Development of an Optical Fiber Management andTransfer System
by Seiichi Naraoka *, Yoshihisa Ito * and Yoshiki Tokiyama *The worldwide explosion of Internet use has been reflected in the burgeoning
growth of users in Japan, requiring provision of optical network infrastructure.
Optical technology is already in use on trunk lines, but implementation for subscriber access has
been delayed. This paper describes a new optical distribution system for central offices, together
with system equipment and components.

ABSTRACT1.

INTRODUCTION

The growing revolution in information technology has
given new impetus to FTTH (fiber to the home). A needhas arisen for new types of telecommunications infrastructure for both voice and data, and specifically for central
office distribution systems that make possible more efficient management.
Conventional central office systems involved installationof station cable, splitter modules, optical branch modules,
AURORA monitoring systems, and distribution frames,
each of which was considered separately. The need formore efficient system management has brought about aunified approach to the system as a whole 1), 2), 7) . The
resulting requirements with respect to these central officeequipment and components are:1) design flexibility for the system as a whole;2) minimal distance between splitter modules (jumperunits) and optical branch modules (optical couplerunits);
3) increase in the number of fibers per distribution
frame: and4) improved flexibility in connection (jumpering) to theentry of the optical branch module (coupler unit).

2.

CENTRAL OFFICE DISTRIBUTION SYSTEM

2.1 System Configuration
Figure 1 shows the configuration of the central office distribution system that has been developed to meet therequirements described above. Conventionally the framefor optical fiber termination was known as an FTM (forfiber termination module); the new term is IDM (integrateddistribution module).

IDM

Outside cable

Coupler function
Splitter function
Filter(optical coupler unit) (optical jumper unit) function

Fiber selection function(fiber selector)

OLT
Central office
distribution cable

Monitor systemPC
OTDR

Figure 1

Configuration of optical fiber distribution management system* Optical Transmission Line Development Dept., FITEL
Photonics Lab.

27

The characteristics of the system are as follows:
1) There are two termination frames (IDM-A and IDMB, instead of the former single FTM for enhanced
design flexibility;2) The splitter module (optical jumper unit) and theoptical branch module (optical coupler unit) are bothhoused in the IDM-A
3) The IDM-A contains 4,000 fibers, twice as many as
before;4) The jumper unit has an optical cord aligning element, facilitating wiring work
There follows a detailed description of the optical coupler unit, optical jumper unit and fiber selector that makeup the system.
2.2 Optical Coupler Unit
The optical coupler unit inserts the test light from the optical testing system to the communications link, and returns
the light from the communication link to the measuring
tool. Figure 2 shows is optical configuration.
The A ports are connected to the optical jumper unit,
and the B ports to the outer cable. The C ports are connected to the fiber selector of the optical testing system.
Optical coupler insertion loss is shown for A port to B
port at a wavelength of 1310 nm (Figure 3) and 1550 nm(Figure 4). Insertion loss for C port to B port at 1650 nm isshown in Figure 5. Table 1 shows the optical characteristics.
2.3 Optical Jumper Unit
The optical jumper unit branches the light from the communications equipment to the individual fibers. Units areof various types for specific applications and service.
Figure 6 shows the optical configuration of a multiplexingunit.

Figure 2

Configuration of optical coupler unit
120

120

80
60

80

Frequency

100

Frequency

N=352
Maximum
8.73 dB
Average7.69 dB
Std. deviation 0.33 dB

100
N=352
Maximum
2.68 dB
Average
1.71 dB
Std. deviation 0.31 dB

60
40

40

202006.8

7.2

7.6

0
1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.42.6

2.8

Figure 3

Figure 5

Optical coupler insertion loss, A port to B port (1310nm)

Frequency

80

Average

1.71 dB

Std. deviation

0.31 dB (1310±20 nm)

Average40

Return loss (dB)

0
1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

Insertion loss (dB)28

A port to B port

B port to C port

60

20

Figure 4

Characteristics of Optical Coupler Unit

Insertion loss (dB)
N=352
Maximum
2.45 dB
Average
1.70 dB
Std. deviation 0.23 dB

100

Optical coupler insertion loss, A port to B port (1550nm)

8.8

Optical coupler insertion loss, A port to B port (1650nm)

Table 1120

8.4

Insertion loss (dB)

3.0Insertion loss (dB)

8.0

7.95 dB

Std. deviation

0.45 dB (1310±20 nm)

Average7.69 dB

Std. deviation

0.33 dB (1650±5 nm)

A portAverage49.3 dB

Std. deviation

2.88 dB (1310±20 nm)

C portAverage42.8 dB

Std. deviation

2.18 dB (1310±20 nm)

Furukawa Review, No. 202001

Optical jumper insertion loss is shown for A port to B
port at a wavelength of 1310 nm (Figure 7) and for C port
to B port at 1650 nm (Figure 8). Table 2 shows the opticalcharacteristics.
2.4 Fiber Selector
2.4.1 General Description
The efficient, low-cost monitoring of immense numbers of
optical fibers requires that the optical switches used inswitching handle as many fibers as possible. And since
they are housed inside the distribution frame they must beof compact, high-density design 3).
Previously used optical switches used single- or multifiber connector ferrules, but this design makes it difficult toachieve compactness or high density 4).
Accordingly a switch was developed that operates on
direct movement of the fiber itself. Also developed was afiber selector with a switch mounted in the case andinstalled in the monitor system.

1.31 µm

2.4.2 Optical Switch Structure
To achieve a compact optical switch, the movable fibers
are single-mode fibers 125 µm in diameter. The fixed
fibers are aligned by bonding to V-grooves formed at 127µm pitch in a plate (Figures 9 and 10).
The movable fiber is brought to the position over the Vgroove for the target fiber and is pressed into the grooveto align the axes and complete connection.
2.4.3 Forming of Fixed Fiber Array in V-grooved Plate
As described above, the fixed fibers are held in V-grooves
formed at a pitch of 127 µm. For ease of manufacture thefixed fiber arrays are composed of 8-fiber ribbons. Tworibbons are superimposed and fibers from the upper andlower ribbons are laid alternately in the grooves (Figure10) 6).
The actual procedure is first to bond the fibers of thebottom ribbon into every other groove (i.e., a pitch of 254µm). Then the fibers of the upper ribbon are laid at an offset of 127 µm from the lower ribbon fibers and bonded inplace. This results in a fixed fiber array in which the fibers
are arranged at a pitch of 127 µm.

1.55 µm801.31 µm

N=384Maximum
14.51 dB
Average13.29 dB
Std. deviation 0.47 dB

7060

Frequency

1.55 µm

1.31 µm

5040302010

1.55 µm

012.2

12.6

13.0

13.4

13.8

14.2

14.6

Insertion loss (dB)

1.31 µm

Figure 8

Optical jumper unit insertion loss, A port to B port
(1550 nm)1.55 µm

Table 2Characteristics of Optical Jumper Unit

: Filter
Insertion loss (dB)Figure 6

Optical configuration of optical jumper unit

80

Frequency

60

14.2 dB

Std. deviation

0.43 dB (1310±20 nm)

Average

54 dB

Std. deviation

0.78 dB (loss difference

between 1310 nm band and 1550 nm
band, and between 1310 nm band

50and 1650 nm band)40

B port to C port

30

Average13.3 dB

20

Std. deviation

0.47 dB (1550±20 nm)

Return loss (dB)

100
13.2

13.6

14.0

14.4

14.8

15.2

Insertion loss (dB)Figure 7

Average

N=384Maximum
15.17 dB
Average
14.47 dB
Std. deviation 0.43 dB

70

A port to B port

Optical jumper unit insertion loss, A port to B port
(1310 nm)A portAverage41.1 dB

Std. deviation

2.25 dB (1310±20 nm)

B portAverage45.1 dB

Std. deviation

4.94 dB (1550±20 nm)

29

Temperature (°C)

Fibers (fixed side)
V-grooved plate
Temperature

50

Insertion loss (dB)

250

0.5
0.4
Insertion loss

0.3
0.2
0.1
006

Fibers (movable side)

Figure 912Time (hr)Basic structure of optical switch

Figure 11 Repeatability of insertion loss in heat-cycle tests

125 µm8-fiber ribbon

Housing
Opening clip

127 µm254 µmV-grooved plate
Fiber selector(inside)8-fiber ribbon

MT connector

Fiber selector(outside)Figure 12 Simplified MT adapter

127 µmFigure 10 Alignment of fixed-fiber array

2.4.4 Temperature Compensation
Optical switches are composed of elements--case, mechanism, V-grooved plate, etc.--each made of different
materials with a different coefficient of thermal expansion.
This means that changes in temperature give rise to positional displacement between the fixed and movable fibers,
and this is particularly pronounced with respect to thedirection of arrangement of the fixed fiber array.
The fixed fibers are arranged in the V-grooves and if thepitch is large the V-groove aperture increases so that acertain amount of displacement can be absorbed withoutcausing problems. When fibers are arranged at a pitch of
127 µm, however, the V-groove apertures are smaller andthis amount of displacement cannot be accommodated.
Accordingly a control method was developed whereby
thermistors are used to detect temperature, and movement of the movable fibers is compensated according to
the temperature detected, shifting the movable fibers tomaintain optimum position at all times 6).
This temperature compensation suppresses positional
displacement between the fixed and movable fibers, and30

makes possible connection with high reproducibility from 0to 50°C. Figure 11 shows the repeatability of insertion loss
in heat-cycle tests from 0 to 50°C.
2.4.5 Simplified Adapter
The fiber selector is connected to the optical coupler module or the cable in order to introduce the test light.
Normally these connections are made using an MT connector.
In the optical switches used up till now these connections were made using an MT clip, and it was therefore
necessary to use a special tool for connection/disconnection. This made the work more inconvenient, and it wasmore difficult to achieve high-density accommodation of
the connections.
Accordingly the simplified adapter shown in Figure 12
was developed, improving working convenience andinstallation density 5).
The simplified MT adapter is constructed of a housing
and an opening clip, and with a view to high-density installation, each housing is designed to accommodate two MTconnectors.
The procedure involves inserting the MT connector into
the housing and opening the clip. It is extremely simple,
and no special tools are required.
Photos 1 and 2 show a commercial fiber selector developed using these elements, and a 2000-fiber opticalswitch that is accommodated inside the fiber selector.

Furukawa Review, No. 20

2001

0.8

Insertion loss (dB)

0.7

Photo 1Fiber selector

0.6
0.5
0.4
0.3
0.2
0.1
00

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.55.0No. of connections (million)

Figure 15 Fiber selector durability

Figures 13 through 15 show the optical characteristics ofthe fiber selector.

3.

CONCLUSION

An optical coupler unit, optical jumper unit and fiber selector have been developed for a central office distribution
system. Future efforts will be directed at reducing costs.
Photo 2

Optical switch

600

N=2000
Average=0.46 dB
Maximum=0.80 dB
Minimum=0.16 dB

Frequency

500
400
300
200
100
00

0.2

0.4

0.6

0.8

Insertion loss (dB)Figure 13 Fiber selector insertion loss

1000

N=2000
Average=45.7 dB
Maximum=50.9 dB
Minimum=40.0 dB

900
800

REFERENCES
1) Izumita et al.; Development of On-Premise Optical Distribution
Management System, Proc. of IEICE 2000, B-10-18 (in Japanese)
2) Uruno et al.; Design of Integrated Distribution Module for OnPremise Optical Distribution Management System, Proc. ofIEICE 2000, B-10-25 (in Japanese)3) Enomoto et al.; Design of Test Access Circuitry for IntegratedDistribution Module, Proc. of IEICE 2000, B-10-26 (in Japanese)
4) Kawazoe et al.; Development of the Optical Fiber Cable Transfer
and Supervisory System, Furukawa Electric Review, No.90, 1992,
p57 (in Japanese)5) Naraoka et al.; Development of Simple MT Connector Module,Proc. of IEICE Societal 2000, B-10-39 (in Japanese)6) Naraoka et al.; 2 x 800 Optical Switch Using Fiber Butt-Joint
Scheme, Proc. of IEICE Societal 1997, B-10-190 (in Japanese)7) Tomita et al.; Optical Fiber Cable Technologies Pursuing Low
Costs, NTT Technology Journal, March 2000, p34 (in Japanese)

Manuscript received on January 6, 2001.

Frequency

700600500400300200
10004042444648505254

Insertion loss (dB)Figure 14 Fiber selector return loss31