ECOC 1975 - ECOC 2013

Announcement
During the planning phase of the Conference it became clear that the
interest in this subject was sufficient to demand a series of
Conferences. Consideration was given to initiating an International or
a European series.
After consultation with representatives from the European countries,
the USA and Japan, it was recommended that this Conference
should be the first of a series of Europ'ean Conferences with the
following Conference to be held in 1976 in France and a subsequent
one in Germany in 1977.
Although the future Conferences will be organised on a European
basis, it is the intention to strongly encourage participation on an
international basis by invitation of the speakers and session chairmen,
and by presentation of papers.
C. P. Sandbank
Chairman, lEE Optical and infra-red devices
and techniques Committee
ii

The Institution of Electrical Engineers is not, as a body, responsible
for the opinions expressed by individual authors or
speakers.
Page No. 168 D. J. Albares
Potential military optical fibre communications
5 J. A. Arnaud
Pulse broadening in multimode optical fibers
131 E. A. Ash, C. W. Pitt and M. G. F. Wilson
Integrated optics for fibre communications systems
60 R. Auffret, C. Y. Boisrobert and A. Cozannet
Wobulation technique applied to optical fibre transfer function
measurement
209 M. Baldwin
Data transmission in naval ships by fibre optics
30 K. J. Beales, W. J. Duncan, P. L. Dunn and G. R. Newns
Preparation of dry glasses for optical fibres
27 K. J. Beales, W. J. Duncan and G. R. Newns
Sodium borosilicate glass for optical fibres
11 A. S. Belanov, E. M. Dianov, G. I. Ezhov and A. M. Prokhorov
Multilayer optical waveguides
153 R. W. Berry and R. C. Hooper
Practical design requirements for optical fibre transmission systems
67 P. W. Black and A. Cook
Properties of optical fibre in cabling
182 R. W. Blackmore and P. H. Fell
8.448 Mbits optical fibre system
204 C. Y. Boisrobert, D. Hui Bon Hoa, M. Treheux and J. L. Gallaup
Digital repeater design
117 J. P. Budin
Transversely pumped NdxLa 1 - xP5014 laser performance
128 J. Conradi, P. P. Webb and R. J. McIntyre
Silicon reach-through avalanche photodiodes for fiber optic
applications
iv
Contents

Page No.
39 J. P. Dakin
A new method for the cheap and simple production of low-loss
silica-based optical waveguides
87 J. F. Dalgleish, H. H. Lukas and J. D. Lee
Splicing of optical fibres
165 D. E. N. Davies and S. A. Kingsley
A novel optical fibre telemetry highway
33 C. R. Day, K. J. Beales, J. E. Midwinter and G. R. Newns
The development of optical fibre using sodium borosilicate glasses
and the double crucible technique
36 F. V. DiMarcello and J. C. Williams
Reproducibility of optical fibers prepared by a chemical vapor
deposition process
135 J. G. Farrington and J. E. Carroll
Sub nanosecond pulsing of GaAs stripe lasers
185 P. H. Fell and A. H. Kent
Television transmission equipment and systems
197 W. A. Gambling and D. N. Payne
Some experimental aspects of propagation in optical fibres
171 C. Game and A. Jessop
Random coding for digital optical systems
51 S. Geckeler and D. Schicketanz
The influence of mechanical stress on the transfer characteristics
of optical fibres
1 D. Gloge
Principles of optical fiber transmission
122 R. C. Goodfellow and W. Milne
The dynamic impedance and high frequency performance of small
area high radiance gallium arsenide L.E.D.s
105 A. R. Goodwin, J. R. Peters and M. Pion
Temperature-stable continuously operating Ga xA1 1 _As injection
lasers
v
Contents

Page No.
96 J. Guttmann, O. Krumpholz and E. Pfeiffer
Multi-pole optical fibre-fibre connector
62 D. W. Harper, A. Forber, J. R. Mellor and J. K. Watts
Medium loss optical fibres and some features of their use in
practical systems
99 I. Hayashi
Status of (Ga.AI)As heterostructure laser research in Japan
177 W. E. Heinlein and H. R. Trimmel
Repeater spacings of 8 Mbit/s and 34 Mbit/s transmission
systems using multimode optical waveguides and LEOs
111 T. Ikegami
Spectrum broadening and tailing effect in directly modulated
injection lasers
57 K. Inada, T. Akimoto, M. Kojima and K. Sanada
Transmission characteristics of a low-loss silicone-clad fused
silica-core fibre
54 A. Isomura, Y. Yamamoto and T. Yamanishi
Plastic coating of optical glass fiber
79 R. Jocteur
Cabling of low-loss optical fibers
8 C.Kao
Estimating the dispersion effects in a practical multimode waveguide
cable for fiber systems
114 G. D. Khoe
Power coupling from junction lasers into single mode optical fibres
138 K. Kobayashi, R. Lang and K. Minemura
Novel methods for high speed modulation of semiconductor lasers
24 K. Koizumi and Y. Ikeda
Low-loss light-focusing fibers made by a continuous process
vi
Contents

Page No. 81 T. Nakahara, M. Hoshikawa, S. Suzuki, S. Shiraishi, S. Kurosaki
and G. Tanaka
Design and performances of optical fiber cables
13 B. P. Nelson and J. R. Stern
Pulse propagation measurements on slightly overmoded glass fibres
73 U. H. P. Oestreich
The application of the Wei bull-distribution to the mechanical
reliability of optical fibers for cables
188 K. Okura, J. Yamagata, S. Senmoto, Y. Minejima and M. Kunita
A video transmission system using fibre cable
141 J. J. Pan
High-performance, wideband fiber optic repeater and its
application
43 D. N. Payne, F. M. E. Sladen and M. J. Adams
Index profile determination in graded index fibres
108 E. G. Rawson, R. E. Norton, R. D. Burnham and D. R. Scifres
A striped-substrate, double-heterostructure source for optical
communication
16 M. H. Reeve and J. E. Midwinter
Studies of tunnelling from the guided modes of a multimode fibre
150 F. F. Roberts
Optical fibres look into the real world
174 M. Rousseau
Transmission code and receiver selection for optical fibres PCM
communications
162 C. P. Sandbank
The prospects for fibre optic communication systems
102 D. Schicketanz
Large signal behaviour of DHS laserdiodes
201 M. I. Schwartz
Optical fiber parameters and optical cable design considerations
viii
Contents

Page No. 48 G. H. Sigel, Jr. and B. D. Evans
Prospects for radiation resistant fiber optics
84 R. J. Slaughter, A. H. Kent and T. R. Callan
A duct installation of 2-fibre optical cable
4 A. W. Snyder
Ray analysis of pulse distortion due to scattering
21 W. J .. Stewart
Fibre characterisation by use of the relation between the
characteristics of leaky modes in optical fibres and the fibre
parameters
19 W. J. Stewart
Mode conversion due to periodic distortions of the fibre axis
203 G. H. B. Thompson
Laterally confined injection lasers for optical communications
147 Y. Vena, Y. Ohgushi and A. Abe
A 40 Mb/s and a 400 Mb/s repeater for fiber optic communication
156 Y. Vena, Y. Ohgushi and T. Yasugi
An optical fiber cable communication system using pulse-interval
modulation
179 D. Williams
The military applications of fibre optical communication
144 J. Yamagata, S. Senmoto, Y. Inamura, H. Kaneko and
T. Takahashi
A 32 Mb/s regenerative repeater for fibre cable transmission
ix
Contents

Abe, A. ..
Adams, M. J.
Akimoto, T.
Albares, D. J. ·.
Arnaud, J. A.
Ash, E. A.
Auffret, R.
Baldwin, M.
Beales, K. J.
Belanov, A. S. ·.
Berry, R. W.
Black, P. W. ·.
Blackmore, R. W.
Boisrobert, C. Y.
Bouillie, R.
Page No.
147
43
57
168
5
131
60
·. 209
27,30,33
11
153
67
·. 182
· .60,204
194
Geckeler, S.
Gloge, D. ·.
Goodfellow, R. C.
Goodvvin, A. R.
Guttmann, J.
Harper, D. W. ·.
Hatta, T.
Hayashi, I. ·.
Heinlein, W. E...
Hooper, R. C. ·.
Hoshikawa, M...
Hui Bon Hoa, D.
Ikeda, Y.
Ikegami, T.
, Page No.
" ,
·. 51
·. 1
119, 122
105
' 96
62
191
99
177
153
81
204,
24
111
Budin, J. P.
Burnham, R. D.
Callan, T. R.
117
108
84 '
Inada, K.
Inamura, Y.
Inao, S...
(somura, A.
57
144
·. 70,,93
54
Carroll, J. E.
Conradi, J.
Cook, A. ·,
Cozannet, A.
Dakin, J. P. ·.
Dalgleish, J. F. '..
Davies, D. E. N.
Day, C. R. ·.
Dianov, E. M. ·.
DiMarcello, F. V.
Duncan, W. J.
Dunn, P. L.
Evans, B. D.
Ezhov, G. I.
135
128
67
60
39
87
165
33
11
36
27,30
30
48
11
Jessop, A.
Jocteur, R.
Kaneko, H.
Kao, C...
Kent, A. H.
Khoe, G. D.
Kingsley, S. A.
Kobayashi, K.
Koizumi, K.
Kojima, M.
Krumpholz, O.
'Kudo, T...
Kunita, M.
Kurokawa, K.
Kurosaki, S.
171
79
144
·. 8
· .84, 185
114
165
138
24
57
96
·. 159
188
159
81
Farrington, J. G. ·. 135 Lang, R. .. 138
Fell, P. H. 182, 185 Lazay, P. D. 40
Forber, A. 62 Lee, J. D. 87
French, W. G. ·. 40 Le Noane, G. 194
Fukuda, S. 191 Liertz, H. M. 76
Lukas, H. H. 87
Gallaup, J. L. ·. 204
Gambling, W. A. 197 Mabbitt, A. W. ., 119
Game, C. 171 Maslowski, S. ·. 64
x
List of Authors

Page No. Page No.
Matsuda, Y. · . 70,93 Shiraishi, S. ·. 81
Maurer, R. D. · . 46 Sigel, Jr., G. H... 48
Mcintyre, R. J ... 128 Simpson, J. R... 40
Mellor, J. R. 62 Siaden, F. M. E. 43
Midwinter, J. E. · . 16,33 Slaughter, R. J ... 84
Mikoshiba, K. ·. 191 Snyder, A. W. · . 4
Miller, C. M. 90 Stern, J. R. 13
Milne,W. 122 Stewart, W. J. · . 19,21
Minejima, Y. 188 Suzuki, S. 81
Minemura, 1

3
4. Maurer, S. J. and Felsen, L. B.: Ray methods for tapped
and slightly leaky modes in multilayered or multiwave
regions. IEEE Trans. Microwave Theory Tech. Vol. MTT-18,
September 1970, pp. 584-595.
5. Kawakami, S. and Nishida, S.: Anomalous dispersion of new
doubly clad optical fiber with a low-index inner cladding.
IEEE J. Quantum Electr. Vol QE-10, No. 12, December 1974,
pp. 879-887.
6. Marcuse, D.: Theory of dielectric optical waveguides,
Academic Press, New York, 1974, pp. 162 and 235.
7. Chase, K. M.: On wave propagation in inhomogeneous media
J. Math. Phys. Vol 13, 1972, p. 360.
8. Olshansky, R. and Keck, D. B.: Material effects on
minimizing pulse broadening, Proc. of the Topical Meeting
on Opt. Fiber Transmission; Williamsburg, January 1975,
pp. TuC5/1-3.

30
PREPARATION OF DRY GLASSES FOR OPTICAL FIBRES
K J Beales, .W J Duncan, P L Dunn and G R Newns
Introduction
A requirement for a communicatlons system is a low loss transmission
medium. In the optical system being developed, the· transmission medium
consists of sodium borosilicate glass fibres'. The two main causes of
absorption loss are transition metal ions and water, which are present
as impurities. The water in the glass arises from three sources;
absorbed on the starting materials, dissolved in the starting materials,
and the furnace atmosphere. The water dissolved in the glass is present
as hydroxyl groups (-OH) which have a strong fundamental absorption band
at about 2800nm and overtone absorption bands at longer wavelengths. A
schematic diagram showing the positions of the fundamental, first, second
and third overtone absorptions at 2800, '400, 960 and 740nm is given in
Fig 1. There are also two structural combination bands at 2200 and 2400nm.
Although the absorption progressively decreases with increase in frequency,
-OH absorbs significantly in the 800-106Onm region. .
In the present work, we have measured the -OH content in bulk glass,
related the -OH content to the water content of the atmosphere during
preparation, investigated methods of preparing drier glasses and estimated
the loss due to -OH in glass and fibre between 530 and 106Onm.
Experimental
The high purity batch powders were melted in a silica crucible contained
within a silica enclosure. Melts were bubbled and then fined under an
atmosphere of the bubbltng gas. The gases used were CO/C0 2 mixtures of
various dew points, dried using molecular sieves. After fining, rods
were pulled from the melt and their optical loss measured between 600 and
1100nm by a calorimetric technique 2 and at 2800nm using a spectrometer.
Fibres were made by a double crucible technique, and the total insertion
loss measured.
Results and Discussion
As the extinction coefficient of -OH in the glass under study is not
known, the intensity of the fundamental peak at 2800nm was used to monitor
the -OH content.
Glasses were made under atmospheres of differing humidity and their water
contents (2800nm peak intensities) related to the dewpoint of the bubbling
and fining gas, see Table 1. The water content was found to be
proportional to the square root of the vapour pressure of water in the gas,
in agreement with the results of Franz for B2033.
To reduce the -OH content of the glasses, the following procedures were
found to be necessary. Surface water was removed by baking the powders
under vacuum at 250 0 c for several days. Water in the glass was removed
The authors are employed at the Post Office Research Centre, Martlesham
Heath, Ipswich, Suffolk IPS 7RE

......... ... ...J
«...
'"
o o
...J
-----
'" '"3
I
32
500 900 1300 1700 2100 2500 2900 3300
FIG. 1 HYDROXYL
IN SODIUM
100
90
80
70
E 60
.>

33
THE DEVELOPMENT OF OPTICAL FIBRE USING SODIUM BOROSILICATE GLASSES AND THE
DOUBLE CRUCIBLE TECHNIQUE
C R Day, K J Beales, J E Midwinter and G R Newns
Introduction
We wish to report work carried out in developing the double crucible fibre
drawing process to the point at which it is limited primarily by the bulk
glass loss. The double crucible method has been described previously1,2.
It is now possible to draw many kilometres of fibre in a continuous
process from platinum crucibles with very high reproducibility of fibre
attenuation. During the course of the work a number of problems have been
identified and controlled independently, and these are described below,
followed by some of the results achieved.
Recontamination
Operation of the crucibles at high temperatures causes leaching of trace
impurities, in particular iron and copper, from the platinum. This effect
was observed by Newns et a13 using the sodium calcium silicate (NCS) glass
system. By careful choice of glass compositions in the sodium borosilicate
(NBS) system,compatible glass pairs can be found which have viscosities
suitable for fibre pulling at temperatures low enough to reduce the leaching
rate to a negligible level. The operating temperature can thus be
reduced from -1100 0 C for NCS glasses to -850 C for NBS glasses. In
current fibre there is no increase in loss with time which can be
attributed to recontamination.
Loading
Relatively large gas bubbles may be trapped in the melt by a poor glass
loading technique. The glasses used for loading the crucibles were in the
form of canes 6 to 8 mm in diameter, pulled directly from the melt, and
subjected to a minimum of handling and exposure to the atmosphere. The
canes must be fed in at low speed so that a positive meniscus is formed
between the melt and the rod. This prevents cold rod from being thrust into
the pool of glass and drawing in gas bubbles. The rod should a1so enter
the melt at a fixed position to prevent fold-over effects which could also
trap gas.
Atmosphere control
When the crucibles are operated open to the air, streams o·f minute
scattering centres can be observed at the core-claddingiriterface of the
fibre. These were postulated to be gas bubbles released as a result of an
electrolytic cell formed be 4 ween the core and cladding glasses and the tip
of the core crucible nozzle. The driving force of the cell appears to be
oxygen in the atmosphere which diffuses through the cladding glass. The
The authors are with the Post Office Research Centre,
Martlesham Heath, Suffolk.

38
Fig. 1 Chemical vapor deposition preform
preparation apparatus.
Fig. 2 Fiber drawing apparatus.

54
PLASTIC COATING OF OPTICAL GLASS FIBER
A. Isomura, Y. Yamamoto, T. Yamanishi*
1. IntroductiQn
In order to obtain practical cables of optical glass fibers, the improvement
of the mechanical properties of glass fiber is one of the most important
problems; the glass fiber is so brittle and its diameter is so small that
handling performances of the fiber must be made easy through improving the
mechanical properties.l) 2) For this purpose some studies were made on
plastic coating, considering important two factors associated with the
mechanical properties of glass fiber: the adhesive property and Young's
modulus of coating plastic, and coating method. We found that glass fiber
coated with a kind of thermosetting plastic in tandem with fiber drawing
had good mechanical properties, and thermosetting plastic prevented the
surface cracks on the fiber from propagating. This paper describes the
approach of our studies, the properties of the improved optical glass waveguide
and some aging stabilities.
2. The approach of our studies
Although there are some methods for improving mechanical properties, we
selected plastic coating method taking into consideration easy set-up in
manufacturing processes, and variety in appricable plastics. On the
studies of plastic coating, we considered chemical and mechanical properties
of coating plastic, and coating methods. For chemical and mechanical
properties we considered the adhesive properties to glass fiber, and the
Young's mudulus of coating plastic. To relax stress concentration at the
cracks on the surface of glass fiber, we should select at first such a
plastic that can adhere to the fiber. When the plastic can adhere to the
fiber, there are some interfacial interaction between plastic and fiber, so
that uniform stress may be loaded to the fiber. Next we had better select
such a plastic that has high Young's modulus. Because the coating layer
must have enough strength to protect against crack propagation. So in case
of plastic having high modulus, the coating thickness may be thin, and then
we can make the optical waveguide diameter small, of course in addition to
these properties, the plastic must not cause fiber-break by heat expansion,
for instance, and have good aging stabilities such as heat aging, water
sensitivity etc.
Furthermore the second plastic coating should be needed for the improvement
of handling performances, because the primary coating is so thin that the
resultant diameter is too small to handle. We coated some plastic on the
primary coating fibers by extrusion. In the second coating we must consider
its large thermal coefficient compared with that of glass. When the
coating thickness is very large, the tensile stress by heat expansion of
plastic may cause fiber-break.
*Sumitomo Electric Ind., Ltd.

63
PRACTICAL USE OF MEDIUM LOSS OPTICAL FIBRES
Many of the present prototype and operating systems use some form of
fibre bundle and conventional LED's and detectors. However, the situation
has been changing rapidly recently and fibre bundles of approximately
300 microns diameter are coming into general use. These bundles typically
contain 19 fibres each of 65 microns diameter. Bandwidths of 20 MHz are
easily achieved over 100 metres.
Recent developments in optical connector technology and device packaging
have improved system construction and performance. In particular, device
to bundle coupling has been improved mechanically and in optical
performance by the incorporation of coupling rods or fibres onto the
active device. These coupling rods or fibres are a permanent part of the
device packaging.
The mechanical and environmental properties of fibre bundles are being
improved. The improvements are primarily being achieved through the use
of better sheathing plastics and through improved fibre to fibre
protection within the bundle.
It is likely that, in the future, even medium loss optical fibres will be
used in the form of a cable containing a number of protected individual
fibres. Such cables already exist and their performance in systems has
proved satisfactory. The individual optical fibres have been protected
with a variety of plastic materials without deterioration in the optical
performance. Tensile strengths of several kilograms have been recorded.
ACKNOWLEDGEMENTS
This paper is published with the permission of the Directors of
Pilkington Brothers Limited and Dr. D. S. Oliver, Director of Group
Research and Development.

10/ E. Weidel, "Light coupl ing prqblems in optical communication systems",
Proc. of the Techn. Progr. Electro-Optics International 174 Conf. ,
Brighton, England, 19. -21. March, 1974
/11/ J. Guttmann, H. J. Heyke, O. Krumpholz, "Dispersion rreasurements
in new' Selfoc I fibres", to be publ ished
/12/ E. Weidel, "Light coupling from a junction laser into a monomode fibre
with a glass cyl indrical lens on the fibre end II , Opt. Comm. vol. 12,
pp. 93-97, 1974
/13/ E. Weidel, "A new focussing element for GaAs laser-fibre coupl ing",
to be pubI i shed
/14/ O. Krumpholz "Optical coupl ing problems in communications systems
with glass fiber waveguides", in Dig. Tech. Papers Topical Meeting
Integrated Optics (Las Vegas, Nev.), 1972, Paper WB5
/15/ M. Borner et al., "Losbare Steckverbindung fUr Ein-Mode-Glasfaser
Lichtwellenleiter", Arch. Elek. Ubertragung, vol. 26, pp. 288-289,1972
/16/ D. Schicketanz, "Connectors for multimode fibers", Siemens Forsch.
Entwickl. Ber., vol. 2, pp. 204-205, 1973
/17/ J. Guttmann and O. Krumpholz, "Theoretische und experimentelle
Untersuchungen zur Verkopplung zweier Glasfaser-Lichtwellenleiter",
Wiss. Ber. AEG-Telefunken, vol. 46, pp. 8-15, 1973
/18/ R. Kersten and G. Zeidler, "Experimente zur Lichtausbreitung in
dielektrischen Hohlleitern", Arch. E lek. Ubertragung, vol. 26,
pp. 365-368, 1972
/19/ J. Guttmann, O. Krumpholz, E. Pfeiffer, "A simple connector for
glass fibre optical waveguides", AEU, vol.29, pp. 50-52, 1975
/20/ J. Guttmann, O. Krumpholz, E. Pfeiffer, "Multi-pole optical fibrefibre
connector", to be pubI i shed
/21/ J. Guttmann, O. Krumpholz, E. Pfeiffer "Optical fibre-stripl ine-coupler"
to be pubI i shed
/22/ O. Krumpholz, E. Pfeiffer "Coupl ing devince connecting a glass fibre
with an integrated optical circuit", Dig. Tech. Papers Topical Meeting
Integrated Optics (New Orleans), 1974, Paper WB7 '
66

STEP INDEX TYPE OPTICAL FIBER CABLE
70
Hiroshi Murata, Shozo Inao and Yoshikazu Matsuda
---
1. Introduction l )
A low-loss optical fiber has been developed and its application to cable
is now being worked out in many countries. The following are the conditions
required of the optical cable. (1) It can be handled in the same
way as the ordinary communication cable. (2) It permits field jointing.
(3) It has transmission properties fit for specific uses. The optical
cable is expected to be used, first of all, as city junction cable and
intra-office cable and then as short haul toll cable, trunk toll cable
and city distribution cable in that order .
Line Repeater Trans. Attenuation
length spacing capacity const.
City junction
cable
5 - 8 km 5 - 8 km
6 - 100
Mb/s
-
Toll cable 50 - 500km 4.5-8 km
32 - 400
Mb/s
5 - 8 dB/km
4 - 8 dB/km
The table above shows an example of the conditions under which the cable
will be used in Japan. We have succeeded in test production and installation
of an optical cable that meets the conditions required of the city
junction cable which will possibily be the first practical application
for the optical fiber cable.
2. Design of optical fiber cable 2 )3)
2.1. Coating of optical fiber
The coating of optical fiber is required from the standpoint of reinforcement,
protection and crosstalk, and coating material and its
outer diameter must be determined from the following consideration:
(1) stress given to the fiber during cable making process and installation
(tension, bend, torsion, etc.) must not exceed its breaking stress;
(2) Coating material and fiber must adhere to each other to prevent
local stress concentration in the fiber; and (3) Loss increase due to
microbend must be small. We trial-manufactured coated fibers as shown
in Fig. 1 (A)-(C) and found that the construction which best filled the
requirements of (1)-(3) was (A), material Nylon and outer diameter 0.5 ­
1.0 mm.
2.2. Stranding and sheathing
In stranding coated fibers, the cable construction must be fixed taking
the following conditions into account: (1) To reduce the mechanical
H. Murata, S. Inao and Y. Matsuda are with The Furukawa Electric Co., Ltd.
Marunouchi, Chiyodaku, Tokyo 100, Japan.

Problems relevant to lateral-stress induced microcurvature effects and
the attenuation temperature coefficient, for fibers coated with 6.10
polyamide material, are discussed in more detail.
A better understanding of those problems has led to designing a more
sophisticated hybrid-type plastic coating, that should help solve much
of them, while fabricating and laying the optical cable.
Also preliminary results on splicing techniques will be presented, with
in view splicing methods that can eventually be applicable to the
industrial cabling process. Two different techniques are described:
splicing using microburners, and microplasma arc welding.
Finally, we discuss problems concerning the assembling phase of reinforced
fibers, with respect to the mechanical requirements as well as
propagation characteristics that the optical cable will have to meet.
80
Reinforced fibres are stranded together with a long winding pitch and
no torsion, around a mechanical support member made of an aromatic
polyamide thread coated with a low Young modulus material. The strand
comprising 6, 12 or 18 fibres is protected against external mechanical
stress by ribbons made of composite materials. Several such strands
can tilen be assembled together. An overall protection is provided by
an outer water proof aluminum-polyethylene protective barrier, including
carrier members with low expansion coefficient and high tensile strength.
The expected outcome of this work should be the design of an optical
cable applicable to a 120 voice channels - PCM type transmission system
(type "TN2") that could replace existing or being presently developed
copper wire pair cables of equivalent capacity, with a reduction in
cross-sectional area by a factor of about 10. (i.e. on the basis of 8q
wire-pairs replaced by 8q fibres each carrying an 8.qq8 Mbits/s signal,
q2 in each direction).
References
1.
2.
Dr R Auffret, Dr C Boisrobert and Dr A Cozannet, "Wobulation
technique applied to optical fibre transfer function measurement"
(See this volume)
M Rousseau, "Transmission code and receiver selection for
optical'fibres FCM communications"
(See this volume)

Cable Testing and Use
85
In addition to making attenuation measurements, the cable has been
in frequent use for demonstrations and trials of analogue television
and PCM data transmission, as reported elsewhere. With a joint
inserted between the fibres at one end of the cable, the full 1480 m
transmission path has been available. The cable structure has proved
easy to use. Access to the fibres by stripping the polyethylene is
straightforward, since the reinforcement wires act as,a guard during
cutting. No specialised stripping tools have been needed.
Records of duct temperature have been kept, but temperature changes
have been only a few degrees, and no attenuation changes attributable
to temperature changes have been expected or observed.
Conclusions
Encouraging results have been obtained with the manufacture and
installation of a flat, 2-fibre cable. The particular design
needs further evaluation, for example in its resistance to damage
by water or vibration, and its behavIDour under conditions of changing
temperature.
Experimental work to develop and improve the cable, and to increase
the number of fibres, is in progress.
Acknowledgements
The fibres used in the cable were supplied by Corning Glass Works.
The authors are indebted to numerous colleagues at Prescot, Tap1ow,
and Wood Lane, and in particular to V.A. Yates t J.E. Tay1or,T.G. Murphy,
D.J. Martin and S.J. Stannard-Powell.
Thanks are due to the Directors of BICC Research and Engineering Ltd.,
BIGC Telecommunications Cables Ltd., and The P1essey Co. Ltd. for
permission to publish.
Reference
(1) R.D. Maurer, Glass Fibres for Optical Communication,
Proc. IEEE Vol. 61 t No.4 t April 1973, pp.452-462
* The cable and its method of manufacture are the subject of
a patent application.

Measurements:
88
1) The coupling efficiency of the splice has been measured uSLng a stepindex,
multimode fibre having a core diameter of 125 microns, a cladding
diameter of 165 microns and a numerical aperture of 0.64 (core index
1.62, cladding index 1.48). The diameter of the nylon fibre coating is
0.9 rom. Six splice were prepared. Three were filled with a silicone
fluid (refractive index of 1. 53) and three were left dry. The measured
efficiencies were:
Dry
With Fll,lid
Coupling Efficiency
79% to 82% •
92% to 94%
Insertion Loss
1.0 db to 0.85 db
0.35 db to 0.25 db
The silicone index-matching fluid reduces the illuminated area in the
plane of the end of the receiving fibre and, consequently, increases the
amount of light coupled into the receiving fibre. The fluid also reduces
the losses caused by surface roughness on the fibre ends and reduces the
Fresnel reflection losses.
2) A dry splice was placed under a tensile load of 0.75 kg. Over a period
of 24 hours, the change in efficiency was less than 2%, the limit
of experimental accuracy. When loaded to failure, the fibre broke 4 cm
from the end of the splicing element indicating that crimping did not
weaken the fibre.
3) Three splices containing silicone index matching fluid were exposed to
10 cycles of +60 0 C to -40 0 C with 2 hour soaking times at each temperature
limit. On each cycle there tended to be a slight increase in efficiency
at +60 0 C and a slight decrease in efficiency at -40 0 C although the
changes were within the ±2% accuracy limit of the apparatus. Thermal expansion
and contraction of the splicing elemnet predicts the opposite effect
- an efficiency decrease at elevated temperatures and an increase at
low temperatures. It is suspected the movement of the plastic coating at
the crimps or temperature sensitive changes in the optical attenuation
characteristics of the index matching fluid are affecting the efficiency.
References: .
1. Someda, C.G.: "Simple, low-loss joints between slngle-modeoptical
fibres", Bell Syst. Tech. J., 1973, 52, pp. 583-596
2. Derosier, R.M. and Stone, J.: "Low-loss splices in optical fibres",
ibid, 1973, 52, pp. 1229-1235
3. Schicketanz, D.: "Connectors for multimode fibres", Siemens Forsch. &
Entwick1ungsber, 1973, 2, pp. 204-205
4. Bisbee, D.L.: "Optical fibre joining technique", Bell Syst. Tech. J.,
1971, 50, pp. 3153-3159
5. Braun, F.A. and Trambarulo, R.F.: "Method of splicing optical fibres",
U.S. Patent 3,768;146, Oct. 30, 1973
6. Trambaru10, R.F.: "Optical fibre connector", U.S. Patent 3,734,594,
May 22, 1973
7. Gloge, D. et a1.: "Optical fibre end preparation for low-loss
splices", Bell Syst. Tech. J., 1973, 52, pp. 1579-1589

Fig. 3
98

114
POWER COUPLING FROM JUNCTION LASERS INTO SINGLE MODE OPTICAL
FIBRES
G.D. Khoe
Introduction
Single-mode optical fibres may become an attractive transmission
medium for' long-distance, high capacity communication
systems (1). Recently (2,3), stripe-geometry double-heterojunction
lasers have been coupled efficiently to these
fibres.
It must be noted that the lowest-order transverse mode,
parallel and perpendicular to the junction plane of the
laser, is required for high coupling efficiency. However,
transverse modes parallel to the junction plane,and consequently
the coupling efficiency, have in general poor
stability against variations in the injection current.
Special types of laser (4) may have stable zero-order transverse
mode operation, but the long-term reliability of these
devices has yet to be established.
This paper presents some simple methods of improving the
coupling efficiency and range of stable zero-mode operation.
An elegant method of adjusting the mode parameters of the
fibre to those of the laser is also described. Finally, a
solution to the alignment problem is given.
Transverse mode stabilization
Transverse modes parallel to the junction plane can be
approximated by Hermite-Gaussian distr'ibutions (5). The
fundamental mode has near-field and far-field patterns
showing only one intensity maximum, while higher order modes
have at least two intensity peaks. In the past, transverse­
-mode selection has been obtained by removing the mirror
reflectivity everywhere except where the field of the
desired mode was found to be high (6).
Instead of removing unwanted reflectivity, one can stimulate
the fundamental transverse mode by locally increasing the
mirror reflectivity where the intensity of this mode on the
mirror is expected to have its maximum. Parallel to the
junction, the size of the region with increased reflectivity
has to be smaller than the stripe width.
A suitable area of the required size and also with the
correct position is the core surface of a single-mode fibre
coupled properly to the laser. The core diameter, generally
3 or 4 microns, is smaller than the usual width of the
stripe, which is 10 to 15 microns. The core surface can be
provided with a partially reflective coating by means of
evaporation, etching and photolithographic techniques, using
the fibre core for automatic alignment of the area to be
G.D. Khoe is with Philips Research Laboratories, Eindhoven,
the Netherlands.

141
HI GH-PERFORMANCE, WIDEBAND FIBER OPTIC REPEATER AND ITS APPLICATION
J. J. Pan
Introduction:
Emerging fiber optic technologies promise to have a large impact on communication
systems, information processing, and CATV industries. However, the inherent fiber
attenuation and dispersion limit the link distance. For these future applications, the
signal level will have to be regenerated by repeaters installed at intervals of several
ki lometers to account for optical losses and dispersion.
This paper reports a wideband optoelectronic repeater utilizing commercially available
light-emitting diode (LED), ava lanche photodetector diode (APD), and low-cost, miniature,
50-ohm amplifier modules which provide system simplicity, cost reduction, and
the possibilities of IC fabrication and single fiber operation. Attention to impedcmce
matching and nonlinearity compensation are key subjects in optimizing system signalto-noise
ratio (SiN) and distortion.
Repeater Design Consideration.
The optoelectronic repeater, as depicted in Figure 1, may have a linear and flat
response from a few MHz up to 500 MHz by choosing an appropriate injection laser
diode. Presently, the repeater performance is limited by the frequency response of
commercial LED's to the vicinity of 120 MHz. An RCA C30817 APD is utilized as
the repeater input detector since it provides a low-noise equivalent power and is
optically broadband. Severa I cascaded 50-ohm amplifier modules serve as the postdetector
ampIifier. The impedance transition between APD and amplifier modules is
matched either by a wideband impedance transformer or an active field-effect transistor.
The latter can provide an optimized match ing across the frequency band with
moderate gain and low noise. In order to compensate the LED's slow response and the
fiber dispersion loss, a compensation network is utilized to equalize the signal level.
Since the LED has low resistance (3 t07 ohms), an inductive reactance at high radio
frequencies, and its modulation depth is determined by the matching network as well
as the signal level; either radial line or tapered microstrip, or a discrete transformer
has to be utilized to match the 50-ohm postdetector amplifier to the LED.
The nonlinearity of the cascaded amplifiers, APD, and LED in the repeater contribute
second- and third-order distortions; particularly, the LED' s nonlinear frequencydependent
distortion analysis, using the Volterra series approach, the phase relations
among the amplifiers, transformers, equalizers, APD, and LED dominate the distortion
performance. However, the simultaneous cancellation of both the second- and thirdorder
distortion products in the repeater will not occur owing to different constraints
on the phase relationship. Therefore, in order to reduce the second-order distortion
components and optimize the third-order distortions, balanced amplifiers and push-pull
LED configuration shou Id be used.
J. J. Pan is with HARRIS Electronic Systems Division

142
The SiN of the repeater is determined by the individual contribution of APD, LED,
and transistor amplifiers. The noise analysis of the transistor amplifier can be found
elsewhere. The APD noise consists of thermal noise, quantum noise, and shot noise.
The contribution from these noise sources depends upon the operation bandwidth,
resistance, and signal level. The dark current noise, leakage current noise, and background
noise are neglected in the analysis. The noise currents of the LED may be due
to a recombination process, admittance thermal noise, bulk material outside the diode
junction, and the light field and its intensity fluctuations. All of these noises except
the latter are device-oriented and cannot be reduced by circuit compensation. The
beat noise of the LED can be neglected in the multimode fiber communication link since
the beat noise is inversely proportional to the number of spatial modes of the fiber as
well as the LED's spectral width. Poor VSWR and admittance mismatching in the circuit
design at radio frequencies will degrade the noise performance considerably.
Repeater Performance.
Both SiN and intermodulation (1M) distortions were measured to evaluate the repeater
performance. The test was performed in a general laboratory environment without any
screen room shielding in order to simulate a practical field condition. The lOO-foot
Corning, low-loss, 19-fiber cables (with a measured loss of 17 dB/km at 9100 A) were
used in this experiment. The cable ends were terminated by a set of SMA connectors
and precisely machined ferru les wh ich are compatible with the SMA connectors on the
APD input and LED output. The modal dispersion loss and modulation transfer function
of the fiber have been considered for equalization computation. At a modulation depth
for the LED of nearly 50 percent, the measured th ird-order 1M products and SiN versus
frequency for the repeater were as plotted in Figure 2.
Repeater Application.
Besides the repeating relay application in communication links and CATV systems, the
fiber optic repeater also can be utilized to construct spectral transformers, fiber modal
transformers, active couplers, an optoelectronic oscillator, combiner, and divider as
well as to reduce noise, nonlinearity, and temperature instabilities of the optical system.
Especially, the active coupler has many superior advantages over the conventional
T- or star-coupler. When a tunable LED is employed in the design, programmable
couplers, dividers, or spectral transformers can be realized. A three-way active
divider and a spectral transformer are illustrated in Figure 3 and Figure 4, respectively.
Conclusion.
The low-cost, compact, optical repeater shown in Figure 3 and Figure 4 is a breadboard
used to demonstrate its high performance as well as its applications. Employing
chip forms for the APD, LED, and amplifiers, IC modules can be constructed which
would reduce the repeater size considerably and also provide an application to single
fiber operation. When the clamping, peak detection, timing coincidence, and
regenerator circuits are included in the design, the repeater may be applied to highspeed
digital applications.
Acknowledgement.
The author would like to express his gratitude to A. Mazzara, L. Lavendol, and
L. R. Allain for their encouragement and support, and M. P. Arnold for his assistance
in the measurements.

144
A 32 MB/S REGENERATIVE REPEATER FOR FIBRE CABLE TRANSMISSION
J. Yamagata, S. Senmoto, Y. Inamura, H. Kaneko and T. Takahashi
INTRODUCTION
This paper presents an outline and some performance evaluations of a 32
Mb/s regenerative repeater for fibre cable transmission use.
The intermediate repeater was developed as a part of a 4 MHz video
transmission system.
OUTLINE OF THE REPEATER
The b10ckdiagram and the parameters of the 32 Mb/s regenerative repeater
are shown and listed in Figure 1 and Table 1, respectively.
The repeater uses a Si avalanche photodiode (APD) as the photo-detector and
a GaA1As laser diode as the optical source.
APD bias voltage is supplied by an internal DC-DC converter which converts
external low d.c. voltage to stable high d.c. voltage.
The preamplifier uses bipolar transistors and has the input impedance of
600 ohms for frequencies less than 30 MHz.
The main amplifier has the reshaping function in addition to amplification.
The peak level of the pulse at the decision point is kept constant by
an AGC whose control range is greater than 40 dB.
A monolithic crystal filter is used as the timing extractor (TIM EXT) ,
because of its high Q and small dimension.
The d.c. restoration circuit (DC RES) is employed in order to compensate
d.c. wander which is caused by a.c. coupling at the amplifiers.
The regenerated pulse enters into the driver(DRIV) which directry modulates
the laser diode. Output light beams from the laser diode are emitted
in two directions, forward and backward. The forward beam is the optical
output carrier. The backward one is monitored by a p-i-n photodiode and
fed back to the driver through a peak detector (PD). By this loop, called
automatic power control loop, the laser diode output power is stabilized.
Figure 2 is a photograph of the repeater. The dimensions of the repeater
are 90 x 50 x 197 rom. The total power consumption is about 3.6 watts.
EXPERIMENTAL RESULTS
Figures 3 and 4 show the error rate and the sinusoidal crosstalk margin
characteristics as a function of the average optical receiving power
for pseudo-random code, respectively.
In the measurement, a graded index fibre with 22 dB/km loss was used.
Each piese of the fibre cable was 200 m in length, and jointed together (
1400 m maximum) by fibre connectors when necessary.
Figure 3 indicates that the pulse dispersion is almost negligible
within such fibre length as 1400 ro, and that the average optical receiving
power necessary for a 10- 9 error rate is approximately -53 dBm.
J. Yamagata, S. Senmoto and Y. Inamura are with Nippon Telegraph and
Telephone Public Corporation.
H. Kaneko and T. Takahashi are with Nippon Electric Company, Ltd.

might have to be spread over 20 years, during which period further
developments in detail are likely. The essential attraction of
fibres over metal conductors for cable TV would be the elimination
of intermediate electronics and the saving of cable size and cost,
while providing a network as flexible in principle as the local
telephone network. Before any decision can be taken to begin investment
in such a new network, it will be necessary to establish, by
means of field trials, that the technical problems of manufacture,
installation, operation and repair can be satisfactorily and
economically solved. Perhaps the main challenges here remain in the
manufacture of fibre cables having low and stable enough loss and
dispersion characteristics, in their pulling into ducts and/or laying
in the ground in lengths of about 2 km without significant change of
characteristics, and in jointing and terminating the fibres in
sufficiently rugged and stable yet compact and cheap \'1ays. In addition
LED's or lasers of adequate performance and demonstrated reliability
must be manufactured.
152
The last series of challenges must also be met, though probably with
different specification limits, for "junction" and "trunk" systems,
lasers rather than LED's being essential for the latter. The market
for each of these is much smaller than that for cable TV, because
(a) the essential function of the exchanges (of which there are about
6000 in the UK) is to concentrate the traffic into much fewer circuits,
and (b) the junction and trunk networks are already well developed
and new provision is needed only to cater for new growth of traffic.
The median length of junction system in the UK is about 4 times that
for prospective cable TV systems, but the market for fibres for the
former might be only about 1%of that for the latter. The median
length for trunk systems is about 100 km in the UK, but because of
the further concentration of circuits (by time-division-multiplexing)
on the trunk systems the market for fibres there is likely to be
similar to that for the junction network.
HEFERENCES
1 • Telecommunication Statistics 1974, UK Post Office Telecommunications
Headquarters TMS5.2, London.
2. Telecommunication Statistics 1973, Union Internationale des
Telecmmnunications, Geneva.
3. Local Distribution - A Time for Change? A G Hare , paper read
to Institution of Post Office Electrical Engineers, London,
March 1975.

PRACTICAL DESIGN REQUIREMENTS FOR OPTICAL FIBRE TRANSllISSION SYSTEMS
R \v Berry and R C Hooper
INTRODUCTION
153
Advances in the various technologies contributing to designs of optical
fibre transmission systems have been very rapid, and show every sign of
continuing apace. In these circumstances, there are some difficulties in
producing realistic estimates of eventual system costs, particularly when
items such as testing and maintenance are to be included. The construction
of laboratory demonstration systems helps to some extent, in that
such systems indicate probable trends in development; but it is only by
working towards the design and installation of practicable field trial
systems that the remaining intangibles can be revealed and working
solutions found.
8.448 Mbit/s SYSTEM DESIGN
An initial 8.1+1+8 Mbit/s laboratory system 1 was constructed in June 1974,
using high-radiance light emitting diodes (l.e.d.), silicon avalanche
photo-diodes 2 (a.p.d.) and same high loss unprotected fibre with a
numerical aperture (n.a.) of 0.5. The system was originally designed
to meet a repeater section error-rate of 1 .6 in 10 10 (equivalent to 2
in 107 for a system of 2500 km length, with a nominal repeater spacing
of 2 km), and this requirement was met with an optical path loss of
37 dB per section.
The demonstration highlighted features which required significant
improvement for practical system use:- (a) compatible voltage supplies
and simple power feed arrangements, (b) an overall reduction in repeater
power consumption, (c) improved fibre-to-device couplings, (d) improved
fibre-to-fibre joints, (e) improved repeater input stage design, (f) a
compact repeater module design, (g) improved stability of the a.p.d. gain
against ambient temperature changes and (h) fibre of specified loss and
dispersion, with good dimensional tolerances, and \nth adequate protection
against mechanical damage.
Compatibility of voltage supplies has required the introduction of a
reliable dc-to-dc converter to provide bias for the a.p.d.; the version
in present use is coupled with a temperature compensation circuit, which
also provides voltage regulation, for the a.p.d. The complete unit takes
1.7 mA from a 6v supply, and can provide up to 90V bias for the a.p.d.
Firm proposals for power-feed arrangements must await the outcome of
further work, but we expect tO,achieve a 12V repeater, \dth a current
consumption (excluding supervisory circuits) of less than 100 mAo
A demountable fibre-to-device coupler using lenses has been developed.
The coupler has been shown to be adequately stable against mechanical
The authors are with the Post Office Research Department,
Dollis Hill, London.

CONCLUSIONS
The practical design and installation requirements of a low bit-rate
optical %ibre transmission system have been taken to a point where the
feasibility of installing a practicable field trial system in the near
future can be clearly seen. The introduction of these systems is
dependent finally on there being an economic advantage over other
equivalent systems.
155
For the 139.264 Mbit/s and higher bit-rate digital systems, further
development is needed before trial systems are installed. Work directed
at this stage towards the practical production of necessary items in a
form suitable for early use in the transmission network will be invaluable
for the rapid assessment of the viability of optical fibre
systems, and for their inclusion in future network plans.
ACKNOWLEDGEMENTS
The authors wish to thank the Director of Research of the Post Office
for permission to publish this paper, and to express their appreciation
of the advice, co-operation and assistance given by their colleagues
in the Post Office and industry in the design and construction of the
systems discussed.
REFERENCES
1 Goodfellow R - "High radiance small area GaAs lamps"
Specialist Conference on the Technology
of Electroluminescent Diodes, Atlanta,
Georgia, Nov 20-21, 1974
2 Lucas A D - "Epitaxial silicon avalanche photodiode"
Opto-electronics 6 (1974) 153-160
3 Personnick S D - "Receiver Design for Digital Fibre Optic
Communication systems I"BSTJ Vol 52 No 6
July-August 1973.
4 Maurer R D - "Glass fibres for optical communication"
Froc IEEE Vol 61 No 4 April 1973 p. 452-462
5 Goell J E - "Input Amplifiers for Optical PCM Receivers"
BSTJ Vol 53 No 9 November 1974
6 Goodwin A R, - "Temperature-stable continuously operating
Peters J R, Pion M Ga Al,i ,As injection lasers". See this volume
x -x

160
Fig. 3 indicates that .ptical average power necessary for the transmission
of a 400 Mb/s signal through a 4 km fiber cable at a 10- 9 err.r rate is
approximately -34 dBm at the receiver input when the laser spectrum-width
is 20 A. Fig. 4 shows the eye diagram of the input to the decision
circuit in the optical receiver.
Fig. 5 shows the calculated repeater spacing vs. fiber loss for tw. laser
spectrum-width. In this calculation lines (3), (4) in Fig. 2 were used.
The measured points agree with the calculation. From these calculated
curves the repeater spacing can be estimated for fiber cable with
different transmission less.
CONCLUSION
A 400 Mb/s fiber transmission system with a repeater spacing of 4 km was
tested using a graded index fiber. The experimental result shows that the
material dispersion is not a limiting factor when the repeater spacing is
less than 4 km and the spectrum-width of the optical s.urce is less than
o
20 A.
ACKNOWLEDGMENT
The authors wish to thank
members of Electrical
Communication Laboratories
and of Engineering Bureau
in NTT for their useful
suggestions.
REFERENCES
Table 1. Parameters of Components
Type: D. H. -C. W. Laser
GaAs Output Pewer: +1 dBm(Peak)
Laser (Into the Fiber Cable)
Spectrum: 20 A(Half-Width)
Silicon Quantum Efficiency: 37 %
APD Excess Noise Factor: 2.4
Break Down Voltage: 124 V
Loss · 6---8 dB/km
Index Profile · Graded
Fiber N. A. · : 0.13
Cable Diameter
Core · 80 .)A

164
At present, despite the technological progress made, the choice is
still inhibited by the availability of the elements and uncertainty
about the ultimate status in production. For example, if CW lasers and
single mode cables with efficient connectors were as readily available
as fibre bundles and LED'snthe current emphasis on applications might
be quite different. It is the rapid change in this situation which
makes the field worth following closely.
The talk will draw on examples of some current activity in fibre optic
communication technology and field demonstration programme to illustrate
and substantiate the argument that both the "next generation" condition
and some of the "not yet invented" condition will be met within five
years from now.

166
A number of experimental optical highway configurations of the type shown
in Fig. 1 have been tried at University College using about 12 ft. of
optical fibre and incorporating 2 or 3 different data inputs. These have
been used for transmission of both speech and TV signals. Fig.2 shows a
typical frequency response of a 3 channel system with clip-on transducers
operating at frequencies of 0.7 MHz, 2.3 MHz and 5.6 MHz. For ease of
handling, it is convenient to employ optical fibre which is covered with
a thick plastic protective coating, the clip-on modulating transducers
are able to operate directly through this plastic coating with a small
increase of drive power.
The fact that such modulators can vary the phase of optical signals is an
indication that optical fibres are microphonic. The effects of such
microphonic noise can be avoided by ensuring that the modulation frequencies
are always above the maximum frequencies of the background
environmental vibrations (say above 50 KHz).
The reference channel is used to provide a convenient local oscillator
signal, it is not a phase reference. The optical source needs to be of
adequate coherence and the technique would not be suitable for the noiselike
signals of' a light emitting diode. It is also necessary for the
relative lengths of the signal and reference fibres to be approximately
the same, or to differ by an amount related to the laser cavity dimensions.
This is not a severe practical restriction. The experimental
system employed a 5 mW gas laser but work will shortly commence on the
development of a system based upon a solid-state laser.
The data highway technique has been demonstrated with both single modeand
multi-mode fibres. However the performance of the system falls off
as the number of modes in the fibre increases, this is due to the increased
conversion loss of the optical mixing process when the photodetector
is illuminated with a complex multi-mode light pattern. An
interesting variation on the above technique is currently under study.
This involves using the characteristic of a multi-mode fibre to operate as
an optical discriminator and considerably simplifies the system by
eliminating the need for a reference fibre. However the output signal is
subject to fluctuations in amplitude due to movement and bending of the
fibre, since this changes the form of the discriminator characteristic.
Apart from the above work on this single fibre (multi-mode) system,
current studies on this project are aimed at incorporating solid-state
optical sources and improving the design of the transducer modulators to
achieve increased modulating frequencies and bandwidths.' A prototype
demonstration system is under construction.
The authors wish to acknowledge the help of their colleagues at University
College London, together with staff at 8TL, GEC and the Post Office. The
work was supported by an 8RC Research Grant.
REFERENCES
1. Davies, D.E.N. and Kingsley, 8.A.:Method of phase-modulating signals
in optical fibres: application to optical telemetry systems. Elect.
Lett., 1974, 10, pp. 21-22.

SUB-CARRIER
OSCILLATOR 'Ii
f l
f,
f,
167
DATA
SOURCE
SIGNAL FIBRE
REFERENCE FIBRE
DEMULTIPLEX 1--+--1
FILTERS
MODULATOR
ACOUSTIC
pRANSDUCER
BEAM
COMBINER
FIG: 1 SCHEMATIC DIAGRAM OF A TWO-FIBRE OPTICAL INFORMATION HIGHWAY
Fig. 2(a)
Baseband spectrum of output from
optical highway showing 3 signals
at frequencies of 0.7 MHz, 2.3 MHz
and 5.6 MHz.
(amplitude scale 10 db/division)
Fig. 2(b)
Baseband spectrum of output from
optical highway showing response
of one of the channels (bandwidth
100 KHz/division)
(amplitude scale 10 db/division)

Conclusion:
170
To summarize, FO offers very attractive solutions to problems in many areas
of -military information transfer. A good start has been made toward translating
this important new communications technology into military applications.

171
RANDOM CODING FOR DIGITAL OPTICAL SYSTEMS
C. Game & A. Jessop
Introduction
The choice of a transmission code is a compromise between producing a
signal which is easily regenerable against one which maximizes repeater
spacing. The code should also provide an independent means of measuring
the binary bit error rate. Over the years wire line systems have evolved
that employ line codes which produce a signal having adequate timing
information for wide-band (low Q) timing extraction circuits and which
can be transmitted by a system with low-frequency limitations. Optical
fibre systems, while retaining the same need for simple and cheap timing
extraction circuits, do not have the same low-frequency limitations.
Wire line systems avoid low frequencies to obviate the need to equalize
cable down to low frequencies, to facilitate the protection of equipment
from surges and to facilitate power feeding and supervision over the
same cable as the signal. These restrictions do not apply to optical
fibre systems, the low frequency limitation being one of a.c. coupling
within the repeater. The implications of this difference and those listed
below should be investigated before choosing a line code for optical systems
Factors Affecting Choice of Code for Optical Systems
Choosing a code involves consideration of the following:
(a) means of limiting the laser mean pulse density
(b) spectrum manipulation (e.g. elimination of d.c. content)
(c) repeater timing information
(d) in-traffic error monitoring at terminals
(e) location of faulty repeaters
(f) data transparency
(g) code re-frame time if applicable
(h) efficient use of information capacity
(i) general simplicity of repeater
(j) non-linearity of source and detector
(k) dispersion in the fibre (pulse broadening)
This paper shows that all the requirements above can be met by the use
of scrambled binary as line code except for point (d) which can be met
by a little added redundancy. Whether or not point (e) needs to be met
depends on whether in-traffic location of a failing repeater is a
requirement. For an optical fibre system with negligible pulse broadening
the maximum repeater spacing is obtained with a binary system whether the
source is peak or mean power limited. This is because the increase in
signal-to-noise ratio due to reduced bandwidth by increasing the code
radix is more than offset by transmitting less power per level. If pulse
broadening is significant t.hen a higher radix code could maximise repeater
spacings. However. progressive improvements in optical fibre attenuation
have usually been accompanied by reduction in dispersion; with currently
available multimode fibres transmission is mainly attenuation limited for
speeds up to 140 Mbit/s.
C. Game & A. Jessop are with STL Ltd., Harlow, Essex, UK.

180
In the short to medium distances, ie up to several hundred metres
applications at the present time a choice has to be made between single
fibre and bundle systems. A single fibre cable would contain several
single fibre go and return paths and some spare fibres, indeed spatial
multiplexing could be used. The essential is one fibre per communication
channel. Some of the factors affecting the choice are:-
the choice of source, laser or LED; the ease of making connectors and
joints; the possibility of data highway components; the ease of
making a robust cable; there is some bandwidth reduction in bundles
due to optical path length variations in fibres; although the bundle
provides redundancy a component of attenuation is due to breakages.
The use of lasers implies pulse analogue modulation.
In order to launch SUfficient power lasers are usually used for single
fibres but Burrus type high radiance LEDs can launch 1 mW of optical
power into multimode fibres and this is adequate for many applications.
Baseband modulation can then be used. Up to now single fibres with lasers
have suffered from limited life but this problem is being solved.
Moderately good joints with 3 or 4 dB loss can readily be made in fibre
bundles with the fluctuation due to fibre position being removed by giant
fibre mixing sections, these can be conveniently mounted in the bulkhead
portion of the connector. Etched and fused low loss joints can also be
made with more difficulty. The alignment tolerance is related to the
bundle diameter and can be obtained satisfactorily with a conventional
connector. With a single fibre the mechanical problem can be solved for
splices but demountable connectors are more difficult since the tolerance
is related to the fibre core diameter and is perhaps 5 or 10 microns. The
cable problem is one of great difficulty. With bundles a bare or perhaps
Imbricated bundle of fibres is encased in a tube which provides tensile
strength and crushing resistance. There is however little scope for
mechanical insulation of fibres. In the single fibre cable each fibre can
be individually protected or cushioned and further strength members
added but the redundancy in the fibre bundle is lost.
Airborne military applications of optical fibres centre around several
systems. There are general data, weapon control and selection and
communication systems. The EM! and good EMC features together with the
lightweight small volume and freedom or earthing problems are significant.
The increasing use of hybrid materials in aircraft construction renders
the interference problem more difficult. There may be point to point links
or databusses, for the latter the star system described by F Thiel can be
discussed but the vulnerability to damage and flexibility of the solution
must be examined, the latter partiCUlarly since aircraft may be used in
more than one role. Short link lengths are envisaged up to 30 metres
with perhaps 6 breaks and the data rates of up to 20 megabits or greater.
Since tolerable system losses are in the range 40 to 70 dB medium loss
fibre (100 dB/Km) is adequate but connector losses are important.
Techniques for installation and repair are needed and the fibre system
including cable must satisfy full military specification. This is an
area where the bundle versus single fibre choice must be made.
In Naval applications there are a similar set of applications with a
greater volume of data. EMI, small volume and freedom in routing cables
is important. Ranges can now be up to 150 metres but moderately low loss
fibre will still be satisfactory. Bandwidths of 60 MHz for analogue
signals may be required in transmitting radar data but microprocessors
will find greater use and there will be a need to interconnect perhaps

181
30 of these. EMI low bulk and the freedom from earth loops together with
greater flexibility in routing is important.
For the Army there are vehicle or restricted area applications
corresponding to the Naval and Air data and communication systems but
there are also applications with long link lengths, 5 Km or greater.
These applications are in trunk communication networks and include
communication in the trunk node itself and from a trunk switch to a radio
village. The emphasis now is upon the lightweight robust cable
incorporating a low loss fibre. Field repair techniques must be developed
since cable breakage is inevitable.
Although significant progress has been made in bringing military fibre
optical communication into an acceptable state of the art technique
further work is required, in particular on cables, connectors, the
standardisation of terminal components together with the optical
components needed for highway or star data systems. In the next generation
planar optical devices can be expected to contribute to the extension of
the range of application of optical fibres.

185
TELEVISION TRANSMISSION EQUIPMENT AND SYSTEMS
P H Fell and A H Kent
Introduction:
The system described here has been envisaged as a general purpose
transmission link suitable for use both in a CCTV/CATV application and also
as part of an integrated multiservice system for use in an expanded local
network. These integrated systems provide a.means whereby all the services
cormnonly specified for the popularly termed "wired city" may be offered.
The use of fibre-optics for these systems has been outlined elsewhere 1 .
The transmission system to be discussed here is the final connection in
one of the schemes described.
Description of TV/Broadband Transmissioh Link
The main design objective in this particular link is simplicity and cheapness
since each individual subscriber will have a receive terminal. The
quality of transmission necessary is that for a CCTV system 2 rather than
the more stringent Broadcast Link specification. With this in mind, the
ways in which a link of 5-10MHz bandwidth could be implemented were
considered. The use of digital transmission was dismissed since it would
require a complex and costly converter at the subscriber's terminal, and
its main advantage, easy regeneration of the signal, would be of little
benefit. The great majority of links will be short; 70% of all
subscribers are within 2.5Krn actual route distance of their local exchange.
The linearity of the specially developed high-radiance small area LEDs 3
was found to be sufficiently good to allow transmission by direct analogue
modulation of the LED light output intensity by a baseband video signal,
and so this was the form of modulation chosen (Fig. I). One video and two
sound channels are transmitted in this particular scheme. The TV sound
channel is transmitted as F.M. on a 6MHz carrier in line with the broadcasting
standard, and the second sound channel is also F.M. at 10.7MHz.
Since these are cormnonly encountered carrier frequencies, ceramic filters
and I.C. demodulators are readily available.
The received signal after detection drives a baseband picture monitor,
and the two sound channels are filtered, demodulated and fed to audio
amplifiers and speakers (Fig.2).
Transmitter
The specially developed high-radiance LED is in the output stage of a
simple feedback amplifier, whereby the standing diode bias current of
about 100mA is modulated linearly to a depth of 50% by the video input
signal. The LED is provided with a short tail of fibre bonded to it for
connection to the main cable fibre.
Detector
The choice of detector photodiode lies between a PIN diode and an
avalanche diode. While some increase in sensitivity is obtained by virtue
of the internal gain of the avalanche diode, it is not considered
sufficient in this relatively low bandwidth high signal/noise system to
justify the extra cost involved.
P H Fell and A H Kent are at Plessey Telecommunications Research Ltd.

189
Figure 3 shows that the optical average power necessary for a 10-9 error
rate is approximately -50 dBm at the input of the repeater. Figure 4
shows the eye diagram at the decision point in the intermediate repeater.
CONCLUSION
A digital video transmission system with an intermediate repeater using
fibre cable was developed. An experimental result suggests that optical
fibre transmission systems with regenerative repeaters will be useful in
short or middle haul transmission links.
ACKNOWLEDGMENT
The authors wish to thank their colleagues in Electrical Communication
Laboratories in NTT for their 6uggestions.
REFERENCES
(1) T. Sakashita et al.,
"Application of Fiber Cable
Transmission Systems to
Telecommunication Networks,"
Topical Meeting on Optical
Fiber Transmission Conf.,
7-9 Jan. 1975, Williamsburg,
Virginia.
(2) K. Oosawa et al., " A
Consideration of Optical
Fiber Transmission System,"
Paper of the Technical Group
on Communication System,
IEeE, Japan, CS74-67, 1974.
(3) P. K. Runge.," A 50 Mb/s
Repeater for a Fiber Optic
PCM Experiment, " ICC '74
Conf., 17-19 June 1974,
Minneapolis, Minnesota.
(4) " Optical Waveguide
Transmission Systems," CCITT
Del. Contr., GM/SGO-B and
GM/SGO-C, Kyoto Meeting, 1975.
TABLE 1 SYSTEM PARAMETERS
Clock Rate 32.064 Mb/s
Over All Error
Rate
10-9
Transmission RZ Unipolar
Code
Video Coding 4 bit/word DPCM
Pre-amp. Transfer Impedance Amp.
Front End using Bipolar
Transistor
Opt.ical Source Output Power(Peak):-13dBm
(GaAs-LED) (Into the Fibre Cable)
Optical Detector Quantum Efficienoy: 0.59
(Si-APD) Excess Noise Factor: 2.5
Break Down Voltage: 85V
Fibre Cable Loss · 8dB,/km
Index Profile · Step
N. A.
•
· 0.14
Diameter ·
Core
Clad
: 85fAm
· 125fm
Fibre Connector Connecting Loss: 0.9dB
·
·

191
SPECTRAL LOSS PERFORMANCES OF OPTICAL FIBER CABLES USING PLASTIC SPACER AND
METAL TUBE
T.,Mizukami, T. Hatta, S. Fukuda, K. Mikoshiba and Y. Shimohori
This paper describes new method of optical fiber cable engineering $uch as
cable designing and manufacturing. Especially, small external forces can
cause lateral deformations, mode coupling, and optical loss in optical fiber,
and therefore, plastic jackets and cable structures must be carefully designed
to provide effective protection. In order to provide such effective
protection as cables for optical fibers with plastic jackets, new cable
structures such as spacer type cable and unit cable using metal tube are
proposed in this paper.
1. Performances of Optical Fibers
The cladding type fibers with lower index intermediate layer, so called Wtype
fiber, is discussed. A paper about fundamental performances of W-type
fiber will be published in IEEE Transactions on MTT. The performances of
W-type fiber with plastic jackets, therefore, are investigated here.
Plastic jacketing for optical fibers is most important process which enforces
individual optical fiber and eliminates external forces. The thickness and
material of jackets should be chosen in consideration of the above two points.
A typical index profile of W-type fiber and typical spectral loss of W-type
multimode fiber with about 100pm thickness of jackets are shown in Fig. 1.
2. Performances of Optical Fiber Cables
Surprisingly small external forces can cause lateral deformations, mode
coupling, and optical loss in optical fibers. The pressure exerted on the
individual fiber in a cable will almost certainly be considerably stronger
and less uniform. In order to eliminate external forces on the fibers
during manufacture of optical fiber cable, there may be two methods: the
first is given by effective jackets designed to optimally. shield against
external forces, the second given by effective cable structures designed to
optimally shield against external forces, too.
This chapter addresses the latter problem.
Fig. 2 shows two typicaLexamples of the cross-sectional view of proposed
optical fiber cable. One of these is suitable for cable with several fibers,
and have sufficient mechanical characteristics. Another gives one of
possibility which realizes the cable with good space factor, that is, the
cable with a lot of fibers in the same cross section. Small size metal tube
with several fibers makes optical fiber cable unit, and these cable units
and fillers are stranded together. Optical fiber cable with a lot of fibers,
therefore, may be able to be manufactured by conventional stranding method.
Typical examples of spectral loss of two kinds of manufactured optical fiber
cables as shown in Fig.2 are illustrated in Fig. 3. In carefully designed
optical fiber cables, there are small differences between optical loss of
fiber before and after cabling.
The authors are with Hitachi Cable Ltd, Japan

J
192
I
r°-;.
nl
I no
i
U n2
I II
INDEX PROFILE OF VI TYPE FIBER
50 ,--------------------,
_.---------- -
.6 .7 .8 .9 1.0 ,. 1
IJAVELENGTH ( lim)
Fig. 1 SPECTRAL LOSS OF W-TYPE l'1ULTlfv/ODE
FIBER WITH PLASTIC JACKET

193
Co J. SPACER TYPE CABLE
Steel tension menber
Plastic spacer
Plastic sheath
Paper and plastic tafY2
Optical tiber with jacket
Steel tension menber
Plastic Sheath
Corrugated metall.? pipe
Pope( and plastic tape
Plastic tiller
Cable unit (4 II type fibers)
He tal tube
(bJ. CABLE BASED ON CABLt- UNIT ( UNIT TYPE)
F;g.2 CROSS SECTIONAL VIEw OF MANUFACTURED
OPT/CAL FIBER CABLE
50 ,...-----------------,
.6
Unit type cable
.7 .8 .9
WAVELENG TH Cf.-lm J
Spacer type cable
Fig.3 SPECTRAL LOSS OF MANUFACTURED OPTICAL
FIBER CABLES
1.0 /.1

194
CONNECTIONS FOR OPrICAL CABLES: DESIGN AND MEASUREMENTS
G Le Noane and R Bouillie
Various connedions problems are to be solved for optical fibre systems purposes.
On the complete system diagram, we can number three connexions types
:
a) - Connection between opto-electronical components and the fibre ends
or an "extremity" cable. It must be collapsible;
b) - Conne±ion between this extremity cable and the optical cable. It
must also be collapsible ;
c) - Connedion between optical cables themselves. They can be fixed or
collapsible.
a) and b) cases suppose to resolve a certain amount of problems such as losses,
reliability, etc •.• but as these conne±ions are a small number, these
problems are not very important, and mean performances can be sufficient. But
in the c) case, the connation number may be great, and the loss problem becomes
the most important.
If we assume cable lenghts to be about .5 km, we can obtain between 10 and
20 connectors between repeaters. System considerations limit to 10 dB total
conne±ion losses, so each cable to cable connexion must be less than 0.5 dB.
From this first assumption, we have made different connector types.
Extremity connectors
We present two of them, for light emitting diodes and photo detectors. Some
experiments have led us to the conclusion that dry connectors are the best
matched to As Ga component life time.
Their principle is displayed on the fig. 2. Losses of 17 dBm have been performed
repetitivily between L.E.D. and CORNING Silica fibres.
We have looked after the best matching lens to connect strip laser diodes to
large core Corning fibres. SELFOC lenses or plastic lenses are used, and the
loss can fall down to less than 1. dB.
Cable connections
A first study allows to realize the junction by fusing the fibre glass into
various small furnaces, Temperature, geometrical arrangement, fusing conditions
are tested.
A second one deals with a collapsible connector, using the automatic x - y
positioning obtained by an elastomer compression to ensure the 2 positioning
we prepare the end surface by using various saws or by polishing.
G. LE NOANE - R. BOUILLIE with the "Centre National d'Etudes des Telecommunications".

202
One Optical Cable Performance Measure.
The cable quality performance factor as which is proposed is
related to microbending loss. The mean and spread of the
as values within a cable can be related to 6 requirements
and repeater spacing. Since as is readily calculated from
loss measurements alone, this provides a convenient method
of evaluating cable designs.
Methods of packaging fibers in cables [5,6] which give
promise of making it possible to control the as values in
a cable are considered.
REFERENCES
[1] Schwartz, M. I.: "Optical Cabling and Splicing", Digest
of Topical Meeting on Optical Fiber Transmission,
Jan. 7-9, 1975, Williamsburg, Virginia, pp. WA2-1 ­
WA2-4.
[2] Gardner, W. B. and Gloge, D.: "Microbending Loss in
Coated and Uncoated Optical Fibers", Digest of Topical
Meeting on Optical Fiber Transmission, Jan. 7-9, 1975,
Williamsburg, Virginia, pp. WA3-1 - WA3-4.
[3] Gloge, D. and Marcatili, E. A. J.: "Multimode Theory
of Graded Core Fibers", BSTJ, Vol. 52, No.9,
November 1973.
[4] Olshansky, R. and Keck, D. B.: "Material Effects on
Minimizing Pulse Broadening", Digest of Topical Meeting
on Optical Fiber Transmission, Jan. 7-9, 1975,
Williamsburg, Virginia, pp. TUC5-1 - TUC5-4.
[5] Gloge, D.: "Optical-Fiber Packaging and Its Influence
on Fiber Straightness and Loss", BSTJ, Vol. 54, No.2,
February 1975.
[6] Miller, R. A.: "Fiber Cabling", Digest of Topical
Meeting on Optical Fiber Transmission, Jan. 7-9, 1975,
Williamsburg, Virginia, pp. WAl-l - WAl-4.

207
APPLICATION TO TWO DIFFERENT SYSTEMS: 2.01.1:8 and 8.1.1:1.1:8 Mb/S
Slide projections on equipments and results will be presented summarizing
the state of art at CNET:
- Fiber bandwidth results
- Miller code compared to pure binary code
- Connectors
- Repeater unit
The repeater power consumption will also be discussed.
As a conclusion a table shows the results obtained on a prototype
transmission designed at CNET and gives the maximum realistic spacings
between repeaters us different choices:
- choice of source
- choice of detector
- choice of cable and connector attenuation.

209
DATA TRANSMISSION IN NAVAL SHIPS BY FIBRE OPTICS
M. Baldwin
Modern warships contain sophisticated weapon systems and sensors which are
interconnected. There are many miles of interconnecting cables to transfer
this information both in digital and analogue form. This information must
not be corrupted, but because of the sheer bulk of cables, they cannot
always be routed and separated to obtain maximum immunity from electromagnetic
interference. The weight of cables is also a problem.
Fibre optics and integrated optics are considered to offer many advantages
and to be the best of the new technologies.
The paper will outline the problems encountered in Naval ships in data
transfer by fibre optics, and discuss results of a trial of a high accuracy
link between a shore based Radar and Gun.
M Baldwin is with Admiralty Surface Weapons Establishment