bluuebunny/crossref_metadata_2025 huggingface dataset:
Progress in Semiconductor Optical Amplifiers
Authors: O'Mahony M.J. , Devlin W.J.
Published: February 2023

Optical amplifiers are the fundamental building blocks required for the development of future all-optical networks. The elimination of electronic bottlenecks will allow the development of new network architectures which, for example, will enable the realisation of a network that has the flexibility to meet rapid changes in demand for capacity. In the past two years there has been dramatic progress in the development of both semiconductor and fibre amplifiers, to the extent that these components can now be considered for real applications.
Experimental verification of accurate model for Erbium doped fiber amplifier in a gain range from 0 to 40 dB
Authors: Pedersen Bo , Dybdal Kristen , Dam-Hansen Carsten , Bjarklev Anders , Povlsen Jørn Hedegaard , Vendeltorp-Pommer Helle , Larsen Carl Christian
Published: February 2023

Based on fundamental Erbium-doped fiber data, theoretical predictions show excellent agreement with all measured amplifier characteristics. 39.6 dB gain is demonstrated using a 654 nm pump source.
Gain Modeling in Erbium-Doped Fiber Amplifiers
Authors: Jopson R. M. , Saleh A. A. M. , Evankow J. D. , Aspell J.
Published: February 2023

Calculation of the gain of erbium-doped fiber amplifiers (EDFAs) generally uses numerical integration of coupled, nonlinear, differential equations and requires knowledge of parameters such as the erbium atom density, spontaneous lifetimes, and the fiber active area, as well as the absorption cross-section, emission cross-section, and confinement factor for each wavelength involved [1], [2]. We derive analytic expressions from which the gain can be calculated by solving one transcendental equation. We show that a complete understanding of the input-output characteristics of a fiber amplifier of any length can be obtained from simple absorption measurements. This remarkable result is valid provided excited-state absorption [2], [3] and gain saturation due to amplified spontaneous-emission noise can be neglected. Measurements of saturated and unsaturated gain agree to better than 0.5 dB with gains predicted from absorption data.
Design and realization of polarisation insensitive semiconductor optical amplifiers with low forward current
Authors: Fernier B. , Gelly G. , Doussière P. , Mersali B. , Accard A. , Peralès A. , Monnot M. , Luc J.P.
Published: February 2023

Polarisation insensitive semiconductor travelling wave amplifiers (TWA's) with high internal gain at low bias current are of great importance for the development of future optical fiber transmissions systems. During the last year, an important effort was carried out worldwide and significant improvements have already been achieved from a better design and fabrication of the active waveguide [1-4]. More recently, we have obtained polarisation insensitive GaInAsP/InP TWA's realized by gas source molecular beam epitaxy (GSMBE) with a high internal gain (28 dB) and a gain wavelength ripple of 3 dB for both TE and TM modes at a very low forward current of only 50 mA [5]. We present consolidated measurements on a large number of TWA'S with different structures, and in order to evaluate the tolerances on the technological parameters, we illustrate with a simple model, the variation of the polarisation sensitivity with gain.
High-gain, polarization-independent semiconductor optical amplifier with a large optical cavity and angled buried facets
Authors: Tsuji S. , Toyonaka T. , Haneda M. , Ono Y.
Published: February 2023

A polarization-insensitive semiconductor optical amplifier with angled buried facets has been fabricated. The TE and TM gains are equal to within 1.2-dB even including the additional effect from the gain ripple at 28-dB gain.
Optical Amplifiers for Trunk and Distribution Networks
Authors: Nakagawa Kiyoshi
Published: February 2023

Optical fiber cable transmission systems have advanced rapidly over the past ten years due to advances in fibers, lasers, and LSI's, and the system capacity has reached the gigabit/s range. The potential of optical fiber transmission systems is incredibly rich. The implementation of advanced optical technologies using optical amplifiers would enable the creation of more economical and higher quality systems [1]. In this paper briefly outlines recent studies on optical amplifiers, and describes their features. The impact of the new amplifier technology is then discussed, and the present and future possibilities for trunk and distribution networks are studied.
100-Channel Common Amplification Using an Er3+-Doped Fiber Amplifier
Authors: Inoue K. , Toba H. , Sekine S. , Sugiyama H. , Nosu K.
Published: February 2023

10 GHz spaced 100 channel signals are simultaneously amplified by an Er3+ -doped fiber amplifier with a net gain of 11~30 dB depending on input power. Bit error rate measurements show that the power penalty characteristic for 100-channel amplification is same as for one-channel amplification.
Transmission Performance of Coherent In-Line-Amplifier Systems
Authors: Saito Shigeru , Imai Takamasa , Naka Akira , Ito Takeshi
Published: February 2023

Optical in-line amplifiers allow fiber transmission systems to increase regenerative repeater spacing1,2. We have reported 2.488-Gbit signal transmission over 2,200 km with a continuous-phase frequency-shift-keying (CPFSK) heterodyne detection system that has twenty-five erbium-doped fiber in-line amplifiers3.
Er3+-doped VAD fibers for lumped amplifiers and distributed active transmission lines
Authors: Morisawa M. , Yoshida M. , Ito H. , Gozen T. , Tanaka H. , Yotsuya M.
Published: February 2023

Er3+-doped silica-based single-mode fibers are attractive for optical amplification in 1.5μ m region1). Lumped amplifiers such as pre-amplifiers, post-amplifiers and repeaters need the fibers with high gain and broad band. On the other hand, low concentration fibers, of which Er3+ concentration is as low as a few ppm, offer attractive prospects for the practical use of distributed active transmission lines2). In this paper, we report two applications of Er3+-doped fibers fabricated by VAD method and molucular stuffing: lumped amplifiers and distributed active transmission lines.
Field Demonstration of FSK Transmission at 2.488Gbit/s Over a 132km Submarine Cable Using an Erbium Power Amplifier
Authors: Bryant E G , Carter S F , Lewis R B J , Spirit D M , Widdowson T , Wright J V
Published: February 2023

We report the first use of erbium power amplifiers and low chirp transmission techniques on an operational submarine cable. Two way transmission at 2.488Gbit/s was achieved over an unrepeatered distance of 132km on the UK-Channel Islands No. 7 submarine cable.
Fluorescence and Amplification Characteristics of Er3+ doped Fluoride Fibers
Authors: Chigusa Y. , Nakazato K. , Hirai S. , Watanabe M. , Suzuki S.
Published: February 2023

Rare-earth doped silica fibers have been extensively developed as optical amplifiers. Especially, Er3+ doped silica fibers have been expected of those at 1.55 μm band[1] [2] and increasing effort has been made to improve the gain and gain-bandwidth of amplification. And the fluoro-zirocnate multi-mode fiber has been also investigated for optical amplification.[3] But, there is no report of Er doped fluoro-zirconate sinle-mode fiber for 1.55μm amplification. In this time, we fabricated Er3+ doped fluoro-zirconate fibers and evaluated these fluorescence spectrum and life-time and amplification properties comparing with Er3+ doped silica fiber.
Designing Optically Repeatered Links Using a new Semiconductor Laser Amplifier Noise Model
Authors: Connelly M. J. , O’Dowd R. F.
Published: February 2023

A semiconductor laser amplfier noise model estimates linewidth broadening in a TWLA cascade. Design procedure giving regenerative spans for various coherent systems are presented.
Intermodulation Distortion in a Multiple-Quantum-Well Semiconductor Amplifier
Authors: Chung Y. C. , Wiesenfeld J. M. , Raybon G. , Koren U.
Published: February 2023

Future wavelength-division-multiplexed (WDM) networks will need an optical power amplifier to boost signal levels. For these applications, multiple-quantum-well (MQW) optical amplifiers are promising due to their inherently larger saturation output powers compared to conventional bulk semiconductor amplifiers [1]. A MQW power amplifier integrated with several tunable lasers has been already demonstrated for the use in future WDM networks [2]. However, a significant limitation on the amplifier performance in these applications is imposed by the intermodulation distortion (IMD) generated by the nonlinear interaction between multiple input signals. When multiple input signals are applied to an amplifier and the channel separations between the signals are less than the reciprocal of the carrier lifetime, the carrier density is modulated at the beat frequency between pairs of input signals. This is the dominant third-order nonlinearity in a semiconductor amplifier [3]. The carrier-density modulation causes gain and refractive index fluctuations at the beat frequency, which, in turn, results in the generation of the intermodulation products. This effect has been extensively studied for the conventional buried heterostructure amplifiers [4]-[5]. However, the IMD in a MQW amplifier can be quite different due to the larger saturation output power and smaller mode confinement factor. In this paper, we report the first measurement of the IMD in a MQW amplifier.
A 980 nm Pseudomorphic Single Quantum Well Laser for Pumping Erbium-Doped Optical Fiber Amplifiers
Authors: Larsson A. , Forouhar S. , Cody J. , Lang R.J. , Andrekson P.A.
Published: February 2023

Erbium-doped fiber amplifiers are expected to significantly influence the future of optical fiber communication systems [1]. Recently, 980 nm was identified as being the most efficient pump wavelength where no excited state absorption exists [2]. To realize practical fiber amplifiers semiconductor laser pumping is considered to be indispensable. There is therefore a need for a high power 980 nm laser diode with a high coupling efficiency into the single-mode optical fiber.
Picosecond pulse gating by high frequency modulation of semiconductor laser amplifiers
Authors: White IH , Lomax AM
Published: February 2023

There has recently been much interest in using optical devices for modulation of optical signals to achieve drop/insert functions in high bit rate time division multiplexed communication systems. Optical semiconductor amplifiers are suited for such applications, in providing optical gain along with switching, in providing high off/on contrast ratios and in operating over a wavelength range directly compatible with diode lasers. This paper reports experimental and theoretical results of high speed electrical modulation of semiconductor laser amplifiers carried out with the aim of determining the maximum switching rate possible using a diode laser amplifier as a gate, the maximum gain and minimum on-time (temporal window during which it transmits signals) possible. Good agreement between experiment and theory has been achieved and it is shown that switching rates as great as 5 GHz and gate "on" times of 150 ps are possible using present amplifier devices.
A Low Cost, Compact, Loss-Less Optical Divider with Erbium Doped Fiber
Authors: Sakai Tetsuya , Tanaka Daiichiro , Wada Akira , Yamauchi Ryozo
Published: February 2023

Rare earth doped optical fibers have attractive features as a fiber laser, fiber sensor, optical amplifier and so on. Especially erbium doped fibers (EDF) have had much attention because of the high gain at 1.5 micron band which is important for long distance transmissions. So far, the high gain and the high saturation output have been pursued, however an erbium doped fiber with high gain efficiency should have other applications like a low-cost simple amplifier and active optical components. This paper describes an EDF with high gain, high gain efficiency and wide gain band. The fiber is applied to a simple and low-cost optical divider which can be used for dividing or tapping from the main line, for instance fiber backbone cable television.
The Appropriateness of Squeezed Light for Long-Distance Communication
Authors: Yurke Bernard
Published: February 2023

Squeezed light allows suitable optical systems to perform at below the standard shot-noise level. Below shot-noise performance of optical interferometers employing squeezed light has been demonstrated in the laboratory [1,2] and it is clear that squeezed state enhanced microscopes and spectrometers could be constructed. There is also considerable interest in the issue of whether optical communications systems could benefit from the use of squeezed light. In fact, much of the early work on squeezed light [3-5] was motivated by quantum communications issues, particularly those involving coherent communication.
Noise Performance of Bus-Configured Optical Networks with Distributed Fiber Amplification
Authors: Goldstein Evan L.
Published: February 2023

Optical bus networks with passive taps have attracted little attention because optical- power limits severely constrain their size. It has recently been realized, however, that such constraints may be overcome using Er3+-doped fiber amplifiers. A numerical analysis [1],[2] has shown that buses with periodic amplification should be capable of supporting large numbers of nodes, even in the presence of saturating signals. Moreover, there is experimental evidence [3] that bus networks with uniformly distributed amplification generate low levels of amplified spontaneous emission (ASE). We here present a simple analysis yielding closed-form expressions showing that the amplified bus can indeed support thousands of nodes, that it can span thousands of kilometers (fiber dispersion and nonlinearity permitting), and that this excellent noise performance results from the slow growth of ASE in low-gain amplifying structures. To support large numbers of nodes, however, the bus’s gain must be well matched to its loss.
OTDR in Optical Amplifier Transmission Systems Using EDFAs Containing Optical Circulators
Authors: Sato Yoshiaki , Nishi Shigendo , Aoyama Koh-ichi
Published: February 2023

Optical time domain reflectometry (OTDR) is an effective technique for locating breaks and for determining the loss distribution along a fiber [1][2]. However, OTDR can not be used with optical transmission lines containing traditional Er-doped fiber amplifiers (EDFAs) because EDFAs require optical isolators to eliminate signal reflection [3]-[5]. The returning backscattered light generated by the forward traveling probe pulse is blocked by optical isolators in each EDFA.
An All-Optical Remote Gain Switching Scheme for Er-Doped Fiber Amplifiers
Authors: Zirngibl M.
Published: February 2023

Er-doped fiber amplifiers (EDFA’s) may find many potential application in optical networks due to their high gain, polarization insensitivity, low noise and immunity to cross-talk. They are especially useful in overcoming splitting losses in multiple access networks. Due to the very long 4I13/2 lifetime of Er3+, fast gain switching, which would be needed for packet switching for instance, is not possible with EDFA’s. To direct traffic flow, however, slow gain switching schemes for EDFA’s may still be very useful. The purpose of this letter is to demonstrate an optical feedback scheme, which allows remote switching of the gain, all-optically over the transmission fiber without the need for any electrical or mechanical control device.
Multichannel amplification characteristics of saturated erbium-doped fiber amplifiers
Authors: Cheng Y.H. , Kagi N. , Oyobe A. , Nakamura K.
Published: February 2023

Erbium-doped fiber amplifiers (EDFAs) are attractive for various optical fiber transmission systems and networks owing to their several advantages such as high gain and low noise. A EDFA with its high output saturation power and wide gain profile is specially suitable for wavelength-division multiplexing (WDM) applications such as multichannel CATV distribution systems [1]. In these applications, the EDFA is normally used as a post (or a booster) amplifier and operates at a saturated region. Although it has been demonstrated that the EDFA is immune to patterning effects and interchannel interference, and has low gain saturation induced crosstalk [2], [3], there is little information about effects of wavelength spacing and fiber length in a saturated EDFA for multichannel applications. In this paper, we report the experimental results on wavelength and fiber length dependence of gain for saturated EDFAs in a two-channel amplification system. The experimental results show that when an EDFA operates at the saturated region in a multichannel system, a shorter fiber length than that in single-channel should be selected to get a flat gain profile, and that the Ge/Al/Er-doped silica fiber is desirable for multichannel amplification use since a gain hole-burning is observed for the Ge/Er-doped silica fiber.
Characteristics of 1.48 μm pumped erbium-doped fiber amplifier with high efficiency
Authors: Kashiwada Tomonori , Shigematsu Masayuki , Kougo Takashi , Kanamori Hiroo , Nishimura Masayuki
Published: February 2023

Erbium-doped fiber amplifiers(EDFAs) are very attractive devices for single-mode fiber communication systems operating in the 1.55 μm wavelength band. [1] The main advantages of EDFAs are polarization-insensitive high gain, high amplification efficiency, low insertion loss, low noise and wide bandwidth. [2] There are two important parameters to evaluate EDFA’s performance; an energy conversion efficiency and a gain coefficient.
Pump Configuration and Length Optimization of Erbium-doped Fiber Amplifier for Low Noise and High Power Operation
Authors: Suyama M. , Yokota I. , Watanabe S. , Kuwahara H.
Published: February 2023

In a ultra-long system with cascaded erbium-doped fiber amplifiers(1) (EDFAs), in order to keep a signal-to-noise ratio (SNR) as high as possible, EDFA(2) having high output power and low noise is highly required as a post-amplifier or as an in-line-amplifier. Such an EDFA is also important for optical pre-amplifiers with large dynamic ranges. Although Way et al. reported a low noise figure (NF) in a saturation region under the condition of sufficiently high pump power(3), the relationship between lowering the NF and optimizing the gain of EDFA was not clear. In this paper, we report that an EDFA having both a high output power (+15dBm) and a low NF (6dB) can actually be realized using 1.48μm pump LDs when the EDFA length is optimized to give a maximum gain for large signal power. In addition, we also show that there is a remarkable difference between forward and backward pump in terms of NF characteristics of EDFA in a deep saturation.
New Laser Structure for Polarization Insensitive Semiconductor Amplifier with Low Current Consumption
Authors: Doussiere P. , Mersali B. , Accard A. , Garabedian P. , Gelly G. , Lafragette J.L. , Leblond F. , Michaud G. , Monnot M. , Fernier B.
Published: February 2023

Due to their low current consumption and their intrinsic simplicity polarization insensitive semiconductor travelling wave amplifiers (TWAs) are very attractive components for long haul non regenerated fiber transmissions systems. It appears up to now that only buried stripe with width less than one micron has enabled to obtain high gain and polarization insensitivity for low bias current [1 - 4], However realization of such narrow stripe leads to poor reproducibility in case of conventional laser structure. We have investigated a new structure, called modified double channel planar buried heterostructure (MDCPBH), which allows to process very narrow stripe with much better reproducibility than previously obtained.
High Damage Threshold Optical Coatings*
Authors: Milam D.
Published: February 2023

Projects at Lawrence Livermore National Laboratory require optical coatings capable of withstanding fluences of 8-10 J/cm2 delivered in single laser pulses with durations of 1-3 ns, or in repeated irradiations, at rates exceeding 100 Hz, by pulses with durations of 10-50 ns. Future fusion lasers will require coatings with higher thresholds. To develop these coatings, we maintain a program that is evaluating sol-gel coatings deposited from solutions, single-layer films made by chemical vapor deposition (CVD) and coatings made by conventional physical vapor deposition (PVD).
Increased Visible Absorptance of Visible Reflectors Due to Ultraviolet Radiation
Authors: Browning Stephen , Young Robert
Published: February 2023

High performance laser mirrors exhibit a decrease in visible reflectance over time when exposed to the ultraviolet radiation emanating from a gaseous laser plasma. This drop in reflectance can lead to cessation of laser action in the worst cases, and unpredictable system performance in any case. Ideally the mirrors would maintain a constant high reflectance for an indefinite time period. An acceptable alternative would be for the mirror reflectance to degrade slightly over a short time to a then-constant value.
Ultra Lightweight Optics in a Cryogenic Environment
Authors: Crowe David A.
Published: February 2023

A high performance infrared spaceborne telescope such as the Space Infra-Red Telescope Facility (SIRTF) will require aspheric optical forms with smooth, low-scatter surface, high performance coatings, and an ultra-lightweight design approach that can perform from room temperature to cryogenic temperature. The design approach must not only be rugged, low risk, and reliable, but also capable of surviving a launch environment and enduring in space for many years. A design approach, which meets performance requirements at cryogenic temperatures employing passive mirrors (without figure control actuators, sensors, electronics, etc.), offers significant advantage in weight, performance, and reliability.
Learjet Observatory Operations in The Tropics
Authors: Hagen Paul H. , Dix M. G. , Russell R. W. , Rossano G. S. , Lynch D. K. , Hackwell J. A. , Rudy R. J. , Retig D. A. , Alvarez P.
Published: February 2023

Tropical operation of an airborne sealed open-port infrared telescope presents problems related to salt corrosion, freezing/thawing, vacuum window degradation, and elevated mirror emissivity.
Advanced Optics Fabrication Trends
Authors: Kaveney William J.
Published: February 2023

Summary not available.
Impinged Droplet Evaporative Cooling for Optical Mirrors Subjected to High Thermal Flux Loads
Authors: Wellman John A. , Meyers John J.
Published: February 2023

Utilization of evaporative cooling for optical mirrors subjected to high thermal flux loads has been investigated. Analytical and experimental results show advantages over convective cooling.
Radiation Effects in Optical Components
Authors: Friebele E.J.
Published: February 2023

Components of high performance optical devices may be exposed to high energy radiation environments during their lifetime. The effect of these adverse environments depends upon a large number of parameters associated with the radiation (nature, energy, dose, dose rate, etc.) or the system (temperature, optical performance requirements, optical wavelength, optical power, path length, etc.), as well as the intrinsic susceptibility of the optical component itself to degradation. Two years ago there was a special session on Radiation Effects in Optical Materials at the Southwest Conference on Optics, [1] and the reader is referred to this volume for an in-depth description of materials effects.
Radiation Damage to Dielectric Mirrors
Authors: Harrison Francis B.
Published: February 2023

We have measured the change in reflectivity of multilayer dielectric (Alumina-Cryolite) high-reflectivity mirrors under simultaneous irradiation by a KrF laser (248-nm) and electrons from a (2 MeV) Febetron 705 accelerator.
Line shape enhancement and broadening effects in dye laser intracavity absorption
Authors: Brink G. O.
Published: February 2023

Questions about the line shape of spectral absorption features observed by dye laser intracavity absorption (ICA) have been discussed in the literature for several years. Simple line shapes have been observed as well as complex line shapes exhibiting asymmetry and enhancement wings. Attempts have been made to interpret these line shapes in terms of various models of ICA with varying degrees of success. The study of these line shapes has been under way for some time in our laboratory with attempts being made to observe the true shape of the absorption features in conditions where they will not be masked by instrumental effects. The results are that the type of line shape observed depends on the degree to which the laser is perturbed by the absorber. If the absorber is strong, i.e., either high density or large oscillator strength, the ICA line shape tends to broaden and develop enhancement wings. If, on the other hand, the absorber is of low density or small oscillator strength, the observed line shape tends to be simple. The line shapes tend to become asymmetrical due to index of refraction effects. Line shapes observed in a variety of experimental conditions are presented, and some results are interpreted in terms of a model of ICA.
Very large optics of the future
Authors: Meinel Aden B. , Meinel Marjorie P.
Published: February 2023

Very large is a relative term when applied to optics. Astronomers work at the dual frontiers of state of the art and available resources. The fundamental limit is dollar resources: ~100 million for terrestrial telescopes and 1 billion for space telescopes. The challenge is to build the largest systems to meet increasingly exacting science requirements within these limits. New concepts, materials, methods, and control technology are increasing the upper limit to size to a point scarcely imagined a few decades ago. We trace the history of successive largest telescopes and see where the arrow of history points. Relatively traditional telescope designs reach the 5-m class, of which the 5-m Palomar telescope is the prime example. Now astronomers are reaching for 10 m, made possible by new technologies to make, test, support, and control the optical system. Beyond this size the multiple mirror telescope offers advantages; its limit is set by the number of 10-m class optical systems that can be beam combined. In space, the 2.5-m Hubble telescope has exceeded the billion dollar limit but will be worth it in terms of the science to be returned. A 20-m optical infrared telescope can probably be assembled in space within this limit, and new concepts and technologies may make future space telescopes of this size work at optical diffraction limits.
Imaging spectrometry: a great leap in remote sensing
Authors: Goetz Alexander F. H.
Published: February 2023

Research during the last five years has revealed the potential of high-spectral-resolution remote sensing for direction identification of the earth’s surface materials. Technological developments in the area of infrared area array detectors, optics, and data systems have made it possible to build imaging spectrometer sensors that cover the wavelength region of reflected sunlight from 0.4 to 2.5 µm in 200 or more spectral bands simultaneously. An imaging spectrometry program being implemented at the Jet Propulsion Laboratory contains four sensor elements. Presently the Airborne Imaging Spectrometer acquires images in 128 bands simultaneously in the 1.2-2.4-µm wavelength region. In late 1986 the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) will be completed. AVIRIS will cover an 11-km wide swath in 224 spectral bands. The Shuttle Imaging Spectrometer Experiment will acquire data on a global basis in 196 spectral bands over a 12-km swath. Finally, the High-Resolution Imaging Spectrometer (HIRIS) is envisioned for the space platform expected to be launched in the mid-1990s. HIRIS would acquire data over a 50-km wide swath.
Design alternatives for future Landsat instruments
Authors: Mika Aram M.
Published: February 2023

As the applications of Landsat data become more sophisticated, users have identified a need for improved spatial, spectral, and radiometric resolution in future instruments. Several sensor-design concepts have been developed to address these projected needs; however, the Landsat user community is diverse, and a sensor design optimized for research purposes may differ markedly from one intended for operational or commercial use. For example, an imaging spectrometer with a multiplicity of bands is an ideal tool for investigating phenomenology and elucidating spectral signatures; but, field-of-view limitation, data-rate constraints, and optomechanical complexity make this instrument less attractive as a primary sensor for an operational/commercial Landsat system. Conversely, instrument designs based on the multispectral linear array (MLA) concept can provide better spatial coverage with fewer (perhaps, 8-24) spectral bands tailored to meet the needs of operational/commercial data customers. The design approaches and missions are complementary, with planned spectrometer experiments providing guidance for optimal band selection for future operational/commercial MLA instruments.
In-orbit spacecraft instrument alignment determination in the 1990s
Authors: Hinkal Sanford W.
Published: February 2023

In any earth orbiting system designed for the sensing of inputs from remote sources, it is of prime importance to identify the location of the remote source. This implies a priori knowledge of the pointing direction of the instrument. In some applications, at the time of input sensing, accuracy must be within a few seconds of arc. Real-time sensing of perturbations to pointing of an instrument in orbit may be needed for attitude determination or control. These perturbations may occur over a large bandwidth.
ATMOS: High resolution spectroscopy of the upper atmosphere from space
Authors: Farmer C. B.
Published: February 2023

The ATMOS instrument, a Michelson interferometer-spectrometer designed for Shuttle operation, flew for the first time on Spacelab Mission 3 in April 1984. Highlights of the flight and measurement results are discussed.
LIMS and HALOE retrieval methods
Authors: Russell James M.
Published: February 2023

The LIMS experiment was launched on the Nimbus 7 satellite to sound the upper atmosphere composition and structure. Broadband earth horizon radiance profiles were measured in the infrared and later ground-processed to infer vertical profiles of temperature and the mixing ratios of O3, H2O, NO2, and HNO3. A key to successful retrieval of information from the radiances is a fast radiative transfer code that will allow sufficient iterations and provide essentially line-by-line transmittance calculation accuracy. The LIMS radiances were calculated using the emissivity growth approximation (EGA) technique, which is based on use of a precalculated data base developed for a wide range of temperature and pressure. This method was used in combination with an onion peeling retrieval technique that does not rely on a prior statistical knowledge. The HALOE experiment will be launched on the UARS satellite in late 1989 to measure vertical profiles of stratosphere O3, HCI, HF, CH4, H2O, NO, and NO2. Unlike LIMS, HALOE uses solar occultation measurements made by both broadband and gas filter correlation radiometry. Retrievals using the correlation measurements require high spectral resolution calculations, and the process can be very time-consuming and expensive in an iterative approach. The FIALOE processing will use a combination of the LIMS EGA method and a fast narrowband line-by-line method to provide the required speed and accuracy in the radiative transfer calculations. The onion peeling retrieval approach and another scheme, which uses information from all tangent altitudes simultaneously, are currently being evaluated.
Inversion procedure for retrieval of aerosol size distributions
Authors: Trakhovsky Eli , Shettle Eric P.
Published: February 2023

This paper discusses an improved procedure for the inversion of aureole forward scattering measurements to obtain aerosol size distributions. It is shown that the use of finite differences of the high angular resolution forward scattering data significantly improves the inversion results compared with using the direct kernel and enables one to resolve the bimodal structure of typical volume size distribution. An addition of proper scaling of the absolute size distribution to the Twomey-Chahine inversion algorithm results in very fast convergence with only three iterations typically required. An averaging and smoothing procedure is used to remove the spurious features of the inverted size distribution. The inversion method has been tested using simulated angular scattering measurements for four different aerosol models. For measurements covering 1.08-10° at a wavelength of 0.25 μm, the size distributions were retrieved with a 15-30% rms error over the radii range between 0.2 and 6.0 μm, with a representative measurement noise of 4%. It is noted that the differential inversion technique is more sensitive to noise than the direct method, since differencing the measurements decreases the signal-to-noise ratio.
Information aspects in the remote sensing of aerosol size distributions
Authors: Viera G. , Box M. A.
Published: February 2023

Many remote sensing experiments, including both multispectral extinction and aureole scattering for the determination of aerosol size distributions, require the inversion of a first kind Fredholm integral equation. Due to the combination of inherent instability and measurement error, this is a notoriously difficult task. We have used the singular function theory, which is the natural framework for the solution of such equations, to study the inversion of both multispectral extinction and aureole scattering measurements. By examining the first few singular values, it is readily seen how many pieces of information may be determined for a given noise level. Equally important, however, is a study of the expansion of a set of typical size distributions in terms of the corresponding singular functions. Thus it is advisable to compare different types of remote sensing experiment (e.g., multispectral extinction vs aureole scattering) as well as different wavelength ranges. In particular, we show that extinction measurements in the visible and near IR provide very little information about the Aitken nuclei mode (radii 0.1 μm).
Understanding low-vision reading
Authors: Legge Gordon E.
Published: February 2023

Reading difficulties usually accompany low vision. Historically, little research has been devoted to the role of vision in reading. This is due in part to an emphasis on cognitive factors in normal reading and in part to the now discredited view that impaired vision should be conserved rather than aggravated by prolonged tasks like reading. Recently, psychophysical methods have been used to study the role of vision in reading. Normal performance has been evaluated for stimulus variables likely to be important in low-vision reading. Comparable low-vision measurements have been made and departures from normal analyzed. Examples to be discussed include the effects of character size, contrast, and blur. Despite fears that the heterogeneity of low-vision conditions might be too great to yield general principles, these experiments have uncovered distinctions, such as the presence or absence of central vision, that predict reading performance. Moreover, the visual requirements of reading are modest and within the capacity of most low-vision subjects. Research of this kind will establish optimal stimulus conditions for low-vision reading, best reading performance that low-vision individuals may hope to achieve, methods for clinical assessment, and principles for designing new low-vision reading aids.
Multilayer dielectric reflectors with extended high-frequency transmission regions
Authors: Baumeister Philip
Published: February 2023

The multilayer consists of a basic period of I dielectric layers of quarterwave optical thickness that is repeated p times: Suppose the basic period Is surrounded by an incident medium and emergent medium of the same (but arbitrary) refractive Index. If its reflectance is zero, the stopband is suppressed. Kard1,2 developed approximations for the R/Tpolynomial of the basic period. The procedure is to set R/T to zero at specific frequencies and to solve linear equations for the refractive Indices. Within certain limitations imposed by the symmetry of the R/T curve and dispersion of the optical materials, any number of contiguous and noncontiguous stopbands may be suppressed.
Comparison of models for calculating the effects of inhomogeneity in thin films
Authors: Carniglia Charles K. , Price J. S.
Published: February 2023

Spectrophotometric measurements of reflectance vs wavelength are often used to determine the optical constants for single layers of dielectric materials coated on transparent substrates. If the thin film is inhomogeneous, each minimum of the reflectance curve is displaced from the value of R expected for a homogeneous film by an amount ΔR. It has been claimed previously1 that, for a linear variation in the refractive index, the degree of inhomogeneity is approximated by Δn/n ≃ ΔR/ (4.4R), where n is the average refractive index of the film and Δn is the total change in index over the thickness of the film. This paper explores the range of validity of this relation by comparing it to the results obtained from two analytical models. The first model makes use of a simple computation for a single inhomogeneous layer which uses only the refractive indices at the interfaces of the film. This model ignores the details of the index variation within the layer. The second model involves a multilayer computer calculation which simulates a linear index profile using many thin layers. When Δn/n < 0.2, the approximate formula gives reasonably accurate answers for fused silica or glass substrates (with refractive indices in the 1.45–1.5 range).
Inversion of the nonlinear equations of reflectance and transmittance of thin films on glass
Authors: Zaghloul A.-R. M. , El-Nahass M. M.
Published: February 2023

We start with the well-known exact Fresnel equations for the reflectance and transmittance of a thin absorbing film on a glass substrate at normal incidence. The optical constants of the film, refractive index and absorption index, and the film thickness itself are all determined. An iterative method is used with a complete sensitivity study of the parameters. Accurate results are obtained. An error analysis is carried out to study the accuracy of the inversion method suggested using simulated results.
Computer-generated holograms using a personal computer
Authors: Yang Cunwu , Ih Charles S.
Published: February 2023

Personal computers and peripherals have become very powerful and sophisticated. A CGH can now be readily made on a personal computer system. Our equipment consists of an IBM-PC, a Western Graphtec MP 1000-01 x-y plotter, and an IBM dot matrix printer. The serial port for asynchronous communication is used to transfer the data to the plotter. The parallel port is used for the printer for data or program printing. The MP 1000-01 plotter is very suitable for plotting holograms because it has a large plotting area (36 × 27 cm), adequate resolution, and best of all it has a built-in firmware spline routing for smooth curve plotting using only a few points. We have also added a switch (and an optional rom) so that the plotter can be changed from the MP-1000 to the popular HP-7475A mode. Because of the limited accuracy (and the speed, a minor factor), we have used a series expansion on the mathematical expressions to obtain the necessary precision. We have made holograms of two spherical waves. The quality of the plotting is comparable with that obtained from large computer systems. We also investigated ways to equalize the dark and white spacings so that the reconstruction efficiency will be more uniform across the hologram. This may also increase the reconstruction efficiency for a phase hologram. Experimental results and related technical problems are discussed.
Intracavity optical bistability in the presence of optically induced absorption
Authors: Dagenais M. , Surkis Elisa , Sharfin W. F. , Winful H. G.
Published: February 2023

Optical bistability in the presence of an optically induced absorption is observed when a thin 13-μm CdS sample is inserted between two mirrors of 90 % reflectivity, in our experiment, a modulated cw laser of ~15-mW peak power is tuned on each side of the free exciton resonance in CdS, and the transmission characteristics are studied. A theoretical calculation including both absorptive and dispersive effects is presented and good agreement is obtained. The absorption coefficient and the index of refraction of the material are connected by Kramers-Kronig relations. Propagation effects are taken into account. Sufficiently long pulses (40 ms) are considered to allow the thermally induced absorption to occur. For detunings above the free exciton resonance, we predict that counterclockwise hysteresis loops will first be observed as the intensity rises; for detunings below the free exciton resonance, only clockwise hysteresis loops are predicted. These predictions were experimentally verified. Power levels of the order of 5–10 mW were sufficient to observe bistability. Cavity effects were also observed.
Quantum theory of optical bistability with a spatially varying field mode in the good cavity limit
Authors: Min Xiao , Kimble H. J. , Carmichael H. J.
Published: February 2023

A straightforward but general extension of the quantum theory of optical bistability is made to include spatial variations of the field mode in the good cavity limit. The analysis proceeds by dividing the field mode into small sections which are each microscopically large in terms of the atomic number to allow truncation of the generalized Fokker-Planck equation but which are macroscopically small to justify the assumption of constant field amplitude. In a linearized approximation, analytic expressions are obtained for the ratio of incoherent to coherent intensity and for the intensity correlation function of the transmitted field for the two particular examples of a Gaussian-mode field in a ring cavity and a plane-wave field in a standing-wave cavity. In the weak field limit the results of the plane-wave ring cavity are recovered independent of the form of the spatial dependence of the cavity mode. However, more generally a nonuniform distribution tends to suppress certain quantum features such as photon antibunching.
Two-dimensional scanner using pseudoplane holograms
Authors: Zhuang B. H. , Ih Charles S. , Xiang L. Q.
Published: February 2023

Plane grating (plane hologram) scanners are easy to make and to operate and can produce very straight scan lines in a specific operation condition.1 This limits their operation to 1-D scanning. For some applications, a 2-D scanning is more convenient and/or desirable. We describe a technique for improving the plane hologram scanner so that straight scan lines can be obtained over wider operating conditions. If the holograms are made with a spherical wave and a plane wave instead of two plane waves, the scan line straightness can be sufficiently improved for 2-D operation. By adjusting the divergence of the spherical wave at the hologram, compensations can be made over considerably large (vertical) deflection angles. This technique can be applied to scanners for which the construction and reconstruction wavelengths may be different. This is advantageous because many hologram recording media are only sensitive at shorter wavelengths but the reconstruction is more economical or convenient at a longer wavelength. Techniques for making the scanners are discussed. Computer simulations and experimental results for the performance of the 2-D scanner are shown.
Holographic tomography in determining the structure of 3-D object fields
Authors: Yu F. T. S. , Zheng L. N. , Lin T. W.
Published: February 2023

An alternative method for determination of 3-D object fields is presented. The holographic multiplexing technique is employed in this method to record the multidirectional projections of the object field. The multiplexed hologram thus generated can be used to reconstruct the different directional projections of the studied field sequentially in the optical system. In addition, it provides series sets of projection data by means of an image sensing device for computer digital postprocessing. With the aid of a digital reconstructed image, the structure of the studied object field can be well determined. Illustrations of the recording and reconstructing systems as well as the algorithm adapted to reconstruct the field image digitally are given. Some preliminary results are also provided.
Holographic calibration of cloud particle measurement systems
Authors: Owen Robert B. , Baumgardner Darrel , Berger Roger
Published: February 2023

While the theoretical limitations of optical array probes used for cloud particle measurements are well known, some details of actual field performance are undetermined. The response to particles in the 25–150-μm range is unresolved and the maximum information content is unknown. There also remains a major problem in the measurement of particle mass, since particle density and morphology is usually impossible to discern from the probe’s array shadow images. In an effort to resolve these problems, a SDL holographic system modified for cold weather operation was used in conjunction with a PMS 2D-C optical array probe to measure snow particles. The 2-D probe was modified to record only those particles which fell totally within its diode array; particle detection triggered a pulse which fired the holographic system's ruby laser. Experimental operations were conducted at the University of Wyoming’s Elk Mountain Observatory. This facility is a well-equipped mountaintop laboratory where a wide variety of ice particle habits occur naturally. Aircraft measurement conditions were duplicated in the observatory's wind tunnel; a cold room was also used. Holographic and 2-D data were successfully obtained in field conditions, laying the groundwork necessary for future complete calibration tests.
Color multiplexing by image holograms
Authors: Guel S. , Ibarra J. , Berriel-Valdos L. R.
Published: February 2023

We propose a multiplexing method using image holograms obtained from black-and-white transparencies, illuminated by a plane wave front. Using different reference beam angles, the hologram for each one of the transparencies is recorded; in such conditions the spatial frequency carrier at the hologram plane is varied. As we are dealing with cosinusoidal gratings, the reconstruction can be made using white light. This implies that for each reference beam angle in the recording step, a different color corresponds in the reconstruction step. Therefore, since each transparency was recorded with a different angle, each will appear in a different color, and by using color filters we can select the desired image. This method also permits the use of different techniques to carry out pseudocoloration.