In its overall responsibility as the major network provider in Germany, the Deutsche Bundespost launches all highly sophisticated technologies in order to serve the telecommunication market with those promising services which the national economy require. In this contribution some background information about the objectives can be found. The basic assumptions for the implementation of the future highly efficient, totally integrated universal network achievable by a step-by-step strategy are mentioned and the existing and intended activities pointed out in more detail. As a result, the reader of the article may recognize that there exists a well defined German approach for handling the challenges of the future development in the telecommunication scenario, though not all the trends of technological development can be assessed in detail.

Direct detection single mode optical fibre systems have evolved rapidly during recent years such that multigabit transmission has now been demonstrated over 100 km spans. At lower line rates, unrepeatered optical path lengths in excess of 250 km have been reported. This progress is largely due to technical advances such as narrow spectral line lasers, low-loss step-index and dispersion-shifted fibre together with high-sensitivity, broad-band receivers. The high speed system developments have placed increased emphasis on the associated signal processing functions such as timing extraction and regeneration, this latter function being provided with gallium arsenide logic devices. This paper will review some aspects of the high-speed and long-span transmission experiments carried out at BTRL. These include an ultra-long-span, 34 Mbit/s system and a 2.4 Gbit/s fully-regenerated high-speed optical transmission test over an installed 32 km fibre.

Single mode fiber optic transmission systems have attracted special interest due to the numerous advantages over the metallic based systems : repeater snan exceeding 30 km, high capacity to volume ratio and easier future evolution since the transmission line should remain unchanged. The current status of the long haul-high rate optical systems in France is described and particularly the monomode experimental link operating at 560 Mbit/s and 1.5μ . A summary will be given of the implementation schedule of the high bit rate systems and some critical characteristics will be discussed as well as the installation problems encountered thus far.

This paper describes a wideband homodyne phase diversity receiver based upon a 3x3 multiport optical coupler. We present receiver sensitivity results for ASK and DPSK modulation formats at 320 and 680 Mbit/s.

This paper looks at the development of the technology which has led to the installation of the first commercial 565 Mbit/s system in the U.K. It examines the practical implementation of the systems and the design considerations such systems must be given, especially for attenuation and dispersion budgets. The results of performance measurements are given and show that the system meets the required specification. Future systems operating at 1550 nm promise to continue the pattern of improving regenerator section capacity as both section lengths and system bit-rates increase.

In June/July 1983 there were 37 applications from 24 groups submitting their application to build broadband metropolitan networks in response to the call from the Home Office/Department for Trade and Industry.

This paper is based on a study of Fibre Optic Local Area Networks (FO LANs) completed by ERA in January 1986, and which investigates the status and trends in technology and markets, and presents ten in-depth case studies of FO LAN installations. It will be assumed that delegates are generally familiar with LAN principles.

The paper describes a fibreoptical wideband local area network, (LION) which is being developed under the European ESPRIT (European Strategic Programme for Research and Development in Information Technology) programme. The consortium consists of Thomson-TITN, CSELT and NKT Elektronik. The network will carry both real-time voice and compressed video traffic, and it will also offer a Transport Service for packet-switched data transmission. The network is composed by a number of subnets operating on 140 Mbit/s and an interconnecting backbone network operating on 565 Mbit/s. In large organisations the total network may span more than 10 miles and it can handle more than 10,000 users. The network will have gateways to ISDN and other public services, and interfaces to host computers and other common resources.

Macrolan is a high performance, local area network (LAN) which was developed for use in the ICL Series 39 range of mainframe computer systems. The star-configured network provides the flexibility of a LAN for installation and reconfiguration, combined with the throughput of a dedicated point-to-point link and the advantages of an optical fibre transmission system. This paper presents the design philosophy involved with the development of the short-haul, optical fibre transmission systems incorporated in the network.

The paper reports initial experiments on two essentially complementary methods of coupling information, both into and from a continuous optical fibre highway, in each case in a non-invasive low-loss manner. Information is coupled onto the bus by means of a piezo-electric transducer which introduces differential phase modulation between the two modes of a polarisation-maintaining fibre. Coupling off is achieved by bending the fibre over a curved former and collecting the emerging radiation with a polymer fibre. The methods may be used in a complementary manner to produce a bi-directional local area network system.

The American National Standards Institute (ANSI) is close to approving a new standard known as Fibre Distributed Data Interface (FDDI). This is a high speed optical communications network based on a packet switching mode of operation. More recently, work has started on a companion standard known as FDDI-II, designed to support both circuit switching and packet switching modes of operation. This paper describes the important features of FDDI and FDDI-II, discusses their operation and implementation and presents some possible applications.

The advantages of ring networks over bus networks are now well established. The main benefits are considered to be greater flexibility and less complexity together with the provision of higher data throughput with guaranteed maximum access times. However, when considering reliability, the obvious potential problem with the ring network is that of an open circuit or failure of a repeater in the ring. Either of these occurrences within a basic ring design would inevitably disrupt service.

The progress of the IEEE 802.3 standard for fibre optic LANs is indicated with reference to both mixed media networks and full fibre networks. For a fibre optic network the most suitable layout is a "snowflake" topology composed of multiport repeaters and active fibre hubs. A range of components is described which enables the realisation of such a topology in conformance with the IEEE 802.3 standard.

The Fused-Head-End technique is a new manufacturing technique by which all types of passive optical fibre components required in a network can be made. Mode spectra launched are analysed using the Central Spot Far Field method. For some years now passive optical--fibre components have been available which are mainly based on the directional and star coupler. In the Fused-Head-End technique these as well as other types of components can be made which may give rise to new possible network configurations.

This paper gives a brief introduction to the beam propagation method, a numerical technique that may be used to analyse and optimise a wide variety of waveguide components. Its use is illustrated by a number of different examples in both cylindrical and planar waveguide geometry.

This paper describes two fibre optic inserts, one using ferrule techniques, the other using expanded beam components, which fit the high power/coaxial contact cavities of the hybrid DIN 41612 indirect two part PCB connector.

For many years research has been engaged to fight 1.55 μm chromatic dispersion of long-haul single-mode fibre links. Some solutions have usually been proposed, like low dynamic spectral width sources, as distributed-feedback lasers, or optical fibres with particular structure, as quadruple-clad or triangular index profile fibres. These solutions present some problems of reliability, reproducibility and performance improvement, which still remain to be solved. A new device is proposed to fight chromatic dispersion and then to improve span x bit-rate product of a given classical step-index fibre link. It consists in a wavelength demultiplexing done by a diffraction grating, in order to spatially separate each longitudinal mode of the laser. Each of them is then coupled to a short multimode fibre whose length is adjusted to compensate exactly for the corresponding delay time induced in the link by its total chromatic dispersion. The ends of these fibres finally converge on a fast photodetector which provides a signal showing no distorsion and being insensitive to the laser mode-partition noise. A bandwidth enhancement of almost one order of magnitude has been demonstrated.

Single-mode optical fibre is well established as a passive, high bandwidth transmission medium for point-to-point communication links. However, the optical waveguide concept lends itself to a much broader application. There have been exciting developments in the rapidly growing fields of interferometric sensors, optical instrumentation and optical signal processing, while in the evolution of data transmission technology, there has been progress towards wavelength multiplexing techniques, local area networking and very long haul 'coherent' systems.

The wavelength dependence of fused single mode couplers has been investigated. Devices utilizing the wavelength dependence, such as wavelength division multiplexers, and dual wavelength couplers have been fabricated. Experiments into the reduction of the wavelength sensitivity have been performed and a broad band coupler manufactured.

A new endless polarisation control system is presented which transforms any incident state of polarisation (SOP) into any desired one. It features five SOP control devices of two different types only, which should facilitate an integrated-optic realization. A scheme is shown how the control devices can be set away from their range limits without disturbing the overall SOP transformation. A microprocessor-based system with an all-fibre polarisation controller has been realized to confirm the theory. A simple version consisting of four SOP control devices can transform a given SOP into any desired one or vice-versa.

We report here the development of a multiplexer-demultiplexer for WDM transmission systems. The device is capable of multiplexing 5 distinct wavelength LEDs at centre wavelengths of 0.75, 0.87, 1.06, 1.30 and 1.55μm using multimode optical fibre. Insertion losses of less than 1dB have been obtained while isolation between all channels is better than -20dB, typically better than -25dB. Devices have been temperature cycled over the range +125°C to -55°C with only ±0.3dB variation in insertion loss. No measurable change in insertion loss was seen when the device was vibration tested over the range 10Hz to 2KHz (10g) or shock tested in all 3 axes.

The limitations of the conventional optical receiver front end circuit configurations are reviewed in the context of the requirements projected for future transmission systems operating at gigabit/s rates. The alternative bootstrapped source follower configuration is proposed, combining low noise with the advantages of tolerance to unbounded line codes, and very wide bandwidths. These have been demonstrated by an experimental design, which has achieved a sensitivity of -28.6 dBm at 2.4 Gbit/s.

This paper discusses the types of LiNbO3 switch available for use in optical networks, their advantages and disadvantages over fibre-based devices, and their possible application in various network topologies. A practical demonstration of such a network, developed at BTRL, is discussed.

LEDs have been fabricated by two routes using material grown by MOCVD in the GaAs/GaAlAs materials system. High internal quantum efficiencies have been achieved in both a simple junction isolated device and in a high specification proton isolated LED.

Measurements have been made of the frequency modulation parameter for a number of distributed feedback lasers at various frequencies and output levels. The results are interpreted in terms of a computer model for DFB lasers and the influence of lasing gain on the optical parameters.

Electric current may be measured very conveniently by utilising the Faraday magneto-optic effect in a monomode fibre looped around a conductor. Devices based on this idea presently suffer from a sensitivity to vibration. This paper explains the nature of the vibrational sensitivity, and proposes a number of techniques which could reduce it to acceptable levels.

We describe a range of fibre optic techniques for the control and measurement of optical polarisation state. These techniques are illustrated by a range of experimental applications including time-resolved optical activity measurements, dual-component laser velocimetry, and magnetometry by Faraday rotation.

This paper analyses on the effect of coherent backscatter on the output of the fibre optic gyroscope. By considering the phases and modulation efficiency of the backscatter beams, the analysis shows that Inertial Navigation performance should be able to be achieved by using relatively long coherence length sources, thus easing source wavelength stabilisation. The fundamental limit to the backscatter noise is shown to be due to the scattered components which are incoherent with the primary beams. The effect of the components which are coherent with the primary beams can be eliminated by use of the correct modulation frequency or polarisation control and tuning of the loop coupler.

The fiber gyro, utilizing the Sagnac effect and under development since the early 1980s, has reached production status as a low-cost rotation rate sensor for various high volume applications, satisfied by drift rates of 10°/h and more. Lower drift rates will be offered by series production fiber gyros within the next two years. Principles, technologies and performance data of SEL fiber gyros are discussed, as well as some principal applications. The paper introduces also the concept of a new class of inertial fiber motion sensors based upon the Kennedy-Thorndike interferometer. Such sensors for inertial velocity can enable inertial strapdown navigation without accelerometers.

The paper describes a technique for minimising the retro-reflections from pulsed-reflectometric optical fibre sensors which may return into a single mode semiconductor laser source. The reported system is pulsed using a Bragg cell, whose drive signal is adjusted to ensure that it does not diffract when light returns from the sensor thereby preventing re-entry into the laser. Using this technique, together with feedback control of the laser drive current, spectral purity and low phase noise of the source can be maintained.

For overcoming the ambiguity of fringe counting in fibre optic interferometers with remote readout two phase shifted (π/2) interference signals are produced employing the residual birefringence of non-ideal monomode fibres. A simple logic circuit determines the sign of the measurand change corresponding to the sign of the phase shift and feeds the counting pulses into an up-down counter. The method is tested by strain measurements with jacketed as well as bare sections of fibre employing a Mach-Zehnder setup.

A novel turbine flowmeter has been developed which by means of a fibre-optic pick-up, provides a completely passive measuring system for gas and liquid flows. A special modification to the standard rotor assembly utilises a magnetic coupling to generate a mechanical motion outside the flowmeter body. The induced periodic displacement is detected optically by a reflective sensor. A modulated signal, whose frequency is proportional to flowrate, is then transmitted via optical fibres to a remote detector. The detector unit can provide either a standard pulse output or convert the signal into flow units.

An inexpensive reflective displacement sensor with optical fibre links has two light output levels which switch when the measurand reaches a preset value. An autoreferencing unit monitors the light from the sensor at one level and continuously updates the system gain to compensate for intensity changes. Prototypes have been built; the paper presents results of repeatability trials.

As the technology of optical fibre telecommunications matures, STC is establishing a leading position in the supply of long haul sub-sea cables and systems. Optical fibres, however, may be used not only for the transmission of data, but also for the acquisition of data (sensing), and by transmitting optical power down a fibre actuation may be achieved.

This investigation and those of other workers indicate that longitudinal fibre gratings with potential as Bragg reflectors can be written optically with guided powers of a few milliwatts. The observations reported here were made using a HeNe laser and demonstrate that the photosensitivity of germanium doped silica is not very frequency dependent. An analysis is made of the energy considerations underlying grating formation and it is concluded that about 1 MJ mole-1 is scattered or absorbed in the core of a fibre when a grating is formed.

The fibre optic displacement sensor described is capable of measuring displacements in the millimetres to metres range. It is based on multimode fibre and connectors, uses an LED source and is insensitive to changes in attenuation in the cables and connectors used. The output is conveniently in the form of an electrical frequency. The theory is discussed and preliminary experimental results are presented.

In this work the use of fluorescence techniques for temperature sensing by optical means are reviewed and some devices described. Consideration is given to a range of suitable fluoresing materials for temperature transducers and those based on chromium and neodymium doped materials are described. Both fluorescence decay-time and fluorescence referenced absorption techniques are discussed and the results obtained from transducers constructed on those principles presented.

A new approach to the measurement of D.C. parameters using optical fiber interferometry is reported. The technique is based on a sensing configuration in which displacement, or linear strain in a transducer, is nonlinearly transposed into fiber strain and thus optical phase shift. An accelerometer based on the technique exhibits a detection sensitivity better than 1 μg and a dynamic range > 2x106.