ALPD technology is a large scale industrial process which permits the manufacture of massive all silica ingots. The system works by direct fusion using a plasma flame, the deposition rate being far in excess of that achieved by other fiber manufacturing techniques. The plasma heating process involves very high temperature which promotes purification by volatilisation. No substrate is required (either tube or mandrel) and thus intermediate operations are completely avoided (collapsing of tube in internal CVD or drying, vitrification and collapsing in O.V.P.O. or V.A.D.) This combination of advantages permits the drawing of large preforms and eventually of large core step-index all silica fibers under highly economic conditions. The latest modification of the process allows index profiling of the optical interface with maintained production efficiency.

Optical cable applications can be divided into four major market segments. These are telecommunication, data, video and military communication. For the majority of the telecommunication, data, and video applications, a loose tube or loose ribbon design can be manufactured without incurring a microbending loss penalty. Fibre performance in the loose tube cables can be maximized by optimizing the lay length, tube dimension and pitch diameter. At present, high quality cables using both single and multimode fibre are being manufactured in volume with no additional microbending loss. For example, single and multimode cables with loss of 0.5 dB/km 1300 nm and very high bandwidths or low dispersion have been successfully installed in many cities. An example of this cable is shown in Figure 1. These cables have been used for direct buried, duct system, aerial or underwater installations.

The design of a demountable connector system for data transmission in fibres presents conventional connector manufacturers with some unique problems. This is due to the extreme accuracy of alignment, both in a lateral and angular axis, which is needed for a low loss connection. All the design work and the various styles which the connector manufacturers have come up with can be reduced to three basic types which aim to overcome this problem and this paper discuss their various advantages and disadvantages:

A high performance optical connector for monomode systems is described in detail. The connector consists of a plug and receptacle with bayonet coupling mechanism. The fiber ends are mounted into identical ferrules, which allow high precision, adjustment of the fibers by a double eccentric system. The main manufacturing steps are explained and test results are shown.

The precision made parts of the multifiber connectors are made of silicon. Silicon is a material which has become very important in the last decades. It is particulary well known in semi-conductor technology, in which a great number of microelectronic components are produced from silicon. However not only microelectronic components may be made from silicon, but also the most minute mechanical components. The basic material of the Silicon-Multifiber-Connector (S.M.C.) is single crystal silicon in wafer form. These discs are 0.5 mm thick and are coated with an oxide layer onto which a photoresist has been deposited. Through a photomask, on which all the patterns of the S.M.C. are mapped, the photoresist is exposed to ultraviolet radiation. Thereby a chemical reaction takes place, resulting in the unexposed areas, necessary for producing the precision etching mask from the oxide layer. The wafers for the S.M.C. are <100> oriented. If this silicon is treated with an anisotropic etchant (e.g. KOH, NaOH), then due to an opening in the oxide layer, a corresponding V-shaped depression is created.

The British Technology Group is responsible for technology transfer between universities and industry in the sectors of information technology, engineering and science. Within the information technology sector there are between 20 and 30 patents in photonics and applications under consideration which have mostly been developed with the support of Research Council funding. BTG incorporates extensive patents and legal expertise associated with the protection of intellectual property by such means as patent, copyright and other forms of legal protection. The group is in a position to provide funds to help with the further development of inventions and such funding is dependent upon the merit of the case in question. The topics covered by the patents in this paper are broadly categorised into Fibres, Couplers, Communications, Profile measurement and sensors. The title of this session refers to fibres and connectors and so these topics are covered in the first two sections. The fibre section includes methods of manufacture and also a sensor (2) which utilises a particular type of fibre. The Fibre Optic isolator (12) may not appear to be a coupler but it is a new utilisation of the Faraday effect to couple light channels while inhibiting reflections.

A historical review of the developments of encapsulations for semiconductor lasers intended for use in fibre optic transmitters and a look to future needs and trends.

Graded-index multimode fibre couplers have been fabricated using the fused biconical-taper technique. The optical characteristics-coupling ratio, excess insertion loss and isolation-of the fabricated couplers were measured and plotted versus the measured fused length and the diameter of the waist of the coupler, d. One important finding was that for d >10µm the coupling ratio is essentially sensitive to the physical parameter of waist diame"er only. This can simplify the fabrication procedure.

Long-wavelength optical telecommunication systems require receivers of optimal sensitivity at optical wavelengths of 1.3 μm and, increasingly, 1.55 μm, to take advantage of the low loss and dispersion of currently-available optical fibre at these wavelengths(1).

Bidirectional-wavelength-multiplexing integrated module has been developed includes the. components, indispensable for wavelength-multiplexing technology, in a single package. It has low cost, small size and light weight. Wavelengths of two LEDs are 780 nm and 880 nm. Optical detector is either APD or PD. Optical power and near-end crosstalk attenuation are more than -20 dBm and 40 dB, respectively and insertion loss less than 4 dB. This module is available in various applications.

Progress in the development of low-loss, high bandwidth, single-mode fibres for optical communication purposes has led to increased effort over the past several years into the development of integrated optical devices and systems. Active devices such as modulators, switches, polarisation controllers have been developed in lithium niobate substrates while passive devices such as junctions, power splitters, wavelength demultiplexers have been formed in glass waveguides. Interconnection of devices to form integrated systems poses special problems and two lines of approach are possible: (i) hybrid systems where devices in different materials are linked by fibres or other coupling methods (ii) monolithic systems where all devices are fabricated in a single substrate material such as GaAs or InP. Increasing effort is being directed towards III-V semiconductors for fabrication of lasers, detectors, waveguides and opto-electronic devices with a view to the design of monolithic integrated optic and opto-electronic systems. In addition to the use of integrated optics in communication systems, important applications are now being found in fibre-optic sensor devices.

A multi-function fibre-optic communication system has been constructed for carrying radar information from a radar head end to a remote display area. High bandwidth video signals have been carried on FM subcarriers on a single fibre per channel basis. The radar video channels were a 20MHz analogue signal, a 10MHz analogue signal, and a 10MHz digital signal composite with a synchronising pulse. The aerial turning data was digitised and transmitted serially via a dedicated fibre with considerable capacity for additional information. Duplex speech and a TV video signal were transmitted over a single fibre using FDM and WDM. All the signals have been carried over a 3Km length of multimode optical cable using 1300nm led sources to reduce material dispersion. The WDM duplex link also used an 850nm led in the return direction.

The principles and applications of local area networks (LANs) are now well publicised. They offer substantial advantages over conventional point-to-point links in a computer environment, since they impose little constraint on system configuration. Peripherals and processing nodes can be distributed on the network in any manner physically convenient to the user. The availability of complete cross-communication between stations permits distributed processing and shared access to storage and input/output media. In certain areas, however, conventional LANs have insufficient performance to cope with the traffic rate. Coupling a processor to main store via a LAN would be an absurdity; this clearly requires the use of a direct point-to-point interface. In some areas LAN flexibility is required, but at a performance level more typical of a dedicated link. This paper describes the implementation of a network which fulfils this requirement: MACROLAN. The transmission medium adopted is optical fibre and is thus a new technology serving a new application. The physical aspects of this network are therefore emphasised in this paper.

This paper presents a complete interactive teledistribution network based on fiber optic technologies, with a modular design allowing a total flexibility in terms of number of programmes and number of subscribers as well as future evolution towards integration of narrow band or future broadband switched services, without modifying the basic existing infrastructure.

Coal mines have a number of unique problems which affect the use of fibre optic technology. These include a potentially explosive atmosphere due to the evolution of methane from coal, and a dirty environment with no cleaning facilities readily available. Equipment being developed by MRDE to allow the exploitation of optical fibres underground includes: A hybrid electrical/fibre optic connector for the flexible power trailing cable of the coal-face shearer; An Intrinsically Safe (IS) pulsed laser transmitter using Frequency Shift Key (FSK) data modulation; An IS Avalanche Photo Diode Receiver suitable for pulsed & continuous wave optical signals; A mine shaft and roadway cable/ connector system incorporating low loss butt-splices and preterminated demountable connectors.

The introduction of fibre optic systems is moving quickly on high capacity national and international trunk routes. This paper presents the evidence that the external plant needed for rugged civil and military requirements is now ready for implementation. The paper deals with the practical aspects of using the new transmission medium in rugged environments. The specialised long haul, high bit rate monomode PTT type system is specifically excluded. A brief survey of the possibilities offered leads to a definition of the relatively short haul defence and domestic systems that are needed now and for the foreseeable future. Special emphasis is paid to the performance of the external cable plant.

Fibre optics provide many advantages in conventional strategic, tactical, ground base and airbourne military situations. These include security, small size and light weight of both cable and electronics, lower power consumption of electronics and immunity to EMI, EMP and RFI just as in the commercial uses of fibre optics. In many military applications the advantages of fibre optics may be critical to mission performance. A major stumbling block has been the development of fibre optic components and systems that meet the environmental, reliability and maintainability requirements of military equipment. Bearing these requirements in mind, this paper identifies some of the techniques used and recent advances made by Codenoll Technology in producing fibre optic data links suitable for military use. Some general tactical and strategic military applications involving these data links will then be discussed.

The 1553B databus (and its DEF STD 0018 equivalent) are a high performance command-response communication link which is electrically implemented via transformer coupling using a three level manchester enclosed signal. An optical transmitter/receiver replacement has been designed which well exceeds present data bus specifications and is totally compatible with interface chip sets currently being developed (Smiths, MEDL, Harris). The transmitters can launch 3 mW into 200 micron covered fibre at a wavelength of 0.88 microns over the range 0 to 25Mbit/s. The receivers operate at power levels of 300 nanowatts to 600 microwatts with a maximum bit period deviation of less than 100 ns (1553B for 150 ns). Interword gaps from zero to greater than 1 second can be tolerated with an interword gap upper limit most probably in excess of 10 seconds (measurements have been limited to 5 seconds max). This has been achieved via signal processing rather than any complex encoding techniques. The units are based on high reliability construction techniques, using a hybrid assembly process, to give a fully hermetic package (20 PIN DIL transmitter 32 PIN DIL receiver, with a common 0.6" row spacing) with an operating temperature range of -55 to +125°C.

This paper gives details of a fully engineered single-mode route between Liverpool and Preston, England. The installation of the cable was completed in late 1983 and the full cable sub-system will be completed in early 1984 with the line equipment following shortly afterwards. This is a 140 Mbit/s system which will operate over 50 km. Details are given of the cable subsystem, the optoelectronic devices and the line terminal equipment. Consideration is given to the systems budget in terms of attenuation.

Four channel wavelength division multiplexing (WDM) in the range of 800-900 nm is Quante's solution to the demands of the German post office BIGFON field trial in Berlin. After a short description of the technical requirements of BIGFON the features of Quante's WDM system as used in Berlin will be outlined. The advantages of a 4 x 140 Mbit/s WDM transmission system with full duplex capability are compared with other possible methods. Possibilities for the future will be outlined in the end and their availability as well as their commercial aspects will be discussed.

Monomode(optical fibres are now of central importance to the British Telecommunications trunk network&apos(l). Measurements aimed at characterizing monomode fibres after manufacture, during cabling or prior to insertion in a route are still in their infancy, and a subject of much debate in the literature and in standards authorities. Broadly speaking, two classes of measurement are required; optical properties (spot size, cut off wavelength, dispersion, refractive index profile) and geometrical properties (core concentricity error, core and cladding circularity, and cladding diameter). The first measurement set have been tackled using optical methods specific to monomode fibres and is not the concern of this work. The geometrical properties may be measured using developing metrology, the capabilities of existing and emerging techniques being reported here. Because Core Concentricity Error (CCE) is the most important and, ironically, the most difficult parameter to assess, this paper will concentrate on this aspect.

With the continual improvements in optical technology it is essential that a measurement programme not only serves to satisfy the transmission performance requirements but also provides sufficient data to provide feedback for cable manufacturing and system design needs. A fibre optic transmission system consists of the electro optic interface, the optical cable link and the opto electric interface. Demountable optical connectors are normally fitted between the component parts of the system. The optical cable link is constructed from factory lengths, currently up to 2km, of multifibre cable field jointed to form a cable section of up to 50km in length. The cable section is then fitted with connectorised terminating units for interface to the terminal line equipment. This paper will discuss measurements on the cable only part of the fibre optic transmission system, that is measurement up to and between the optical connectors. Both multimode and single mode systems are discussed and the differences highlighted.

This paper outlines the overall line coding requirements for 140 Mb/s optical fibre transmission system operating at a wavelength of 1.3μm. It was concluded that choice lay between 5B6B and 7B8B alphabetic block codes. Consequently, a detailed investigation of the parameters of both codes were carried out and a comparison between them was given. It was also concluded that although the difference between 5B6B and 7B8B codes is slight, 5B6B code offers advantage in terms of circuit complexity and power consumption.

There are several potential advantages to using highly coherent single mode laser sources in optical fibre gyroscopes. These include the potentially high output power and the relative ease with which a single mode source may be modulated in both frequency and intensity. However most systems use incoherent (edge emitting LED's) sources to avoid the detrimental effects of coherent backscatter. In this paper we demonstrate some techniques whereby the effects of discrete reflections and backscatter may be minimised resulting in gyroscope noise levels of approaching 0.1 degrees/hr/hz.

The principle stimulus for fibre optic technology is undoubtably high capacity telecommunications links. However, optical fibre sensors are becoming an increasingly important subject, and it is probable that this will become an important aspect of transducer technology in the none too distant future. It is also conceivable that fibre optics will make a significant contribution to signal processing technologies, especially for high data rate systems. In this paper, we examine some of the underlying reasons why this may be so and present some examples of the simple processors which have been realised to date. There is a range of processing functions which it is apt for fibres to perform, which may be classified as tapped delay line and spatial processors. The technology is currently in its infancy, but may have much to offer for a wide range of applications.

Optical fibres are used in three application areas in automobiles. Illumination of the dashboard is done with a single lamp and monofilament fibres or woven tapes which illuminate the front panel. Fibre-optic multiplexing can replace the conventional wiring harness. Different trial systems (two-fibre links, bidirectional transmission, star-coupled architecture) are reviewed. Problems still exist in component performance, high costs and unknown reliability of optoelectronic systems. Fibre-optics are also used in sensors; for headlight monitoring, liquid-level sensing and other applications.

The potential for use of fibre-optic devices, with emphasis on sensing applications, within the constraints of nuclear power-related environments is reviewed and discussed. The various process environments encountered within the nuclear power industry provide a wide range of opportunities for optical sensing technology and fibre-based devices offer potential advantages in a number of areas. The small volume and flexibility of fibres together with the multiplexing capability of fibre-optic systems are particularly attractive. The effects of operation in a radiation environment must be carefully addressed. They will be dependent on a combination of other environmental and operational parameters and the use of optical fibres in such circumstances is not automatically precluded. Enhanced lifetimes may be achieved via optical and thermal bleaching techniques.

Instrumentation in Gas Turbines must operate in extremely harsh environments. Electro-optical methods are being increasingly used to measure such variables as displacement, temperature and gas flow and fibre optics are often required to enable sensitive electronic components to be placed remote from the hostile region. This paper reviews applications of fibre optics in Rolls-Royce up to the present. In addition the case for using fibre optic sensors for the measurement of other parameters in future will be presented, along with a discussion of the prospects for fibre optic data transmission on the next generation of digitally controlled engines.

Graphics is one of the fastest growing areas of computer application today. From monochrome to full colour high resolution eventually all draughtsmanship and engineering drawings will be produced by computer. The ability to provide and update drawings or change perspective and size at the touch of a button with perfect prints everytime spells the end of the drawing board. The problem associated with this revolution is one of bandwidth and distance. Computer graphics employ up to 60MHz pixel rates and using coaxial cable means the operators have sometime to be within 50 metres of the controller. However, using fibre optic links, full resolution can be maintained at 5000 metres of more, allowing drawing offices to be situated anywhere on a site.

The widespread belief that developments in fibre optics derived from applications in the telecommunications industry, if applied to instrumentation and control, might give cost/performance advantages, has resulted in the formation of the United Kingdom Optical Sensors Collaborative Association (OSCA). The objectives of OSCA are to encourage the early exploitation and application of existing information through information exchange and sponsorship on sensors and systems. Optical and opto-electronic techniques for measuring primary variables - temperature, pressure, flow, etc - in industrial measurement and control fall centrally within OSCA's remit. The current membership of OSCA was given in the presentation. Full membership of OSCA is open to all instrumentation manufacturers with manufacturing and R and D facilities in the EEC, and to contractors and users of such equipment. Affiliate members are chosen because of the contribution they can make to the knowledge which is developed and shared amongst the full members. Full members have preferential exploitation rights to OSCA's intellectual property arising from sponsored work. As will be seen from the membership list, many different spheres of industrial activity are represented - instrument manufacturers, process plant users, utilities, aerospace and automotive companies.

Optical fibre sensors are being developed for industrial and consumer markets and may be intrinsically safe, free from interference and cheap to install. First generation devices for measurement of key quantities seem likely to use multimode technology and be 'point' temperature/displacement/force types. Three main design approaches are described with examples: intensity-modulation with referencing, colour modulation with simple wavelength detection, and rate-modulation using hybrid techniques.

Incoherent optical sensors based simply on the measurement of the amplitude of light transmitted by the sensor head are subject to errors unless care is taken to ensure the stability of light sources and detectors, the constancy of launch conditions and freedom from unintentional fibre microbending losses and variations in connector coupling. Sensors based on spectral filtering techniques, however, make use of wavelength-dependent variations in transmission, reflection or scattering processes which greatly exceed the normal spectral variations of transmission which may normally occur in optical fibre and connectors. This paper reviews the types of spectral filtering sensors which have been developed with classification into analogue and digital sensors.

The use of simple mechanical optical transducers to monitor position, flow, pressure and other applications in the process control field is discussed. Opinions are expressed as to future fibre and connector 'standards' for industrial fibre optic links, opto-mechanical sensor techniques and the network topology of a 'plant wide' process control system.

The use of fibre optics in laser Doppler velocimetry (LDV) promises increased versatility of the technique and novel optical designs. This paper discusses the properties of optical fibres and related components relevant to LDV design, and the likely limitations on system performance. The discussion is illustrated by descriptions of prototype systems constructed in these laboratories: a high power (~ 0.5 W) argon ion laser based system; a compact system incorporating a piezo-electric phase shifter to provide directional information; and a diode laser based system.

An electric field sensor capable of measuring alternating fields at frequencies up to 150MHz has been demonstrated. The sensor uses the linear electro-optic effect, allowing the construction of an all dielectric probe. With modifications to the light source and receiver, the sensor should be capable of measuring fields at frequencies up to 1 GHz.