An investigation is made into the options for digital video distribution in the LAN or local network environment with a view to providing two-way interactive video services for each customer on the network. Limitations of present access protocols and topologies are discussed and possible ways around these limitations are presented.
Our firm has developed the SUMINET-4100 series, a fibre optic local area network (LAN), to serve the communications system trunk line needs for facilities, such as steel refineries, automobile plants and university campuses, that require large transmission capacity, and for the backbone networks used in intelligent building systems. The SUMINET-4100 series is already in service in various fields of application. Of the networks available in this series, the SUMINET-4150 has a trunk line speed of 128 Mbps and the multiplexer used for time division multiplexing (TDM) was enabled by designing an ECL-TTL gate array (3000 gates) based custom LSI. The synchronous, full-duplex V.24 and V.3.5 interfaces (SUMINET-2100) are provided for use with general purpose lines. And the IBM token ring network, the SUMINET-3200, designed for heterogeneous PCs and the Ethernet can all be connected to sub loops. Further, the IBM 3270 TCA and 5080 CADAM can be connected in the local mode. Interfaces are also provided for the NTT high-speed digital service, the digital PBX systems, and the Video CODEC system. The built-in loop monitor (LM) and network supervisory processor (NSP) provide management of loop utilization and send loop status signals to the host CPU's network configuration and control facility (NCCF). These built-in functions allow both the computer system and LAN to be managed from a single source at the host. This paper outlines features of the SUMINET-4150 and provides an example of its installation.
The Fibre Distributed Data Interface (FDDI) is a flexible, high-speed token-passing twin ring network which is being specified by ANSI to provide synchronous and asynchronous data transmission, as well as isochronous channels for real-time digitised speech and video. Unlike existing open standard LANs, where fibre optic variants have been introduced following successful implementation on conductive media, FDDI has been designed from the start as a fibre optic network. This has involved issues of standardisation in such areas as duplex optical connectors, fibre characteristics, optical bandwidth, bypass relays and keyed cable assemblies. This paper gives an overview of the fibre optics aspects of the development, including the overall optical design, special component requirements, and practical issues of application.
A structure for OSI levels 1 and 2 of a local area network suitable for use in a variety of industrial environments is reported. It is intended that the LAN will utilise optical fibre technology at the physical level and a hybrid of dynamically optimisable token passing and CSMA/CD techniques at the data link (IEEE 802 medium access control - logical link control) level. An intelligent token passing algorithm is employed which dynamically allocates tokens according to the known upper limits on the requirements of each device. In addition a system of stochastic tokens is used to increase efficiency when the stochastic traffic is significant. The protocol also allows user-defined priority systems to be employed and is suitable for distributed or centralised implementation. The results of computer simulated performance characteristics for the protocol using a star-ring topology are reported which demonstrate its ability to perform efficiently with the device and traffic loads anticipated within an industrial environment.
Cost has been the barrier to using fiber optic links in low datarate, short haul applications of less than 5 Mbaud and up to 150 meters. New fiber optic links using plastic (acrylic) fiber, however provide a cost effective alternative to coaxial cable and twisted wire pairs in such applications. The large core fibers with a diameter of 1 mm do not require the tight alignment tolerances needed in glass- or plastic clad silica fibers for reasonable light coupling at the source and detector interfaces. Looser alignment tolerances also let manufacturers package transmitters and receivers in plastic housings, thus lowering component costs.
A topic of the paper is fiber-optic integrated network (FOIN) suited to the most hostile environments existing in coal mines. The use of optical fibres for transmission of mine instrumentation data offers the prospects of improved safety and immunity to electromagnetic interference (EMI). The feasibility of optically powered sensors has opened up new opportunities for research into optical signal processing architectures. This article discusses a new fibre-optic sensor network involving a time domain multiplexing(TDM)scheme and optical signal processing techniques. The pros and cons of different FOIN topologies with respect to coal mine applications are considered. The emphasis has been placed on a recently developed all-optical fibre network using spread spectrum code division multiple access (COMA) techniques. The all-optical networks have applications in explosive environments where electrical isolation is required.
The source and receiver requirements for a coherent optical communication system are outlined and the performance of a practical system using readily available distributed feedback (DFB) semiconductor lasers is described. Techniques for reducing the linewidth of these lasers are presented.
A polarisation tracking heterodyne optical receiver is reported which uses a dither technique to achieve the required polarisation control and performance measurements in a 70 Mbit/s ASK system are presented. Other techniques for achieving polarisation insensitive coherent detection are outlined and compared with the polarisation tracking receiver.
A miniturized D( to 300Mb/s optical transmitter and receiver modules have been developed. The optical transmitter utilizes an InGaAsP/InP surface emitting LED (the center wavelength is 1315nm) as a light source. The pulse width distortion is maintained less than ± 0.2nsec because the compensation circuit is employed to adjust the LED's response. The optical receiver utilizes an InGaAs/InP PIN-photodiode which responsivity is 0.82A/W for 62.5/125 GI 0.29NA fibers. Pre-amplifier using a Si-IC, has a transimpedance of 10kΩ and bandwidth of 200MHz. Automatic Threshold Control (ATC) circuit utilizes high speed peak-hold circuit technique to respond to burst signal within several handred nano-seconds. And in order to prevent the appearance of error pulses at extinct input, Automatic Threshold Bias-level Control (ATBC) circuit is employed. By the use of ATC and ATBC circuit, the receiver can receive the burst optical signal, which include a continuous extinct level, in short settling time and slight pulse width distortion.
Combining appropriate zero-order and first-order fields in an overmoded optical fibre, produces an offset intensity distribution whose radial position varies with their relative phase and polarization. This may be used to achieve phase (or polarization) diversity detection in a coherent optical receiver, by detection of this intensity distribution on a four segment photodetector. In-phase and Quadrature signals (or orthogonally polarized signals) are produced from each diametrically opposed pair of photodiode segments.
The most interesting feature of the new videocommunication networks is their ability to carry interactive services in addition to the classical distributed ones. This is achieved using various architectures which are discussed here together whith their main characteristics. As services and traffic demands are expected to expand over the next years, the technical solutions must lead to upgreadable network capacity. Several upgreaded network architectures are presented including fiber share and the emerging coherent techniques. Finally, a technico-economic approach is made based on a common geometrical model, in order to distinguish the most cost-effective configurations.
Optical fibres are making ever-increasing inroads into areas traditionally satisfied by older, more established technologies. In particular, sensors which rely on the external modulation of the properties of an optical fibre (intrinsic sensors) are receiving much attention since they can be made extremely sensitive and can be used for distributed measurements. Distributed sensing provides some particularly exciting prospects for acoustic, magnetic and electric field monitoring. To date, however, the great majority of experimental and commercial fibre sensors employ telecommunications-grade fibres, largely as a result of their ready availability. Not only does this policy frequently lead to a design compromise, but in some cases makes the performance marginal or untenable as a result of excessive environmental sensitivity. Consequently, attention is now being given to the design of special sensor fibres with enhanced (or depressed) sensitivity to specific measurands.
A quarter of a century has elapsed since the emergence of ruby laser invented by Maiman in 1960, the optics industry achieved a marked evolvement to support the basis of the in-formation society, and served as a member of the hightech industry constituting the kernel of industrial structure.
The applications and advantages of optical fibres in the military field are reviewed. The role of DTE in providing a mechanism for civil exploitation of MoD technology is discussed together with selected optical fibres cases on the DTE database.
Over the past several years, electric utilities operating within the United States have become interested in diversifying into the commercial telecommunications business by constructing fiber optics systems primarily in the static wire of their transmission systems. This paper will discuss how legal and regulatory obstacles were overcome by American utilities which have entered this market. It will conclude with an assessment of the steps which must be taken by a utility in order to enter the telecommunications market.
A technology for the integration of optical waveguides in a glass substrate through photolithography and ion exchange has been successfully developed. This technology is a very good candidate for the mass production of performant branching devices such as couplers and Wavelength Division Multiplexers (WDM's). A description of the process and the results achieved on optical components are given. The advantages of the technology are discussed and the status about its industrial implementation is given.
The difficulties in deciding whether a fibre optic is suitable for use where it might be exposed to ionizing radiation are discussed. Some recommendations are made regarding the interpretation of test data and the subsequent prediction of fibre behaviour.
Large numbers of passive fibre components (PFC) are required in multinoded networks, built in multimode graded-index fibre. A new technique, called Fused-Head-End (FHE), for manufacturing N-to-M splitters and couplers has been described. The physical properties are studied in terms of modes and mode conversion. If coherent sources are used, modal noise is unavoidable. The mechanism of the PFC in generating modal noise is quantified. The FHE splitter/coupler directly pigtailed to a LED, allows hierarchically structured ring networks and switches to be made which are self-routing. The FHE technique can also be applied to make single-mode PFCs. The first experimental results of a device to be used as a (de)multiplexer and splitter/coupler are reported.
A two-axis magnetically levitated actuator is configured as an optical fiber micro-manipulator. Noise equivalent displacement capability of 0.01nm//Hz is demonstrated, with absolute positional stability of the order of 0.1μm°C, guaranteeing effectively perfect coupling of singlemode fibers to themselves and to thin-film waveguides. Freedom from mechanical stops allows coupling to 16 or more output fibers to effect a 5ms switching operation, and continuous coupling optimization under software control.
Use of optical fibres for sensors and gyroscopes require a number of in-line components. One important device is a polarising element. We report here design considerations using polished fibre substrates with dielectric or metal overlays. The first type of design involves use of a high index planar dielectric film to selectively couple out TE-polarised light from the polished region of a fibre coupler block. The second type of design employs metal films and polarising action is achieved by coupling to surface plasma waves or the w+ resonance in very thin metal films.
The demand for branching devices for use in optical fibre systems is increasing rapidly with the expansion of such systems into the broadband subscriber loop, local area networks and data links. This paper describes a number of all-fibre single mode devices, based on the fused biconic branching coupler design. The paper highlights the versatility of such devices in providing certain functions such as switching and wavelength division multiplexing which are particularly suited for use in broadband systems.
Two experimental fibre components are described which exploit the properties of highly birefringent monomode optical fibre. In the first the generation of a travelling ultra-sonic flexure wave on the fibre produces a frequency shift of the input optical signal. In the second a variable axial tension modulates the differential phase retardance between the two guided polarisation eigenmodes to produce an arbitrary output polarisation state from a linear input state (or vice versa) without loss of optical power.
Novel opto-electronic signal processing schemes for the measurement of ac and dc electric currents via the Faraday effect in monomode optical fibres are described. The problems associated with operating point drift and signal fading due to environmental perturbation are addressed and success in the laboratory environment is demonstrated. For several of these processing schemes, optical data buses are demonstrated employing transducers with zero optical power consumption.
The design, construction and testing of a fibre optic pressure sensor based on a reflecting Fabry-Perot etalon is described. The etalon comprised one fixed mirror and a second mirror designed to flex under the action of the pressure being monitored. A single multimode fibre was used to connect the passive, remote sensor to the transmitter/receiver section, and dual wavelength referencing was used to eliminate the effects of bending-induced attenuation in the fibre.
An experimental pressure sensor for pressures up to 1000 bars is described, in which a side-hole fiber is exposed directly to an unknown hydrostatic pressure. The cross-section of the fiber resembles that of a PANDA fiber but it has two open channels in place of the stress applying parts. A hydrostatic pressure acting from outside on the fiber builds up an anisotropic elastic stress in the fiber core which elasto-optically induces birefringence. The resulting phase delay, which changes linearly with pressure, is counted bi-directionally in a polarimetric setup. Thus the sensor operates in an incremental mode. With a pressurized fiber length of 10 cm, a phase sensitivity of 7.78 rad/(bar•m) at X = 1300 nm, and a resolution of the optical phase of 7/2, a pressure resolution of π/2 bars is achieved. In the pressure range of 100 - 1000 bars where unambiguous phase evaluation is possible, the overall accuracy is better than ± 0.5%. In one fiber, phase evaluation becomes ambiguous below 100 bars, near the point where the birefringence vanishes.
Fibre optic distributed pressure sensors will play an increasingly large role in safety devices for automation systems due to their inherent 'fail to safe' characteristics, freedom from environmental noise, and small size. Distributed microbend sensors provide the first volume applications of optical sensors for this market. Details of control systems and products will be discussed as well as advances in the state-of-the art.
Optical fibre and sensor based systems have been developed for monitoring in industrial environments where conventional instrumentation is either prohibited or inoperative because of a variety of hazards or difficulties. The systems are based upon sophisticated forms of wavelength encoding but nonetheless utilise robust and inexpensive instrumentation. They have a major attraction of utilising unified instrumentation for monitoring a variety of parameters. Preliminary results from two industrial on-site demonstration projects are presented. These involve monitoring pressure, temperature, mass density, radiation and rotary speed at a chemical plant with an explosion hazard and an electric power testing plant with extra high voltage and severe electromagnetic interference hazards. Both applications require long term monitoring reliability for pressure and temperature which the demonstration projects have shown to be within the capability of the newly developed system technology. The application of such optically based monitoring systems already promises to lead to significant improvements in production efficiency at the chemical plant and to reduce outage times and saving in servicing costs of in service circuit breakers.
Fibre optics can offer several advantages for sensing applications in vehicles. Electromagnetic immunity is very attractive for both data transmission and sensing applications, particularly in the region of the engine compartment. Fibre optics will have their greatest impact where their use enables engine parameters previously inaccessible to be monitored. This paper discusses the application of fibre optics to various aspects of internal combustion engine monitoring including combustion sensing and in-cylinder pressure measurement. Analysis of intensity of the light emitted from combustion of the fuel in the cylinder allows a number of parameters of combustion to be measured and experimental results are presented. Fibre optics provide a remote sensing ability which allows the detection and processing electronics to be mounted in a less hostile environment. A fibre optic pressure sensor is described that offers a simple low cost device providing another useful combustion parameter.
This paper addresses the present state-of-art of practical optical fibre sensors for process control. Results are presented for the first part of a major project to establish fibre optic instrumentation systems for process control on offshore oil rigs. The project, designed in three phases, has an aim to examine different instrumentation concepts, to laboratory test available components, to build and to hold tests of a fibre optic instrumentation system on an offshore installation. The aim of the first phase is: (i) Examining the feasibility of optical fibre instrumentation for process control on offshore oil platforms. (ii) Studying different architectures for a suitable instrumentation system. (iii) Surveying available sensors and components on a worldwide basis. (iv) Testing sensors and other transmission components. The work reported here was designed to investigate the working principles, performance and limitations of commercial sensors and to evaluate possible architectures of a complete instrumentation system.
In the choice of techniques for optical sensing, colour measurementoffers the attraction of intensity independence so that connector and other variable losses are not important. The use of diffraction gratings and zone plates for displacement sensing is well known but the use of such dispersive elements in low cost systems is sometimes precluded by poor temperature stability or high cost. This paper describes an approach to solving these constraints so that colour measurement techniques can find wider application. Colour filters offer a very simple means whereby the perceived colour of light can be varied. Their temperature stability will limit the accuracy of devices built around such filters and experimental data on a variety of filters is presented. A number of examples of the use of filters in sensor designs are given and the limitation of accuracy and resolution discussed. The advantages of the use of filters for colour modulation optical displacement sensors include the inherent flexibility offered by the design and their potentially low cost.
Several on-off optical fibre temperature probes have been designed with liquid crystals as thermosensitive dements. These probes have been multiplixed with succes in a two sensors system. When the OTDR technics is used as signal processing it can be shown that an internal signal reference exists. Light intensity fluctuations effects on the sensors can be efficiently cancelled
A rotating scanner prototype wich allows to multiplex a number of optical fiber sensors is described. In order to alleviate radial and axial tolerances, the device makes use of quarter pitch graded index lenses. Considerations on insertion losses are made. The system has been tested by using thermochromic temperature sensors. Details about design and experimental results are reported.
This paper describes a novel fibre optic methane sensor which has several advantages over previously published fibre optic techniques. It is based on a scanning Fabry Perot etalon filter and is self-referencing, requiring only a single optical sensing path and photodetector. A laboratory version of the sensor, employing a white light source, has been constructed and tested, and was found to be capable of detecting 0.25% by volume methane in air, with a response time of approximately 1.5 seconds.
A number of optical and opto-electronic techniques have been developed for the demodulation of inthrferometric fiber optic sensor (IFOS) in recent years. Many of these techniques allow passive operation of the actual sensor, and may find application in certain IFOS multiplexing topologies. This paper will briefly review IFOS demodulation techniques, highlighting which are applicable to multiplexing, and comparing practical performance features such as sensitivity, bandwidth, dynamic range and linearity. Recent advances in the area of passive demodulation and multiplexing will then be discussed.
A novel fibre-optic temperature sensor using the red fluorescent emission from ruby crystal, wavelength separated to provide a temperature variant region and a self-generated reference region is described. The principle of this device relies on separating optically the R-line, the variant quantity, from the total emission, which is used to supply the reference. The ratio of the two quantities is then taken to give an accurate temperature measurement which is then calibrated against a standard thermometer. From the calibration curve, a linear profile is seen in the temperature range 293 to 433K and the accuracy of the probe was recorded to be +3K with the response time limited by the mechanical construction in this early work. The upper range level is limited by deviation in the quantum efficiency about 500K.