict signal deterioration, but dis- persion and often backscattering must also be taken

into account.

Measurements suitable for the determination of the above specification parameters are presented along

with numerous references. Generally, it is found

that the performance of a passive component depends

upon its location within a fiber link and upon the nature of the components it interfaces with. Passive device parameters are therefore both intrinsic

and extrinsic, and specifications must necessarily

include a description of measurement conditions - at least until such conditions are standardized within

the industry.

Carlo G. Someda

Experimental evaluation of optical fibers: A review

In "Fiber and Integrated Optics," D. B. Ostrowsky,

ed.. Plenum Press, 1979 *****

0. Krumpholz

Measuring parameters of fibres and fibre cables

Proc, Third Eur. Conf. Opt. Commun., Munich, 38-42;

1977

The most important parameters of an optical fibre waveguide are attenuation, numerical aperture,

refractive index profile, core diameter, and pulse response or frequency basebandwidth. Various tech- niques to determine these characteristics have been evaluated and are discussed.

Michael K. Barnoski and S. D. Personick

Measurements in fiber optics

Proc. IEEE 66:429-441; 1978

Recent advances in optical-fiber technology dictate

that attention must be given to establishing accurate and precise measurement techniques. In this paper measurements currently employed to determine

the characteristics of optical fiber waveguides are reviewed. Included in the review are techniques for measuring attenuation, delay distortion, refractiveindex profile, fiber diameter, and mechanical

strength. Since establishment of accurate measurement procedures cannot be accomplished without some knowledge of the physical mechanisms controlling the parameters to be measured, a brief review of the dominant causes of attenuation and modal delay in fibers is also included.

1.2 Multiple Parameters

F. Bigi and G. Bonaventura

CCITT studies on optical fibres cables measurements

Tech. Digest, Symp. Optical Fiber Meas.-1980, 129-

135; 1980, U.S. Govt. Printing Office

*****

J. F. Clarke and I. Mackenzie

A microprocessor based system for characterisation

of optical fibres

Digest, Mess, in der opt. Nachrichten. , Berlin, 47-

52; 1980, VDE-Verlag
L. G. Cohen and S-J. Jang M. Kaiser

An interrelationship between loss and dispersion in multimode fibers

Tech. Digest, Symp. Optical Fiber Meas.-1980, 55-58;

1980, U.S. Govt. Printing Office.

Universelle Messanordnung fur Faser-Lichtleiter

(Universal measurement arrangement for fiber lightguide)

Digest, Mess, in der opt. Nachrichten. , Berlin, 90- 95; 1980, VDE-Verlag

Leonard G. Cohen, Peter Kaiser, and Chinlon Lin

Experimental techniques for evaluation of fiber transmission loss and dispersion

Proc. IEEE 68:1203-1213; 1980

This paper describes state-of-the-art measurement

techniques for the characterization of fiber loss

and dispersion. Special emphasis is placed on the achievement of high measurement accuracy, and on

novel techniques to determine the loss and dispersion of single-mode and graded-index fibers in the

0.8 to 1.7-iin wavelength region where fiber loss and

material dispersion are both small.

W. E. Freyhardt

Betriebsmessverfahren fur Lichtwellenleiter und optische Kabelstrecken (Working measurement procedures for optical waveguide and optical cable links)

Digest, Mess, in der opt. Nachrichten., Berlin, 53-

61; 1980, VDE-Verlag

M. Hof

Das "Optical Time Domain Reflectometer" zur Messung

von Dampfung, Modemixing, Kopplungsverlusten, etc.,

an Fiberoptik-Kabeln (The optical time domain reflectometer for measuring attenuation, modemixing,

coupling losses, etc., in fiberoptic cable)

Digest, Mess, in der opt. Nachrichten., Berlin, 41-

45; 1980, VDE-Verlag

G. Thomas Holmes

Propagation parameter measurements of optical waveguides

SPIE 224:138-143; 1980

Improvements in optical waveguide manufacturing pro- cesses have reduced the attenuation rate to approximately the material limit imposed by Rayleigh scat- tering. Today there is a need to develop measurement techniques or procedures which can be used to predict the overall system insertion loss and bandwidth. Multimode propagation in graded waveguides

makes it difficult to define the attenuation rate

and bandwidth without referencing the particular

source power distribution used in making the measurement. This paper will discuss the problems in making these measurements and will present a recent

model and results which can be used to predict sys- tem performance.

F. P. Kapron, F. M. E. Sladen, P. M. Garel-Jones, D.

G. Kneller

Attenuation and pulse broadening along concatenated

fiber links

Tech. Digest, Symp. Optical Fiber Meas.-1980. 63-66;

1980, U.S. Govt. Printing Office

R. Th. Kersten and T. Le-Hiep

Messung von Faserreigenschaften im Wellenlangenbereich 0.85 bis 1.7 um (Measurements of fiber char- acteristics in the wavelength range from 0.85 to 1.7 m)

Digest, Mess, in der opt. Nachrichten., Berlin, 66-

71; 1980, VDE-Verlag

F. Krahn and D. Rittich

Messtechnik fur optische Nachrlchtentechnik bei hoheren Wellenlangen (Measurement techniques for

optical telecommunications at longer wavelengths)

Digest, Mess, in der opt. Nachrichten., Berlin, 45- 46; 1980, VDE-Verlag

R. E. Love

Waveguide fiber standards

Tech. Digest, Symp. Optical Fiber Meas.-1980, 135- 143; 1980, U.S. Govt. Printing Office

E. F. Murphy, R. W. Lapierre, C. F. Laing

Industrialized system for the automated measurements

of the optical properties of waveguide fibers

Tech. Digest, Symp. Optical Fiber Meas.-1980, 105-

111; 1980, U.S. Govt. Printing Office

F. Scudieri

Differential interferometric method for optical fiber testing

Appl. Opt. 19:404-408; 1980

A new differential interferometric method of deter- mining the optical characteristics of cylindrical

systems is presented. In particular it is applied

to the study of a step-index optical fiber where
small changes in geometric and optical characteristics have been introduced.

M. P. Smid

The preparation of standards for "optical fibers and

cables" within the International Electrotechnical

Commission

Tech. Digest, Symp. Optical Fiber Meas.-1980, 121-

127; 1980, U.S. Govt. Printing Office

Bruno Costa

Comparison between various fibre characterization

techniques

Proc. (Supp.), Opt. Commun. Conf., Amsterdam, II-1--

II-5; 1979

B. L. Danielson, G. W. Day, and D. L. Franzen

Propagation measurements in rmiltimode optical wave- guides

Proc, Fiber Opt. Comm.-78, 205-207; 1979, Information Gatekeepers

This talk provides an overview of the difficulties

associated with adequate propagation measurements.

Work at NBS and other laboratories is reviewed.

G. W. Day

Fiber measurements: Quality and cost

Proc, Int. Conf. Commun. Boston, 10.4.1-10.4.3;

1979, IEEE

Several points which should be considered by groups writing standard measurement procedures for optical

fiber waveguides are discussed. These include the quality of measurements, the factors limiting that

quality, the prospect for improvement, and the cost

of measurements. Some of the points are illustrated

with data from measurement comparisons.

M. Eriksrud, A. Hordvik, N. Ryen, and G. Nakken

Comparison between measured and predicted transmission characteristics of 12 km spliced graded-index

fibers

Opt. Quantum Electron. 11:517-523; 1979

Cumulative attenuation and dispersion were measured

along a 11.7 km fibre link consisting of 10 spliced

fibres and compared to measurements on the individual fibres. Four different procedures were used

for the loss measurements, and the effect of transient losses in the link provided transient losses

due to high-order modes were eliminated in the indi- vidual measurements. Pulse dispersion measurements

were made without the use of any mode scrambler.

The cumulative dispersion measurements clearly

showed a significant correlation between non-adjoining fibres, and the observed pulse width exhibited

more of a linear than a square root dependence on length.

Ikutaro Kobayashi, Kenji Okada, and Masamitsu Tokuda

Measuring equipment for optical fiber transmission

systems

Rev. Elect. Commun. Lab. (Japan) 27:1029-1048; 1979

Measuring equipments have been designed for use on a field trial of optical fiber transmission systems.

Examination results have been good through their

full use in the field trial.

These developed measuring equipments consist of about fifteen kinds of sets and formulate a hierarchical measuring system for optical transmission

systems.

However, many problems remain to be solved in order

to obtain more accurate results. Many of the problems are closely concerned with the performance or unstableness of optical device used. Many efforts

have been focussed on improving characteristics or searching for measuring methods immune from un- stableness.

F. Krahn, W. Meininghaus, and D. Rittich

Measuring and test equipment for optical cable

Philips Telecomm. Rev. 37:241-249; 1979

This article gives an overview of the instrumentation used in fibre optic communications. It goes

into the properties of equipment required for the field measurement of optical attenuation and dispersion, and for fault location.

I. Nouchi, A. Jacques, and L. D'Auria

Characteristics against length of silicone-clad

silica optical fibres

Electron. Lett. 15:315-316; 1979

The letter is concerned with length dependence of

the transmission characteristics of a low-loss silicone-clad silica fibre (up to 5 km). It is observed that a quasi -steady-state condition (fibre

characteristics independent of launching conditions)

is obtained at 100 m long before true equilibrium

(bandwidth proportional to L"-^'"^) attained at 2.5

km.

Robert W. Ramirez

Evaluating fibers digitally

Laser Focus 15:46-52; April 1979
Masamitsu Tokuda, Tadatoshi Tanifuji, Mitsuhiro

Tateda, and Ikutaro Kobayasi

Far-end measuring methods for transmission charac- teristics of graded index fiber

Conf. Rec, Int. Conf. Commun. 36.2.1-36.2.6; 1979, IEEE Boston,

The optical loss measuring system composed of stable light source (LED), dummy fiber and accurate optical power meters has been developed. Measuring conditions, such as dummy fiber length and cut fiber

length used to measure the input power into measured

fiber, were studied to estimate optical loss of long

spliced fibers from those of each constituent fiber.

A novel far-end automatic measuring system of base- band frequency response based on frequency-domain

techniques has been proposed. Measured fiber (graded index fiber) is excited by step index multimode

fiber. It has been found that the method is excellent in regard to baseband frequency response repro- ducibility. Simple and useful formula has been pro- posed to estimate baseband bandwidth of spliced long

optical fibers from that of each constituent fibers.

It has been determined that transmission characteristics could be measured using far-end measuring

methods by making use of these methods during the field trial

.

M. Eve, P. C. Hensel, D. J. Malyon, B. P. Nelson, J.

R. Stern, J. V. Wright, and J. E. Midwinter

Transmission studies on three graded-index fibre

cable links installed in operational ducts

Opt. Quantum Electron. 10:253-265; 1978

This paper reports the transmission measurements

made on 40 km of graded-index fibre which have been cabled and installed in operational ducts for use in 8 and 140 Mbit s" systems. Extensive loss and bandwidth measurements were made at all stages of the programme, both before and after cabling and also in the field using two mobile test vehicles.

The problems of obtaining meaningful and reproducible measurements are discussed and the stability of the measurements between the various cabling and installation stages is assessed. The results have

been analysed in conjunction with additional laboratory measurements and a number of important propagation effects have been brought to light.

M. Eve, P. C. Hensel, D. J. Malyon, B. P. Nelson, and J. V. Wright

Techniques for measuring the transmission properties

of optical -fibre cables

Post Off. Elect. Eng. J. (GB) 71:122-129; 1978

This article describes the techniques used by the British Post Office to measure the transmission pro- perties of optical -fibre cables, both in the laboratory and in the field. The measurements include the determination of loss, bandwidth and refractiveindex profile. Fault location by the observation

and measurement of backscattered light in the fibre

is also described.

Hienz Friedberg and Werner A. Krai

Grasfaserkabel and Messverfahren (Glass fiber cable

and measurement methods)

Nachrichten Elektronik 32:85-88; 1978

Ikutaro Kobayashi, Yohji Jujii, Nobuo Suzuki, Kohichi Aoyama, and Masaki Koyama

Measuring equipment for an experimental optical

fiber transmission system

Rev. Elect. Commun. Lab. (Japan) 26:712-726; 1978

Measuring equipment have been trial developed for

use on an experimental optical fiber transmission

system. Efforts have been focused on the following

i terns

:

(1) Standardizing measuring methods.

(2) Realizing handy measuring equipment for practical use.

(3) Clarifying inherent problems in measuring fiber

transmission characteristics etc. The developed measuring equipment were fully used

for testing laid fiber cables.

Five fiber measuring equipment have been manufactured for trial

.

(1) Fiber transmission equipment.

(2) Splice and connector monitoring meter.

(3) Spectral loss measurment set.

(4) Material dispersion measurement set.

(5) Optical power meter. Many measuring methods are applicable to one measuring set. Their methods have been compared with each other and one has been chosen in order to minimize

measuring errors.

Manufactured equipment would become prototypes of measuring equipment for practical use in future applications. Through manufacturing these prototypes, practical or inherent problems involved in optical fiber measuring equipment become clear.

Ikutaro Kobayashi and Masaki Koyama

Step-index multimode fiber transmission charac- teristics

Rev. Elect. Commun. Labs. (Japan) 26:500-508; 1978

This stepsulti parti

(1)

(2)

(3)

(4)

(5)

paper reports results of investigating various

index fiber characteristics and formulas reng from measurements and theoretical study. In cular, emphasis is put on the following items: Determining fundamental optical fiber charac- teristics for communication channel use. Accumulating measured data on fiber transfer

functions and other transmission characteristics. Determining fundamental fiber parameters.

Finding feasible optical fiber application

fields. Clarifying inherent optical fiber problems.

Various measured characteristics and their formulas

are shown. They are very important in designing

fiber transmission systems as well as understanding

fundamental fiber characteristics. Through the
fiber investigation, it has also proved important to treat fiber transmission characteristics in the fre- quency domain.

R. E. Love and D. B. Keck

Characteristics of optical fiber waveguides

Opt. Eng. 17:114-119; 1978

The design and performance of optical cables, con- nector hardware and communciation systems are gov- erned by the light transmission and coupling characteristics of waveguide fibers. These characteristics depend upon waveguide design and materials as well as manufacturing tolerances. Measurement methods and limitations are discussed, and use and in- terpretation of waveguide specifications in designing optical links and predicting overall performance

are shown.

K. Mikoshiba and H. Kajioka

Transmission characteristics of multimode W-type

optical fiber: Experimental study of the effect of the intermediate layer

Appl. Opt. 17:2836-2841; 1978

The transmission mechanism of a multimode W-type optical fiber is clarified by the experimental study

of the effect of the intermediate layer on the transmission characteristics. It is shown that control of the layer width is an effective means for achieving the desired loss and bandwidth. A W-type - fiber with a thick intermediate layer has a trans- mission loss on the order of 2 dB/km. To determine

the transmission characteristics of a W-type fiber applicable to system design, the length dependence

of several fiber characteristics is investigated.

Concepts such as splices used as mode scramblers and

the effect of the intermediate layer as a barrier

against OH absorption loss are introduced. The wavelength dependence of microbending loss of a W- type fiber is also described.

William M. Simpson, G. Thomas Holmes, Walter F. Love and Miles E. Vance

Semi -automated measurements of the transmission

medium

SPIE 150:133-150; 1978

The measurement sequence for the characterization of graded-refractive-index optical waveguide fibers in

a manufacturing environment is presented. The sequence has been designed for minimum human inter- action and high throughput. The optical fibers,

characterized by attenuation rate, bandwidth, numerical aperture, and optical core diameter, are mea- sured on a quality assurance system driven by a minicomputer. This semi -automated sysem, consisting

of optical and electronic hardware and software for complete characterization, is described. Finally,

the measurement methods and current test conditions

are presented.

P. W. Black, A. Cook, A. R. Gilbert, M. M. Ramsay,

and J. R. Stern

The manufacture, testing and installation of rugged

fibre-optic cables Proc, Third Eur. Conf. Opt. Commun., Munich, 50-52;

1977

S. Kawakami

New principles to measure loss and mode-conversion

parameters of multimode fibres

Elect. Lett. 13:706-707; 1977

We derive an equation that relates the differences

between the mean transit times of modes of a multimode fibre with loss, multimode dispersion and mode- conversion parameters. The concept of dynamic equilibrium is developed for the temporal difference.

Further, we propose a new method of simultaneous measurement of loss and mode-conversion parameters

which utilises the temporal difference.

E. A. J. Marcatili

Factors affecting practical attenuation and dispersion measurements

Tech. Digest, Opt. Fiber Trans. II, Williamsburg,

TuEl-1—TuEl-4; 1977, Opt. Soc. Am.

T. Matsumoto and I. Kobayashi

Transmission characteristics of a graded-index

multimode fiber

Tech. Digest, IOOC-77, Tokyo: 439-441; 1977

A graded-index multimode fiber is a promising trans- mission line of communication systems because of its wide bandwidth. Its characteristics, however, are said to be critical and depend on some conditions.

In this paper, the characteristic dependence of a graded-index multimode fiber on wavelength and exci- tation conditions is studied experimentally.

Tomoyuki Otsuka, Eizo Miyauchi, and Toshiaki Ogino

Automated measurement system for optical fibers

Fujitsu Sci. Tech. J. (Japan) 13:69-90; 1977

This paper reports on an automated measurement sys- tem which allows rapid and reliable characterization

of optical fibers.

The system consists of five optical measuring setups

for loss spectrum, far-field, near-field, impulse response and baseband frequency response. The system

adopts a minicomputer PANAFACOM U-300 with an interface for data acquisition and data processing con- trolled by FORTRAN based programs.

The average measurement time has been reduced at least to one-tenth compared with that by conventional manual methods. The repeatedly measured results
indicate that loss spectrum can be measured with an accuracy of +0.02--0.15 dB, core and cladding dia- meters of ±1%, refractive index profile constant of ±3%, numerical aperture of ±1%, pulse width and bandwidth of ±14% in terms of standard deviation.

M. Chown and R. Worthington

Measurement of transmission properties of optical fibers

Elect. Commun. 51:242-248; 1976

Now that attenuation in optical fibers has been reduced to a commercially viable level, the early

preoccupation with this parameter is giving way to a study of the more complex parameters concerned with transmission quality.

L. Jeunhomme, A. Cozannet, R. Bouillie, and J. P. Hazan

Mesure des caracteristiques de transmission de con- ducteurs optique (Measurements of the transmission

characteristics of optical conductors)

L'Onde Electron. 56:564-571; 1976

The measurement methods used and the main results obtained in three French laboratories (Laboratoires

de Marcoussis, CNET Lannion, LEP) are presented

here. The measurements of interest here concern mainly the users of optical conductors in transmission systems and therefore, the interest is focused

onto the transmission characteristics. The influence of the measurement conditions on the obtained

result is shown for some specific characteristics

and we deduce conclusions for a better definition

and a normalisation of measurement methods. Especially, measurements performed with the steady-state

launching conditions are seen to be necessary, in order to obtain significant results.

L. Jeunhomme, A. Cozannet, R. Bouillie, Hazanand J. P.

Measurement methods of optical conductors trans- mission characteristics

Digest, Second Eur. Conf. Opt. Fibre Commun., Paris, 123-134; 1976

The measurement methods used and the main results obtained in three french laboratories (Laboratoires

de Marcoussis, CNET Lannion, LEP) are presented

here. The measurements of interest here concern

mainly the users of optical conductors in transmission systems and therefore, the interest is focused

onto the transmission characteristics. The influence of the measurement conditions on the obtained

results is shown for some specific characteristics

and we deduce conclusions for a better definition

and a normalisation of measurement methods. Especially, measurements performed with the steady-state

launching conditions are seen to be necessary, in order to obtain significant results.

J. E. Midwinter

Trends in optical fibre transmission research

Nature 261:371-376; 1976

Recent advances i low loss optical

systems design an ed the fact that propagation of li best, poorly unde

are now being use retical analyses cabled fibres and standing of this

bill ties and its

n the manufacturing technology of fibers have made possible serious

d testing. But this has highlightthe mechanisms involved in the ght in multimode fibres were at rstood. New measurement techniques

d to check more sophisticated theoof propagation in "imperfect" and

are leading to a deeper undernew transmission medium, its possi1 imitations.

L. G. Cohen, P. Kaiser, J. B. MacChesney, P. B. O'Connon, and H. M. Presby

Transmission properties of a low-loss near-para- bolic-index fiber

Appl. Phys. Lett. 26:472-474; 1975

Pulse dispersion, refractive-index profile, and loss measurements were made on a low-loss graded-index

optical fiber fabricated by a chemical vapor deposition technique. The transmission loss spectra had a minimum value of 3.8 dB/km at 1.06-iim wavelength.

The core refractive index had a power-law profile

with an exponential coefficient of 2.2+0.1. Mode- mixing effects and the near-parabolic-index profile

in a 5.6-km extrapolated fiber length (actual length

= 1.12 km) reduced modal dispersion by a factor of

17 from the result expected for an ungraded step- index fiber.

W. J. Stewart

Fibre characterization by use of the relation between the characteristics of leaky modes in optical fibres and the fibre parameters

Proc. , First Eur. 21-23; 1975, lEE Conf. Opt. Fibre Comm., London,

A. H. Cherin, L. G. Cohen, W. S. Holden, C. A. Burrus, and P. Kaiser

Transmission characteristics of three Corning

multimode optical fibers

Appl. Opt. 13:2359-2354; 1974

The loss spectra, refractive-index profiles,

numerical apertures, and pulse dispersion char- acteristics of three multimode optical fibers made

by Corning Glass Works have been measured at Bell Laboratories. The lowest transmission loss, 4.3-6.8

dB/km, was observed at 1.06-um wavelength; in the 0.8-0.9-um spectral region the losses ranged from

6.6 dB/km to 11.6 dB/km. The numerical apertures of the fibers, designated as Nos. 1, 2, and 3, were calculated from the measured refractive-index dif- ferences to be 0.133, 0.157, and 0.121, respectively. Pulse dispersion due to multimode effects in fiber No. 1 (1 km long) was 8.4 nsec at 0.9-ym

wavelength; the valuess were 6.0 nsec for fiber
No. 2 (0.363 km long) and 2.6 nsec for fiber No. 3 (0.290 km).

Donald B. Keck

Spatial and temporal power transfer measurements on

a low-loss optical waveguide

Appl. Opt. 13:1882-1888; 1974

Experimental measurements of the spatial and temporal transfer of power of a 225-m length of low-loss

optical waveguide have been made. In particular, measurement of the angular attenuation showed sub- stantial loss of the high order modes, which re- flected itself in an ~8.2 nsec/km decrease in mea- sured dispersion. Additionally there was a reduction of the effective numerical aperture from 0.15

to 0.12. Negligible mode coupling was observed in this particular waveguide, which allowed a phenomenological calculation of temporal output for an assumed uniform excitation of all modes. This agreed well with experimental measurements. Calculation of this output from knowledge of the index profile is presently not in agreement, and some possible reasons are indicated.

D. Gloge and E. A. J. Marcatili

Multimode theory of graded-core fibers

Bell Sys. Tech. J. 52:1563-1578; 1978

New technologies of fiber manufacture and a demand

for unusual fiber qualities in communication systems

have intensified the interest in a comprehensive

theory of multimode fibers with nonuniform index distributions. This paper deals with a general class of circular symmetric profiles which comprise

the parabolic distribution and the abrupt core- cladding index step as special cases. We obtain

general results of useful simplicity for the impulse

response, the mode volume, and the near- and far- field power distributions. We suggest a modified

parabolic distribution for best equalization of mode

delay differences. The effective width of the re- sulting impulse is more than four times smaller than that produced by the parabolic profile. Of course,

practical manufacturing tolerances are likely to influence this distribution. A relation is derived

between the maximum index error and the impulse

response.
AHENUATION MEASUREMENTS

2.1 General

J. P. Dakin and W. A. Gambling

Theory of scattering from the core of a multimode

fibre waveguide

Opt. Commun. 10:195-199; 1974

A theory suitable for the interpretation of mea- surements of light scattering from cl added multimode

optical fibres is presented. The model used is based on geometrical optics and enables the effects

of depolarization, the angular distribution of the propagating beam, as well as refraction and reflection at the core cladding interface to be taken into account. Good agreement is obtained between the theory and experiment.

G. W. Day and G. E. Chamberlain

Results of a recent attenuation measurement com- parison among U.S. optical waveguide manufacturers

Proc. (Supp.), Opt. Commun. Conf., Amsterdam,

19.4-1—19.4-4; 1979

A. Diekema, L. H. M. Engel, G. A. M. Goltstein,

P. Matthijsse, and J. W. Versluis

Comparative measurements regarding the attenuation

of optical fibres for the Eindhoven-Helmond field

trial

Tech. Digest, Symp. Optical Fiber (teas. -1980,

Boulder, 27-30; 1980, U.S. Govt. Printing Office

R. M. Hawk

Multimode waveguide attenuation measurements

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 1-9; 1980, U.S. Govt. Printing Office *****

W. Heitmann, C. R. Day, and U. Zwick

Breitbandige spektral Dampfungsmessungen an Licht- wellenleitern--ein Messvergleich der Gruppe COST 208 (Broadband specral attenuation measurements on optical waveguide—a measurement comparison of Group

COST 208)

Digest, Mess, in der Opt. Nachtrichten. , Berlin, 116-120; 1980, VDE-Verlag

M. Kaiser and U. Zwick

Vergleich verschiedener r<tessverfahren fur die Faser- dampfung (Comparison of different measurement proce- dures for fiber attenuation)

Digest, Mess, in der opt. Nachrichten. , Berlin, 139-

141; 1980, VDE-Verlag

Jun-ichi Sakai

Microbending loss evaluation in arbitrary-index

single-mode optical fibers. Part 1: Formulation

and general properties

IEEE J. Quantum Electron. QE-15: 35-44; 1980

Microbending loss formula is derived for arbitraryindex profile optical fibers by using analytical curved fiber fields to the first-order perturbation

theory. Relation between loss and fiber curvature

power spectral statistics is studied in detail. Normalized frequency giving the minimum microbending

loss value scarcely depends on the power spectrum. The larger the propagation constant differnece be- tween the guided and quasi-guided modes, the smaller

the microbending loss is in regard to wavelength,

relative index difference, and normalized frequency

dependence. The obtained formulas for single-mode

fiber show the same dependence as the graded-index

multimode fiber, with respect to fiber structure and curvature statistical parameters.

Jun-ichi Sakai

Microbending loss evalution in arbitrary-index

single-mode optical fibers. Part II: Effects of core index profiles

IEEE J. Quantum Electron. QE-16:44-49; 1980

Microbending losses in single-mode fibers with

several types of core refractive index profiles are compared. Numerical calculations were carried out

to characterize fibers with step, power-law, W and ring-shaped index profiles. Step-index and W fibers exhibit a small excess loss near the single-mode

operation upper limit. However, permissible offset misalignment in fiber splice at constant microbending loss is nearly identical for step, power-law,

and W fibers. An index dip at the core center has

an undesirable influence on the required splicing

accuracy. The effects of fiber curvature statistics

and index profile parameters are investigated in detail

G. Cancel lieri

Misure di attenuazione nell fibre ottiche (Mea- surement of attenuation in optical fibres)

Alta Freq. 47:151-154; 1978

10
M. H. Reeve, M. C. Brierly, J. E. Midwinter, K. I. White

Studies of radiative losses from multimode optical

fibres

Opt. Quantum Electron. 8:39-42; 1976

We describe measurements in which the radiative

losses from a multimode fibre have been resolved

into three components. These are the Rayleigh Scatter component from the material, the loss by

tunnelling from the modes closest to cut-off into the surrounding material, and the forward scatter

loss caused by imperfections in the fibre that are large compared to a wavelength.

R. M. Hawk

Multimode waveguide attenuation measurements

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 1-9; 1980, U.S. Govt. Printing Office *****

W. Heitmann, C. R. Day, and U. Zwick

Broadband spectral attenuation measurements on optical fibres--an interlaboratory comparison by members of Cost 208

Digest, Sixth Eur. Conf. Opt. Commun., York, 148-

151; 1980, lEE

2.2 Direct Methods

R. Bondiek

Prazisionsmessender fur optische Messungen (Preci- sion source for optical measurements)

Digest, Mess in der opt. Nachrichten. , Berlin, 84-89; 1980, VDE-Verlag

A. H. Cherin

A fiber concatenation experiment using a standardized loss measurement method

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 19-22; 1980, U.S. Govt. Printing Office

A. H. Cherin and W. B. Gardner

Measurement standards for multimode telecommunication fibers

SPIE 224:144-148; 1980

The emergence of optical fibers as an important com- munications medium has created the need for stan- dardized test procedures for evaluating fiber trans- mission characteristics.

In this paper we will review some of the standardization efforts aimed at improving the agreement

between optical fiber measurements made at different

location. We will alos outline the characteristics

that a standardized test procedure should have to be useful to the fiber optics industry. In addition,

the procedures followed in an industry wide round

robin measurement study will be described to illus- trate the current status of standardized fiber optic

loss measurements.

Allen H. Cherin and William B. Gardner

Fiber measurement standards

Laser Focus 16:60-65; August 1980

G. T. Holmes

Launch dependent attenuation measurements on a 10- kilometer concatenation experiment

Digest, Sixth Eur. Conf. Opt. Commun., York, 144-

147; 1980, lEE

L. C. Hotchkiss

Automated loss measurement set for optical cables

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 23-26; 1980, U.S. Govt. Printing Office *****

P. Kaiser

Loss measurements of graded- index fibers: Accuracy

versus convenience

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 11-14; 1980, U.S. Govt. Printing Office

*****

K. Kimmich and U. Zwick

Automatisierter Messplatz fur spektrale Dampfungsmessung optischer Fasern bis 1800 nm (Automatic mea- surement facility for spectral attenuation measurement of optical fibers to 1800 nm)

Digest, Mess, in der opt. Nachrichten., Berlin, 62-

65; 1980, VDE-Verlag

A. B. Sharma, E. J. R. Hubach, S. J. Halme

An accurate method for the measurement of fiber

attenuations

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 15-18; 1980, U.S. Govt. Printing Office

F. T. Stone and P. H. Krawarik

Mode elimination in fiber loss measurements

Appl. Opt. 18:756-758; 1979

11
Mitsuhiro Tateda, Tsuneo Horiguchi, Masamitsu

Tokuda, and Naoya Uchida

Optical loss measurement in graded-index fiber using

a dummy fiber

Appl. Opt. 18:3272-3275; 1979

The utility of an auxialiary fiber, called a dummy

fiber, is investigated for optical fiber loss mea- surements. The dummy fiber is spliced and used to excite the test fiber. Excess loss caused by un- desirable modes is found to be reduced to less than 0.05 dB by using a 500-m dummy fiber and choosing

the test fiber cut length to be 2 m for reference.

Loss linearity to the fiber length is examined on 6 km-spliced fibers, and satisfactory agreement is obtained between the total loss and the sum of the individual fiber and splice losses.

fluctuations near the fiber axis, and the influence

of a central index dip on fiber losses. The NA- dependent spectral -loss characteristics of a plastic-clad silica fiber, and of 0.22 and 0.34 NA Ge-B-doped fibers are presented as examples.

Robert Olshansky and Susan M. Oaks

Differential mode attenuation measurements in graded-index fibers

Appl. Opt. 17:1830-1835; 1978

An automated apparatus is described for measuring

mode-dependent scattering and total attenuation in graded-index waveguides. Measurements are reported

for two low-loss waveguides and several high-loss

waveguides. The results illustrate the ability of this technique to identify different types of loss mechanisms.

P. H. Wendland and D. N. Horwitz

A decibel measuring instrument for fiber optics

Proc, Fiber Opt. Commun.-79, Chicago, 121-124; 1979

Decibel power units are widely utilized to characterize the output of sources, the loss of cables and connectors/splices, and the response of photo- receivers. This paper describes the operation and design of a portable instrument which makes these measurements in both absolute dBm units and relative

dB units over a 900 dB range.

L. Wilson and M. J. Buckler

Automated spectral loss measurement of optical fibres

Opt. Laser Tech. 10:197-199; 1978

An automated system that precisely measures the

spectral loss of optical fibres at wavelengths from 0.63 vi to 1.51 u has been developed. A description

of the system, along with measurement techniques

used and typical results are given in this paper.

Ettore Bianciardi, Giovanni Cancel lieri, and

Mauri zio Zoboli

Non-destructive spectral loss measurements in coated

and jacketed fibres

Digest, Fourth Eur. Conf. Opt. Commun., Genova, 183-

188; 1978

A non destructive spectral attenuation measurement

for uncoated fibres has been extended also to coated

and jacketed ones. This measurement technique has also been performed using different kinds of Light

Emitting Diodes as optical sources. This method is proposed as complementary with respect to the back- scattering technique.

P. Kaiser

NA-dependent spectral loss measurements of optical fibers

Trans. lECE Japan £61:225-229; 1978

Steady-state losses of optical fibers have been obtained by launching beams of different numerical apertures and by measuring the losses and the cor- responding radiation patterns at both ends of the fiber. The steady-state losses are associated with

that radiation pattern whose distribution remains essentially unchanged. Other information obtainable

from NA-dependent loss measurements include, for example, the excess scattering losses in gradedindex fibers due to the increased concentration

M. Eve

Novel technique for the measurement of differential mode attenuation in graded-index fibres

Electron. Lett. 13:744-745; 1977

A novel technique for the determination of differential mode attenuation in a graded-index fibre is presented. Its originality lies in its experimental

simplicity and small data processing involved.

P. Kaiser

Numerical -aperture-dependent spectral-loss measurements of optical fibers

Tech. Digest, IOOC-77, Tokyo, 267-270; 1977

Numerical -aperture-dependent loss measurements are not only required for accurately determining the steady-state losses, but they are also a powerful

tool to probe the detailed loss characteristic of an optical fiber. The losses of silicone-clad and Ge- doped silica fibers are discussed as examples.

B. N. Klyushinik, A. I. Maltabar, N. I. Voloshina,

and V. N. Petrova

Measurement of attenuation indices for polymer

lightguides

12
Opt. Spectrosc. (USSR) 43:662-664; 1977

The form of the light transmission of polymer lightguides is investigated as a function of their

length. The layout of the measuring device and

typical results are given. A procedure for processing the results by the method of least squares in order to find the attenuation coefficients is pre- sented and proved. Student's distribution is used

to find confidence intervals for the attenuation

coefficients. Typical values of the resulting dis- crepancies are less than 2%. A simple exponential

dependence between the light flux and the length of the fibers is established in the region of lengths

investigated.

T. Yamada, H. Hasimoto, K. Inada and S. Tanaka

Launching dependence of transmission losses of graded index optical fiber

Tech. Digest IOOC-77, Tokyo, 263-266; 1977

This paper reports the launching dependence of transmission losses of a graded index optical fiber

in comparison with a step index optical fiber. The launching dependence of a graded index fiber was much smaller than that of a step index fiber when

the fibers are free from random bends.

T. Naruse, Y. Sugawara, M. Tanaka, Y. Hattori,

K. Yoshimura, T. Yamanishi, and N. Uchida

Fiber parameter dependence of excess loss for stepindex fibers

Tech. Digest, IOQC-77, Tokyo, 271-274; 1977

Experimental investigations have been made for step- index fibers to clarify effects of core and outer diameters of fiber, refractive index difference, and jacket diameter on loss increase due to bending and microbending. On the basis of the results, low loss fiber cables stable to temperature change have been fabricated by carefully controling manufacturing

processes.

R. Olshansky

Differential mode attenuation in graded-index

optical waveguides

Tech. Digest, IOOC-77, Tokyo, 423-426; 1977

The causes of differential mode attenuation and its effect on optical measurements are discussed. An automated measurement is described ^'or determining

the mode-dependence of both the total and scattering

losses of optical waveguides. Results will be reported which illustrate the ability of this technique to identify the sources of attenuation from

analysis of its mode-dependence.

R. Olshansky and D. A. Nolan

Mode dependent attenuation in parabolic optical fibers

Appl. Opt. 16:1639-1641; 1977

A previous study of excess attenuation caused by

slowly varying perturbations is extended to optical fibers with parabolic index profiles. For random

diameter variations, total losses are found to be essentially the same in step and parabolic fibers.

M. Eve, A. M. Hill, D. J. Maylon, J. E. Midwinter,

B. P. Nelson, J. R. Stern, and J. V. Wright

Launching independent measurements of multimode

fibres

Digest, Second Eur. Conf. Opt. Fibre Commun., Paris, 143-146; 1976

The problems of launching

with a view to obtaining r of loss and bandwidth on 1 The use of a mode scrambli

as a means of standard! zin tion in order to overcome effectiveness of the techn

by measuring the bandwidth

using three different meas different sources.

dependence are discussed

eproducible measurements

ow loss multimode fibres,

ng technique is suggested

g the input mode distributhese problems. The

ique has been demonstrated

of a step-index fibre urement systems employing

The possibility is also examined of producing a standardized distribution which matches the stable mode distribution of a fibre so that relevant loss measurements may be made on lengths of fibre which

subsequently form part of a multi kilometre route.

I. S. Goldfarb and T. M. Lozovskaya

A method of measuring the light transmission of glass-fiber without disturbing the integrity of the objects being tested

Sov. J. Opt. Technol. 43:738-740; 1976

The equipment is shown schematically, its operation

described, and its mode of operation analysed. Results are compared with standard methods and good

agreement is found. Application to measurement of transmission of optical cables already laid in place

is briefly discussed.

R. Olshansky, M. G. Blakenkamp, and D. B Keck

Length-dependent attenuation measurements in graded- index fibers

R. Olshansky, S. M. Oaks, and D. B. Keck

Measurement of differential mode attenuation in graded-index fiber optical waveguides

Tech. Digest, Opt. Fiber Trans. II, Williamsburg,

TuE5-l~TuE5-4; 1977, Opt. Soc. Am.

Digest, Second Eur. 111-113; 1976

Conf. Opt. Fibre Commun., Paris,

A launch condition commonly used in attenuation mea- surements establishes very different modal power distributions in step and parabolic fibers. By uni- formly illuminating the fiber core with a launch beam having a limited numerical aperture, one can

13
avoid exciting the high-order guided modes and leaky modes of a step fiber. This is not true for para- bolic fibers, which are thus predicted to show a length-dependent attenuation when measured by this method. Length-dependent attenuation measurements

of several four-kilometer long parabolic fibers are reported. The attenuation neasured by a standard method is found to yield a value which is 1.2 dB/km

higher than the steady-state attenuation.

the bulk glass are seen to be exceedingly important

in the waveguides and easily measured in them.

Arthur R. Tynes

Measuring loss in optical fibers

Bell Lab. Rec. 50:303-311; 1972

R. Olshansky and D. A. Nolan

Mode-dependent attenuation of optical fibers:

Excess loss

Appl. Opt. 15:1045-1047; 1976

A theory is presented for calculating the excess

loss produced by random perturbations of optical fibers. The theory is applicable to perturbations

whose longitudinal spatial frequencies are below the range required for mode coupling. To illustrate the method, losses due to diameter variations are calculated for the case of a step-inde^ optical fiber. The diameter variations are found to produce a strong attenuation of the higher order modes. The

total excess loss is approximately wavelength inde- pendent.

P. Kaiser and H. W. Astle

Measurement of spectral total and scattering losses

in unclad optical fibers

J. Opt. Soc. Am. 64:469-474; 1974

Spectral losses in unclaa optical fibers have been measured in the region between 0.5 and 1.12 \m with

the filtered light of a xenon-arc lamp. Total losses were obtained nondestructively by measuring

the light refracted from the fiber when it was im- mersed in a higher-index liquid. The radial irra- diance distribution of the refracted light was used

as a measure of the mode spectrum. Because scattering losses could be shown to approach the Rayleighscattering limit, and total losses were between 5 and 8 dB/km, i.e., 75 to 85% per kilometer, for some

of the highest-purity synthetic vitreous silicas, we tentatively conclude that the spectral losses of unclad fibers represent a good approximation to the spectral losses of the bulk material.

A. R. Tynes, A. David Pearson, and D. L. Bisbee

Loss mechanisms and measurements in clad glass fibers and bulk glass

J. Opt. Soc. Am. 61:143-153; 1971

Optical -loss mechanisms and transmission losses were investigated in clad glass fibers and in the bulk glass from which they were drawn. Measurements of

the total losses, absorption losses, and scattering

losses in both the fibers and in the bulk materialsare presented and compared. Photomicrographs of scattered light were made at 90° with 0.6328-um

laser light propagating in the fiber core. These

revealed the presence of an extremely large number

of discrete light-scattering centers, both in the core and in the cladding. Similar photomicrographs

of the bulk materials also show the presence of dis- crete scattering centers. Scattering centers have

also been observed by means of an electron microscope; they have been shown to be crystalline, by both electron diffraction and x-ray diffraction.

2.3 OTDR Methods (See also 5.3)

E. Brinkmeyer

Backscattering in single mode-fibres

Electron. Lett. 16:329-330; 1980

The scattering process in single-raode optical fibres

is considered in terms of wave optics rather than geometrical optics, which is inadequate in this

case. Surprisingly, however, the result for the backscattering signal at the input end of the fibre

is nearly the same as for multimode fibres.

D. B. Keck and A. R. Tynes

Spectral response of low-loss optical waveguides

Appl. Opt. 11:1502-1506; 1972

The attainment of 20-dB/km attenuation in experimental single-mode glass optical waveguides has spurred

interest in their use for optical communications.

The primary wavelength region of interest is in the red or near-infrared region of the spectrum. In this work independent attenuation measurements from 600

nm to 1060 nm have been made on low-loss waveguides

and bulk cladding glass, using both laser and scan- ning-prism monochromator sources. Three bands were observed in the waveguides, at 725 nm, 875 nm, and

950 nm, and identified as due to OH in the glass.

Absorptions too small to be precisely measured in

A. J. Conduit, A. H. Hartog, and D. N. Payne

Spectral- and length-dependent losses in optical fibres investigated by a two-channel backscatter

technique

Electron. Lett. 16:77-78; 1980

Spectral-and length-dependent losses in optical fibres have been investigated using a two-channel technique for backscatter-waveform analysis. Results are compared with measurements obtained by the "cutback" method over the wavelength range 0.82-

1.07 um. Attenuation measurements at 0.95 urn show a significant variation in OH" concentration along the fibre.

14
A. J. Conduit, J. L. Hullett, A. H. Hartog, and

D. N. Payne

An optimized technique for backscatter attenuation measurements in optical fibres

Opt. Quantum Electron. 12:169-178; 1980

A technique which gives maximum range and sensitivity for estimating fibre attenuation from the back- scattered light has been evolved. With this tech- nique stability problems in the source and receiver

are overcome by taking two different time samples

for each pulse launched into the fibre, the attenuation being derived from the ratio of the two samples. An analysis indicates that an optimum

operating strategy exists in terms of the choice of system parameters such that the range over which

attenuation can be measured is maximized. Results indicate that local loss measurements can be per- formed on fibre sections which are remote from the source by a distance corresponding to a fibre attenuation of 27 dB. Furthermore, preliminary experimental results are presented to demonstrate the viability of the technique.

B. Costa, B. Sordo, U. Menaglia, L. Piccari, and

G. Grasso

Attenuation measurements performed by backscattering

measurements

Electron. Lett. 16:352-353; 1980

An optical fibre was circulated between various

laboratories in Italy and the attenuation characteristics measured, using different experimental

arrangements. The results were compared, and found

in excellent agreement, demonstrating the repeatability of the technique and its suitability as a reference method for attenuation measurements.

B. Costa, B. Sordo, U. Menaglia, L. Piccari, and

G. Grasso

Comparison of attenuation measurements performed by the backscattering technique with different experimental set-ups

Digest, Sixth Eur. Conf. Opt. Commun., York, 160-

164; 1980, lEE

B. L. Daniel son

An assessment of the backscatter technique as a means for estimating loss in optical waveguides

NBS Technical Note 1018, U.S. Govt. Printing Office;

1980

This technical note addresses some of the problems

associated with determining the accuracy of the backscatter technique as it is applied to the esti- mation of attenuation in optical waveguides. The basic theoretical assumptions involved in optical time domain reflectometry are reviewed; the effect

on calculated loss values resulting from a departure

from these assumptions is then examined. The approach taken is to employ computer modeling of the various scattering and other loss mechanisms using

the bulk material properties of optical fibers. Computer responses permit a numerical comparison

between the direct (insertion) method of measuring

attenuation and several methods of estimating attenuation from analysis of backscatter data. Numerous

examples are given of physical effects which can produce discrepancies in attenuation values calcu- lated from backscatter signals. Also, some experimental comparisons are made between backscatterderived and directly measured attenuation values in step and graded-index optical waveguides. Finally,

the conditions necessary for good agreement between

the direct and backscatter methods are discussed and suggestions for minimizing these errors are made.

P. Divita and U. Rossi

The backscattering technique: Its field of applicability in fibre diagnostics and attenuation measurements

Opt. Quantum Electron. 11:17-22; 1980

The evaluation of power decay along the fibre by means of the backscattering technique may be altered

by the presence of unknown irregularities. In the present paper the effects of such imperfections are estimated; it is demonstrated that mainly local in- homogeneities and numerical aperture fluctuations

influence backscattered power. Finally an efficient

and simple method for the separation of the power

decay contribution from the irregularity contribution is proposed.

M. Eriksrud, S. Lauritzen, and N. Ryen

Backscatter attenuation measurements in graded index fibres

Electron. Lett. 16:877-879; 1980

A comparison is made of the attenuation values ob- tained by the backscattering technique and the more conventional cutback method, and the backscattering

technique is shown to provide highly accurate and reliable results.

P. Healey

Optical time domain reflectrometry by photon

counting

Digest, Sixth Eur Conf. Opt. Commun.. York, 156-159;

1980, lEE

P. Healey and P. Hensel

Optical time domain reflectometry by photon counting

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 85-89; 1980, U.S. Govt. Printing Office

15
p. Healey and P. Hensel

Optical time domain reflectometry by photon counting

Electron. Lett. 16:631-633; 1980

A photon counting technique has been used to extend

greatly the range of optical time domain reflecto- metry or "backscatter" for fault location in optical fibre systems. A range of more than 40 dB of one- way fibre loss has been achieved even when the break

was index-matched to eliminate any reflection.

B. Hillerich

Optisches Sampling Reflektometer (Optical sampling

reflectometer)

Digest, Mess, in der opt. Nachrichten. , Berlin, 16- 21; 1980, VDE-Verlag

D. L. Phil en

Optical time domain reflectometry on single mode fibers using a Q-switched Nd:YAG laser

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 97-100; 1980. U.S. Govt. Printing Office

Luigi Piccari

Optical fibre attenuation measurements by the back- scattering method: Effect of noise

Opt. Quantum Electron. 12:413-418; 1980

The backscattering method is now a well-established

technique for the measurement of attenuation in multimode optical fibres. In this paper the effect

of noise is evaluated in order to optimize the pre- cision of the measurement, its dynamic range and the time required to collect the data. An experimental

set-up is described and the experimental results

reported.

A. J. Rogers

Polarisation optical time domain reflectometry

Electron. Lett 16:489-490; 1980

A proposed new optical fibre technique will allow measurement of the spatial distribution of physical

fields, and will also allow location of anomalous

features in single polarisation state monomode optical fibres such as are under discussion for very

high bandwidth communication.

D. Schicketanz

Zukunftige Moglichkeiten des optischen Impuls- reflektometers (Future possibilities of optical

impulse reflectometers)

Digest, Mess, in der opt. Nachrichten., Berlin, 10-

14; 1980, VDE-Verlag

E. Wei del

Versweiger fur Ruckstreumessungen (Coupler for backscatter measurements)

Digest, Mess, in der opt. Nachrichten., Berlin, 187- 190; 1980, VDE-Verlag

P. DiVita and U. Rossi

Backscattering measurements in optical fibres: Separation of power decay from imperfection contribution

Electron. Lett. 15:467-469; 1979

A very simple and effective method is proposed for separating the actual decay of optical power from contributions due to fibre imperfection in measurements using the backscattering technique.

S. M. Jensen

Observation of differential mode attenuation in graded-index fiber waveguides using OTDR

Tech Digest, Opt. Fiber Commun., Washington, 120- 121; 1979, Opt. Soc. Am.

Jim McNaughton

Optical time domain reflectometry in an optical cable manufacturing facility

Proc, Fiber Opt. Commun. -79, Chicago, 117-120; 1979

A simple optical Time Domain Reflectometer (optical

TDR) system has been developed and this paper de- tails the use of this device for measurements and troubleshooting of optical cables in an optical cable manufacturing facility. Included in this re- port is a detailed description of the operation and construction of the optical TDR and its use to locate fiber breaks and anomalies in standard optical cables, flat cables, and special optical cable

types. How this device is used to measure optical cable lengths and cable attenuation is also dis- cussed. Specific examples will be described which

show how the optical TDR can be used to locate small-scale aberrations in an optical cable induced

by abnormalities in the manufacturing process. It will be shown that the optical TDR is a very powerful and useful device in an optical cable plant

environment.

M. D. Rourke, S. M. Jensen, and M. K. Barnoski

Fiber parameter studies with the OTDR

In "Fiber Optics, Advanced Research and Development," Bernard Bendow and Shashanka S. Mitra, eds. Plenum Press; 1979

16
L. Stensland and G. Borak

Precision measurements with OTDR

Digest, Colloq. Meas. Tech. for Opt. Fibre Sys.,

London, 8/1-8/2; 1979, lEE

M. K. Barnoski, S. M. Jensen, and M. D. Rourke

OTDR differential -modal -attenuation measurements

Digest, Fourth Eur. Conf. Opt. Commun.

133-139; 1978 Geneva,

The optical time-domain reflectometer has been used

to continuously observe the approach of fiber attenuation to the steady-state in a graded index fiber. Data which was obtained from a 4-km continuous fiber and which shows the approach to steady-state attenuation for various launching conditions are presented.

M. K. Barnoski, M. D. Rourke, S. M. Jensen, and

R. T. Melville

Optical time domain reflectometer

Appl. Opt. 16:2375-2379; 1977

By using an optical time domain reflectometer a new measurement technique which allows displaying the length dependence of the fiber attenuation by ana- lyzing backscattered light has been developed. This paper compares the backscatter and insertion-loss

techniques. In addition, results of several experiments which illustrate the versatility of an optical time domain reflectometer are described.

Bruno Costa and Bruno Sordo

Experimental study of optical fibres attenuation by

a modified backscattering technique

Proc.

1977 Third Eur. Conf. Opt. Commun., Munich, 69-71;

Bruno Costa, Carlo DeBernardi, and Bruno Sordo

Backscattering technique by wavelength dependent measurements

Digest, Fourth Eur. Conf. Opt. Commun., Genova,

140-144; 1978

The wavelength dependence of the light back-scattered in an optical fibre is measured. Data on the accuracy of the attenuation measurement by the back- scattering method are obtained by comparing the spectral loss curve resulting from the conventional

differential method with loss values from back- scattering at various wavelengths.

Finally an extensive comparison of the attenuation

values obtained by the two techniques for a large number of graded index fibres is carried out.

Douglas L. Franzen, B. L. Daniel son, and G. W. Day

A simple first positive system nitrogen laser for

use in optical fiber measurements

IEEE J. Quantum Electron. QE-14:402-404; 1978

A near infrared laser operating on several transitions of the first positive system of N2 ^^^ deve- loped for measurements associated with optical

fibers. The laser features a simple, longitudinal,

segmented design giving pulsewidths of 60 to 80 ns

full width at half maximum (FWHM) and peak powers of over 600 W in the 0.86 to 0.89 \im region in addition

to significant output near 1.04 and 1.23 ym. Back- scatter-reflection returns from optical fibers have

been obtained using the laser.

E. G. Neumann

Optical time domain reflectometer: A comment

Appl. Opt. 17:1975; 1978

A modification to the experimental arrangement of

the backscattering method for the investigation of attenuation characteristics of optical fibres is proposed, that allows end fire launching of the light beam into the fibre. Advantages of this new technique are simplicity, high launching efficiency,

control of launching conditions. Results are pre- sented relative to reproducibility, accuracy, length

and mode dependence of attenuation.

S. D. Personick

Photon probe--an optical -fiber time-domain reflec- tometer

Bell Sys. Tech. J. 56:355-366; 1977

This paper describes an optical time-domain reflec- tometer that incorporates a gated photomul tiplier

receiver. The instrument can detect extremely weak reflections from fiber breaks (more than 55 dB below

the 4-percent reflection of a perfect break} with 0.5-m distance resolution. In addition, backward

Rayleigh scattering, which occurs roughly uniformly

along a fiber, can be used to estimate the attenuation vs position within a fiber. Therefore, regions

of high attenuation can be located nondestructively

from one end of the fiber.

M. K. Barnoski and S. M. Jensen

Fiber waveguides: A novel technique for investigating attenuation characteristics

Appl. Opt. 15:2112-2115; 1976

Light from a pulsed GaAs injection laser is coupled

into a glass fiber via a taper coupler. The time dependence of the light backscattered within the fiber as the pulse travels down the waveguide is recorded. From these data the total loss may be determined, as well as an estimate of the scattering

and mode mixing characteristics of the fiber.

17
M. K. Barnoski, M. D. Rourke, and S. M. Jensen F. T. Stone

A novel technique for investigating attenuation

characteristics of fiber waveguides

Digest, Second Eur. Conf. 75-79; 1976

Opt. Fibre Commun., Paris,

Light from a into a glass The time depe

in the fiber

the waveguide

determined, a mode-mixing c fiber. The a the location magnitude of

B. Hillerich

pulsed GaAs injection laser is coupled

fiber waveguide via a taper coupler, ndence of the light backscattered wi this recorded as the pulse travels down

. From this data the total loss may be

s well as an estimte of the scattering,

haracteristics, and length of the pproach can also be used to determine

of in-line connectors or faults and the their insertion loss.

Pulse-reflection method for transmission-loss mea- surement of optical fibres

Electron. Lett. 12:92-93; 1976

A method for attenuation measurement of optical fibres by pulse reflections at the fibre's end is described. This method may be suitable for evaluating the attenuation of optical -fibre cables in the field.

Launch dependent loss in short lengths of gradedindex multimode fibers

Appl. Opt. 17:2825-2830; 1978

In this paper we describe the effect of different

launching conditions on the loss measured with a calorimeter in short {~l-m) lengths of multimode op- tical fiber. A qualitative description of the rela- tion between the energy distribution in the fiber

and various excitation variables is given, and many examples are presented that illustrate the effect

that launch conditions have on the fiber loss. The

use of launch-dependent loss phenomena to diagnose

loss mechanisms in optical fibers is discussed. In particular, loss plots are shown for two germaniadoped silica-core fibers that indicate a strong

absorption loss mechanism located deep within the fiber core.

F. T. Stone, B. R. Eichenbaum, and C. R. Lovelace

Loss measurements in optical ribbons using calori- metry

Appl. Opt. 17:2484-2486; 1978

G. J. Cannell

F. P. Kapron, R. D. Maurer, and M. P. Teter

Theory of backscattering effects in waveguides

Appl. Opt. 11:1352-1356; 1972

Associated with a signal transmitted down a waveguide are multiple back and forth scatterings. These produce a delayed decaying interference trailing a sharp signal pulse. An analytical description

of this phenomenon enables an estimate of its effect

on an optical waveguide's information-carrying capacity. For the example of a signal-to-interference

ratio of 100 in a 1-km fiber of 20-dB attenuation, a bit rate limitation occurs when the fractional back- scattered power captured per unit length exceeds 1.3 dB/km.

2.4 Other Methods

6. Cancellieri and M. Zoboli

Enhanced-sensitivity nondestructive measurement of

optical fiber loss

Alta Freq. 47:256-259; 1978

A nondestructive method has been developed to the point where it allows the measurement of very low attenuation constants in optical fibers. A complete

analysis of the relative errors shows that a sub- stantial improvement is obtained, if the difference

between two measurements of scattered power is per- formed electrically.

Continuous measurement of optical-fibre attenuation

during manufacture

Electron. Lett. 13:125-125; 1977

An online method of continuously monitoring the at- tenuation of an optical fibre during its manufacture

is described. It provides a complete attenuation/

length profile of the fibre. The present system can measure an overall attenuation of 30 dB, and the results agree with corresponding offline differential measurements to better than ±1 dB/km.

L. A. Franks, M. A. Nelson, T. J. Davies, P. Lyons, and J. Golob

A technique for measuring optical fiber transmission

using the time dispersion of Cerenkov radiation

J. Appl. Phys. 48:3639-3650; 1977

A technique based on measurement of time dispersion

in a 5-f unction Cerenkov pulse has been developed

for determining the attenuation coefficient a(x) of low-loss optical fibers. The time domain amplitude

distribution of the transmitted polychromatic pulse

is transformed to the wavelength domain by accurate measurement of the differences in arrival times of spectral bands isolated by interference filters.

Since the Cerenkov pulses are generated in the fiber

by a short burst of relativistic electrons, a{x) can

be measured over a wide and continuous range of path

lengths without breaking the fiber. The technique

has been demonstrated over the 500-800-nm spectral

region for fiber lengths up to 800 m.

18
Walter Heitmann

Attenuation measurement in glasses for optical com- munications: An immersion method

Appl. Opt. 15:256-260; 1976

In fiber waveguides for optical communication losses

of a few dB/km have been realized. To measure the attenuation in bulk glass rods, which are often used

as starting material for fiber production, an accuracy of at least 1 dB/km is desirable. With the method reported, the losses were determined from transmission measurements on 3-cm long samples. To eliminate surface losses the samples were immersed

in a liquid of about the same refractive index. For

two types of synthetic vitreous silica--Suprasil 1 and Suprasil Wl— the attenuation was measured be- tween 400 nm and 750 nm. These loss-spectra show that for Suprasil 1, with the exception of the region of OH absorption, the limit of the intrinsic

losses of pure silica is reached, while Suprasil Wl shows considerably higher attenuation in the whole

region. The measuring accuracy achieved so far was estimated to be about ± 1 dB/km.

J. A. Lewis

Laser heating of an optical fiber

Appl. Opt. 15:1304-1306; 1976

For use in absorption measurements in low-attenuation glass fibers, we calculate the periodic temperature-rise at the surface of a glass cylinder heated

by a chopped laser beam. Specifically, we give the mean temperature, setting the operating temperature

of the experiment, and the peak-to-peak temperature,

determining the sensitivity of the measurements.

K. I. White

A calorimetric method for the measurement of low optical absorption losses in optical communication

fibres

Opt. Quantum Electron. 8:73-75; 1976

Walter Heitmann

Attenuation measurement in low-loss optical glass by

polarized radiation

Appl. Opt. 14:3047-3052; 1975

For the production of fiber waveguides suitable for

optical communications cables, glasses with extremely low attenuation are required. A new method is described for measuring the optical attenuation of bulk glasses in the wavelength range of 0.4-1.1 ym. Using a quartz halogen source with highly stabilized

radiation power, a linearly polarized, monochromatic, collimated beam was produced, passing the sample

at the Brewster angle. Transmission loss, residual reflection, and surface scattering were measured by

low-noise photodiodes and integrating digital volt- meters. A stability of 10"^ and a resolution of 10"^ or better were achieved. Results for two dif- ferent kinds of commercial glasses, fused quartz

(Ultrasil) and synthetic vitreous silica (Suprasil

Wl), are reported and discussed.

D. A. Pinnow and T. C. Rich

Measurements of the absorption coefficient in fiber

optical waveguide using a calorimetric technique

Appl. Opt. 14:1258-1259; 1975

Irene Broquet

La diffusion dans les fibres optiques multimode

(Scattering in multimode optical fibers)

Ann. Telecomm. 29:195-208; 1974

An investigation into the losses due to scattering

in optical fibers has required the realization of two devices for the evaluation of these losses. One

of them is an Ulbricht sphere adapted for measuring

the total coefficient of attenuation by scattering. The other device permits a polar diagram of the scattering to be obtained and enables one to see how

the energy is distributed in the space. The »'esults of the measurements taken with regard to several so- called multimode fibers are presented. Several theoretical models are considered and an attempt is made to find among them those that account best for

the phenomena observed.

R. L. Cohen

Loss measurements in optical fibers: 1. Sensitivity

limit of bolometric techniques

Appl. Opt. 13:2518-2520; 1974

A new technique for measuring the attenuation of light in clad fibers is discussed. The basic approach is to measure the temperature rise produced

in the fiber by the absorption of the light. Calcu- lations indicate that the theoretical limit of sen- sitivity, which should be approachable with a rela- tively simple experimental configuration, is a loss

of about 2.5 X 10"'/cm with 1 mW of light power and

a 1-cm long sample. The theoretical sensitivity

limit should improve with the square root of the sample length. A variation of the basic approach,

which may make it possible to monitor attenuation in fibers as they are being drawn, is also discussed.

R. L. Cohen, K. W. West, P. D. Lazay, and J. Simpson

Loss measurements in optical fibers: 2. Bolometric

measuring instrumentation

Appl. Opt. 13:2522-2524; 1974

This paper describes two approaches to measuring

transmission losses in optical fibers by the thermal -rise technique. Rapid and convenient loss determinations can be made on short (~10-cm) lengths

of fibers. Values of loss as low as -10"' cm

(0.043 dB/km) can be measured with transmitted light

power of ~100 mW.

19
F. W. Ostermayer, Jr. and W. W. Benson

Integrating sphere for measuring scattering loss in optical fiber waveguides

Appl. Opt. 13:1900-1902; 1974

An integrating sphere for light scattered from fused

silica optical fiber waveguides that is relatively

simple to construct and easy to use is described.

The novel feature is the use of a solid sphere of fused silica to facilitate coupling the scattered

light out of the fiber cladding into the detector.

The fiber is inserted into a slot in the sphere, and glycerine is used to index match between the fiber

and sphere. The sphere is coated with high reflectivity barium sulfate, and a silicon photodiode

detects the radiation in the sphere. The construction, operation, and performance tests on the sphere

are described.

T. C. Rich and D. A. Pinnow

Evaluation of fiber optical waveguides using

Brillouin spectroscopy

Appl. Opt. 13:1376-1378; 1974

Optical scattering loss in fiber optical waveguides

is the sum of the bulk material scattering and ex- cess scattering loss due to imperfections in the waveguide structure. The recently developed

Brillouin spectroscopic technique for evaluating

bulk scattering has been extended to fiber waveguides, and a detailed investigation has been per- formed on a borosilicate clad-pure fused silica core waveguide. The technique has been found to be useful in evaluating scattering due to waveguide imperfections that have been determined to occur at the core-cladding interface. In addition to providing a measure of the waveguide scattering loss, the Brillouin technique has also been found to be useful

in determining the molar composition of the boro- silicate cladding glass and the partition of guided

optical power between the core and cladding regions.

The unusual capabilities of this technique should

make it generally useful for characterizing inte- grated optical structures.

A. R. Tynes

Integrating cube scattering detector

Appl. Opt. 9:2706-2710; 1970

The construction, calibration, and use of an inte- grating cube scattering detector used to measure

scattering losses in optical fibers is described.

The detector consists of six 1-cm sq silicon solar

cells, each sensitive surface of which comprises one interior surface of a cube 1 cm on edge. Small holes in the center of two opposite faces of the cube permit the optical fiber to pass through the detector so that all the scattered light falls on a photosensitive surface.

20
3. BANDWIDTH/DISTORTION MEASUREMENTS

3.1 General

I. Kobayashi

Bandwidth measurement in multimode optical fibers

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 49-54; 1980, U.S. Govt. Printing Office

D. Gloge

Effects of chromatic dispersion on pulses of arbitrary coherence

Electron. Lett. 15:686-687; 1979

Chromatic signal distortion in fibre waveguides de- pends on the coherence of the optical carrier. The theory derived here covers carriers of arbitrary co- herence and arbitrary dispersion characteristics. It gives simple estimates for the available signal

bandwidth.

H. M. Presby, D. Marcuse, and L. G. Cohen

Calculation of bandwidth from index profiles of optical fibers: 2. Experiment

Appl. Opt. 18:3249-3255; 1979

The impulse response and bandwidth of Ge02-doped and B203-doped multimode optical fibers are calculated

from their measured refractive index profiles. The computational method is based on the WKB solution of

the guided mode problem in which the pulse delay

time of each mode is determined with profile dispersion being taken into account. Accurate profiles

are obtained by a newly developed focusing technique, which allows measurements to be made on wholefiber samples. The predicted bandwidths of the GeOo-doped fibers range from approximately 200 to 1200 MHz-kffl and are in good agreement with the band- widths and impulse responses previously measured by

frequency-domain and time-domain optical shuttle

pulse techniques on kilometer lengths of the fibers.

A. H. Hartog

Influence of waveguide effects on pulse-delay mea- surements of material dispersion in optical fibres

Electron. Lett. 15:632-634; 1979

The effect of the waveguide structure on pulse-delay measurements of material dispersion in optical fibres is examined. It is shown that waveguide dis- persion has only a small influence on the measured

values and introduces an uncertainty in the wavelength of zero material dispersion of order +3 nm.

D. Marcuse

Interdependence of waveguide and material dispersion

Appl. Opt. 18:2930-2932; 1979

Theoretical work on dispersion in single-mode fibers sometimes uses the assumption that waveguide dispersion D and material dispersion D are separate ef- fects that contribute additively to the total amount

of dispersion D^^^. Using Gloge 's LP-mode approximation we compute the dispersion of the LPqi (HE,j^) mode by solving the eigenvalue equation taking dis- persion of core and cladding materials into account. The dispersion of the LPgi mode is computed by numerical differentiation of the solution of the eigenvalue equation. The difference Dj^ - Dj^ is compared to waveguide dispersion 0^, which is computed by

ignoring the dispersive properties of the core and cladding materials. We find large percentage deviation between D_^^^ - D^ and D^. The assumption of addivity of material and waveguide dispersion is thus not quite correct. However, because of the

small contribution of waveguide dispersion to the

total dispersion of the LPq, mode, even a large per- centage error in the waveguide dispersion has little influence on the over-all dispersion of the LPqj^ mode.

A. B. Sharma and S. J. Halme

Frequency response of optical fibers using a combi- nation time-frequency domain technique

Appl. Opt. 18:1870-1879; 1979

F. M. E. Sladen, D. N. Payne, and M. J. Adams

Definitive profile-dispersion data for germaniadoped silica fibres over an extended wavelength

range

Electron. Lett. 469-470; 1979

New results are presented for the wavelength dependence of the profile-dispersion parameter P in optical waveguides fabricated from germanosilicate

glasses. These results show that P is independent

of both Ge02 concentration and thermal history of the glasses.

K. Jurgensen

Gaussian pulse transmission through monomode fibers,

accounting for source linewidth

Appl. Opt. 17:2412-2415; 1978

When Gaussian pulses are transmitted thorugh a monomode dielectric optical waveguide, the pulses are broadened. The total width of a received pulse consists of three components: The width of the emitted

pulse and the broadening caused by dispersion in the waveguide together with both the bandwidth of the pulse and the linewidth of the source. The broadened

pulses have an oscillating distortion function

superimposed on them which deteriorates their resolution. The transmission capacity of an optical monomode transmission system can be calculated from

the results of this paper by insertion of the appro- priate parameters.

21
E. Nicolaisen and J. J. Ramskov-Hansen

A novel technique for investigating dispersion char- acteristics of fiber waveguides

Digest, Fourth Eur. Conf. Opt. Commun., Genova, 171-

178; 1978

A new experimental technique for measuring the dif- ferential phase is presented along with results demonstrating excellent agreement between time and frequency domain measurements. Calculated curves of the delay distortion will also be given for comparison.

E. J. Bochove and A. Cozannet

Low-pass filter characteristics of multimode graded

index fibres

Opt. Quantum Electron. 9:135-141; 1977

On the basis of ray model solutions, the response of

a lossless multimode graded-index fibre to a modu- lated source is calculated. The results demonstrate

great sensitivity of the bandwidth of the fibre to

small variations in index profile.

J. J. Ramskov-Hansen and E. Nicolaisen

Propagation in graded index-fibers: Comparison

between experiment and three theories

Appl. Opt. 17:2831-2835; 1978

We compare the measured impulse response of a graded-index fiber by three different theories: the WKB method applied for an arbitrary profile; the a- profile approximation; and perturbation theory. We find that the WKB method gives both a qualitatively

and quantitatively good agreement. The perturbation

theory gives a qualitatively good calculation of the width of the impulse response (the dispersion). The a-profile approximation gives a very poor result.

We also investigate the influence of the launching

conditions on the impulse response and find that the dispersion for this fiber decreases with the excitation of higher order modes. This is found to be in agreement with the WKB theory.

I. W. Sandberg, I. P. Kaminow, L. G. Cohen, and

W. L. Mammel

On the phase of the modulation transfer function of

a multimode optical-fiber guide

Bell Sys. Tech. J. 57:99-109; 1978

We consider the range of validity of a Hilbert- transform approach in which the measured magnitude

of the modulation-transfer-function of an optical

fiber is used to compute the fiber's impulse

response. It is argued that a key "minimum-phase

assumption" can fail to be satisfied in important

cases, and a few closely related experimental and

analytical results are presented.

I. W. Sandberg

A note concerning optical -waveguide modulation

transfer functions

Bell Sys. Tech. J. 57:3047-3057; 1978

A necessary and sufficient condition is given for

the modulation-transfer-function of certain multimode optical fiber guides to be zero free in the closed right-half of the complex plane, and to be structurally stable with respect to that property.

The condition is of interest, for example, in con- nection with the possibility of determining the phase of a modulation-transfer-function from its amplitude.

Mashiro Ikeda and Kenichi Kitayama

Transmission characteristics of mode scrambler

loaded long length spliced graded index fibers

Tech. Digest, IOOC-77, Tokyo, 419-422; 1977

Transmission characteristics of long length spliced

graded index fibers are described. The spliced transfer function has been determined by the condition that the fiber is excited by the steady state mode exciter and the mode scramblers are loaded just

after all splices. Under these conditions, the spliced transfer function presumed by the unit transfer function is in good agreement with the measured transfer function. It has been found that,

transmission band width can be widened by loading

the mode scramblers.

Charles Vassallo

Linear power responses of an optical fiber

IEEE Trans. Microwave Theory Tech. MTT-25:572-576;

1977

It is known that an optical fiber behaves linearly

in terms of power when the modulation frequency is smaller than the spectrum width of the light source.

In order to calculate the impulse or frequency power responses with a modal calculation, it is shown that

the powers carried by the different modes are inde- pendent in usual cases. Different formulas are pro- posed for the linear responses when there is no mode

coupling, and the corresponding validity conditions

are given.

Bruno Crosignani and Paolo Di Porto

Propagation of coherence and very high resolution measurements in optical fibers

SPIE 77:49-56; 1976

Two methods for measuring the dispersion associated

with propagation of different modes in guiding structures are presented. While the usual measurements are based on the direct observation of the distortion undergone by propagating pulses, in the first method one obtains information on the delays among the different modes by observing the changes

of the coherence properties of a continuous signal.

In the second method, one observes the temporal

variation of the output intensity once the input

signal has been frequency modulated. These methods

22
allow one to appreciate time differences of the order of some picoseconds, so that sufficient delays

can be obtained over short fiber lengths. Experiments are illustrated in which delays of this order

of magnitude have been actually measured.

James P. Wittke

M. J. Buckler

Optimization of concatenated fiber bandwidth via differential mode delay

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 59-62; 1980, U.S. Govt. Printing Office

Dispersion-limited modulation bandwidths of optical fibers

RCA Rev. 35:198-215; 1974

The information-carrying capacity of an optical

fiber is often limited by dispersive effects in the fiber. For relatively short transmission paths

(under 500 meters) modal dispersion, caused by the difference between group velocities of the different

propagating modes, is dominant. Measurements of the modulation transfer functions of three types of optical fiber, two step-index filters and a gradedindex fiber, have been made using both frequencyand time-domain techniques. A simple ray model pre- dicts many of the properties of the lowest-loss

step-index fiber, while the assumption of strong

attenuation in the higher-order modes is necessary

to explain the data on the high-aperture step-index

fiber. The graded-index fiber shows anomalously

large pulse broadening.

D. Gloge

Dispersion in weakly guiding fibers

Appl. Opt. 10:2442-2445; 1971

Optical signals transmitted through cladded glass fibers are subject to delay distortion because of

(1) dispersion in the material, (2) dispersion

caused by the waveguide characteristic, and (3) delay differences between modes. We isolate these effects and evaluate their significance for cases of practical interest. These concern fibers in which

the refractive index of the cladding is only slightly lower than that of the core.

M. J. Buckler, J. W. Shiever, and F. P. Partus

Optimization of multimode fiber bandwidth via differential group delay analysis

Digest, Sixth Eur. Conf. Opt. Commun., York, 33-36;

1980, lEE

M. Horiguchi, Y. Ohmori, and H. Takata

Profile dispersion characteristics in high-bandwidth

graded-index optical fibers

Appl. Opt. 19:3159-3167; 1980

To study profile dispersion effects on transmission

bandwidth in high-bandwidth graded-index fibers, baseband frequency responses of various graded-index

fibers with different profile parameters have been characterized in the 0.78-1.50-um wavelength range. The test graded-index fibers were made by the MCVD

technique. Intrinsic intermodal dispersions of these fibers were determined using a combination of

a GaAlAs laser and a grating monochromator, a mode- locked Nd:YAG laser, an InGaAsP/InP laser, and stimulated Raman scattering in a single-mode fiber

as the light sources. Transmission bandwidth functional dependences on wavelength are presented. The transmission bandwidth of the individual functional dependences on wavelength are presented. The trans- mission bandwidth of the individual fibers changed

by more than 400% within the experimental spectral

range. The maximum transmission bandwidth so far observed was 3.74 GHz-km at 1.225-ym wavelength for

a fiber with 0.20 N.A. Transmission bandwidth spectra were compared with computer calculated results based on Olshansky's theory.

3.2 Time Domain Methods

E. F. Anderson

Differential propagation delay in optical multi fibre

cables

Electron. Lett. 16:389-391; 1980

Pulse propagation delays in different GI -fibres within a cable have been measured as a function of temperature between -15° and +50°C. Two types of optical cables have been tested. Variation in pro- pagation delay differences between fibres of up to 0.65 ns/km were observed.

Chinlon Lin, Leonard G. and Herman M. Presby

Cohen, William G. French,

Measuring dispersion in single-mode fibers in the 1.1-1.3 ym spectral region--A pulse synchronization

technique

IEEE J. Quantum Electron. QE-16:33-36; 1980

We describe a novel technique for measuring dispersion in low-loss single-mode fibers in the 1.1-1.3

411 spectral region. The spatial equivalent of the pulse delay time as a function of wavelength is ob- tained in the measurement. The technique makes use

of the wavelength-dependent pulse synchronization

condition in a pulse-pumped near IR fiber Raman os- cillator. Experimental results on three single-mode

germanium-doped silica fibers are compared, and the importance of matching the minimum dispersion wavelength with the local loss minimum in fiber design

is discussed.

23
W. F. Love

Bandwidth spectral characterization of Ge02-P205-

SiOp multimode optical waveguides

Digest, Sixth Eur. Conf. Opt. Commun., York, 113-

115; 1980, lEE

J. Piasecki

Subpicosecond measurement of response of optical fibres

Electron. Lett. 16: 498-500; 1980

A novel technique is described for measuring the impulse response of short samples of monomode and multimode optical fibres, with a resolution better

than 0.1 ps. The times of arrival of the modes of multimode fibre are resolved.

H. F. Schlaak and M. Gwiazdowski

Ein optisches Faserlangenmessgerat und dessen Eigneschaften (An optical fiber length measurement

apparatus and its characteristics)

Digest, Mess, in der opt. Nachrichten. , Berlin, 22-

29; 1980 VDE-Verlag

Douglas L. Franzen and G. W. Day

Measurement of optical fiber bandwidth in the time domain

NBS Technical Note 1019, U.S. Govt. Printing Office;

1980

A system is described for determining optical fiber bandwidth from time domain information. A measurement gives the optical fiber transfer function (or frequency response) relating the output waveform to the input. An analysis is given of the variables

affecting the measurement. This includes a discussion of such input related topics as launching con- ditions, mode scramblers, and laser diode sources; output related topics include a discussion of optical detectors. Laser diodes are evaluated with respect to short pulse performance, near field emission, material dispersion limits, and other spectral

behavior like chirping; detectors are evaluated with respect to time response, linearity, and uniformity.

Overall system architecture, precision, and dynamic

range are discussed. A number of bandwidth related

topics are briefly presented and typical experimental results given. This includes examples of: mode mixing via microbending, profile compensation, pro- file dispersion, intramodal broadening, material dispersion constants, relative magnitude-phase

behavior, and Gaussian predictions of frequency

response.

S. Seikai and K. Fussgaenger

Experimental method for the separation of material

and modal dispersion of optical fibres

Digest, Sixth Eur. Conf. Opt. Commun., York, 173-

176; 1980, lEE

B. Costa, F. Esposto, and B. Sordo

Wavelength dependence of differential group delay in graded-index optical fibers: Application to fiber- links characterization

Tech. Digest, Opt. Fiber Commun., Washington, 122-

125; 1979, Opt. Soc. Am.

S. Seikai and K. Fussgaenger

Experimental method for the separation of material

and modal dispersion of optical fibres

Digest, Mess, in der opt. Nachrichten., Berlin, 98- 101; 1980, VDE-Verlag

Nori Shibata, Mitsuhiro Tateda, Shigeyuki Seikai, and Naoya Uchida

Spatial technique for measuring modal delay dif- ferences in a dual -mode optical fiber

Appl. Opt. 19:1489-1492; 1980

A simple spatial method using a coherent light

source and an interferometer is proposed for measuring the group delay time difference between the

LPqj^ and LPij^ modes in a dual -mode optical fiber. Experimental results obtained by this method are in good agreement with those obtained by the sweptfrequency and pulse methods. Moreover, a group de- lay time difference of 4 psec is measured. Results

suggest that this spatial method can be applied to a short fiber less than 1 m in length and/or small time differences around 1 psec by using a laser

diode with a short coherence length.

Douglas L. Franzen and Gordon W. Day

Measurement of propagation constants related to material properties in high-bandwidth optical fibers

IEEE J. Quantum Electron. QE-15:1409-1414; 1979

The material contribution to group index and material dispersion were measured in high-bandwidth

graded-index optical fibers. A shuttle-pulse technique provided measurements of group index with pre- cisions and accuracies of 0.1 and 0.2 percent using

5 m lengths of optical fiber. Material dispersion

in fibers was measured over the 0.8-0.9 um wavelength region using different wavelength, shortpulse laser diodes. The influence of material dis- persion on fiber bandwidth measurements was evaluated for laser diode sources. Limitations arising

from source linewidth were experimentally determined

from measurements on a fiber with high microbending

enhanced bandwidth.

24
p. Geittner

Dispersion measurements on PCVD optical fibres using

a mode locked synchronously pumped dye laser system

Proc, Opt. Commun. Conf. 14.2-4: 1979 Amsterdam, 14.2-1-

The use of a mode locked synchronously pumped dye laser system allows a very detailed and almost com- plete characterization of the dispersion characteristics of optical fibres. Profile and material dispersion as well as profile disturbances, homogeneity, actual and optimum o-parameters of the fibres can be selectively determined as a function

of wavelength. First experimental results on PCVD fibres confirm the high quality of the PCVD production process.

An optical fiber dispersion characterization test

set was developed at Kennedy Space Center with the

aid of the University of Central Florida, Orlando,

Florida. This development included the test algorithm development, hardware design, and signal pro- cessing software implementation for an HP-9825 computer. To date, the dispersion characterization

test was run on fibers up to 2.4 Km in length. Test

results showed that the impulse response of the 2.4 Km fiber has a 0.675 ns full duration at half the maximum value (FDHM), which corresponds to an FDHM dispersion of 0.28 ns/Km. Also, the 3dB bandwidth

of the 2.4 Km fibers is 560 MHz, which corresponds

to 1.34 GHz'Km fiber bandwidth capacity (bandwidthlength product). Test set modifications are planned

to allow testing of fiber lengths of up to 8 Km.

Harish R. D. Sunak

Chinlon Lin, L. G. Cohen, W. 6. French, and H. M. Marcuse

Pulse dispersion measurements in conventional Selfoc fibers

Measuring dispersion in single-mode fibers in the 1.1-1.3 \m spectral region—A pulse synchronization

technique

Proc. , Opt. Commun.

14.3-5; 1979 Conf., Amsterdam, 14.3-1--

We describe a novel technique for measuring dis- persion in low-loss single-mode fibers in the 1.1- 1.3 ym spectral region. The spectral equivalent of the pulse delay time as a function of wavelength is obtained in the measurement. Measurement results on three single-mode germanium-doped silica fibers are compared, and the importance of matching the minimum

dispersion wavelength with the local loss minimum is discussed.

Katsunari Okamoto

Comparison of calculated and measured impulse responses of optical fibers

Appl. Opt. 18:2199-2206; 1979

The principal purpose of this paper is to compare calculated and measured impulse responses of multimode optical fibers to substantiate the validity of the theoretical approach now being used by investigators. To perform the comparison efficiently, a new, practical method of analysis of the impulse response of inhomogeneous optical fibers is presented first. The necessary input data for calculating

the impulse response are refractive indices at N points, refractive index in the cladding, core

radius, and the wavelength of the light source. The calculated impulse responses are compared with the measured ones for several multimode optical fibers,

showing good agreement.

Michael E. Padgett and Sedki M. Riad

Optical fiber dispersion characterization study at Kennedy Space Center Proc, Fiber Opt. Commun. -79, Chicago, 63-66; 1979,

Information Gatekeepers

Appl. Opt. 18:1106-1109; 1979

Measurements of pulse dispersion in conventional

Selfoc fibers have been carried out. The principal

light source was a pulsed mode-locked ruby laser. Qualitative agreement has been found with theory,

which predicts multimode operation and, hence, large

pulse dispersion in such fibers under greatly mis- matched launching conditions. Under such conditions, we have observed dispersion equivalent to -20

nsec/km.

B. Rehfeld

Measurement tehcnique of the transfer function of fibers in optical communication cables

Conf. Rec, Int. Conf. Coimun., Boston, 36.6.1-

36.6.4; 1979, IEEE

A transmission path can be completely described by the baseband function ][ (u). Therefore, it is also used to specify the baseband-related transmission

properties of optical fibers in optical cables. The attenuation and the group delay distortions can be derived from the baseband transfer function. The values submitted in this paper were measured on optical cables of the local network of West Berlin.

K. F. Barren, D. J. Carpenter, and C. Pask

Interpretation of optical -fibre baseband frequency measurement

lEE J. Microwave Opt. Acoust. (UK) 2:41-44; 1978

The excitation of optical fibres by a focused laser

beam is described and the particular modes excited

are identified. The results are used to reanalyze

an experiment on baseband frequency measurement. Misconception in the original analysis concerning

the role of the source are pointed out.

25
K. Behm

Dispersion measurement of CVD-fabricated fibres with

a finite number of layers

Digest, Fourth Eur. Conf. Opt. Commun., Genova, 64-

70; 1978

The graded index profiles of fibres which are pro- duced by the CVD-method have stairlike perturbations

because of a finite number of layers. Furthermore

germanium doped fibres exhibit an additional index oscillation in each layer. The influence of these profile perturbations on fibre dispersion has been investigated experimentally and theoretically. For

the example of a germanium doped fibre with a 50 ym diameter core and a NA of 0.23 we conclude that the core should contain at least 35 layers, if a total pulse broadening of 3 ns/km and a 3-dB width broadening of 0.4 ns/km is allowed. For minimal dispersion, however, it should consist of more than

200 layers.

Leonard G. Cohen and Chinlon Lin

A universal fiber-optic (UFO) measurement system

based on a near-IR fiber Raman laser

IEEE J. Quantum Electron. QE-14:855-859; 1978

A universal fiber-optic measurement system, which is useful for measuring loss and dispersion in the 1.06-1.6 isn wavelength region, is described. The source is a silica fiber Raman laser pumped by a mode-locked and Q-switched Nd:YAG laser at 1.06

urn. Subnanosecond multiple-Stokes pulses in the 1.1-1.6 \sn wavelength region are generated in a lowloss single-mode silica fiber. The use of this near-infrared fiber Raman laser for characterizing

various transmission properties of single and multimode test fibers is demonstrated. Loss spectra, intramodal dispersion, and intermodal dispersion

data are obtained in the wavelength region of mini- mum loss and minimum loss and minimum material dis- persion for silica fibers.

L. Jeunhomme, J. P. Pocholle, and J. Raffy

Wavelength dependence of modal dispersion in graded

index optical fibres

Electron. Lett. 14:364-366; 1978

We describe a method based on the selective mode

excitation at different wavelengths for studying the profile dispersion influence on the modal dispersion. By using this technique, we are able to determine either the optimum wavelength at which the fibre should be operated or the correction needed

for optimising the index profile at a given wavelength.

Chinlon Lin, L. G. Cohen, W. G. French, and V. A. Foertmeyer

Pulse delay measurements in the zero-material

dispersion region for germanium- and phosphorusdoped silica fibres

Electron. Lett. 14:170-172; 1978

Wavel ength-dependent

and phosphorus-doped

centration was measu

second pulses in the Zero dispersion for

the 1.3-1.33 vm regi tion. P20c-doped si

si on near 1.28 ym, i tion.

pulse dispersion in germaniumsilica fibres of different con- red using mode-locked subnano- 1.064-1.55 ijm wavelength range. Ge02Si02 fibres was observed in on depending on the concentralica fibres showed zero disperndependent of doping concentraTakonori Okoshi and Katsuro Sasaki

Precise measurement of the impulse response of an optical fiber

Trans. lECE Japan, £61:964-965; 1978

By refining the decon volution technique proposed

previously by the same authors for determining the impulse response of optical fibers, the time resolution has been improved. In some cases an impulse

response consisting of several independent pulses is obtained; probably these pulses correspond to separate LP-mode groups.

D. N. Payne and A. H. Hartog

Pulse delay measurement of the zero wavelength of material dispersion in optical fibres

Nachrichtentech. Z. (Germany) 31:130-132; 1978

Pulse delay measurements on fibres are reported over

a wide wavelength range straddling the zero of material dispersion. Results for phosphosilicate and a range of germania-doped fibres indicate that the wavelength of negligible material dispersion lies in the range 170—1350 nm. The optimum wavelength

depends on the concentration for fibres containing

germania.

F. M. E. Sladen, D. N. Payne, and M. J. Adams

Profile dispersion measurements for optical fibres

over the wavelength range 350 nm to 1900 nm

Digest, Fourth Eur. Conf. Opt. Commun., Genova, 48-

57; 1978

B. Sordo, F. Esposto, and B. Costa

Experimental study of modal and material dispersion

in spliced optical fibres

Digest, Fourth Eur. Conf. Opt. Commun., Genova, 71-

78; 1978

Material dispersion in spliced graded index fibres

is measured and found to follow a linear addition

law. Measurements of pulse dispersion in spliced

fibres show that best combinations can be found that minimize total pulse dispersion, when dealing with

near optimum profile fibres. Evidence of pulse com- pression effects with a GaAlAs laser is reported.

26
R. Olshansky and S. M. Oaks

Differential mode delay measurement

Digest, Fourth Eur. Conf. Opt. Commun., Genova, 128-

132; 1978

A differential mode delay (DMD) measurement has been developed to analyze the detailed features of pulse

broadening in graded- index optical waveguides. DMD data can be interpreted directly in terms of deviations from the optimal alpha profile, a^, and is sensitive to small profile changes. The measurement

thus appears to be a fast, practical alternative to direct profile measurement.

Karl Behm

Dispersion measurement of CVD-fabricated fibers with

a refractive index dip on the fibre axis Proc, Third Eur. Conf. Opt. Commun., Munich, 28-30;

1977

A series of graded index fibres with varying index

dips have been fabricated and their dispersion has been measured. The output pulse shows a distortion

which is typical for this profile perturbation and may deteriorate optical communication at high bit rates considerably. Technologies to reduce the dip

are discussed.

C. Boisrobert, A. Cozannet, P. Lamouler, L. Martin,

H. Diraison

L. G. Cohen and Chinlon Lin

Pulse delay measurements in the zero material

dispersion wavelength region for optical fibers

Appl. Opt. 16:3136-3139; 1977

Subnanosecond pulses in the 1120-1550-nm region are generated by multiple-order stimulated Raman scat- tering in a small core single-mode silica fiber

pumped by a Q-switched and mode-locked Nd:YAG laser

at 1064 nm. These near ir pulses are injected into various km long test fibers, and relative time delay

changes between different wavelengths are used to determine dispersion in a region where fiber material dispersion is small. Zero material dispersion

has been observed in germanium and boron-doped

single-mode and multimode test fibers.

W. Eickhoff and 0. Krumpholz

Pulse response and microbending losses of an optical

glass-fibre waveguide with a bump in its index profile

Electron. Lett. 13:256-257; 1977

It is shown that a short light pulse is spilt into

two separate output pulses when transmitted through

a graded-index fibre with a refractive-index bump in its centre. For the fibre investigated, the bump

acts as a monomode waveguide. This monomode waveguide turned out to be much less sensitive to microbending than the multimode graded-index waveguide,

which is in agreement with existing theories.

Mesure des distorsions de temps de propagation de groupe sur les fibres optiques a saut d'indice (Mea- surement of group delay distortion in step index

fibers)

Proc, URSI, Meas. in Telecomm., Lannion, 445-447;

1977

K. Inada, R. Yamauchi, T. Yamada, H. Hashimoto,

S. Tanaka, and N. Uchida

Bandwidth change of graded and step index optical fibers under production process and splicing

Proc, Third Eur. Conf. Opt. Commun., Munich, 31-34;

1977

Remy Bouillie, Jean-Claude Bizeul and Marcel Guibert

Response en frequence des fibres optiques: Resultats experimentaux (Frequency response of optical fibers: Experimental results)

An. Telecomm. 32:149-157; 1977

The authors discuss measurements and results per- formed on the transfer function of graded and step index fibres. The principles and the set up are at first described: they measure the amplitude of the transfer function by means of fine recurrent pulses,

the spectra of which are compared by spectral analysis before and after their passage through the fibre. The experimental results will be compared

with theoretical studies; then the influences of different parameters such as numerical aperture, in- dex profile, mode conversion. . .will be discussed.

A law is established which gives the transfer function of spliced fibres. This law is experimentally

verified up to 12 kilometers. From these results

they draw some conclusions on the performances of these fibres for digital transmission.

D. N. Payne and A. H. Hartog

Determination of the wavelength of zero material dispersion in optical fibers by pulse-delay measurements

Electron. Lett. 13:627-629; 1977

Pulse-delay measurements on fibres are reported, made over a wide wavelength range straddling the zero of material dispersion. Results for phosphosilicate and a range of germania-doped fibres indi- cate that the wavelength of negligible material dispersion lies in the range 1270-1400 nm. The optimum wavelength depends on the concentration for

fibres containing germania.

Tadatoshi Tanifuji and Masahiro Ikeda

Pulse circulation measurement of transmission char- acteristics in long optical fibers

Appl. Opt. 16:2175-2179; 1977

27
A pulse circulation method to measure the length

dependence of transmission characteristics in optical fibers is described. In principle, the method

has the advantage that no unnecessary power is branched off in the loop. Using this method, the length dependence of transmission characteristics of step and graded index fibers has been measured and found to be different in both cases. It is con- cluded that the difference is due to the material dispersion effect, which significantly influences

pulse spreading in long length graded index fibers.

J. V. Wright and B. P. Nelson

Pulse compression in optical fibres

Electron. Lett. 13: 351-363; 1977

A shift in the emission wavelength of s.h. GaAs lasers has been observed during individual pulses.

In conjunction with material dispersion, this leads

to pulse compression after transmission through an optical fibre. The use of this device as a source

in bandwidth measurements readily leads to erroneous

conclusions when results are analysed.

This paper describes time-domain instrumentation

that was designed to measure impulse response and delay of nultimode optical fibers that are being

used in an experimental optical communications

system at Bell Laboratories. Time-domain data is transformed to frequency-domain by a minicomputer, and the result is displayed as the fiber's baseband frequency response.

I. G. Goyal , A. Kumar, and A. K. Ghatak

Calculation of bandwidth of optical fibres from experiments on dispersion measurement

Opt. Quantum Electron. 8:80-82; 1976 *****

J. -P. Hazan and L. Jacomme

Characterizing optical fibres; a test bench for pulse dispersion

Philips Tech. Rev. 36:211-216; 1976

Y. Ueno, S. Aoki, and Y. Ohgushi

Material dispersion measurement of an optical fiber

by FM radar method

IEEE J. Quantum Electron. QE-13:18D-19D; 1977 *****

L. G. Cohen

Pulse transmission measurements for determining near

optimal profile gradings in multimode borosilicate

optical fibers

Appl. Opt. 15:1808-1814; 1976

Dispersive differences between BpO^ and Si02 con- stituents make nonparabolic profiles optimal equalizers of intermodal group delays in fibers with graded 6203-5102 cores and uniform B2O3-SIO2 cladding. Pulse dispersion measurements were correlated

with profile shapes in a systematic study of nultimode fibers with near power law gradients. Far field spatial ray filters were used to diagnose

impulse response shapes so that new fibers could be fabricated with closer-to-optimal profile gradients.

One of the fibers had an a = 1.77 power law exponent

that was nearly optimal for \ = 907.5 nm wavelength

and caused 2a = 0.26-nsec/km full rms output pulse

spreading. When expected material dispersion ef- fects were deconvolved from the output pulse spreading, the resultant pulse width was approximately 75 times less than the result expected for a comparable

step-index fiber. This is the largest pulse width

reduction reported yet.

Jurgen W. Dannwolf, Samuel Gottfried, G. Arthur

Sargent, and Robert C. Strum

Optical -fiber Impulse response measurement system

IEEE Trans. Instrum. Meas. IM-25:401-406; 1976

Robert Olshansky and Donald B. Keck

Pulse broadening in graded-index optical fibers

Appl. Opt. 15:483-491; 1976

This paper reports on some theoretical and experimental investigations of the radial refractive index

gradient that maximizes the information-carrying

capacity of a multimode optical waveguide. The pri- mary difference between this work and previous

studies is that the dispersive nature of core and cladding materials is taken into consideration.

This leads to a new expression for the index gra- dient parameter a which characterizes the optimal

profile. Using the best available refractive index

data, it is found that in high-silica waveguides,

the dispersive properties of the glasses significantly influence the pulse broadening of near-parabolic fibers, and that the parameter a^, must be altered by 10-20% to compensate for dispersion dif- ferences between core and cladding glasses. These predictions are supported by pulse broadening mea- surements of two graded-index fibers. A comparison

is made between the widths and shapes of measured

pulses and pulses calculated using the WKB approximation and the near-field measurements of the index profiles. The good agreement found between theory

and experiment not only supports the predictions

made for the value of a^, but demonstrates an ability to predict pulse broadening in fibers having

general index gradients.

T. A. Orofino and F. C. Unterleitner

Optical fibers for dispersion in the time domain

Appl. Opt. 15:1907-1909; 1976

28
L. G. Cohen R. W. Dawson

Shuttle pulse measurements of pulse spreading in an optical fiber

Appl. Opt. 14:1351-1360; 1975

Partially transparent mirrors were pressed against

fiber ends so that length dependence of pulse

spreading could be determined without cutting the fiber into pieces. Measurements were made by com- paring the widths of laser pulses (X = 0.9 um) through the output end mirror, which returned from

9-1/2 successive round trips (2014-m extrapolated

length) along a 106-m multimode fiber. Mode mixing

was significant in this fiber fabricated by Corning

Glass Works), and a square root of length pulse

width dependence was observed. However, some of the mode-mixing effects on pulse width were caused by the way in which the fiber was wound on a drum.

L. G. Cohen and S. D. Personick

Length dependence of pulse dispersion in a long

multimode optical fiber

Appl. Opt. 14:1357-1360; 1975

Shuttle pulse measurements performed on a 1280-m

long multimode optical fiber were used to determine

pulse dispersion along a 6400-m extrapolated length. The fiber's steady-state mode coupling length was determined without breaking the fiber. The impulse responses for one, three, and five trips thorugh the fiber were recorded and Fourier transformed to yield

the corresponding baseband frequency responses. It was concluded that the coupling length was approximately 840 m, and that the impulse response became increasingly more symmetrical for fiber lengths be- yond this coupling length. This agrees with theory.

L. G. Cohen and H. M. Presby

Shuttle pulse measurements of pulse spreading in a low loss graded-index fiber

Appl. Opt. 14:1361-1363; 1975

Shuttle pulse measurements in a multimode optical

fiber were used to determine pulse dispersion, at A = 0.9-un wavelength, in eight increments from 148-m

to 2516-m extrapolated length. There was relatively

little mode mixing in this low loss fiber (minimum

loss = 1.7 dB/km at X = 1.04 ym), and the observed

pulse width was primarily due to the grading of the refractive-index profile.

B. P. Nelson and J. R. Stern

Pulse propagation measurements on slightly overmoded

glass fibres

Proc, First Eur. Conf. Opt. Fibre Commun., London,

13-15; 1975, lEE

Pulse widening in a multimode optical fiber excited

by a pul sed GaAs LED

Appl. Opt. 13:264-265; 1974

A 1-km length of low-loss multimode optical fiber

made by Corning Glass Works was excited by the pulsed output of a GaAs LED. The pulses were 3.6 nsec wide and had a spectral width of 460 A. After traveling through the fiber, the pulse had a half- power width of 6 nsec, of which 4.2 nsec was esti- mated to be due to material dispersion.

D. Gloge, E. L. Chinnock, and T. P. Lee

GaAs twin-laser setup to measure mode and material dispersion in optical fibers

Appl. Opt. 13:261-263; 1974

Two synchronously self -pul sing GaAlAs lasers,

emitting at slightly different wavelengths, are combined in a setup which evaluates mode and material dispersion in multimode fibers. The results

show that material dispersion which causes a pulse

broadening of 3.6 ns/km, which may represent a serious limit to the bit rates achievable in a multimode fiber system using an LED source.

S. D. Personick, W. M. Hubbard, and W. S. Holden

Measurements of the baseband frequency response of a 1-km fiber

Appl. Opt. 13:266-268; 1974

Typical light-emitting diodes have a spectral width

between 300 A and 500 A. This is sufficient to cause significant pulse broadening as a result of material dispersion in a long optical glass fiber.

An experiment was performed to measure the magnitude

of this effect in a fiber of 1-km length. The experiment measures the average intensity transfer

function of the fiber.

C. A. Burrus, E. L. Chinnock, D. Gloge, W. S. Holden, Tingye Li, R. D. Standi ey, and D. B. Keck

Pulse dispersion and refractive-index profiles of some low-noise multimode optical fibers

Proc. IEEE 61:1498-1499; 1973

The refractive-index profile and impulse response of three low-loss multimode optical fibers have been measured. Pulse dispersion of about 1.5 ns or less

was observed in two of the fibers, each 1 km long.

E. L. Chinnock, L. G. Cohen, W. S. Holden, R. D. Standi ey, and D. B. Keck

The length dependence of pulse spreading in the CGW- Bell-10 optical fiber

Proc. IEEE 61:1499-1500; 1973

29
Previous measurements of pulse broadening in the CGW-Bell-lO optical fiber showed very low dispersion

(< 2 ns/km). We recently measured pulse spreading

as a function of length in this fiber. The data indicate a (length)-'-''^ dependence, at wavelengths of 0.6328, 0.9, and 1.06 ym, for long fiber lengths

(>550 m) which are of practical significance.

agreement with a simple ray analysis which neglects

the index discontinuity at the fibre wall.

3.3 Frequency Domain Methods

S. D. Personick

Baseband linearity and equalization in fiber optic

digital communication

Bell Sys. Tech. J. 52:1175-1195; 1973

If a sequence of digitally on-off modulated optical

pulses is injected into a dielectric waveguide,

these pulses may begin to overlap after a sufficient

distance of propagation because of material dispersion and/or group delay spreading. In general, the pulses will not add linearly in power, which can complicate the problem of equalization of the square-law (power) detected overlapping output

pulses at baseband. This paper illustrates impor- tant situations in which the guide may be treated as "pseudo-linear" in power, meaning that the detected

guide output pulses appear to add linearity.

D. Gloge and E. L. Chinnock

Fiber-dispersion measurements using a mode-locked

krypton laser

IEEE J. Quantum Electron. QE-8:852-854; 1972

Mode delay and material dispersion limit the signal

bandwidth of potential fiber communication systems.

200-ps pulses from a krypton laser, mode-locked at

three different wavelengths, prove to be adequate

for measuring both effects in relatively short

fibers (33 m). The results are in good agreement

with theory.

D. Gloge, E. L. Chinnock, R. 0. Standley, and W. S.

Hoi den

Dispersion in a low-loss multimode fibre measured at three wavelengths

Electron. Lett. 8:527-529; 1972

Short pulses from mode-locked lasers (neodymium/

yttrium-iron-garnet and krypton) were used to measure mode and material dispersion in 20 m of a multimode fibre at 1060, 647 and 568 nm. Uniform

illumination of the cone of acceptance at the input caused a 200 ps pulse to broaden to 400 ps.

D. Gloge and E. L. Chinnock

Study of pulse distortion in Selfoc fibres

Electron. Lett. 8:526-527; 1972

A 100 ps gallium-arsenide laser pulse was observed

to increase in width by only 100 ps in 70 m of a fibre with an internal refractive-index gradient

(Selfoc). This is shown to be in satisfactory

Tsuneo Horiguchi, Tadatoshi Tanifuji, and Masamitsu

Tokuda

Baseband frequency response of a graded-index fiber

excited by a step index fiber

Appl. Opt. 19:2589-2596; 1980

Input modal power distribution and baseband frequency response of a graded-index fiber have been inves- tigated theoretically and experimentally, when the fiber was excited by a step-index fiber. It is found that the bandwidth of the graded-index fiber

is measured with good reproducibility and accuracy

by using the step-index fiber as an exciter. An appropriate choice of step-index fiber parameters is made with respect to the test graded-index fiber.

L. Jeunhomme and P. Lamouler

Intermodal dispersion measurements and interpretation in graded-index optical fibres

Opt. Quantum Electron. 12:57-59; 1980

We describe in this paper a frequency-domain mea- surement configuration allowing the determination of intermodal dispersion, differential mode attenuation

and mode-coupling effects in graded-index optical fibres. Attention is mainly given to intermodal dispersion which is obtained with a resolution of 5 ps km"^ and a dynamic range of 15 dB. Spatial (or modal) resolution is examined from both the theoretical and experimental point of view and the high

degree of resolution of the experiment is illustrated. Interpretation of the results for deducing the index profile errors and correcting the preform

manufacturing process shows the usefulness of the method for improving fibre quality.

Mitsuhiro Tateda, Shigeyuki Keikai, and Naoya Uchida

Frequency characteristics of graded-index fibers

Appl. Opt. 19:765-759; 1980

Frequency response of graded-index multimode fibers, whose index profile parameter a deviates from the optimum value, is investigated both theoretically

and experimentally. The frequency response of the fiber with optimum a diverges periodically. How- ever, that of the fiber with nonoptimum a does not exhibit periodic divergence but has periodic curvature changing points whose period is inversely pro- portional to the amount of a deviation. The period

is about a fifth of the divergence period of the fiber with optimum a when the a deviation is 0.1. The optimum a difference between \ = 0.82 and 1.27

un is found to be 0.07 for Ge02P205-doped silica

fibers by measurement of frequency responses at these wavelengths.

30
G. Cancel! ieri and M. Mezzetti

Scanning technique for investigating optical fibre

dispersion

Opt. Quantum Electron. 11:305-317; 1979

Differential mode del fomed, both for stepfibres, using a sinus

source. From a diffe

it is possible to get fibre baseband respon

of skew rays, and in theoretical model of

is used for computing

fibres where mode cou

ay measurements have been per- index and for graded-index

oi dally modulated optical

rential mode delay measurement,

all the information on the

se with or without the effect

particular of leaky rays. A mode coupling is developed and

the baseband response for pllng is not negligible.

A novel technique to measure the wavelength dis- persion of optical fibers in the 0.8-1.6 ym range, where germanium avalanche photodiodes possess ade- quate quantum efficiency, is described. Dispersion

is defined as dx/dx, which can safely be changed to the difference formula At/ax, when At is small, where t is the transit time of the wave and x is the light wavelength. A monochromatic light, whose

amplitude is modulated by a sinusoidal baseband

signal, is launched into the optical fiber. The phase of the sinusoidal baseband signal changes with

the monochromatic light wavelength variation due to the dispersion of the fiber. The phase variation

gives an accurate value of at. The wavelength dis- persion is obtained directly from the values of both

At and AX. Using this technique, the wavelength

dispersion of a single mode optical fiber, for example, is measured in the single mode wavelength

range from 0.92 to about 1.6 urn.

G. Cancel lieri, M. Mezzetti, C. G. Someda, and

M. Zoboli

Simplified procedure for indirect tests of optical- fibre transfer function

Electron. Lett. 15:234-236; 1979

Tadatoshi Tanifuji, Tsuneo Horiguchi, and Masamitsu

Tokuda

Baseband-frequency-response measurement of gradedindex fibre using step-index fibre as an exciter

Differential mode delays and attenuations are mea- sured by scanning the fibre output field, at one source modulation frequency. The results allow a simple evaluation of the baseband transfer function. A cylindrical lens can be used to simplify

the data collection.

L. Jeunhomme, P. Lamouler, and F. Alard

Electron. Lett. 15:203-204; 1979

For measuring reproducibility the baseband frequency

response of a graded-index fibre, a mode exciter

utilising an ordinary step-index multimode fibre has been proposed. The input mode power distribution

and the frequency response of the fibre with the exciter are altered very little for axis offset.

Input mode distribution excited indicates that excitation of nearly all modes takes place.

Frequency domain determination of intermodal dis- persion in graded index optical fibres

Proc. , Opt. Commun. Conf., Amsterdam, 12.1-1--

12.1-4; 1979

G. Cancel lieri

Time-dispersion measurement in optical fibre by near- and far-field scanning technique

S. Machida, N. Imoto, and Y. Ohmori

Multimode fibre baseband frequency response measurement with single frequency output extracted from modulated InGaAsP laser

Electron. Lett. 15:607-609; 1979

A new method to measure multimode fibre frequency

response is presented by using a single longitudinal mode extracted from modulated semiconductor laser

output. Intensity fluctuation noise, caused by r.f. modulation, is utilised as a broadband baseband signal. Baseband frequency response of a 1.98 km graded-index fibre is measured up to 1.5 GHz in 1.1- 1.5 vJTi wavelength region. This method provides a simple and accurate measurement of intermodal dis- persion excluding chromatic dispersion effect.

Akira Sugimura and Kazuhiro Daikoku

Wavelength dispersion of optical fibers directly measured by "difference method" In the 0.8-1.6 ym range

Rev. Sci. Instrum. 50:343-346, 1979

Electron. Lett. 14:465-467; 1978

The time-dispersion measurement technique here

reported, based on a differential mode-delay mea- surement, is a very simple one (only one modulation

frequency is used); but, nevertheless, it has good features in accuracy and repeatability. It allows investigation of the mechanisms of fibre time dis- persion and the effect of leaky rays.

Leonard G. Cohen, Ivan P. Kaminow, Harry W. Astle, and Lawrence W. Stultz

Profile dispersion effects on transmission band- widths in graded index optical fibers

IEEE J. Quantum Electron. QE-14:37-41; 1978

Transmission bandwidths of optical fibers would be maximized if their refractive index profiles were optimally graded. However, dispersive differences

between fiber material constituents make the optimal power law profile exponent a depend on wavelength.

This profile dispersion effect is significant for germanium borosilicate fibers and makes their ob- served transmission bandwidths change by more than

300 percent within a 650-1050 nm wavelength range.

31
Measurements are made in spectrally filtered white

light from a xenon arc lamp that is si nusoi dally modulated by an electrooptic crystal. Reduction of sine wave envelope intensity due to transmission in

a fiber gives its baseband frequency response. The functional dependence of bandwidth on wavelength is used to diagnose whether a is larger or smaller than

the optimal value which minimizes intermodal dispersion at particular wavelengths.

Masahiro Ikeda and Henichi Kitayama

Transfer function of long spliced graded-index

fibers with mode scramblers

L. Martin, A. Cozannet, and C. Boisrobert

Amplitude and group delay distortion measurement in optical fibers--new technique using a link analyzer

Trans. lECE Japan E61:219-222; 1978

In this paper we distortion in opt

are derived from

show how we modif

previously design quency recording:

fibres are given broadband remote

report on amplitude and group delay

ical fibres. Theoretical results

the ray optics calculations. We

ied our frequency domain equipment

ed for amplitude and phase vs fre- experimental datas on step index

in 5-45 MHz frequency range. Final operation system is discussed.

Appl. Opt. 17:63-67; 1978

Transfer functions of long spliced graded-index

fibers are determined with the steady state mode exciter and the mode scramblers loaded just after each splicing. Under these conditions, the total transfer function calculated by the linear combination of each fiber's transfer function is in good

agreement with the measurement results. It has been found that the transmission bandwidth can be widened

by using mode scramblers.

D. B. Keck and R. Bouillie

Measurements on high-bandwidth optical waveguides

Opt. Commun. 25:43-48; 1978

Frequency response measurements on six high-bandwidth optical waveguides made by the doped deposited

silica process are reported. One of these had an extrapolated bandwidth in excess of 3 GHz-km. From

plane wave measurements the actual or optimum waveguide profile may be determined given the other.

Data taken on a germanium borosilicate waveguide is

in agreement with interference measurements.

M. Maeda, K. Nagano, Y. Minai, and M. Tanaka

Baseband frequency response measurement system for

optical components

Appl. Opt. 17:651-654; 1978

Knowledge of the baseband frequency responses of

optical components is prerequisite to the design of optical fiber transmission systems. The sweep-frequency method is effective for obtaining frequency

responses because of its large SNR. However, the

use of GaAs lasers as optical signal sources in- volves several problems such as resonances below 1 GHz and spectrum broadening. In order to overcome

these problems, a single transverse mode GaAs laser called a buried heterostructure GaAs laser was employed as an optical signal source in the sweep- frequency measurement system. This measurement

system has a wideband flat sweep-frequency range of 0.5-1300 MHz as well as a wide dynamic range of more

than 60 dB at optical levels.

Tadatoshi Tanifuji and Masahiro Ideda

Simple method for measuring material dispersion in optical fibres

Electron. Lett. 14:367-369; 1978

A simple and accurate method, using a sinusoidally modulated l.e.d., is proposed to measure material dispersion of optical fibres. By this method, material dispersion was measured using a step and a graded index fibre. The results were in good agree- ment with those of other methods.

L. G. Cohen, H. W. Astle, and I. P. Kaminow

Frequency domain measurements of dispersion in multimode optical fibers

Appl. Phys. Lett. 30:17-19; 1977

A newly developed technique for directly measuring

fiber dispersion in the frequency domain as a function of wavelength is described. A number of ger- manium- and boron-doped fibers have been examined.

The least dispersive borosilicate graded-index fiber

has a 1-dB bandwidth of 1 GHz, after 1.06 km of pro- pagation at X = 908 nm. Frequency domain measurements were inverted into the time domain after assuming that the phase of a power transfer function could be calculated from its amplitude spectrum.

L. G. Cohen, H. W. Astle, and I. P. Kaminow

Frequency domain measurements of dispersion in multimode optical fibers

Tech. Digest, Opt. Fiber Trans. II, Williamsburg,

TuE3-l—TuE3-4; 1977, Opt. Soc. Am.

Itutaro Kobayashi, Masaki Koyama, and Kohichi Aoyama

Measurement of optical fiber transfer functions by

swept-frequency technique and discussion of fiber

characteristics

Electron. Commun. Japan 60-C:126-133; 1977

A new technique based on sweeping of the baseband

frequency is proposed for determination of the fre- quency characteristics of step index fibers. First

the principle, advantages and measurement setup are

32
presented and then the baseband frequency characteristics and their dependence on distance are discussed in detail. The frequency characteristics show marked dependence on shape and variation in fibers

with lengths from short to medium range and much new information is obtained. The hitherto unsettled

problem of "L or /L" concerning the distance dependence of the fiber characteristics is also investigated. The relationship between bandwidth and loss

is studied and a quantitative separation of loss into "selective" and "basic" components is achieved. Finally, the fluctuations of fiber characteristics

and the main features of fiber transmission systems

are briefly discussed and problems to be solved in the future are clarified. The present technique of baseband frequency sweep seems owing to its high

frequency resolution, high SNR and high accuracy, which are sufficient for practical purposes.

K. Yoshida, S. Seiki, M. Tokuda, and N. Uchida

Baseband frequency response of multimode step-index

fibers measured using a new type of mode scrambler

Electron. Commun. Lab. Tech. J. (Japan) 26:2601-

2611; 1977

For measuring frequency response of multimode step- index fibers, a mode scrambler utilizing sinusoidal bend and a new setup based on the attenuation com- parison method have been proposed. The mode scrambler can control input mode power distribution

with good reproducibility. Double beam method is used in the setup for nondestructive measurement of the frequency response with high accuracy.

C. Y. Boisrobert, A. Cozannet, and C. Vassal

Shigeyuki Seikai, Masamitsu Tokuda, Koji Yoshida,

and Naoya Uchida

Baseband frequency response of multimode step-index

fibers measured using a new type of mode scrambler

Tech. Digest, IOOC-77, Tokyo, 411-414; 1977

For measuring frequency response of optical fiber, a mode scrambler utilizing sinusoidal bend and a new

setup based on the attenuation comparison method

have been proposed. Measurements for multimode

step-index fibers have revealed that long fiber response can be anticipated from short fiber

response by an appropriate choice of scrambler

parameters.

Paolo Spano

Chromatic delay in light emitting diodes, measurements and theory

Proc, Third Eur. Conf. Opt. Commun., Munich, 151-

153; 1977

As already observed, the driving of LED at radio frequency causes the different parts of the optical

spectrum to be differently dephased among themselves

as if they were emitted at different times. Several measurements of the phenomenon are presented to- gether with a possible interpretation.

Masamitsu Tokuda, Shigeyuki Seikai, Koji Yoshida,

and Naoya Uchida

Measurement of baseband frequency response of multimode fibre by using a new type of mode scrambler

Electron. Lett. 13:146-147; 1977

For measuring the frequency response of an optical

fibre, a mode scrambler utilising a sinusoidal bend

and a new set-up based on the attenuation-comparison

method have been proposed. Measurements for multimode step-index fibres have revealed that the long- fibre response can be closely predicted from the short-fibre response, using an appropriate choice

for the scrambler parameter.

Swept frequency transfer function measurement

applied to optical fiber

IEEE Trans. Instrum. Meas. IM-25:294-297; 1976

Up to now, most of the experimental work on propa- gation through optical fibers was done using pulse measurements techniques. Short-light-pulse sources almost monochromatic and easy to drive to high-peakpower pulses are available on the optoelectronic

components market; this is one of the main reasons

why fiber manufacturers characterize their fibers by the broadening of the transmitted light pulse. This

parameter does not provide enough information on the fiber behavior to the digital transmission system

experts, unless one assumes a very-stable pulse

shape at the fiber input and uses fast Fourier transform computation on time-domain signals.

This paper presents the more classical technique

which is being used on transmission cables and devices. Tlie central unit is the network analyzer

which can simultaneously provide attenuation versus frequency and phase rotation versus frequency of any optoelectronic device coupled between the reference

and the test inputs. Various light sources have been selected for their sinusoidal modulation faci- lities; most of our measurements were made with fast-light-emitting diodes (GaAlAs 0.82 ym) and some

of them with a CW injection laser (GaAlAs 0.82 um).

R. Bouillie, J. C. Bizeul, and M. Guibert

Dependence over 7 kilometers of the transfer

function of graded index fibres

Digest, Second Eur. Conf. Opt. Fibre Commun., Paris, 135-142; 1976

In this paper we discuss measurements and results performed on the transfer function of graded index

fibres. The principle and the set-up are at first

described. Then material dispersion, quality of the

index profile and mode conversion are taken into account. A law is established which gives the transfer function of spliced fibres. This law is experimentally verified up to 8 kilometers.

From these results we draw some conclusions on the performances of these fibres for high bit rate sys- tems.

33
L. G. Cohen, H. W. Astle, and I. P. Kaminow

Wavelength dependence of frequency-response mea- surements in multimode optical fibers

Ben Sys. Tech. J. 55:1509; 1976

A newly developed technique for directly measuring

fiber dispersion in the frequency domain as a function of wavelength is described. Spectrally fil- tered white light from a xenon arc lamp is sinusoidally modulated in the range to 1 GHz by an elec- trooptic modulator and injected into a fiber. The procedure is to vary the modulation frequency and measure the corresponding sideband output power with

a photomul tipl ier and spectrum analyzer. Ratio mea- surements between the test fiber and a short reference fiber give the baseband frequency response. A number of germanium- and boron-doped fibers have been examined. The least dispersive borosilicate

graded-index fiber has a 1 dB bandwidth of 1 GHz, after 1.07 km of propagation at x = 908 nm. The width broadens gradually with increasing wavelengths

up to X = 1100 nm.

R. Auffret, C. Bcisrobert, and A. Cozannet

Wobulation technique applied to optical fibre trans- fer function measurement Proc, First Eur. Conf. Opt. Fibre. Commun., London, 60-61; 1975, lEE

J. Piasecki, B. Colombeau, M. Vampouille,

C. Froehly, and J. A. Arnaud

Nouvelle methode de mesure de la reponse impulsionnelle des fibres optiques (New method of measuring

the impulse response of optical fibers)

App. Opt. 19:3749-3755; 1980

A new technique for measuring the temporal transfer

function of optical fibers is described. The method

consists of placing the fiber under test in one arm

of a Mach-Zehnder interferometer excited by a broad- band source. The temporal impulse response is ob- tained from a holographic reconstruction. The method requires only short lengths of single-mode or multimode fibers (less than 1 m). We have measured

a dispersion of 0.3 nsec/km.nm at 0.59 ym with a single-mode fiber, in good agreement with theory. The arrival times of the various modes of multimode

fibers are resolved.

K. Daikoku and A. Sugimura

Direct measurement of wavelength dispersion in optical fibres--difference method

Electron. Lett. 14:149-151; 1978

A new method is described for direct and precise measurement of wavelength dispersion in the core of

an optical fibre over a wide wavelength region.

D. Gloge, E. L. Chinnock, and D. H. Ring

Direct measurement of the (baseband) frequency

response of multimode fibers

Appl. Opt. 11:1534-1538; 1972

Incoherent light, transmitted via multimode fibers,

represents a potential carrier for information that

is directly modulated on the light envelope. The amplitude and phase characteristics of the envelope

(baseband) signal are affected by the fiber waveguide because of group delay differences among the modes. We report on a technique that determines the baseband frequency response of the fiber system by

comparing the beat spectra of light from a free- running laser before and after transmission through

the fiber. As an example, we describe the measure- ment of 30 m of cladded multimode fiber. The 3-dB bandwidth was 700 MHz, somewhat larger than pre- dicted on the basis of the computed group velocity

differences.

F. M. E. Sladen, D. N. Payne, and M. J. Adams

Measurement of profile dispersion in optical fibres:

a direct technique

Electron. Lett. 13:212-213; 1977

A new technique allows direct determination of the wavelength-dipersive material properties of glasses

within the fibre. Results obtained over a wide

wavelength range are reported for both borosilicate

and fluorine-doped cladding materials. The latter

exhibits low profile dispersion.

F. M. E. Sladen, D. N. Payne, and M. J. Adams

A method for the direct measurement of the inhomo- geneous dispersion parameter in optical fibres

Tech. Digest, Opt. Fiber Trans. II, Williamsburg,

TuE2-l—TuE2-4; 1977, Opt. Soc. Am.

3.4 Other Methods

W. D. Bomberger and J. J. Burke

Interferometric techique for the determination of dispersion in a short length of single mode optical fiber

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 101-104; 1980, U.S. Govt. Printing Office

B. Crosignani, B. Dai no, P. Di Porto

Coherence properties of electromagnetic fields pro- pagating in multimode waveguides and application to the measurement of dispersion

Digest, Second Eur. Conf. 115-121; 1976

Opt. Fibre Commun., Paris,

We present two methods which allow to measure mutual

modal delays of the order of few picoseconds in optical fibers. Both methods are based on the observation of interference effects between different

34
modes, which depend on the coherence properties of the exciting source and on the dispersion properties

of the employed fiber. We present some results obtained by using a continuously tunable dye-laser

as exciting source.

35
4. INDEX PROFILE MEASUREMENTS (FIBERS AND PREFORMS)

4.1 General

D. Marcuse and H. M. Presby

Index profile measurements of fibers and their

evaluation

Proc. IEEE 68:666-688; 1980

The refractive index distribution in the core of a multimode optical-fiber waveguide plays an important

role in determining the transmission properties of the guide. The closer the index profile is to the required ideal distribution, the greater the resulting information carrying capacity of the fiber. This review paper discusses methods for measuring

the refractive index distribution in optical fibers

and for predicting their impulse response and signal

bandwidth from the measured profiles. Some attention is also given to preform and single-mode fiber

profiling.

H. M. Presby and D. Marcuse

Profile characterization of optical fibers and preforms

Tech. Digest, Symp. Optical Fiber Meas.-1980,

Boulder, 31-36; 1980, U.S. Govt. Printing Office

Herman M. Presby and Dietrich Marcuse

The index-profile characterization of fiber preforms

and drawn fibers

Proc. IEEE 68:1198-1203; 1980

The information carrying capacity of multimode optical fibers is mainly determined by the quality of

the refractive index distribution of their cores

which, in turn, is determined by the distribution

existing in the fiber's parent— the preform. This paper reviews methods that can be used to measure

the index profiles of preforms—both multimode and single mode. Attention is also given to the effects

of profile perturbations and means of eliminating

them, as well as to applications of the techniques

to fiber profiling.

results show that models (1) and (2) are limited in their usefulness in representing practical profiles, while the approximation (4) is easily applied to a variety of practical profiles.

H. M. Presby and D. Marcuse

Preform index profiling

Tech. Digest, Opt. Fiber Commun., Washington, 52-53;

1979, Opt. Soc. Am.

Herman M. Presby, Dietrich Marcuse, and William 6. French

Refractive-index profiling of single-mode optical fibers and preforms

Appl. Opt. 18:4006-4011; 1979

The application of the focusing method to measure

the refractive-index profiles of single-mode optical fibers and preforms is described. In this automatic

and nondestructive technique, the fiber or preform

is immersed in index-matching oil, and collimated

light is passed transversely through it. The intensity distribution of the transmitted light is detected with a video camera and processed with the aid

of a computer-controlled video analysis system that

provides the profile within a few minutes. The pro- files of boron-doped and germanium-doped fibers and preforms with maximum An varying from 0.006 to 0.012 were measured with a repeatability of better than 1% and with a resolution better than 1 pm. The pro- files of the preforms are in good agreement with

those of the fibers and also with those of slab samples taken from the tips of the same preforms.

J. P. Hazan, J. P. Cabanie, and J. J. Bernard

Method of assessing index profile data

Electron. Lett. 14:416-418; 1978

We describe a practical method for assessing profile

data which is applicable to a large class of profiles. It is repeatable, can be used routinely with little computational hardware and visualises clearly

and quantitatively the local a value along a radius.

A. E. Karbowiak and D. H. Irving

Modelling optical fibers with arbitrary refractiveindex profiles

Opt. Quantum Electron. 11:507-516; 1979

The characteristics of various models of refractiveindex profile are examined. Four models are considered: (1) power-law profile, (2) truncated even

polynomial profile, (3) truncated all-term polynomial profile, (4) Gauss-Chebychev approximation.

The characteristics of the various models are examined with particular reference to the ray-delay

times and the shape of the impulse response. The

H. M. Presby, D. Marcuse, and L. M. Boggs

Rapid and accurate automatic index profiling of optical fibers

Digest, Fourth Eur. Conf. Opt. Commun., Genova, 162-

170; 1978, lEE

An automatic computer controlled video-analysis sys- tem has been developed to measure the refractive in- dex profiles of optical fibers based on interference

microscopy. Its use in determining the profiles for

two distinct arrangements is discussed. In one, samples of the fiber are prepared for observations

36
by cutting and polishing them into very thin slabs;

in the second, the fiber is observed directly

requiring no sample preparation at all, other than index-matching the cladding. Repeatabilities of the resulting profile measurements are within +5 parts

in 10"^ for the slabs and about +3 parts in 10"^ for

the whole-fiber samples.

T. Okoshi

Optimum profile design of optical fibers and related requirements for profile measurement and control

Tech. Digest. IOOC-77, Tokyo, 391-394; 1977

This review paper first describes various approaches

to the optimum design of refractive-index profiles

of multimode and single-mode fibers. In the latter

half, requirements for profile measurement and control are discussed; it is concluded that the present

technologies are far from satisfactory to realize

the really optimum profiles.

P. V. H. Sabine

Refractive index profile determination in optical

waveguides

A.T.R. Aust. Telecommun. Rev. 11:3-13; 1977

An adequate characterisation of optical fibres, and

of waveguides for integrated optical circuits,

demands a precise quantitative description of the refractive index variation over a cross-section of the particular component. The first part of this paper review available techniques for measuring this refractive index profile (RIP). The second part of this paper presents practical results for RIP mea- surements in stress-induced channel optical waveguides.

B. Costa and B. Sordo

Measurements of the refractive index profile in optical fibres: Comparison between different

techniques

Digest, Second Eur. Conf. Opt. Fibre Commun., Paris,

81-86; 1976

In this work we analyze two well known techniques

for the measurement of the refractive index profile

of optical fibres: they are the "near-field" technique and the reflection technique.

As regards the near field method we have calculated

a correction factor that takes accurately into account the effects of leaky skew rays in step index

fibres. For what concerns the reflection method we have introduced an experimental Improvement that consists in immerging the fibre in a suitable

liquid, so greatly enhancing the sensitivity of the measurement. Finally we have used both methods on the same samples of optical fibres and compared the results which resulted in good agreement.

C. A. Burrus and R. D. Standley

Viewing refractive-index profiles and small-scale inhomogeneities in glass optical fibers: Some techniques

Appl. Opt. 13:2365-2369; 1974

Methods which have proved to be useful for measuring

core-cladding refractive-index differences, for approximating refractive-index profiles, and for viewing various inhomogeneities in solid multimode

optical fibers are described. Optical, transmission-interference, and scanning-electron-beam microscopy have been used, and the illustrations include

examples of photomicrographs made by each of these techniques.

4.2 Interferometric Methods (Longitudinal)

I. D. Aggarwal , D. C. Leiner, and J. J. McAlarney

Refractive index modulation in optical fibers

fabricated by the vapor oxidation process

In "Fiber Optics, Advances in Research and Development," Bernard Bendow and Shashanka S. Mitra, eds.. Plenum Press; 1979

Masao Hoshikawa, Shuzo Suzuki, Naoki Yoshioka, and

Gotaro Tanaka

Simple method of refractive-index profile measurement: Q-fiber method

Trans. lECE Japan E61:217-219; 1978

This method can reduce the measuring time considerably and can improve spatial resolution by using

a Q(quasi )-fiber, in comparison with an usual fiberpolishing method.

The overall measuring error was less than ±0.03% for

the case of index difference il%.

Dennis C. Leiner

Measuring fiber index profile

Opt. Spect. 12:32-34; 1978 *****

H. M. Presby and H. W. Astle

Optical fiber index profiling by video analysis of interference fringes

Rev. Sci. Instrum. 49:339-344; 1978

An electronic technique to make fringe displacement

measurements on the output field of an interference

microscope to 1/1000 of a fringe, not including sys- tematic errors, is described. The method, based

upon line-selected video signal analysis, is applied

to the evaluation of the refractive index profile of

a graded index optical fiber. The index difference

at a given point between the core and cladding is

37
determined to better than 1 part in 10^, implying a precision in the profile parameter a of +0.005, an order of magnitude better than existing techniques.

H. M. Presby, D. Marcuse, and H. W. Astle

Automatic refractive-index profiling of optical fibers

Appl. Opt. 17:2209-2214; 1978

A video-based system, which analyzes the output

field of an interference microscope directly, has been developed to measure automatically the refrac- tive-index distribution of optical fibers. Selected

regions of the fringe field, detected with a sili- con-vidicon, are digitized to 8-bit accuracy by an addressable video digitizer controlled with a pro- grammable calculator. The calculator also makes

fringe displacement measurements, corrects for certain misalignments, computes and plots the profile,

and determines a best-fit power-law (a) curve. Profiles, with relative An measured accurate to a few

parts in 10 , obtained at different wavelengths and for different fiber orientations are presented.

J. Stone and H. E. Earl

wavelength for Ge02-Si02, TiOg-SiOo, P205-Si02,

Al203-Si02, and Cs20-Si02 optical fibers. The mea- surements are obtained by electronically processing

the output of an interference microscope illuminated

by a monochromatic light source variable over the 0.5-1.1-ym range. The Anf(x) results are utilized

to calculate the precise grading of the refractive

index profile characterized by an exponent a(x)

required to achieve a minimum modal dispersion. The material dispersion for these compositions is also calculated with the aid of available n{x) data for

SiOoH. M. Presby, W. Mammel , and R. M. Derosier

Refractive index profiling of graded index optical fibers

Rev. Sci. Instrum. 47:348-352; 1976

Details of a method of determining the refractive

index distribution of graded-index optical fibers based on interference microscopy are discussed.

Sample preparation techniques, observational methods, and data reduction and analysis by a computer

fitting program are described. Representative data

for optical fibers prepared by chemical vapor depo- sition are shown.

Optical fiber refractometry by interference microscopy: A simplified method

Appl. Opt. 17:3647-3652; (1978)

Index of refraction profiles of optical fibers are obtained by a new interference technique closely

related to Mach-Zehnder microscope interferometry.

Data are obtained from specially prepared samples

using a conventional reflected light microscope. Excellent agreement is obtained with the results

using the Mach-Zender method but at a considerable

reduction in the cost and complexity of instrumentation.

A. Nicia

Interference patterns from very thick samples for determining the profile of graded-index fibres

Electron. Lett. 13:309-310; 1977

Recent studies have pointed out the need for very

thin (10 im) fibre samples prepared for interferometric analysis of the refractive index profile of

an optical fibre. We show that this is not necessary for all graded-index fibres with reasonable

dispersion properties. Sample thicknesses of 125

urn, or more, can be used for fibres with a core diameter of about 50 ym.

H. M. Presby and I. P. Kami now

Binary silica optical fibers: Refractive index and profile dispersion measurements

Appl. Opt. 15:3029-3036; 1976

The variation of the core-cladding refractive index difference Anf(x) is determined as a function of

J. Stone and R. M. Derosier

Elimination of errors due to sample polishing in refractive index profile measurements by inter- ferometry

Rev. Sci. Instrum. 47:885-887; 1976

The surface contouring caused by routine polishing

of fibers and preforms in preparation for measurement of the refractive index profile has been

studied. By observation of the surface interference

fringes the effect of polishing on doped preforms Is visualized. It is found that composition-dependent

thickness variations occur which can cause a sizable error in the refractive index variation deduced by

interference measurements in preforms (several percent) and in fibers (-50%). The difficulty 1s eli- minated by several minutes of additional polishing

on a hard lap.

B. C. Wonsiewicz, W. G. French, P. D. Lazay, and

J. R. Simpson

Automatic analysis of interferograms:

waveguide refractive index profiles

Appl. Opt. 15:1048-1052; 1976

Optical

Compensation of mode velocities in optical waveguides can be achieved by fabricating fibers having

graded refractive index cores. One technique for measuring these index profiles Is interference

microscopy. We have developed a machine aided method for analysis of interference micrographs for the rapid determination of optical waveguide refractive

index profiles. Our method consists of digitizing

the interference micrograph with a scanning microdensltometer, followed by computer determination of the position of the center line of each fringe. The

data obtained are then converted Into refractive

38
index and fiber radius information, which is used to calculate a best fit power law function.

D. Gloge, I. P. Kami now, and H. M. Presby

Profile dispersion in multimode fibres: Measurement

and analysis

Electron. Lett. 11:469-471; 1975

An electronically scanned interference microscope

has been used to measure the refractive-index pro- file and its dispersion in optical fibres. From

these measurements, we find that the power-law pro- file that best equalises modal delays in Ge02-Si02

fibres should have an exponent that varies between

1.9 and 2.5 in the wavelength range from 0.5 to 1.1 m and is close to 2 at 0.9 ym.

P. D. Lazay, J. R. Simpson, W. G. French, and B. C. Wonsiewicz

Interference microscopy: Automatic analysis of optical fiber refractive index profiles

Proc, First Eur. Conf. Opt. Fibre Commun., London,

40-42; 1975, lEE

J. Stone and C. A. Burrus

Focusing effects in interferometric analysis of graded-index optical fibers

Appl. Opt. 14:151-155; 1975

The effects of ray bending due to graded refractiveindex profiles have been studied in relation to the measurement of optical -fiber refractive-index profiles by microscopic interferometric techniques. In particular, the wavefront curvature produced by a simple parabolic profile has been calculated analytically. It is concluded that profile measurements

by currently used methods require samples for which

the fiber thickness (length) is much less than the effective focal length of the fiber. For parabolic

profile fibers with diameter d > 100 pm, this poses

no problem; however, for small -core versions of this

fiber, sample thicknesses of 10-15 \m may be required and an alternate measurement technique is described. Interferograms made on a Leitz transmi tted-light interference microscope are included in illustrations.

W. E. Martin

Refractive index profile measurements of diffused

optical waveguides

Appl. Opt. 13:2112-2116; 1974

Refractive index profiles resulting from the fabrication of optical waveguides by diffusion techniques

are measured using a reflection interferometric

technique. In Cd-diffused ZnSe waveguides, the index variations are found to be complementary error

functions that closely follow the composition

changes for deep (>5 ym) diffusions. Shallow {<5

ym) diffusions produce waveguides in which the index

profile is a complementary error function that differs significantly from the composition profile. The relationship between composition and refractive

index is determined for Cd compositions less than

10%. Refractive index profiles in commercially

available diffused glass waveguides (SELFOC rod and fibers) are also described.

Eric G. Rawson and Richard G. Murray

Interferometric measurement of SELFOC dielectric constant coefficients to sixth order

IEEE J. Quantum Electron. QE-9:1114-1118; 1973

A simple and sensitive interferometric technique

which yields accurate measurements of the 2nd-,

4th-, and 6th-order coefficients of the series ex- pansion for the radial distribution of the dielectric consstant of SELFOC or other GRIN rods is reported. Such data are required, for example, in predicting temporal dispersion in SELFOC fiber waveguides. The interferometer directly measures the relative phase delay along meridional -ray paths of different initial field angles. The mathematical

analysis consists of finding the 2nd-, 4th-, and 6th-order coefficients which yield the best least

squares fit to the measured phase shifts. The 4th- order results are found to be in good agreement with those of I. Kitano and co-workers. As an experimental application we describe a small, mechanically

stable, diffraction-limited collimator for use with

an optical fiber waveguide.

4.3 Interferometric Methods (Transverse)

Yasuo Kokubun and Kenichi Iga

Refractive-index profile measurement of preform rods

by a transverse differential interferogram

Appl. Opt. 19:846-851; 1980

A nondestructive refractive-index profile measure- ment of optical -fiber preform rods by means of a transverse-differential -interference method is given. The error resulting from the data reading of

a fringe center is investigated by computer simulation and is confirmed to be less than about 1% of the index differenc between the core and the cladding. The refractive-index profile of a preform rod was measured, and it almost coincided with that of the fiber drawn from the rod. The elliptic deformation of the core and its variation along the longitudinal axis were measured.

K. Iga, Y. Kokubun, and T. Omoto

Nondestructive measurement of refractive index profiles of optical fiber preform rods

IEEE J. Quantum Electron. QE-15:80D-81D; 1979

39
H. M. Presby, D. Marcuse, H. W. Astle, and L. M. Boggs

Rapid automatic index profiling of whole-fiber

samples: Part II

Bell Sys. Tech. J. 58:883-902; 1979

Automatic, nondestructive methods have been devel- oped for measuring and analyzing the refractive

index-matching oil and illuminated transversely to its axis in a single-pass interference microscope.

The output field of the microscope is automatically

processed with a video-digitized, computer-controlled system, and the profile is determined by the solution of an integral equation that can handle arbitrary variations in the index distribution. The resulting profiles are reproducible to approximately

1 percent and can be determined within a few minutes

after fiber fabrication. Details of a rapid video scanning procedure and of error estimates involved

in solving the integral equation are presented along

with representative profiles.

Kenichi Iga and Yasuo Kokubun

Formulas for calculating the refractive index profile of optical fibers from their transverse inter- ference patterns

Appl. Opt. 17:1972-1974; 1978

A set of successive approximation formulas for cal- culating the refractive index profile of optical

fibers from their transverse interference patterns

has been derived. The probing ray refraction due to the index gradient in the core is corrected for by these formulas, and the accuracy of index determination is improved. The error is confirmed to be less than 3 x 10"% of the index difference by means of computer simulations. The index profiles of some optical fibers are practically determined with the help of these formulas.

Y. Kokubun and K. Iga

Index profile measurement of optical fibers by means

of a transverse interferogram—further considerations on its accuracy

Trans. lECE Japan £61:184-187; 1978

The accuracy of the formulas for calculating the refractive index profile from its transverse inter- ference pattern is investigated in detail by com- puter simulations. The principle error is confirmed

to be about 10"% of the index difference between

the core and the cladding. The transverse interference patterns from a multimode graded index fiber

and a thin fiber of which core diameter is several microns are obtained by using an interferometer

microscope and their refractive index profiles were practically determined with the help of these formulas. Their o parameters were obtained.

K. Iga and Y. Kokubun

Precise measurement of the refractive index profile

of optical fibers by nondestructive interference method

Tech. Digest. IOOC-77, Tokyo, 403-406; 1977

The accuracy of the transverse interference method

has been raised up by fully correcting a probing ray refraction due to the index gradient of the fiber. A simulation shows that the accuracy is in principle

within 0.3 % of the index difference between the core center and the cladding. The index profiles of some fibers were practically measured and it was confirmed that this method can be used for a precise, nondestructive, and fast measurement.

Yasuo Kokubun and Kenichi Iga

Precise measurement of the refractive index profile

of optical fibers by nondestructive interference method

Trans. lECE Japan £60:702-707; 1977

In this paper, the accuracy of the transverse inter- ference method has been raised up by fully correcting a probing ray refraction due to the index gra- dient of the fiber. A simulation shows that the accuracy is in principle within 0.3 % of the index difference between the core center and the cladding. The index profiles of some fibers were prac- tically measured and it was confirmed that this method can be used for a precise, nondestructive,

and fast measurement.

Y. Maruyama, K. Iwata, and R. Nagata

Determination of axially symmetric refractive index distribution from directions of emerging rays

Appl. Opt. 16:2500-2501; 1977

A successful verification of a method for numerical reconstruction of axially symmetric refractive index distribution is reported. Directions of rays emerging from a test object are used as input data for reconstruction. They are obtained by numerically

calculating the spatial frequency of the fringes in an interferogram. It is also shown that the same data can be obtained directly by counting moirS

fringes arising from two slightly displaced inter- ferograms. An acrylic resin immersed in liquid is used as a test object. The reconstruction is carried out with errors of a few percent.

Yasuji Ohtsuka and Yutaka Shimizu

Radial distribution of the refractive index in light-focusing rods: Determination using Interphako

interference microscopy

Appl. Opt. 16:1050-1053; 1977

An interferometric technique for the determination

of the radial distribution of the refractive index

in light focusing plastic rods (LFR) has been deve- loped using the shearing method of Interphako inter- ference microscopy. We have derived mathematical

expressions for the shape of interference fringes across the rod assuming the index distribution of LFR is described by n(r) = n (l-ar^+br^ +cr°+dr*') in which a, b, c, and d are distribution constants.

The distribution constants were determined using a least-squares technique on a computer from the

40
actual shape of fringes. Results for the repre- sentative cases are shown. 4.4 Other Transverse Methods

M. J. Saunders and W. B. Gardner

Nondestructive interferometric measurement of the delta and alpha of clad optical fibers

Appl. Opt. 16:2368-2371; 1977

It is shown that interferograms generated by passing

light perpendicular to the axis of a fiber can be used to obtain the maximum refractive index difference and the index profile shape to better than ±10%

accuracy in regions of the core where a is constant.

This techique avoids the time consuming sample pre- paration required for the slab method, the propagation problems associated with the near-field technique, and the surface quality problem associated

with the reflection technique.

F. T. Stone

Rapid optical fiber delta measurement by refractive

index tuning

Appl. Opt. 16:2738-2742; 1977

A technique is presented for rapidly measuring A of

optical fibers with profiles closely approximating

n(r) = n(o)[l - A(r/a)°], the A<<1 limit of the two- parameter Gloge-Marcatili profile. Error analysis

indicates an accuracy of about ±9%. The method is as follows: Using a Michel son interferometer

together with a microscope, the transverse optical

path through the center of a fiber immersed in index matching fluid is set equal to the optical path

through the fluid. This is accomplished by varying

the temperature of the fluid. The value of A can then be determined from a knowledge of the refractive index of the fluid inferred from temperature

measurements. Good agreement is shown between A values measured by this technique and those measured

by two other interferometric techniques. The pos- sible use of this method to determine a, or to determine the actual profile if it does not follow

the assumed shape, is discussed.

M. E. Marhic, P. S. Ho, and M. Epstein

Nondestructive refractive-index profile measurements

of clad optical fibers

Appl. Phys. Lett. 26:574-575; 1976

An interferometric method in conjunction with Abel inversion is used to precisely measure the index of refraction profile of clad optical fibers without

perturbing them. The sample is immersed in index- matching fluid, so that fiber index variations cause

only small phase shifts for rays propagating perpendicular to the axis, making interferometric methods

applicable.

P. L. Chu and D. Peri

Holographic measurement of refractive-index profile

of optical fibre preform

Electron. Lett. 16:876-877; 1980

A holographic method of measuring the refractiveindex profile of an optical fibre preform is presented. It uses the principle of shearing inter- ferometry. The method is simple and allows measurements to be repeated even after the preform has been withdrawn for fibre drawing.

T. Okoshi and M. Nishimura

Automated measurement of refractive index profile of VAD preforms by fringe-counting method

J. Opt. Commun. 1:18-21; 1980

A new method for measuring the refractive index pro- file of a preform rod produced by the VAD (Vaporphase Axial Deposition) scheme is proposed. This method, called the fringe-counting method, features

a relatively good accuracy and efficient data col- lection for such relatively "thick" samples as the preform.

An automated, computer-controlled measuring system

has been developed and used in the experiment. Com- puter simulations shown that the developed system

has an accuracy good enough for most practical pur- poses (below 0.2% in most cases).

T. Okoshi, M. Nishimura, and M. Kosuge

Nondestructive measurement of axial ly nonsymmetric

refractive-index distribution of optical fibre pre- forms

Electron. Lett. 16:722-724; 1980

A nondestructive computer-aided measurement of the arbitrary two-dimensional refractive index distribution of an optical fibre preform is described. The angle of refraction of rays in the preform is measured by an optical set-up which features the use of

a triangular mask for converting the angle of rays

to their displacement. The index distribution is computed from the information on these refraction

angles.

D. Peri and P. L. Chu

Index profile determination in transition region of optical fibre preform

Electron. Lett. 16:916-918; 1980

It is shown that the refractive-index profile in the transition region of an optical fibre preform can be obtained by a combination of a measurement of the deflection function and a ray-tracing procedure.

41
I. Sasaki, D. H. Payne, and M. J. Adams

Measurement of refractive index profiles in optical

fibre preforms by spatial-filtering technique

Electron. Lett. 16:219-221; 1980

A nondestructive technique based on spatial filtering is presented for measuring the refractive-index

profile in an optical-fibre preform. The method is simple, accurate and has sufficient resolution to enable detailed profiles of single-mode preforms to be obtained.

C. Seakeang, P. L. Chu, and T. W. Whitbread

Nondestructive measurement of refractive-index pro- file and cross-sectional geometry of optical fiber

preforms

Appl. Opt. 19:2025-2030; 1980

A modified focusing method for measuring simultaneously the refractive-index profile and the crosssectional geometry of an optical fiber preform is presented. In this method the preform is immersed

in index-matching liquid, and colli mated light is made to impinge on the preform laterally. The in- tensity distributions of the transmitted light are detected on two planes inside the preform core. From

the recorded light intensity distributions, the de- flection function is calculated. After the preform

has been rotated through 180° and the necessary data have been collected, a numerical inversion is per- formed to obtain the 2-D index profile. In this paper, the principle, the experimental setup, and results are described. The sensitivity of the method to measurement erors and the accuracy of the in- version formula were investigated by computer simu- lations. It was found that the error of the index profile measurement was <1%.

L. M. Boggs, H. M. Presby, and D. Marcuse

Rapid automatic index profiling of whole-fiber

samples: Part 1

Bell Sys. Tech. J. 58:867-882; 1979

A new interferometric method not requiring any sample preparation is presented for determining the refractive-index profiles of optical fibers. The whole fiber is immersed in index-matching oil and placed transversely under an interference microscope. The determination of the refractive index distribution for an arbitrary, circularly symmetric

fiber core requires the solution of an integral

equation. In this first of two papers on the sub- ject, we describe a method which accomplished its solution by assuming that the fiber core consists of

a large number of concentric circular cylinders of step-wise constant refractive index. The index dis- tribution can then be obtained by determining the index values of each layer successively. The method

has been applied to double- and single-pass inter- ferometric arrangements which are being compared

here. The single-pass method is reproducible to about 1 percent and provides the complete index distribution within minutes with the help of a com- puter-controlled video-analysis system. The results

of this method are in excellent agreement with

profiles obtained from polished slabs of the same

fiber.

P. L. Chu and C. Saekeang

Nondestructive determination of refractive-index

profile and cross-sectional geometry of optical

fibre preform

Electron. Lett. 15:635-636; 1979

A nondestructive method is presented to determine

simultaneously the refractive-index profile and the cross-sectional geometry of a preform. In this method, a plane wave is made to impinge on the pre- form laterally and the power distribution of the scattered pattern is recorded. From the recorded

power, the ray pathlength difference is calculated. After the preform has been rotated through 360° and

the necessary data collected, a numerical inversion

is performed to obtain the index profile and crosssectional geometry.

P. L. Chu and T. Whitbread

Nondestructive determination of refractive index profile of an optical fiber: Fast Fourier transform

method

Appl. Opt. 18:1117-1122; 1979

A nondestructive technique of determining the re- fractive index profile of an optical fiber is pre- sented. This method involves collecting the pathlength data of rays passing through the fiber due to side-illumination and taking the fast Fourier trans- form of these data followed by a numerical integration. It is found that this technique yields

results in good agreement with measurements from the near-field scanning technique. The advantage of the present method is that it can readily be extended to fibers of noncircular cross section.

P. L. Chu and T. Whitbread

Measurement of refractive- index profile of optical fibre preforms

Electron. Lett. 15:295-296; 1979

An experimental system for nondestructive measurement of the refractive- index profile of an optical fibre preform is reported. The result shows that

the profile does not significantly change from the preform stage to fibre stage.

P. L. Chu

Nondesctructive refractive-index profile measurement

of elliptical optical fibre or preform

Electron. Lett. 15:357-358; 1979

A nondestructive method of determining the refrac- tive-index profile of an elliptic optical fibre or preform is reported. For the fibre, the pathlength

data obtained from interference microscopic measurement are used. For the preform, the ray exit angles

42
are used. These data are put into an integral that

can be inverted numerically to obtain the reconstructed.

D. Marcuse

Refractive index determination by the focusing method

Appl. Opt. 18:9-13; 1979

We show that it is possible to determine the refractive index distribution of a fiber or preform with slight index variation by observing the power dis- tribution of the light field that is focused by the

core acting as a lens. This method requires index matching of the cladding and illumination of the core at right angles to its axis with a broad beam

of incoherent colli mated light. The refractive

index distribution is obtained after two numerical integrations to be performed by computer. The first

integration establishes the relation between the output and input ray positions from the observed

power distribution, the second uses this information

to determine the refractive index distribution.

However, it is not necessary to solve a large system

of simultaneous equations. The sensitivity of the method to measurement inaccuracies was tested by

computer simulation. It was found that the method

has a built in smoothing effect that attenuates

rather than amplifies measurement errors.

lens focused just outside the core boundary.

Recording and processing the light distribution

follow the aid of a computer-controlled video- analysis system. The refractive index profile of the preform is computed from the intensity distribution, plotted, and fitted with a power-law curve within several minutes time. The repeatability of the index measurement is better than \%, and excellent agreement is obtained with profiles determined

interferometrically using slab samples from the tips

of the same preforms.

H. M. Presby and D. Marcuse

Optical fiber preform diagnostics

Appl. Opt. 18:23-30; 1979

A sensitive, nondestructive, and noncontacting method is described for obtaining structural information

on the preforms from which optical fibers are pro- duced. The technique allows the determination of the core size and the core eccentricity from direct

observation of light traversing the preform normal

to its axis. Also observable are the core-cladding

interface structure, individual deposition layer structure and variations, imperfections within the core and the cladding, and the presence of an axial refractive-index depression. Results and implications from a variety of multimode and single-mode

preforms are presented along with a theoretical analysis of the observations.

D. Marcuse and H. M. Presby

Focusing method for nondestructive measurement of optical fiber index profiles

Appl. Opt. 18:14-22; 1979

A new method to determine the refractive-index dis- tributions of the cores of optical fibers is presented. The fiber is immersed in index matching oil to eliminate light refraction at the outer core

boundary. Collimated light is passed transversely

through the fiber core and is detected with a microscope focused just above the plane of the core boundary. The intensity distribution in the image plane

is recorded with the aid of a computer-controlled

video-analysis system. The refractive-index profile

of the fiber core is then computed from this intensity distribution. In this paper we present error

estimates and show how well the focusing method

agrees with the interferometric slab method. The repeatability of the index measurement is approximately 2%, an error which is easily attributable to incident light level fluctuations.

H. M. Presby and D. Marcuse

Preform index profiling (PIP)

Appl. Opt. 18:671-677; 1979

An automatic and nondestructive focusing method to determine the refractive index distributions of optical fiber preforms is presented. The preform is immersed in index matching oil, and collimated light

is passed transversely through it. The intensity

distribution of the transmitted light is detected

with a vidicon camera equipped with a low f-number

Charoon Saekeang and Pak L. Chu

Nondestructive determination of refractive index profile of an optical fiber: Backward light scat- tering method

Appl. Opt. 18:1110-1116; 1979

A new nondestructive technique is presented for determining the refractive index profile of an optical fiber from its backscattered pattern arising

from a normally incident laser beam to the fiber

axis. The proposed method requires no sample pre- paration or index matching liquid. The principle of the method is to construct a deflection function

from the measured pattern. The index profile can

then be determined by the inversion of an Abel integral equation. Good agreement is obtained between

the index profile determined by this technique and that measured by the near-field scanning technique.

L. S. Watkins

Laser beam refraction traversely through a gradedindex preform to determine refractive index ratio and gradient profile

Appl. Opt. 18:2214-2222; 1979

A technique is described which permits the deter- mination of geometric and refractive index characters of graded-index preforms from measurements of the refraction of rays traced through the preform

perpendicular to the preform axis. A computer pro- gram was developed to trace rays through gradedindex preforms to display the refracting effect of the index properties and relate the ray incidence

43
angle to its deflection in traversing the preform.

An experimental apparatus has been developed in which a narrow beam of laser radiation is directed

at the preform and its deflection angle measured. Comparison between the experimental results and the

ray trace calculations using an interactive curve- fitting procedure gave nondestructive determinations

of the refractive index ratio A and index gradient

profile parameter a as well as measurement of the core dimensions.

amplitude and phase filters. We present also here a new technique for coding information issuing from

the scanning apparatus, which makes possible real time coding, thus avoiding image data storage. We describe an optical setup for the simulation of transaxial tomography together with a method for measuring three dimensional refractive index pro- files (for instance in fibers). This process can also be fully automatized and performed in real time with incoherent illumination.

K. F. Barren and C. Pask

Nondestructive index profile measurement of non- circular optical fibre preforms

Opt. Commun. 27:230-234; 1978

We present quantitative results for the effect of noncircularity on a method recently proposed by Chu

for the measurement of the refractive index profile

of an optical fibre preform. Analytical studies

show how Chu's method can be applied to elliptical

preforms.

Ernst Brinkmeyer

Refractive- index profile determination of optical fibers by spatial filtering

Appl. Opt. 18:1117-1122; 1979

Kazuo Hotate and Takanori Okoshi

C. Saekeang and P. L. Chu

Nondestructive determination of refractive-index

profile of an optical fibre: Forward light scat- tering method

Electron. Lett. 14:802-804; 1978

A nondestructive technique is presented for deter- mining the refractive-index profile of an optical fibre from its forward-scattered pattern arising

from a normally incident laser beam. This method

does not require any index-matching liquid and is not limited to single-mode fibres. It uses as essential information only the angular positions of the extrema in the measured pattern.

Ernst Brinkmeyer

Refractive- index profile determination of optical fibers from the diffraction pattern

Appl. Opt. 16:2802-2803; 1977

Semi automated measurement of refractive-index pro- files of single-mode fibers by scattering-pattern method

Trans. lECE Japan E61: 202-205; 1978

Semi automated measurement of the refractive-index

profiles of single-mode fibers using the scatteringpattern method developed by the same authors is described. The scattering-pattern method features

very high resolution, typically 0.2 um: hence at present it is the only method suitable for single- mode fibers. The measurements have been performed

by using a semiautomated system. This system consists of an automated measuring apparatus of the scattering pattern of softwares for calculating the refractive-index profile. The obtained profiles are compared with those of preforms.

P. L. Chu

Nondestructive measurement of index profile of an optical -fibre preform

Electron. Lett. 13:736-738; 1977

A simple and fast nondestructive method of measuring

the index profile of an optical -fibre preform is presented. In this method, a laser beam is shone perpendicularly to the preform axis, and the exit

angle of its backscattered ray is recorded as a function of the distance of the incident ray from

the horizontal axis. A numerical integration

involving these exit angles gives the profile.

K. Hotate and T. Okoshi

A. Landraud

Tomographie transaxiale par voie optique: Application a la mesure d'indicie des fibres (Transaxial

tomography by an optical method: Application to the measurement of fiber indices

Opt. Commun. 25:305-310; 1978

Usual transaxial tomography requires lengthy and computer performed calculations. It can be shown

that a coherent double diffraction optical process

gives good results without numerical treatment. The filter used is a so-called "p" filter; we describe a fully automatized technique for the realization of

Semiautomated measurement of refractive-index pro- files of single-mode fibers by scattering-pattern method

Tech. Digest, IOOC-77 Tokyo, 399-402; 1977

Semiautomated measurement of the index profiles of single-mode fibers using the scattering-pattern

method developed by the same authors is described.

The scattering-pattern method features very high

resolution, typically 0.2 urn; hence at present it is the only method suitable for single-mode fibers.

The obtained profiles are compared with those of preforms.

44
T. Okoshi and K. Hotate

Refractive-index profile of an optical fiber: Its measurement by the scattering pattern method

Appl. Opt. 15:2756-2764; 1976

This paper describes a new method {the scatteringpattern method) for determini.ng the refractive-index

profile in an optical fiber from its scattering pattern for a normally incident laser beam. The pro- posed method is applicable to an arbitrary profile

and is nondestructive. The spatial resolution is high, and the accuracy is good when the fiber dia- meter and the refractive-index variation are rela- tively small. The drawback is that a large number

of data are required; however, this difficulty has been overcome by using the automated measuring system described in this paper. The profile obtained

shows good agreement with design data.

T. Okoshi and K. Hotate

Computation of the refractive index distribution in

an optical fibre from its scattering pattern for a normally incident laser beam

Opt. Quantum Electron. 8:78-79; 1976

index optical fibers and preforms is presented. The technique is based on an analysis of the backscattered light when a beam from a cw laser impinges

transversely upon the fiber or preform. A geometrical-optics analysis shows that, under appropriate

assumptions, a combination of the refractive indexes and the radii of the core and cladding can be deter- mined from unique characteristics of the backscattered radiation pattern. The theory is compared to experimental observations with excellent agreement.

4.5 Near-Field Methods

K. F. Barrel and C. Pask

Leaky ray correction factors for elliptical multimode fibres

Electron. Lett. 16:329-330; 1980

Leaky ray attenuation in elliptical graded-index

fibres is related to the changes in the ray para- meter that are induced by fibre ellipticity. Para- bolic index fibres are described in detail. Results

are given for the correction factors which must be applied to the measured near-field intensity in order to obtain the refractive-index profile.

D. Marcuse and H. M. Presby

Light scattering from optical fibers with arbitrary

refractive-index distributions

J. Opt. Soc. Am. 65:367-375; 1975

A scattering theory is presented, which is capable

of predicting the light-distribution pattern that arises when a clad optical fiber of arbitrary core refractive-index distribution is illuminated by a laser beam perpendicular to its axis. Theoretical

predictions are compared to experimental results in the backscattering direction, with excellent agree- ment for fibers of practical interest leaving core

and cladding diameters on the order to 50 and 150

\isn, respectively. Considerable sensitivity to para- meter variations has been observed and implications

for diameter and refractive- index distribution

determinations are discussed.

Yung S. Liu

Direct measurement of the refractive indices for a small numerical aperture cladded fiber: A simple method

Appl. Opt. 13:1255-1256; 1974

M. Young

Calibration technique for refracted near-field scan- ning of optical fibers

Appl. Opt. 19:2479-2480; 1980

M. Young

Linearity and resolution of refracted near-field

scanning technique

Tech. Digest, Opt. Fiber Meas.-1980 Boulder, 37-40;

1980, U.S. Govt. Printing Office

J. J. Ramskov-Hansen, M. J. Adams, A. Ankiewicz, and

F. M. E. Sladen

Near-field correction factors for elliptical fibres

Electron. Lett. 16:580-581; 1980

Correction factors for use with the near-field scanning method of index profile determination of elliptical fibres are presented. Theory and experiment

show that different correction factors are required

for the major and minor axes.

H. M. Presby and D. Marcuse

Refractive index and diameter determinations of step index optical fibers and preforms

Appl. Opt. 13:2882-2885; 1974

A new method to determine the index of refraction in combination with the diameter of the cores of stepP. V. H. Sabine, F. Donaghy, and D. Irving

Fibre refractive-index profiling by modified near- field scanning

Electron. Lett. 16:882-883; 1980

45
A modified bounded-mode near-field scanning method

for determining the refractive-index profiles of

optical fibres is described. The technique is simple to implement and allows the fibre numerical aperture and geometry to be measured.

B. Daino, S. Piazzola, and A. Sagnotti

Spatial coherence and index-profiling in optical fibers

Opt. Acta. 26:923-928; 1979

A simple relation is proved to exist between the coherence properties of the light emerging from the end cross-section of multi-mode optical fibres,

excited by means of spatially incoherent sources,

and their refractive index distributions. Experimental results showing the possibility of visualizing the index profile are reported.

K. I. White

The measurement of the refractive index of optical fibres by the refracted near field technique

Digest, Fourth Eur. Conf. Opt. Commun., Genova, 146-

155; 1978

The refracted near field technique gives a direct measurement of an optical fibre profile without any need for computation or correction. Sample preparation is simple and end degradation is not a problem.

Leaky modes make no contribution. The method is ap- plicable to both multimode and monomode fibres and, as well as the profile, yields the numerical aperture of the fibre together with the core and clad

diameters, core central ity and ellipticity. It thus avoids the drawbacks associated with other techniques while giving more information. This paper dis- cusses in detail both the theory of the method and also practical aspects of the experiment. Typical results are presented for both multimode and mono- mode fibres.

K. I. White

Practical application of the refracted near-field

technique for the measurement of optical fibre

refractive index profiles

Opt. Quant. Electron. 11:185-196; 1979

Both the theoretical basis and experimental realization of the refracted near-field technique for the direct measurement of optical fibre profiles are presented. The technique requires minimal sample

preparation, no computation and is applicable to both single and multimode fibres. Both the core and

the cladding are profiled. After outlining the problems associated with other techniques, the use

of this method for the measurement of fibre profile,

numerical aperture and geometry is discussed. Leaky mode rejection and resolution are treated in detail.

A fitting procedure for determining the a- value of a profile is given. The experimental apparatus is fully discussed. Results are presented to illus- trate both t|ie applical^ility of the technique to single and multimode fibres and also the rejection

of leaky modes. The experimental sensitivity is shown sufficient to reveal an index fluctuation

having a wavelength <1 urn and an amplitude of <0.0001.

B. Daino, S. Piazzola, and A. Sagnotti

A new method for measuring the index profile of optical fibers

Digest, Fourth Eur. Conf. Opt. Commun., Genova, 156-

161; 1978

We report a new non-destructive method for measuring

the index profile of optical fibers.

By means of simple arguments we show that a direct

relation exists between the absolute value of the complex degree of coherence of the transmitted light

and the value of the refractive index in every point

of the exit face of an optical fiber.

M. J. Adams, D, N. Payne, F. M. E. Sladen, and

A. Hartog

Resolution limit of the near-field scanning technique Proc, Third Eur. Conf. Opt. Commun., Munich, 25-27;

1977

The near-field intensity distribution in a fullyexcited fibre is calculated by superposition of pro- pagating modes. It is shown that the resolution of the near-field scanning technique is limited by the number of modes supported by the fibre. Experimental confirmation is given.

M. Eve

Near field and far field power distributions in a multimode graded fibre

Opt. Quant. Electron. 9, 459-464; 1977

It is shown in this paper that the near field and

far field power distributions corresponding to any distribution of rays in an arbitrary graded fibre, reach a steady state along the fibre. This steady state is usually a function of the input distribution of rays and of the refractive index profile of the fibre. The case of parallel beam injection is considered and an analytical expression for the near field power distributions for any arbitrary profile

is found. This suggests a new method of refractive

index profile measurement which is free of leaky ray corrections and can be very sensitive near the opti- mum profile for time dispersion.

K. Petermann

Uncertainties of the leaky mode correction for near- square-law optical fibres

Electron. Lett. 13:513-514; 1977

It is shown that the leaky-mode correction as used, for example, for the near-field scanning technique.

46
becomes uncertain for near-square-law fibres if they deviate from perfect circular symmetry. Results for

the transition of the leaky-mode behaviour are presented.

W. J. Stewart

A new technique for measuring the refractive index profiles of graded optical fibres

Tech. Digest, I00C-77:395-398; 1977

A new near-field technique has been devised that

offers substantially better performance than existing methods. In particular no leaky mode correction

is necessary, detail resolution is improved and both

core and cladding are profiled, enabling the absolute indices to be determined.

G. T. Summer

A new technique for refractive profile measurement

in multimode optical fibres

Opt. Quantum Electron. 9:79-82; 1977

M. J. Adams. D. N. Payne, and F. M. E. Sladen

Length-dependent effects due to leaky modes on multimode graded-index optical fibres

Opt. Commun. 17:204-209; 1976

The radiation losses of tunnelling leaky modes in graded-index optical fibres are calculated theoretically, and it is shown that the near-field intensity profile has a length dependence. Consequently

measurements of the near-field intensity distribution do not give the refractive index profile

directly, and a correction factor must be applied.

We have investigated this factor and find that it depends only on a single normalisation involving

fibre length, core radius and normalised frequency. A further use of the correction factor is to determine the total power attenuation due to the loss of leaky modes.

M. J. Adams, D. N. Payne, and F. M. E. Sladen

Correction factors for the determination of optical

fibre refractive index profiles by the near-field

scanning technique

Electron. Lett. 12:281-283; 1976

Numerical calculations are presented of the correction factor for use with the near-field scanning method of index profile determination. It is shown

that a single curve can be applied to a range of possible profiles, and a numerically obtained average curve is given.

Bell Sys. Tech. J. 55:1489-1508; 1976

A novel technique for measuring the refractive index profile of optical fibers is demonstrated, which offers substantial advantages over alternative methods. The method consists of illuminating a small area of the fiber core and measuring the total transmitted power. The transmission of leaky modes

is accounted for in the manner reported previously

by other authors. The index profiles of germaniumdoped fibers obtained by this technique are compared

to interferometric measurements. The resolution is shown to be, limited by wave optics effects to about

X {4n/2A)" , where A e An/n. The distortion of the inaex profile as the wavelength varies and waveoptics effects are investigated.

Robert Olshansky

Leaky modes in graded index optical fibers

Appl. Opt. 15:2773-2777; 1976

Leaky mode attenuation coefficients for graded index

optical fibers are derived using the WKB approximation. For the case of a parabolic index profile,

the attenuation coefficients for explicitly evalu- ated and used to calculate the leaky mode contribution to near field and attenuation measurements.

Failure to observe the expected leaky mode contributions in several graded index fibers is interpreted

as evidence for the presence of an additional loss mechanism.

F. M. E. Sladen, D. N. Payne, and M. J. Adams

Determination of optical fiber refractive index profiles by a near-field scanning technique

Appl. Phys. Lett. 28:255-258; 1976

A simple and rapid method is descri mining the refractive index profile

fiber by observation of the near-fi distribution. It is shown that in presence of tunnelling leaky modes and that these cause a length-depen

measurement. A correction factor i may be applied to the measured inte once the fiber length, core diamete

aperture are known. Examples are g ments made on both step and graded

bed for deterof an optical eld intensity

many cases the

is unavoidable

dent error in the

s developed which

nsity profile

r, and numerical

iven of measureindex fibers.

D. N. Payne, F. M. E. Sladen, and M. J. Adams

Index profile determination in graded index fibres

Proc, First Eur. Conf. Opt. Commun., London, 43-45;

1975, lEE

4.6 Reflection Methods (Longitudinal)

J. A. Arnaud and R. M. Derosier

Novel technique for measuring the index profile of optical fibers

T. Wilson, J. N. Gannaway, and C. J. R. Sheppard

Optical fibre profiling using a scanning optical

microscope

47
Opt. Quantum Electron. 12:341-345; 1980 Electron. Lett. 14:811-812; 1978

A scanning optical microscope is used to measure

directly the refractive-index profile of an optical

fibre. The effects of illuminating the fibre end with a highly convergent beam of light are considered.

J. Stone and H. E. Earl

A theoretical model is developed that demonstrates

the presence of a ring in the far-field pattern when

a graded-index fibre is excited by a colli mated beam incident at a given radius from the core centre.

The angular position of this ring can be used to ob- tain an estimate of the fibre refractive-index profile, provided a correction for the finite beam spot

size is applied.

Surface effects and reflection refractometry of optical fibres

Opt. Quantum Electron. 8:459-463; 1976

Refractive index profiles of several types of sili- ca-based low-loss optical fibres have been measured

by the surface reflection technique. When polished

samples are used inaccurate data are obtained. For germanium- and phosphorous-doped samples good re- sults are obtained using samples prepared by frac- turing the end of the fibre. For borosilicate

fibres rapid changes due to atmospheric exposure

result in inaccurate data.

W. Eickhoff and E. Wei del

Measuring method for the refractive index profile of optical glass fibres

Opt. Quantum Electron. 7:109-113; 1975

A new method for measuring the refractive index pro- file of optical glass fibres is described. This simply monitors the reflection of a focused laser beam from a polished fibre end face. Detailed tests

on the accuracy and resolution of the method are described and the index profiles of several fibres

are given as an example of its feasibility.

Masahiro Ikeda, Mitsuhiro Takeda, and

Haruo Yoshikiyo

Refractive index profile of a graded index fiber: Measurement by a reflection method

Appl. Opt. 14:814-815; 1976

4.7 Other Methods

S. Tanaka, G. Tanaka, M. Hoshikawa, and N. Inagaki

Non-destructive refractive index profile identifica- tion of optical fiber preform utilizing x-rays

Digest, Sixth Eur. Conf. Opt. Commun., York, 165-

168; 1980. lEE

A. Ankiewicz, M. J. Adams, D. N. Payne, and F. M. E. Sladen

Parallel-beam excitation method for estimating

refractive-index profiles in optical fibres

K. Maeda and J. Hamasaki

A method of determining the refractive index profile

of a lenslike medium

J. Opt. Soc. Am. 67:1672-1680; 1977

A simple method to obtain the fourth-order coefficient of the series expansion for the radial distri- bution of a lenslike medium is described. The coef- ficient is obtained by measuring the position of a discontinuity of the far-field intensity pattern. The relation between the coefficient and this position is calculated by using either the ray theory or the wave theory. By using a ray model, the position

of the discontinuity and the macroscopic intensity

distribution is easily obtained.

L. Jeunhomme and J. P. Pocholle

Measurement of the numerical aperture of a step- index optical fibre

Electron. Lett. 12:63-64; 1976

We describe a simple method for measuring the numerical aperture of a step-index fibre. The value obtained by this method depends only on the index difference between the core and cladding, and it is then possible to deduce the index difference from

this measurement.

G. B. Brandt

Two wavelength measurements of optical waveguide

parameters

Appl. Opt. 14:946-949; 1975

Optical waveguide parameters, guide index of refraction and thickness, can be measured from the knowledge of mode propagation constants at two different

wavelengths. This method is as accurate as the two- mode method and can be used for both single-mode

guides and multimode guides. The index of refraction of various optical components must be known at

both the wavelengths; in cases where these indices

are not directly available it is possible to inter- polate this information from the known properties of other glasses. This paper describes the experimental and analytical aspects of the two-wavelength measurement technique.

48
5. CHARACTERIZATION OF DISCONTINUITIES

(JOINTS, SPLICES, CONNECTORS, COUPLERS, DEFECTS)

5.1 General transverse displacement and fiber parameter mis- matches.

N. K. Cheung and N. M. Denkin

An automatic inspection system for single fiber

connector plugs

Tech. Digest, Symp. Opt. Fiber Meas.-1980 Boulder,

45-48; 1980, U.S. Govt. Printing Office

P. DiVita and U. Rossi

Realistic evaluation of coupling loss between dif- ferent optical fibers

J. Opt. Coranun. 1:26-32; 1980

Coupling between two multimode optical fibers with

different numerical aperture and core diameter and including lateral displacement is studied. Calcula- tions are performed for fibers with any index profile and any power distribution among ray congruences. The propagation effects in the second fiber

are also taken into account in a rigorous way. Finally asymptotic expressions of losses for small values of mismatch and error parameters are given

together with a discussion on the minimization of coupling losses.

K. S. Gordon and F. M. E. Sladen

Difficulties encountered in the measurement of optical fiber interconnection performance

Tech. Digest, Symp. Opt. Fiber Meas.-1980 Boulder,

67-72; 1980, U.S. Govt. Printing Office

Ken-ichi Kitayama, Masaharu Ohashi, and Shigeyyuki

Seikai

Mode conversion at splices in multimode graded-index

fibers

IEEE J. Quantum Electron. QE-16:971-978; 1980

Mode conversions occuring at a splice in multimode

graded-index fibers are investigated theoretically,

and their effects on impulse responses are verified

experimentally. The relation describing the mode behavior at a splice in existence of a geometrical offset and fiber parameter mismatches is derived by

taking a skew ray as well as meridional ray into consideration. Then the mode transfer matrix is obtained to determine the variations in mode power distribution and impulse response due to the mode conversions occuring at a splice. The measured mean delay time difference between lower and higher mode

pulse responses and baseband frequency response for spliced graded-index fibers are compared with the theory obtained from the transfer functions of individual fibers and the mode transfer matrix which

describes the mode conversions at a splice due to a

S. C. Mettler

A general characterization of splice loss for multimode optical fibers

Bell Sys. Tech. J. 58:2163-2182; 1979

The Gaussian point transmission model for calculating optical fiber splice loss is extended to the general case of splice loss between fibers which

differ in one or more intrinsic parameters —core

radius, index of refraction profile shape, and maxi- mum index of refraction difference between core and cladding. The model is first verified for splices

with index-of -refraction profile mismatch. The average difference between calculated and measured

splice loss due to profile parameter mismatch is 0.04 dB. Comparisons are also made between calcu- lated and measured splice loss for ten different

splices with mismatch in all three intrinsic parameters. The average difference between the calculated loss and the average of several measured

losses for these ten cases was 0.06 dB. The additional losses introduced by transverse offset mea- sured for one set of mismatched fiber splices agree

with the calculated values within 0.1 dB. Loss due

to misalignment of elliptical core fibers is calcu- lated and measured with agreement within 0.06 dB for

the maximum loss case. Both the model and the experimental data show that, for a given percentage

mismatch, index of refraction profile parameter mis- match and core ell ipti city contribute significantly

less to splice loss than mismatch of core radius or numerical aperture. A family of curves for splice

loss vs transverse offset is presented for various

numerical aperture mismatches and core radius mis- matches, since these parameters are typically the largest components of splice loss in practical loss

in practical fiber optic systems.

S. Nemoto and T. Makimoto

Analysis of splice loss in single-mode fibres using

a Gaussian field approximation

Opt. Quantum Electron. 11:447-457; 1979

By using a Gaussian field approximation to the fundamental mode in a single-mode fibre, a very simple formula is derived for the splice loss in the two fibres when transverse, longitudinal and angular

misalignments exist simultaneously. It is shown that the effects of the three misalignments on the splice loss are more significant for step-index

fibres than for parabolic-index fibres, and also

that matching oil in the gap between the fibres is effective for the end separation, but produces a reverse effect for the tilt. Calculated coupling

efficiency between step-index fibres is compared

with the experimental data reported so far, and good

agreement between them is observed.

49
Y. Fuji! and N. Suzuki

Precise angular misalignment measurement in optical fibre connector plugs

Electron. Lett. 14:243-245; 1978

A new precise measurement of angular misalignment in optical fibre connector plugs is described.

M. J. Adams, D. N. Payne, and F. M. E. Sladen

Splicing tolerances in graded-index fibers

Appl. Phys. Lett. 28:524-526; 1976

Calculations are presented showing that, in general,

a parabolic-index fiber is more sensitive to lateral misalignments within a splice than a step-index

fiber. However, misalignments result in the excitation of leaky modes in graded-index fibers, and this

can lead to optimistic joint loss measurements. Effective losses are given for various lengths of fiber following the splice, and it is shown that a parabolic-index fiber may appear more tolerant to misalignment than a step-index fiber when short lengths are used.

D. Gloge

Offset and tilt loss in optical fiber splices

Bell Sys. Tech. J. 55:905-916; 1976

Transverse offset and angular misalignment (tilt) are serious causes of loss in multimode fiber

splices. Our computation of these losses in multi- mode graded-index fibers reveals that the loss depends strongly on the power distribution in the fiber. We find that offsets of 0.1 of the core radius (or tilts of 0.1 of the fiber numerical aperture) cause a loss of 0.1 dB in the case of steady-state conditions, and between 0.34 and 0.38

dB if the power distribution is assumed as uniform.

We compare these results with measured offset loss values and conclude that the steady-state distribution better reflects transmission line conditions

than the uniform distribution.

C. M. Miller

Transmission vs tranverse offset for parabolicprofile fiber splices with unequal core diameters

Bell Sys. Tech. J. 55:917-927; 1976

A geometrical optics model is presented that is based on defining a local numerical aperture as a function of fiber radius with a uniform power dis- tribution. Transmission vs transverse offset char- acteristics for parabolic-profile fiber splices are calculated for unequal fiber-core diameters. We show that the often-used assumptions of equal -mode excitation, equal -mode attenuation, and no-mode coupling are not adequate to calculate realistic

transmission vs offset characteristics. Splice-loss measurements with long fiber lengths on each side of the splice show less than the calculated sensitivity

to small offsets and greater than the calculated

sensivitity to large offsets.

5.2 Insertion Methods

P. Kaiser, W. C. Young, N. K. Cheung, and L. Curtis

Loss characterization of biconic single-fiber con- nectors

Tech. Digest, Symp. Opt. Fiber Meas.-1980 Boulder,

73-76; 1980, U.S. Govt. Printing Office

U. Unrau and A. K. Agarwal

Modekontrollierte Messungen an Verzweigungsgliedern

fur optische Nachrichtensysteme (Mode controlled

measurements on couplers for optical telecommunications systems)

Digest, Mess in der opt. Nachrichten. , Berlin, 173-175; 1980, VDE-Verlag

Y. Daido, E. Miyauchi, T. Iwama, and No. Tokoyo

Measurement method of fiber connection loss using

steady-state power distribution

Tech. Digest, Opt. Fiber Commun., Washington, 112-

114; 1979, Opt. Soc. Am.

A. H. Cherin and R. P. Rich

Measurement of loss and output numerical aperture of optical fiber splices

Appl. Opt. 17:642-645; 1978

An ensemble of optical fiber splices has been evaluated to determine how source launching conditions

and length of fiber between the source, splice, and detector affect the splice loss and far field output

NA. The loss of a splice is strongly dependent upon

the energy distribution and NA of the beam at the input of the splice. For the range of NA's considered, the splice loss varied by 0.5 dB. The average NA at the output of the ensemble of splices was greater than its corresponding input NA by as much

as 12%. The splice appears to act as a transformer

converting the input energy distribution into one at the output that contains a greater amount of its energy in higher order modes. As a consequence of this, the loss of a fiber following the splice in a long transmission path is greater than the loss the fiber would exhibit if measured with steady state excitation conditions.

T. C. Chu and A. R. McCormick

Measurements of loss due to offset, end separation,

and angular misalignment in graded index fibers

excited by an incoherent source

Bell Sys. Tech. J. 57:595-602; 1978

Transmission losses versus fiber end offset separation, and angular misalignment of graded index

fibers excited by an incoherent source, have been measured in two independent experiments. The

50
measurement setup, fiber diameter, and length were different in the two experiments, yet the measurement results are strikingly similar. The loss mea- surements clearly show that transverse offset is much more critical in connector and splice design

than angular misalignment and end separation. Two- tenths of the fiber core radius in axial separation

combined with 1° in angular misalignment may cause

0.5 dB loss.

source and the fibers used play an important role in determining how delay distortion is affected by

splice misalignment. The first fiber exhibited a great deal of mode mixing and a very small increase

in delay distortion as the fibers were offset in the splice. In contrast, the second fiber exhibited

very little mode mixing, but increased markedly in delay distortion as the fibers in the splice were

displaced.

Iwao Hatakeyama and Haruhiko Tsuchiya

Fusion splices for optical fibers by discharge

heating

Appl. Opt. 17:1959-1964; 1978

A new type of electric discharge fusion splicing

apparatus for optical fibers offering several ad- vantages is developed and evaluated. An average

splicing loss of 0.10 dB is obtained for step-index

multimode silica fibers with a 50-pm core diameter. Tolerances in discharge energy, fiber misalignment,

compression force and stroke length during fusion, and end face conditions are discussed experimentally. No accurate fiber axis adjustment is necessary

in this apparatus. Mechanical strength of the splice is also excellent.

A. H. Cherin and P. J. Rich

Multigroove embossed-plastic splice connector for joining groups of optical fibers

Appl. Opt. 14:3026-3030; 1975

To install and maintain successfully an optical

fiber communications system, techniques for splicing

individual and groups of optical fibers under field

conditions must be developed. In this paper a technique for splicing groups of optical fibers with a one piece multigroove embossed plastic connector is described. Using 132-um multimode fibers with 94-ym

core diameters, the average transmission loss of the splice joints measured was 0.12 dB with a standard deviation of 0.11 dB and a range of loss values from

0.0 dB to 0.53 dB.

Jun-ichi Sakai and Tatsuya Kimura

Splice loss evaluation for optical fibers with

arbitrary-index profile evaluation for optical

fibers with arbitrary-index profile

Appl. Opt. 17:2848-2853; 1978

A method is presented for calculating offset and tilt losses for fiber splices with axially symmetric

arbitrary-index profiles by approximating the profile with a staircase function. This method is applied to a large-core dual -mode fiber with zero

intermodal dispersion as well as to single-mode

fibers with step- and parabolic-index profiles.

When a splice loss of 0.2 dB is permitted, the nor- malized offset misalignment is found to be 0^^=0.635 for the dual -mode fiber at normalized frequency

v=4.605 and a power-law exponent a=4.5. The D^ value compares favorably with the values 0.560 and 0.614 for conventional step- and parabolic-index

single-mode fibers, respectively. The dual-mode fiber is superior to the step- and parabolic-index

fibers with respect to permissible splice offset

tolerances.

0. L. Bisbee

Measurements of loss due to offsets and end separations of optical fibers

Bell Sys. Tech. J. 50:3159-3168; 1971

If fibers are to be coupled together by means of detachable connectors, there is a need to know how

much light will be lost by misalignment or axial separation of the fiber ends.

Measurements were made of coupling efficiency from

one fiber to another versus offset and end separation with an without index-matching liquid between

the ends for a single-mode and a multimode fiber at X-0.6328 ym. Graphs are presented for offsets as great as 3 radii and for end separations up to 127

pm. Maximum coupling efficiency of 97 percent was obtained, and about 50 percent was obtained with an offset of 1 radius.

5.3 OTDR Methods (See also 2.3)

A. H. Cherin and P. J. Rich

Delay distortion characteristics of optical fiber

splices

Appl. Opt. 16:497-500; 1977

The delay distortion characteristics of optical

fiber splices are evaluated. Two 1.35-km graded

index fibers with different transmission characteristics were each bisected and spliced together to determine how longitudinal and transverse displace- ment of fibers in a splice affect the delay distortion characteristics of a transmission path. The transmission characteristics of both the optical

A. J. Conduit, D. N. Payne, and A. H. Hartog

Optical fibre backscatter-loss signatures: Identi- fication of features and correlation with known defects using the two channel technique

Digest, Sixth Eur. Conf. Opt. Commun., York, 152-

155; 1980, lEE

51
A. LeBoutet

Contribution to splice loss evaluation by the back- scattering technique: A statistical comparison with

insertion loss data

Tech. Digest, Symp. Opt. Fiber Meas.-1980 Boulder,

77-80; 1980, U.S. Govt. Printing Office

K. Okada, K. Hashimoto, T. Shibata, and Y. Nagaki

Optical cable fault location using correlation tech- nique

Electron. Lett. 16:629-630; 1980

The letter describes a correlation based optical cable fault location technique which using a 1.3 urn wavelength, can detect a broken point 10 km distant

from source.

T. Asahara, Y. Ueno, M. Shimizu, and S. Naruse

Optical fiber fault locating method for long haul optical fiber communications link

Proc, Opt. Commun. Conf., Amsterdam, 14.5-1--14.5-

4; 1979

A new optical fiber fault locating method which is suitable for in-service monitoring of long haul optical fiber communication link. The system accuracy

was within 24 m in the field experimental system.

B. Costa, F. Esposto, C. D'orio, and P. Morra

Splice loss evaluation by means of the back-scattering technique

Electron. Lett. 15:550-551; 1979

The results of a detailed experimental analysis on joint loss measurements by the back-scattering method are presented. A comparison with more usual in- sertion-loss technique is performed. High sensitivity and accuracy are found when measuring very similar fibres; a suitable procedure is indicated

for measuring slightly different fibres.

P. Matthijsse and C. M. DeBlok

Field measurement of splice loss applying the back- scattering method

Electron. Lett. 15:795-797; 1979

A method is proposed to measure mean splice loss applying the back-scattering method from one end of the fibre link only. To eliminate the influence of the difference in backscattering properties of the spliced fibres, each backscattering coefficient is measured separately beforehand.

P. Matthijsse and C. M. DeBlok

Measurement of splice insertion loss using the back- scattering method Proc, Opt. Commun. Conf., Amsterdam, 9.5-1--9.5-4;

1979

To inspect the quality of splices in optical fiber

links the backscattering method (optical time domain reflectometry) seems to be a powerful method. In this paper it is shown that this method is suited

for measuring splice insertion loss only if special

precautions are taken in view of the difference in backscatter coefficients.

J. Guttman and 0. Krumpholz

Location of imperfections in optical glass-fibre

waveguides

Electron. Lett. 11:216-217; 1975

An echo-pulse technique for the location of fibre

imperfections is described. The technique has been successfully applied to a plastics-coated Selfoc fibre and a plastics-coated silica-based fibre.

Both showed a break. In the Selfoc fibre, an additional fibre defect was located. The same method

may be used to measure rapidly the fibre length.

A. LeBoutet

Analysis of backscattering results applied to cable connection

Proc. 1979

Opt. Commun. Conf., Amsterdam, 9.6-1--9.6-6;

That article deals with an analysis of results obtained by the backscattering technique applied to connectors. It tends to prove that the connector

cannot be characterised in its junction plan only but has effects on the following fiber and is also affected both by the preceding fiber and injection

conditions.

A more rigorous and realistic method of evaluation

of the connector loss is also suggested for system

application.

52
MODAL CHARACTERIZATION OF MULTIMODE FIBERS

6.1 General

0. G. Leminger and G. K. Grau

Near-field intensity and modal power distribution in multimode graded index fibres

Electron. Lett. 16:678-679; 1980

A relation between the

the near-field intensi near-field intensity ( speckle patterns) is u modal power distributi

a unique modal power d field intensity. For follow relations alrea

modal power distribution and

ty is derived. Whereas the averaged over all possible

niquely determined by the

on, it is impossible to derive istribution from a given nearspecial additional assumptions

dy known from literature.

Ken-ichi Kitayama, Mitsuhiro Tateda, Shigeyuki

Seikai, and Naoya Uchida

Determination of mode power distribution in a para- bolic-index optical fiber: Theory and application

IEEE J. Quantum Electron. QE-15:1161-1165; 1979

A novel measurement meathod for determining mode

power distribution in a multimode parabolic-index

fiber is developed. Using this method, the mode

power distributions are obtained in terms of the principal mode number by numerically processing the measured Fraunhofer diffraction patterns of the near-field patterns on an output fiber endface. As

an example, differential mode attenuation of a multimode parabolic-index fiber is measured. It is confirmed experimentally that the method is practically applicable to the mode power distribution mea- surements in a parabolic-index fiber.

C. M. Miller and R. B. Kummer

Direct measurement of mode coupling effects using a mandrel wrap mode filter

Digest, Sixth Eur. Conf. Opt. Commun., York, 99-102;

1980, lEE

Y. Dai do, E. Miyauchi, T. Iwama, and T. Otsuka

Determination of modal power distribution in gradedindex optical waveguides from near-field patterns

and its application to differential mode attenuation measurement

S. Piazzola and G. DeMarchis

Analytical relations between modal power distribution and near-field intensity in graded-index fibres

Electron. Lett. 15:721-722; 1979

Modal power distribution is an Important characteristic of optical fibres. Under the assumption that modes belonging to the same degenerate mode group

carry the same amount of power, simple expressions

are derived relating near-field intensity and modal power distribution in a-exponent index-profile

optical fibres.

Appl. Opt. 18:2207-2213; 1979

A technique is introduced that determines power dis- tribution in fibers from the measured near-field

pattern, assuming that: (1) the optical power dis- tributes uniformly among degenerated modes with the

same propagation constant, (2) enough modes are excited to ensure the validity of calculation by

geometrical optics, and (3) the phase of each propagation mode has no correlation. Experiments verified that the fibers have the function of flattening

power distribution among modes with the same propagation constant. This fact shows that assumption

(1) does not severely limit the applicability of the technique. Wave optical calculation is done to determine the numbers of modes that must be excited

to satisfy assumption (2). As an example of application of the technique, differential mode attenuation of graded-index fibers is determined from

longitudinal variation of the measured near-field

pattern.

W. F. Love

Novel mode scrambler for use in optical -fiber band- width measurements

Tech. Digest, Opt. Fiber Commun., Washington, 118-

120; 1979, Opt. Soc. Am.

W. J. Stewart

Method for measuring power distributions in graded

and step-index fibers

Tech. Digest, Opt. Fiber Commun., Washington, 116-

118; 1979. Opt. Soc. Am.

F. T. Stone and P. H. Krawarik

Effects of different mode filters on optical -fiber measurements

Tech. Digest, Opt. Fiber Commun., Washington, 122-

123; 1979, Opt. Soc. Am.

H. R. D. Sunak, M. A. De Batista, and J. Neto

Measurements of mode conversion coefficients in multimode optical fibres

J. Inst. Electron. Telecomm. Eng. (India) 25:302-

305; 1979

In order to assess quantitatively the quality of optical fibres preliminary measurements have been caried out with a very simple system, and the nor- malized mode conversion coefficient (D) has been calculated. The values of D obtained are of the

53
order of 2x10"^ rad m' for the fibres and these compare very favourably with the results obtained in other laboratories.

L. Jeunhomme and J. P. Pocholle

Selective mode excitation of graded index optical fibers

Appl. Opt. 17:463-468; 1978

A method is described permitting

small number of modes in graded

order of the launched mode being determined. Using this launchin

possible to determine the index difference of graded core fibers

pared with those obtained by oth Other important fiber parameters

ferential attenuation and the di tion delay time as a function of are also obtained, giving an ins mental propagation characteristi

excitation of a index fibers, the easily varied and

g technique, it is profile and index results are comer techniques.

such as the dif- fferential propagathe mode parameter,

ight into the fundacs of the fiber.

Kenichi Kitayama and Masahiro Ikeda

Mode mixing effects in optical fibers caused by

sheathing and multi stranding: Measurements

Appl. Opt. 17:3660-3564; 1978

Mode coupling coefficients were measured in a multi

mode stepindex fiber at different steps of the process of manufacturing a multistrand optical fiber

cable. It was established that the mode coupling

coefficients of the unsheathed fiber were relatively

small and nearly the same for all the guided modes.

By sheathing with nylon and multi stranding, the mode coupling coefficients between lower-order modes increased rapidly due to microbends, while in the vicinity of the highest-order mode, they remained

unchanged. From impulse response waveforms and baseband frequency responses, it was observed that

mode mixing effects became more noticeable as the mode coupling coefficients increased. Also, it was found that the excess loss caused by microbends was relatively small

Kenichi Kitayama and Masahiro Ikeda

Mode coupling coefficient measurements in optical fibers

Mitsunobu Miyagi , Shojiro Kawakami , Masaharu Ohashi

,

and Shigeo Nishida

Measurement of mode conversion coefficients and mode dependent losses in a multimode fiber

Appl. Opt. 17:3238-3244; 1978

Richard Payne and Lionel 0. Bouthillette

Effect of cladding modes on the far-field radiation

pattern for a multimode step-index optical fiber

Appl. Opt. 17:2132-2134; 1978

Hiroshi Shigesawa, Toyoki Matsuo and Kei Takiyama

Measurements of excitation condition and quantitative mode analysis in optical fibers

IEEE J. Quantum Electron. QE-16:36-44; 1980

The purpose of this paper is to describe an accurate method for determining the pulsed-power distribution

along optical fibers and also to present a technique

for measuring the launching conditions produced by an input laser beam. Experimental results demon- strate both the accuracy and the effectiveness of those methods for investigating the transmission

characteristics of optical waveguides. Various factors having an important influence upon the accuracy

are discussed, and appropriate methods for minimizing the systematic errors also are presented.

K. Thyargarajan, Anurag Sharma, and A. K. Ghatak

Efficient coupling of incoherent light into optical fibers and bundles

Appl. Opt. 17:2416-2419; 1978

The excitation efficiencies of a few lower order

modes in a W-type fiber have been studied when the modes are excited with tilted as well as off -set Gaussian beams. The effect of beam size, angle of incidence, the radius of curvature of the incident

wavefront, and the off-axis displacement on the ex- citation efficiencies has been obtained. It is found that in order to couple maximum power into the fundamental mode, the incident wavefront must be plane and the beam must be incident axially along

the fiber with a suitable value of the beam size.

Appl. Opt. 17:3979-3983; 1978

The measuring method of the mode cient was developed to apply to

It is shown that a mode coupling calculated from each mode group Measurements were made with two and short-length multimode stepresult, it was observed that in by nylon, there existed a strong

lower order modes. When it is a mode coupling is generated by mi correlation length and standard curvature were estimated as 2.0 respectively.

coupling coeffimultimode fibers. coefficient can be

pul se waveform.

cases of long-length

index fibers. As a the fiber sheathed

mode coupling in ssumed that this crobendings, the deviation of the mn and 4.2x10" TM"''-,

Hideaharu Tokiwa, Yasuharu Suematsu and Kazuhito

Furuya

Estimation of coupling length in mode-coupled multimode optical fibers

Trans. lECE Japan E61:192-195; 1978

A method to estimate the coupling length of the fiber in which modes couple each other due to the random bending of fiber axis is given. The coupling

length is estimated from the comparison of the measured transfer function to the theoretical one which

is derived previously. The coupling length of a graded-index fiber is estimated to be about 0.8 km

54
using this method. Further, the coupling length of recent graded-index fibers is presumed to be about

several km. For step-index fibers, it is estimated

to be in the range between 0.5-5 km.

the identification of individual modes in a fibre carrying up to 80 or 100 modes in all and provides a non-destructive method for the study of the length

and bend dependence of the energy carried by the highest order modes.

Masahiro Ikeda, Yasuji Murakami, and Kenichi Kitayama

Mode scrambler for optical fibers

Appl. Opt. 16:1045-1049; 1977

Mode conversion at a splice was measured. Even the best splice, whose transmission loss was less than 0.01 dB, caused a mode conversion equaling about 11%

of the total power. Spliced fiber transmission

characteristics were influenced by the splicing con- ditions. To avoid deviations in characteristics due

to splices a simple and effective mode scrambler was fabricated. Its insertion loss was less than 0.3 dB for a laser diode. Each mode's output waveform was found to be the same as the total output waveform.

Massahiro Ikeda, Akira Sugimura, and Tetsuhiko

Ikegami

Multimode optical fibers: Steady state mode exciter

Appl. Opt. 15:2116-2120; 1975

The steady state mode power distribution of the multimode graded index fiber was measured. A simple

and effective steady state mode exciter was fabri- cated by an etching technique. Its insertion loss was 0.5 dB for an injection laser. Deviation in transmission characteristics of multimode graded

index fibers can be avoided by using the steady

state mode exciter.

S. Zemon and D. Fellows

Characterization of the approach to steady state and

the steady state properties of multimode optical fibers using LED excitation

Opt. Commun. 13:198-202; 1975

A simple technique has been developed to characterize the approach to steady state and the steadystate properties of multimode fibers using LED excitation. Results are given for 6 mil Selfoc fibers whose far-field pattern for the steady state is in excellent agreement with a calculation by Marcuse.

To first order, the steady-state mode distribution

fits a simple model of uniform modal excitation of a fiber with a reduced numerical aperture.

J. E. Midwinter and M. H. Reeve

A technique for the study of mode cut-offs in multimode optical fibres

Optoelect. 6:411-416; 1974

We describe a technique of using a variable wavelength source to study mode cut-offs up to a V value

of 20 for the optical fibre by means of the radiated

(scattered) power leaving the fibre. This allows

55
7. GEOMETRIC MEASUREMENTS

Mustafa A. G. Abushagur and Nicholas George

Measurement of optical fiber diameter using the fast Fourier transform

Appl. Opt. 19:2031-2033; 1980

The variation of the fringe spacing of the far zone scattered intensity of an illuminated optical fiber

has been plotted vs the scattering angle, theoretically and experimentally. A method for measuring

fiber diameters by taking the Fourier transform of

the scattering intensity is described. Theoretical

and experimental results have been compared at various angles for different fiber diameters.

D. H. Smithgall and C. M. Schroeder

A comparison of techniques to measure the diameter

of lightguide fiber

Tech. Digest, Symp. Opt. Fiber Meas.-1980 Boulder, 41-44; 1980, U.S. Govt. Printing Office

L. S. Watkins and R. E. Frazee, Jr.

High speed measurement of the core diameter of a step-index optical fiber

Appl. Opt. 19:3756-3762; 1980

The forward scattering light pattern from a clad

optical fiber illuminated perpendicular to its axis

is characteristic of the outer diameter, the core diameter, and their respective refractive indices. This pattern is detected by a diode array detector

to produce a video signal representation of the scattering pattern. Electronic circuits have been developed to analyze the scattering pattern and detect the angular position of the modulation char- acteristics of the pattern. This provides a deter- mination of the core to outer diameter ratio of the

fiber. Using linearization circuits and the outer

diameter measurement signal, linear measurement

signal voltages of both core ratio and core diameter

are derived. The measurement of core ratio refers

to a particular radius vector and means that deter- minations of circularity and concentricity can also

be made.

R. Bouillie and L. Jeunhomme

Measurement techniques for physical characteristics

of optical fibers

Conf. Rec, Int. Conf. Commun., Boston, 36.1.1-

36.1.4; 1979, IEEE

We present here a review of the relevant characteristics of optical fibers and of the corresponding measurement techniques, essentially based on the conclusions of CCITT study group XV. We also describe a recent and new approach for characterizing the information carrying capacity of the fioer

by its intermodal dispersion.

Kashiko Kodata, Haruko Takenka

Measurement of mechanical deformation of dielectric

fibres by light scattering method

Opt. Quantum Electron. 11:497-505; 1979

This paper describes an experimental method to detect quantitative changes of both refractive index and diameter of unclad dielectric fibres, such as fused silica fibre and nylon 6 fibre, due to tensile

stress. The technique employed here is based on the variation in the position of a fringe in back- scattered light, which is generated when a laser beam is incident at a right angle to the axis of the

fibre. This procedure makes it possible to measure

refractive index, diameter and ellipticity to within

an accuracy of 0.048%, 2.6% and 0.05%, respectively.

D. Marcuse and H. M. Presby

Automatic geometric measurements of single-mode and multimode optical

Appl. Opt. 18:402-408; 1979

An automatic method has been developed to measure

the outer diameter, the core diameter, the degree of elipticity, and the core concentricity of both

single mode and multimode optical fibers. A short length of fiber {~1 cm) is prepared by scoring and breaking, and one end face is observed with a microscope utilizing transmitted light illumination. The image is processed with a computer-controlled auto- matic video-analysis-system which tracks and locates

the outer and core boundaries, performs various fitting routines, calculates the desired quantities,

and produces a plot of fiber boundaries and core

offset, all within 3 min. The reproducibility of the measurements depends upon the quality of the sample and is on the order of 0.1 ym for eccentricity values of good fiber samples with surfaces free from dirt and cracks and on the order of 1/2% for

the core radius.

A. van der Meulen and L. Strackee

Accurate determination of fiber radii in the hypermicrometer range by multi wavelength laser light

scattering

Appl. Opt. 18:3751-3757; 1979

Laser light scattering from fused silica fibers,

with radii in the hypermicrometer range (1-10 um) has been studied. The vertical polarized component

of the scattered radiation has been observed over an angular range from 2° to 135°, the angular

resolution being 0.3°. The experiments were carried

out using the discrete visible wavelength lines from

a Kr ion laser. The experimentally observed total number of minima in the angular range between 0° and

90° has been compared with computations based on the model of an infinitely long circular cylinder. In this way it is possible to perform a fast and accurate (better than 1%) determination of fiber radii without the necessity of calibration, over a large

range of physical acceptable refractive indices. Alternatively, measuring the near forwardscattering

56
over a carefully predetermined collecting aperture

suffices to estimate quickly the fiber radius to within 5.0% over the same refractive index range. When the refractive index is known beforehand, the accuracy of both methods can be improved to within

5.0% and 1%, respectively. When a full comparison

with the theoretical angular scattering curves is performed, the fiber radius is obtained with an accuracy better than 0.1%, as well as the refractive

index. The full curves are calculated by Dave's computational procedure adapted for cylinders.

Charoon Saekeang and Pak L. Chu

Diameter determination of graded- index optical fibers from backward-scattered pattern

Appl. Opt. 18:3276-3281; 1979

The backscattered pattern of an optical fiber with

arbitrary refractive- index profile is used to determine the fiber diameter. Two methods are presented:

the fiber diameter can be determined either by

noting the position of a particular fringe maximum

or by counting the total number of fringes in the pattern. This method is fast in that it does not require any mechanical moving part, and the measurement error is 1%. This method is based on the prior

knowledge of the refractive-index profile of the fiber, but it is shown that the error incurred by

assuming the wrong profile is less than 1%. It is also shown in this paper that the method can be used

to monitor the diameter variation while the fiber is being pulled. This is done by tracking the dis- placement of a particular fringe. It is shown that

this method is also applicable to fibers with elliptical cross section.

Noriyoshi Shibata, Kaname Jinguji, Masao Kawachi

and Takao Edahiro

Nondestructive structure measurement of optical

fiber preforms with photoelastic effect

J. Appl. Phys. (Japan) 18:1267-1273; 1979

The photoelastic effect is used to measure nondes- tructively the structure parameters of optical -fiber

preforms. An He-Ne laser beam is introduced perpendicular to the preform axis, the transmitted beam is optically retarded by residual stresses in the preform, and the optical retardation is measured. A procedure for determining the core diameter and the refractive-index profile from the measured optical

retardation is presented. It is applied to a stepindex preform and a graded-index preform fabricated

by the M.C.V.D. (Modified Chemical Vapour-phase

Deposition) technique.

Hiroshi Takahashi, Seiji Shibuya, and Toshiaki

Kuroha

Applicative investigation of X-ray non-destructive

inspection technique for measurement of core dia- meters and germanium doping concentration profiles

of optical fiber preforms

Proc, Opt. Commun. Conf.

14.4-4; 1979 Amsterdam, 14.4-1-

X-ray non-destructive inspection technique was applied to measurement of the germanium doping con- centration profiles of optical high-silica glass

fiber preforms non-destructively. Due to the big

difference of the mass absorption coefficient be- tween germanium and other elements such as silicon,

phosphorous and boron, the core diameter of the pre- form can be determined, and quantitative information

of germanium doping concentration profiles can be obtained. An excellent point of this method is capability of application to opaque porous preforms

which are fabricated by the Vapor-phase Axial Depo- sition (VAD) and the Outside Vapor-phase Oxidation

(OVPO) processes.

E. Johansen and P. V. H. Sabine

Structural characteristics of optical fibres

A.T.R.-Aust. Telecomm. Rev. 12:25-39; 1978

the first part of this papier outlines the modified

chemical vapour deposition fibre fabrication process. Various inherent structural characteristics

of the fibres are related to particular manufacturing operations and techniques for investigating

these characteristics are discussed. The scanning electron microscope, and in particular the secondary electron imaging and microprobe modes, is shown to provide a powerful analytical tool for examining the physical and compositional properties of fibres. Measurement of the near-field intensity distribution

is found to be a rapid and convenient technique for investigating som important optical transmission

properties of the fibre—most notably, for determining the refractive index profile. The primary pur- pose of this paper is to show that a greater under- standing of the fibre can be obtained by correlating

results from all three techniques. Practical results illustrating this correlation procedure are presented. The particular fibres described are experimental step index and step index-barrier layer fibres manufactured at the AWA Research Laboratory under contract to Telecom Australia.

P. H. Krawarik and L. S. Watkins

Fiber geometry specifications and its relation to measured fiber statistics

Appl. Opt. 17:3984-3989; 1978

Fiber quality requirements can be specified in a number of ways; the most typical is to state a required diameter and give a tolerance band to allow

for manufacturing variations. Actual fiber diameter

statistics have been shown to be close to Gaussian

for certain range of fiber lengths. The fiber sta- tistics are discussed showing the bounds of stationarity and their relation to fiber specifications.

Thus the fiber statistics in terms of standard deviation and sample length can be related to the specification. Not only variations within one fiber are important, but also from fiber to fiber. Thus,

the effect of mean-to-mean differences in fibers and their influence in meeting fiber specification for given standard deviations are considered. In considering these factors, the following conclusions are made. There is a bandwidth which can be related to the fiber drawing process, and measurement of fiber

diameter for the purpose of characterization must be made at a rate greater than this bandwidth to

57
guarantee fiber quality. Since fiber drawing is a predominately random process, specifications should

be written which relate to a statistical description

of the process. If a tolerance band is used for the specification of fiber diameter, it ought to com- prise two parts. One part will allow for the random fiber diameter variations. The second part must provide for the deviations of the mean diameter of each complete length from the nominal.

Structural property measurement methods for preformrods and fibers have been studied. An automatic

system for a dimensional nonuniformity measurement,

using backscattering pattern analysis, has made pos- sible a rapid and precise measurement of rod dia- meters, core diameters, structure distortions and torsions. An automatic system for a refractive

index profile measurement in interferometry has also

been made, using an ITV and automatic image processing.

David H. Smithgall, Laurence S. Watkins, and

Ralph E. Frazee, Jr.

An optical fiber diameter measurement system using forward scattered light

IEEE Trans. Ind. Electron, and Control Instrum. IECI-25:108-112; 1978

Forward scattering of light by an optical fiber pro- duces an interference fringe pattern in which the fringe spacing is inversely proportional to the fiber diameter. An electrooptic system has been developed to produce and detect this scattering pattern, thus providing a measure of fiber diameter.

The system measures the fiber diameter by a fringe

counting techique with an accuracy of +0.2 \jm over a range of diameters 50-150 um. Measurement are up- dated at a 1-kHz rate. The system design allows the fiber to move laterally within a one-centimeter dia- meter window without affecting the measurement

accuracy.

The signal-processing circuitry employs a micro- processor to format the measurement output in engineering units to a digital display, and as an analog

output suitable for feedback control of the fiber

diameter. In addition, the processor computes the mean and standard deviation of an arbitrary length

of fiber, providing a measure of the quality of the fiber drawn.

D. Marcuse and H. M. Presby

Optical fiber coating concentricity: Measurement

and analysis

Appl. Opt. 16:2383-2390; 1977

Backscattering of laser light that is incident at right angles to the axis of an optical fiber is utilized to evaluate the degree of eccentricity of a plastic jacket on the fiber. An analytical treat- ment of the problem based on ray optics is shown to

be in excellent agreement with experiments, which

are capable of detecting core-to-jacket offsets on the order of 1 um.

D. Marcuse and H. M. Presby

Measurement of optical fiber coating concentricity

Tech. Digest, Opt. Fiber Trans. II, Williamsburg,

PD2-1-PD2-4; 1977. Opt. Soc. Am. *****

H. M. Presby

Detection of geometric perturbations in optical fibers

A. R. Tynes, R. M. Derosier, and W. G. French

Measurement of single-mode fibre core-cladding

concentricity

Electron. Lett. 14:113-115; 1978

Single-mode fibre core-cladding concentricity has been measured by using a fibre splicing technique.

In this technique a short length of fibre is broken

in two and one length is rotated about its own axis

a degrees with respect to the other length and then

the two lengths are spliced together. The splice

loss when a = 180° is a direct measure of the fibre butt-joint offset and hence also of the concentricity of the core and the cladding. A submicrometre

sensitivity for this measurement has been achieved.

M. Ito, M. Okada, and T. Miya

Automatic measurements of fiber parameters: Dimensional nonuniformity and refractive index profiles

Electron. Commun. Lab. Tech. J. (Japan) 26:2585-

2589; 1977

Appl. Opt. 16:695-700; 1977

A sensitive, quick, and nondestructive method to assess the short range geometrical uniformity of op- tical fibers is presented. The technique is based

on an analysis of the backscattered light arising

from a beam that is incident at right angles to the fiber's axis and is capable of measuring diameter

variations on the order of 0.1 pm. Geometric per- turbations arising in selected fibers pulled with oxy-hydrogen torch, electric furnace, and C02-laser

techniques are shown in an almost instantly read snapshotlike form. The production and detection of intentionally introduced short range diameter varia- tions are also demonstrated.

D. H. Smithgall and L. S. Watkins

A high speed optical fiber diameter measurement and characterization system

IEEE J. Quantum Electron. QE-13:19D-20D; 1977

*****

58
D. H. Smithgall, L. S. Watkins, and R. E. Frazee,

Jr.

High-speed noncontact fiber-diameter measurement

using forward light scattering

Appl. Opt. 16:2395-2402; 1977

The forward scattering of light by an optical fiber

produces an interference fringe pattern, and the fringe period is inversely proportional to the fiber

diameter. An electrooptic system has been developed

to produce and detect this scattering pattern to provide an instrument which will measure fiber dia- meter during the drawing operation. The system measures the fiber diameter at a 1-kHz rate with a precision of 0.25 nn and an accuracy of ±0.25 ym over a range of 50-150- um diams. The instrument

allows the fiber to move laterally in a 1-cm diam window maintaining the above accuracy. The system

can be calibrated optically and does not need a standard fiber for this procedure. The instrument

has been used for months without the need for re- calibration. In addition to the digital diameter

output, the system employs a microprocessor to compute mean and standard deviation values for various

sample lengths and provides suitable signals for feedback control of fiber diameter.

P. L. Chu

Determination of the diameter of unclad optical fibre

Electron. Lett. 12:14-16; 1976

It is shown that the backward-scattered interference

pattern of an unclad optical fibre can be adequately

described by Airy's rainbow theory. A formula is derived from which the diameter of the fibre may be calculated if the position of the raimbow maximum is measured from the scattered pattern. The error in- volved in this method is less than 3%. Comparison

between this method and Marcuse's method is also

made, and it is found that the present method can lead to a more reliable result.

P. L. Chu

Determination of diameters and refractive indices of step-index optical fibres

Electron. Lett. 12:155-157; 1976

A method is given whereby the radii and refractive

indices of the core and cladding of a step-index

optical fibre can be determined uniquely from the backward- scattered pattern. The technique is based

on the analysis of various rays that contribute to the formation of the back-scattered pattern.

W. Eickhoff and 0. Krumpholz

Determination of the ellipticity of monomode glass

fibres from measurements of scattered light intensity

Electron. Lett. 12:405-407; 1976

A nondestructive method is proposed to determine the core ellipticity of a monomode fibre from measurements of the scattered light intensity.

Sandor Holly

Lateral interferometry monitors fiber diameter

Laser Focus 12:58-60; 1976

H. M. Presby

Ellipticity measurement of optical fibers

Appl. Opt. 15:492-494; 1976

The experimental aspects of a sensitive, nondestructive, and noncontacting method to measure the non- circularity of dielectric cylinders are presented.

The technique makes use of the variation in the position of a fringe in the backscattered light

arising from a beam that is incident at right angles

to the cylinder's axis, as the cylinder is rotated.

The method has been applied to optical fibers, and ellipticities as small as 0.997 have been measured.

The results are in agreement with photomicroscopy measurements and with theoretical predictions.

John W. Y. Lit

Radius of uncladded optical fiber from back- scattered radiation pattern

J. Opt. Soc. Am. 65:1311-1315; 1975

The back-scattered pattern produced by a planepolarized beam incident normally on a large uncladded optical fiber can be used to determine the refractive index and the radius of the fiber. The geometric-optics method is used to analyze the pattern. A new procedure to find the radius of the fiber is proposed. The procedure can make use of nearly the whole of the back-scattered pattern,

without need to measure exactly the positions of all of the individual fringes. Special attention is given to the limits of accuracy.

H. M. Presby

Refractive index and diameter measurements of unclad

optical fibers

J. Opt. Soc. Am. 64:280-284; 1974

A new method is presented to determine the refractive index and the diameter of unclad optical fibers. The technique is based on an analysis of the back-scattered light when a beam from a cw laser impinges upon the fiber. A geometrical -optics

analysis shows that the position of a sharp cutoff

in the radiation pattern determines the refractive

index, whereas the distance between certain successive minima gives the diameter. The theory is com- pared to experimental observations, with excellent

agreement.

59
L. S. Watkins

Scattering from side-illuminated clad glass fibers

for determination of fiber parameters

J. Opt. Soc. Am. 64:767-772; 1974

The theoretical characteristics of the scatteredlight pattern from a clad glass fiber illuminated by

a laser beam perpendicular to its axis agree closely

with results of experimental measurements of the scattered light. A simplified geometric ray-tracing

technique shows that for fibe>-s with medium and

small core sizes, specific angle ranges of the scat- tering pattern provide determinations of fiber dia- meter independent of core parameters. Measurements

of the fringe modulation give relatively sensitive

determinations of core diameter. Light scattering

is a useful technique for determining the diameters

of both clad and unclad fiber. Total -diameter

determinations have accuracies of +0.2 m and core diameters, ±0.5 un for 0.02 refractive-index difference between core and cladding.

L. G. Cohen and P. Glynn

Dynamic measurement of optical fiber diameter

Rev. Sci. Instrum. 44:1749-1752; 1953

This paper describes a novel technique for monitoring the outside dimensions of clad or unclad optical fibers. An oscillating mirror is used to deflect a laser beam with constant velocity across a fiber in order to measure the time interval during which the fiber intercepts the beam and casts a shadow on a photodetector. For 110 u fibers, individual mea- surements made every 1/60 sec are repeatable within

a spread of ± 1% from the 330 usee mean time interval (rms deviation = ±0.6%). Results are displayed

in digital form, but can be converted to an analog

signal for use in a servo loop to control the pulling rate of fiber drawing machines. An additional feature of the technique is that fibers with non- circular cross sections can be monitored by making

sequential diameter measurements along orthogonal

axes of the fiber.

50
8. FIELD MEASUREMENTS

R. Auffret, L. Pophillat, and Y. Kervarrec

Appareillage de terrain pour la mesure de 1' attenuation et de la band passante des liaisons optiques

(Field measurement set for attenuation and bandwidth

of optical links)

Electron. Lett. 16:798-799; 1980

The letter deals with a quite simple apparatus

capable of bandwidth and insertion loss measurements

of installed optical links. The performance is such that the measurement is possible whatever the distance between two regenerators.

possible to determine the index profile and index difference of graded core fibers; results are com- pared with those obtained by other techniques. Other important fiber parameters, such as the dif- ferential attenuation and the differential propagation delay time as a function of the mode parameter,

are also obtained, giving an insight into the fundamental propagation characteristics of the fiber.

K. C. Byron, G. J. Cannell, I. S. Few, and

R. Worthington

Field measurement of fiber optic cables

K. Hiepe-Wohlleben, M. Kaiser, R. Rossberg

Feldmassige Dampfungs - und Dispersionsmessung an einem Lichtleit-Erdkabel (Field measurements of attenuation and dispersion in lightguide underground

cable)

Proc, Third Eur. Conf. Opt. Commun., Munich, 34-35;

1977

Digest, Mess, in der opt. Nachrichten. , Berlin, 103-107; 1980, VDE-Verlag

R. Novak

Prazise fledtaugliche Methode und Apparatur fur die Dampfungsmessunger an PTT Glasfaser Anlangen (Pre- cise field suitable method and apparatus for attenuation measurement on PTT glass fiber installations)

Digest, Mess in der opt. Nachrichten., Berlin,

108-115; 1980, VDE-Verlag

W. Eickhoff, 0. Krumpholz, E. Pfeiffer, M. Rode, and

E. Wei del

Field measurement equipment for fibre optical waveguide cables

Digest, Fourth Eur. Conf. Opt. Commun., Geneva, 179-

182; 1978

Fibre measurement equipment for loss, dispersion and

fault location is described. Insertion loss mea- surements in excess of 60 dB are possible with a re- producibility of about ± 0.1 dB. The dynamic range

for pulse response measurements is more than 50 dB using light pulses with a 3 dB pulse width of 300

ps. Fault location measurement can be performed

with an accuracy of 1 m. The equipment developed is compact, portable and easy to handle.

L. Jeunhomme and J. P. Pochelle

Selective mode excitation of graded index optical fibers

Appl. Opt. 17:463-468; 1978

A method is described permitting excitation of a small number of modes in graded index fibers, the order of the launched mode being easily varied and determined. Using this launching technique, it is

61
SINGLE MODE FIBER CHARACTERIZATION

V. A. Bhagavatula, W. F. Love, and D. B. Keck

Electron. Lett. 16:695-696; 1980

A technique to measure the local (2-3 mm) values of cutoff wavelength x in single-mode waveguides is described. The technique, insensitive to the length

of waveguide used, involves the spectral measurement

of refracted power. The feasibility of using the cutoff wavelength determined by this technique to predict the zero dispersion wavelength is also

studied.

I. Sasaki, D. N. Payne, R. J. Mansfield, and M. J. Adams

Variation of refractive-index profiles in single- mode fibre preforms measured using an improved highresolution spatial -filtering technique

Digest, Sixth Eur. Conf. Opt. Commun., York, 140-

143; 1980, lEE

P. D. Lazay

Effect of curvature on the cutoff wavelength of single mode fibers

Tech. Digest, Symp. Opt. Fiber Meas.-1980 Boulder,

93-96; 1980, U.S. Govt. Printing Office

J. Streckert

Charakterisierung und Messung der Kennwerte eiwel- liger Glasfasern (Characterizing and measuring the characteristic value of single mode glass fiber)

Digest, Mess in der opt. Nachrichten. , Berlin, 126-128; 1980, VDE-Verlag

F. Mohr and U. Zwick

Messung der Eigenschaften von Monomodefasern (Mea- suring the characteristics of monomode fiber)

Digest, Mess in der opt. Nachrichten., Berlin, 121-125; 1980, VDE-Verlag

M. Monerie, P. Lamouler, and L. Jeunhomme

Polarisation mode dispersion measurements in long

single mode fibres

Electron. Lett. 16:907-908; 1980

A frequency domain determination of polarisation

mode dispersion in single mode fibres is described,

which allows one to obtain directly the group delay

difference for long fibres. The results of such measurements are shown on a birefringent fibre with elliptical cross-section which maintains an extinction ratio between linearly polarised eigenstates

greater than 10 dB over 1 km.

M. Monerie, P. Lamouler, and L. Jeunhomme

Measurement of polarization mode dispersion

Digest, Sixth Eur. Conf. Opt. Commun., York, 110-

112; 1980, lEE *****

C. Pask and R. A. Sammut

Experimental characterisation of graded-index

single-mode fibres

Electron. Lett. 16:310-311, 1980

A simple and accurate method is presented for ex- perimental characterisation of graded-index singlemode fibres using their far-field radiation patterns

and the "equivalent-step" method.

Akara Sugimura, Kazuhiro Daikoku,

and Tetsuo Miva

Nobuyuki Imoto,

Wavelength dispersion characteristics of single-mode

fibers in low-loss region

IEEE J. Quant. Elect. QE-16:215-225; 1980

Wavelength dispersion characteristics of single-mode

silica fibers in a very low-loss region, including

zero dispersion wavelengths, are studied in detail using a "difference method." Wavelength dispersion

of single-mode fibers is compared for fibers with

same material dispersion but with different waveguide structure. Material dispersion is evaluated

by extracting waveguide dispersion from experimental

results. Effects of waveguide dispersion on the

zero dispersion wavelength of the single-mode fiber

in a longer wavelength region are clearly analyzed.

Single-mode fiber design consideration is given from

the wavelength dispersion point of view.

K. I. White, B. P. Nelson, J. V. Wright, M. C. Brierly, and A. Beaumont

Characterisation of single mode fibres

Tech. Digest, Symp. Opt. Fiber Meas.-1980 Boulder.

89-92; 1980, U.S. Govt. Printing Office

Ernst Brinkmeyer

Spot size of graded-index single-mode fibers: Pro- file-independent representation and new determination method

Appl. Opt. 18:932-937; 1979

A simple nondestructive method is described for determining the spot size ^g (width of the fundamental mode)--one of the most important quantities

to characterize monomode optical fibers. The theory

involves the definition of effective values of core

radius and normalized frequency. Thereby, graded62
index fibers can be replaced by equivalent stepindex fibers. The experiment consists in illuminating the fiber perpendicularly to its axis and deter- mining the position of the first minimum in the dif- fraction pattern. In this way, just one measurement

yields oj regardless of the index profile and for

any operating wavelength, provided the cutoff wavelength is known.

Kazuo Hotate and Takanori Okoshi

Measurement of refractive-index profile and transmission characteristics of a single-mode optical fiber from its exit-radiation pattern

Appl. Opt. 18:3265-3271; 1979

A new exit-radiation pattern method for measuring

the refractive-index profile of a single-mode fiber

is proposed and used experimentally. In this method

the profile is computed from the far-field exitradiation pattern of the HE,i mode at the end of the single-mode fiber. This metnod can be applied to a cabled fiber, and the propagation constant, field

profile, and group delay of the HEj^^ mode, and the single-mode limit can be obtained as well as the index profile. The principle, computer simulations,

experimental setup, and experimental results are first described. The profile obtained shows a good

agreement with that obtained from the interference

fringe pattern measured before drawing the fiber. Computations of the group delay of the HE,, mode and

the single-mode limit from the measured exitradiation pattern are discussed.

Yasuyuki Kato, Ken-ichi Kitayama, Shigeyuki Seikai,

and Naoya Uchida

Novel method for measuring cutoff wavelength of

HE21' TE,01' and TMqi modes

Electron. Lett. 15:410-411; 1979

J. P. Pocholle

Single mode optical fiber characterisation by the

LP]^^ mode radiation pattern

Opt. Commun. 31:143-147; 1979

We describe a method for determining the V-value

from the far-field radiation pattern of dual mode

optical fibers (this method is an extension of the work by Gambling et al . for the LPj^j^ modes). The method involves measurements of the maximum radiation angle and the angle of the first minimum.

Curves are presented which can be used with dual mode fibers, determining the core diameter, the refractive index difference between core and cladding, as well as the V-value in the single mode regime for longer wavelength operation with the help

of dispersion curves of the dopant materials.

Yasuji Murakami and Haruhiko Tsuchiya

Bending losses of coated single-mode optical fibers

IEEE J. Quantum Electron. QE-14:495-501; 1978

Peaks appear in bending losses of coated single-mode

fibers due to interference between the guided mode and rays which are radiated from the guided mode and

are reflected at cladding-coating boundary. This paper reports derivation of bending loss formulas

for coated slab waveguides and coated fibers. Plane wave concepts are also used to explain the appearance of the loss peaks. Measurements were performed

by using two coated single-mode fibers. The agree- ment between theory and experimental results is found to be excellent. It is possible to obtain the refractive index difference from measured peak wavelengths.

Mitsuhiro Tateda

A new measurement method for the cutoff wavelength

of HEoi-, TEqi- and TMq, -modes using a polariser is described. Trie experimental results show that

higher measurement accuracy and sensitivity are obtained compared with the previous method.

Yasuji Murakami, Akio Kawana, and Haruhiko Tsuchiya

Cut-off wavelength measurements for single-mode

optical fibers

Appl. Opt. 18:1101-1105; 1979

A new technique has been proposed for direct measurement of the cut-off wavelength, at which the first higher-order mode disappears. It uses a change of a near-field pattern of a fiber, which is excited by a variable wavelength source. The cutoff wavelength can be measured with +5-nm accuracy.

The most suitable fiber length for precise measurement is 10-20 ran. It is found, furthermore, that

the first higher-order mode under the condition near

cut-off rapidly attenuates because of waveguide im- perfections, in which the loss due to core-cladding

boundary distortions is the most dominant.

Single-mode-fiber refractive-index profile measurement by reflection method

Appl. Opt. 17:475-478; 1978

A new technique for measuring the refractive index

profile of single-mode fibers based on the reflection method is described, and experimental results

are demonstrated. When the core radius of a test

fiber is only a few times larger than the laser beam

spot size, the reflected power distribution does not indicate the refractive index correctly. However,

the true index profile can be calculated from the beam spot size and the reflected power distribution

with high accuracy: 0.3-ijm spatial resolution and

5% relative refractive-index resolution are obtained

for practical single-mode fibers.

W. A. Gambling, D. N. Payne, H. Matsumura, and S. R. Norman

Measurement of normalized frequency in single-mode

optical fibres

Electron. Lett. 13:133-135; 1977

63
It is shown that methods of measuring the normalised

frequency in single-mode fibres through observation

of mode cut-off wavelengths give erroneous results.

This is because the various loss mechanisms which

exist in a practical fibre can have an appreciable

effect near cut-off.

W. A. Gambling, D. N. Payne, H. Matsumura, and R. B. Dyott

Determination of core diameter and refractive-index

difference of single-mode fibres by observation of

the far-field pattern

Microwaves, Opt. Acoust. 1:13-17; 1976

A method is described for determining unambiguously,

from the far-field pattern of single-mode fibres,

the core diameter and the refractive-index difference between core and cladding. It involves mea- surements only of the half -power width of the main

lobe and the width of the first minimum. Universal curves are presented that can be used with single- mode fibres or any fibre operating in the single- mode regime. Independent determinations of core diameter over the range 4-8 um by an etching technique are in excellent agreement with those obtained

from the far-field pattern.

Yutaka Katsuyama, Masamitse Tokuda, Naoya Uchida, and Motohiro Nakahara

New method for measuring V- value of a single-mode

optical fibre

Electron. Lett. 12:669-670; 1976

A simple method is proposed for the direct measure- ment of the V-value for a single-mode optical fibre. This method consists of measurement of loss peaks,

corresponding to cutoff wavelengths of the higher

modes, which are easily observed for a fibre with a bend.

64
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NBS TN-1043

2. Performing Organ. Report No, 3. Publication Date

June 1981

4. TITLE AND SUBTITLE

The Characterization of Optical Fiber Waveguides

A Bibliography with Abstracts, 1970 - 1980

5. AUTHOR(S)

G. W. Day, Editor

6. PERFORMING ORGANIZATION (If joint or other tlian NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

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10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a significant

bibliography or literature survey, mention it here)

This bibliography contains approximately 450 citations of papers concerning

the characterization of optical fiber waveguides. Papers from scientific

journals, trade journals, and conferences are included along with book

chapters. The citations are organized by parameter measured and measurement

method. Where published abstracts are available, they are included.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate i<ey words by semicolons)

Bibliography, measurements, optical fibers, optical communications

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