An expanded-beam connector for singlemode fibres has been developed that exhibits coupling losses of 1 dB or less and offers significant advantages over currently available butt ferrule connectors. The connector incorporates a novel lens system that will compensate for relatively large lateral alignment errors of the fibre, thus permitting utilisation of piece-parts with relaxed radial tolerances. The connector can be assembled directly onto laser pigtails or rack splitters without the need for splices.

Splicing of optical fibres is a key aspect of the manufacture and installation of both landline and submerged optical fibre systems. In many landline applications the splices are housed in large cable joints and are not subjected to any strain in service. A number of techniques have been described in the literature (refs. 1-3) that are suitable for these relatively benign environments. They generally employ solvents and/or mechanical methods to remove the fibre primary and secondary coatings before cleaving and aligning the fibre ends in a splicing machine. Some of these techniques are also suitable for use in submarine cable systems where a cable joint housing is used between lengths of optical cable (ref.4). However, for efficient cable manufacture and lay it is desirable that the cable should be produced in repeater section lengths. Since fibre is not yet produced in such lengths it is necessary to splice sections together and to reinstate the primary and secondary coatings over the splice with the same diameter as the parent fibre coating. As these splices will be incorporated directly into a cable they will be subjected to the same manufacturing and service strains as the fibre and must therefore have high strength. Submarine systems must also be extremely reliable, which demands high reliability from the splices over the 25-year design life of the system. This paper describes the process developed to produce high strength splices reliably and the results of dynamic and static fatigue testing are given. The process is now in production at STC-Submarine Systems Ltd.

The fusion welding of single-mode fibre in the field requires readily portable equipment, and preferably single-man operation, implying that joint monitoring equipment should be contained in the welding machine. The essential preliminary to low-loss splicing is fibre cleaving to within 0.5 degrees of squareness. A hand-held cleaver that achieves this was designed. A fusion-welding machine which includes monitoring of core transmission by local light injection and detection was developed. The machine is microprocessor-controlled, so that fibre alignment and the welding process are automatic. The mean splice loss is 0.054dB. Field experience is also reported.

The first generation of components for use in single-mode optical fibre transmission systems are now becoming commercially available. To achieve the full potential of single-mode technology, however, new automated packaging techniques are required that will result in a significant reduction in packaging costs, and that will also allow the production of new advanced hybrid components. This paper briefly reviews new techniques for packaging single-mode optical components that are under development at the British Telecom Research Laboratories.

We report on a family of high performance, hand-held cleaving tools developed by Thomas & Betts for use by field installation personnel. The cleaving tools are characterized by simplicity of use (cleaving requires only two actions, each operator insensitive) and consistency of cleave quality (100% of cleaves are below 3 degree angle, 80% below 1 degree. Minimum tool life 3000 cleaves).

The use of fused single-mode directional couplers as highly efficient and stable beam splitters is well known1. The degree of coupling achieved in such a device depends critically upon the guidance conditions prevailing in the constituent fibres, and thereby upon the wavelength of operation. For example, Figure 1 shows the wavelength dependence of the power emerging from the two output ports of a device which is nominally a 3 dB coupler at 1300 nm. The variation in coupling ratio with wavelength can be exploited to form the basis of a range of low loss wavelength multiplexing devices.

Simple, low-cost and industrial couplers were developped for use in videocommunication networks. In the beginning, it was the C.N.E.T. (Centre National d'Etudes des Telecommunications) which defined a new technique for the manufacturing of Y couplers with two ports in-one port out. This method uses easy and totally mechanics ways and gives components having most interesting characteristics. Meanwhile, because of the development in french videocommunication, in which there is a great need for multi mono couplers, we , with the help of the C.N.E.T., did find a way for producing such components. The very interesting fact is that we use the same technology to produce mono or multi mono Y couplers. The utilized technique allows large production with good accuracy for both kind of couplers.

This paper examines the application of fibre optics in cable TV networks in 3 time frames, namely:- - its use to the present time. - its use in the immediate future, in particular its application in the new switched-star type of network being introduced. - its long-term use in the anticipated all-fibre, all-digital integrated wideband local network.

The sensitivity and performance of single-mode Optical Time Domain Reflectometers has to date been insufficient to fully satisfy the requirements of the long haul telecommunications industry. Three approaches to the problem have been considered, namely conventional direct detection, long wavelength photon counting and coherent detection. The relative merits of these techniques are discussed with particular emphasis on the significance of new optical component developments.

Repeatable measurements of the bandwidth of multimode fibres, with a good understanding of the systematic errors involved are required for the design and maintenance of communication systems. A measurement system is described which facilitates a close comparison between results obtained using time and frequency domain techniques. The optical layout provides an alternative to the "cut-back" method for system response measurements. Systematic errors associated with each technique are illustrated and methods to overcome them are presented.

PIN-FET receivers developed for 8, 34 and 140 Mbit/s have been displayed in real systems generating confidence in the base technology 1,2. We have now extended this to 565 Mb/s and 1.3 Gbit/s for systems to be installed in the near future. At data rates beyond 1 Gbit/s, alternatives to the PIN-FET become attractive. We present here results of a study into these alternatives and compare these with current 565 and 1.3 Gbit/s PIN-FET receivers.

A computer program was developed to aid the design of fibre optic receiver preamplifiers for low/medium bit rate systems. The program calculates the preamplifier feedback resistance and, in the case of avalanche photodiode, the optimum multiplication factor. The program can work with any of the three basic receiver types viz: straightforward termination, high impedance integrating type and the transimpedance type. It can be used to understand the effects of various system parameters on the receiver sensitivity without having to actually construct the circuits.

Serial time division multiplex (TDM) databuses,while very flexible, are limited at high data rates by the transit time between terminals. The pauses in transmission necessary to allow for propagation delays reduce the effective data rate, and may cause problems with signals requiring rapid updating. We propose a hybrid protocol combining T.D.M. channels at low frequency with frequency division multiplexed channels carrying high speed data. A laboratory system using a 17 x 17 transmissive star has been constructed to demonstrate the feasibility of this approach, using TDM channels in the 0-10MHz band together with FDM channels in the 10-50MHz band.

The Ethernet local area network (LAN) is briefly described in its standardised IEEE 802.3 form, and opportunities for applying fibre optics are reviewed, both as enhancements of a coaxial network and as a complete fibre optic network. An inter-repeater link is described for interconnecting coaxial segments. Various alternatives are considered for implementing a full fibre network, and it is shown why the active hub approach is preferred.

The NKT Tele-Ringnet is a combined digital telephone and data network based on a fibre optical ring topology. The purpose of NKT Tele-Ringnet is to carry telephone and data communication as a digital PABX does. However, the optical system is not based on individual lines to a central mother exchange. It is a ringnet with an 8 Mbit/s transmission rate interconnecting simple telephone concentrators. The advantage is that all the telephone and data traffic can be multidropped over a large campus. In addition the signals are carried by an optical dual fibre cable which has many advantages compared with conventional cobber cables, i.e. low attenuation, large noise immunity, no electromagnetic radiation, small size and low weight.

The paper begins with a reminder of the particular need for standards in LANs. We then describe the requirements of High Integrity LANs. Current developments in LAN standards are then outlined. It is argued that the requirements of industrial LANs lead ideally to reconfiguring fibre optic rings, for which there are two major emerging standards. These two (IEEE 802.5 and ANSI FDDI) and the Cambridge Ring are discussed and compared. One implementation - the HILAN is discussed.

This paper details the FOCOM 1800 Series Fibre Optic Communications Network. It will seek to cover the relevant historical aspects of the equipment, including the origin, the concept and development phases, through to its current applications. The ongoing and future developments will be noted and the paper will conclude with a summary of benefits to the User.

A low-cost, high performance data link design is described for optical fibre LAN/MAN applications. The transmission rate is 140 Mbit/s and the signalling rate is 280 MBaud using a biphase line code. This signalling rate is within the maximum switching speed of high performance commercial SLEDs and ECL. Multimode transmission was used for LAN applications but for MANS, single mode transmission up to 23 km has been demonstrated using a commercially available semiconductor laser.

The development of a fibre optic based digital communication system for use in power system protection and control equipment for use within electricity substations is discussed. Emphasis is given to systems wholly within the substation confines and their interfacing to public and private multiplexed telecommunication systems. Particular reference is made to the system used in a Current Differential Protection for EHV transmission circuits.

Historically the safety of fibre optic systems, of the types used in industrial process applications where there could be flammable atmospheres, has been accepted implicitly. During the last 18 months this acceptability has been questioned, particularly in view of the rapidly increasing optical power available in fibre optic systems. This paper describes initial work undertaken on behalf of OSCA (the UK Optical Sensors Collaborative Association) to establish whether optical fibre systems could be a source of ignition, and, if so, what the significant parameters are. Early studies had suggested that small particles heated by optical radiation emerging from a fibre, particularly if the radiation was focussed, could theoretically constitute a potential source of ignition.

This paper describes a fibre optic multiplexing system developed for use on a motor car and discusses some of the experience gained. It also describes some of the environmental factors affecting such a system.

As the expansion of fibre optic systems continues and the amount of installed single and multiway ruggedised fibre cable increases there has been a growing interest in "IN-SITU" fibre cable repair systems. Until recently, fibre cable repairs have been centred around conventional techniques (1, 2 & 3) i.e. termination and fusion splicing. The repair conditions dictated by these techniques requires the utilisation of the following facilities and materials:- 1. Epoxy resin systems and their applicators. 2. Good polishing facilities. 3. Passive hand held tools: e.g. cable strippers, wire cutters, fibre cleaver etc. 4. Active tools (electrically powered); e.g. Arc fusion splicer, heat gun, heat curing fixtures etc. 5. Connectors for terminated fibres. 6. Completed internal and external splice protection (for fusion splicing). 7. Visual inspection (microscopes).

A fiber optic connector has been developed and tested to insure performance and reliability when used in the AN/GRC-206 military radio sets manufactured by Magnavox Corp. This paper describes the design features Cannon has implimented into the production connector, the qualification test program to simialate field conditions (including unique new tests and criteria for F.O. connectors) and the optical production acceptance cable testing which simulates and predicts connector performance in the field. Test data is presented along with pictures of test set-ups and equipment.

In medical applications of the laser, particular radiation patterns of light on the tissue to be treated are often required. This need can be satisfied by unconventionally shaped fibre tips. The most promising examples of such tips are briefly reviewed. The most important fa-brication methods are also considered as well as the medical or surgical applications which are under investigation.

New forms of medical sensor are under development in many commercial and academic research laboratories around the world. The consideration of fibre optic sensors in solving medical problems is based on the unique advantages of optical fibres: small size, flexibility and immunity to electromagnetic interference.

Laser light has many special properties but those most relevant to medical applications are the monochromaticity, the ease of precise control and the ability to focus the full out-put of a high power laser on to a very small area. The latter property makes it practical to deliver laser light of appropriate wavelengths to internal parts of the body via single flexible fibres and to limit the effect to the desired target organ with greater accuracy than is possible with other techniques. Many lasers are currently under investigation for their biological effects, ranging from wavelengths in the far infra-red to the far ultra-violet, both continuous wave and pulsed. The properties of the most important ones are outlined in tables 1 and 2.

Man's curiosity has led him to seek methods of investigating the inner workings of the human body, but it is only recently that it has become possible to properly visualise the inner cavities of the human frame. Physiologists such as William Beaumont have occasionally had the opportunity to see the function of the gastrointestinal tract, in this case the gastric fistula of Alexis St Martin who was injured following an accidental firearm explosion. Rigid instruments, down which lights are shone, can be used to visualise the respiratory passages, the gullet, the rectum, and the bladder, and in the past artists were employed to record what was seen. Such instruments are still in use, although light from a powerful source is now conducted down the instrument using a fibreoptic bundle. The first semi-flexible instrument which could be inserted into the stomach and used to visualise its walls was developed by Schindler and Wolf in Germany in 1932. The optics consisted of a series of convex-lenses, transmitting an image back to the eye, but again the view obtained was limited and since its optics were side viewing, the gullet could not be viewed. The advent of fibre-optics revolutionised the situation, and the first fibrescope conducting the image up a fibreoptic bundle was a side-viewing instrument, developed by Hirschowitz, Curtiss, Peters and Pollard by 1958, and used for viewing the stomach. Since those pioneering days, the development of fibrescopes for viewing every potential cavity in the human body has proceeded in leaps and bounds.

The feasibility of the use of optical fibres to supply light to, and relay information from, an absolute moire fringe displacement sensor has been demonstrated and a prototype built. Fringe interpolation techniques are employed which reduce the susceptibility of the sensor to adventitious intensity fluctuations. The system is designed to operate over a displacement range of 100 μm and can resolve displacements down to 12 nm: nonlinearity is ±0.8 μm, while hysteresis and repeatability are better than 0.3 μm. The system is largely immune to intensity variations on the input light channel, however differential attenuation between any of the four return light channels more seriously affects the measurement. In order to try and avoid this problem an optical arrangement has been investigated in which intensity information corresponding to four quadrature points on the moire-fringe profile is carried in a single return optical fibre using wavelength separation.

Single-mode optical fibres may be applied to a wide range of measurands, and exhibit extreme resolution. We describe here optical signal processing techniques which recover both the phase and state of polarisation of the measurand-modulated guided wave, either separately or simultaneously. The discussion is illustrated by a description of temperature sensors developed in our laboratories and recent experiments on the measurement of low frequency and quasi-static strain are also reported.

A novel extrinsic optical fibre displacement sensor is described which intensity modulates an incoherent light source. Light is transmitted along multimode graded index fibre into a GRIN-rod lens coupler system. The transmission and reflection properties of this system are fully categorized. Linear movement of a partially reflecting mirror parallel to the axis of the lens coupler forms the basis of the measurement technique. This device exhibits several important features which makes it suitable for use in a process control environment. Firstly, the measurement is largely independent of the modal power distribution present at the sensor. Secondly, it can be made independent of any fluctuations in the source output power using only a single transmit and return fibre. Finally, the mechanism has a dynamic range of several millimetres which makes it eminently suitable for connection to a Bourdon tube thus providing measurement of both pressure and temperature. The characteristics of a prototype sensor in which a Bourdon tube provides conversion of the measurand to displacement of the mirror are reported, together with the requirements of the associated telemetry system. In addition a series of pressure measurements against detected optical power showing a linear relationship are presented which demonstrate the ability of the device to give an accurate measurement of both pressure and temperature.

This paper investigates the feasibility of running a quartz force sensor with an optical drive. The general theory behind optical (strictly speaking, photothermal) driving of a resonant structure is presented and this is used in conjunction with empirical results obtained from an existing system to clarify problem areas and to suggest improvements. A straightforward method for optical reading is briefly described.

This paper describes the development of a fibre optic pressure transducer based on the combination of an optical displacement sensor with a conventional pressure sensing mechanism. The fibre optic displacement sensor utilised was of the wavelength modulation type and had previously been demonstrated to have a resolution of 6.5um over a range of 10mm when illuminated by a white light sourcel. In the work described here the source was replaced by a near-infra-red light emitting diode whose spectral bandwidth provided a displacement range of lmm. This sensor was fitted to a conventional pressure sensing mechanism which produced a displacement of lmm in response to an applied pressure of 30mbar. This paper reports on the evaluation of the transducer and gives the results of the performance in terms of hysteresis and linearity.

The paper describes recent progress made in developing an interferometric fibre optic sensor array based on time domain reflectometry.

Optical fibre intensity based sensors, though simple in concept, are limited by the fact that intensity referencing must be provided to produce an accurate device. This paper describes a referencing system that has been evaluated yielding errors as low as 1% for up to 20 dB in-line power attenuation. It goes on to consider techniques whereby several such sensors may be multiplexed into a passive optical network.