Although the vast majority of work on optical fibers is concerned with their use as a communication medium, there has also been a significant amount of effort devoted to the use of fibers as sensors or as components in 1 sensor systems. This paper presents a review of some of this work on fiber sensor systems.
This paper discusses the installation of a fiber optic entrance link in operation for nearly one year at Alabama Power Company's Barry Generating Plant. Optical and electronics selection and installation of this system are shown to be straightforward and trouble-free. The reasons why optical entrance links are the first electrical utility application to become technically and economically practical are reviewed. An economic analysis compares optical entrance link systems with conventional protection systems. This analysis shows that fiber optic entrance links should be used in the majority of future utility installations.
Fiber optic transmission is currently being used in a variety of applications. In many of these applications, a link analysis is required to determine whether the fiber optic link meets dispersion and attenuation requirements. Two applications that require link analysis are long distance point-to-point links operating at high data rates such as interoffice telephone trunks, and data bus applications where many subscribers connect to a high data rate transmission medium for multi-point distribution.
Coaxial cables that carry data over long distances, say 500 to 3000 miles, require repeaters every 20 miles, more or less, depending on the information bandwidth and cable design. The same coaxial conductors may also carry dc power to the repeaters, and usually this additional function has little if any effect on the design of the cable as determined by rf considerations. The situation is very different when fiber-optic cable is used in the same application. Conductors and insulation for repeater power are a major factor in cable size and cost. This paper reports optimum sizes of conducting and insulating layers for repeater power. The resulting cable design is suitable for a benign environment. However, most routes of practical interest impose extra requirements such as strength and armor that increase the cable size and cost beyond our estimates, which serve as a base from which to upgrade the design. For example, we find that a basic cable 3000 miles long, powered from only one end can be less than a quarter inch in diameter. In all cases the optimum design varies along the length of the cable. Repeaters are connected in series, and so the insulation is thickest near the power supply where voltage is highest. The optimum conductor crossection tapers the other way being thinnest near the power supply.
The YAV-8B Electromagnetic Immunity and Flight-Test Program was established to evaluate the susceptibility of wire and optical fiber signal transmission lines to electromagnetic interference when these lines are installed in a graphite/epoxy composite wing and to demonstrate the flightworthiness of fiber optics interconnects in the vertical/ short takeoff and landing aircraft environment. In response, two fiber optic systems were designed, fabricated, and flight tested by McDonnell Aircraft Co. (MCAIR), a division of the McDonnell Douglas Corporation, on the two YAV-8B V/STOL flight test aircraft. The program successfully demonstrated that fiber optics are compatible with the attack aircraft environment. As a result, the full scale development AV-8B will incorporate fiber optics in a point-to-point data link. We describe here the fiber optic systems designs, test equipment development, cabling and connection requirements, fabrication and installation experience, and flight test program results.
This paper describes an optical data link designed to meet high performance, reliability, and cost requirements at 1.25 and 10 Mb/s. Several new technologies are embodied in this design. This link utilizes a fast, broad-area, low-brightness light-emitting diode (LED) optical source, a low-loss optical fiber having a large core and high numerical aperture (N.A.), and a PIN photodiode detector. Rather simple circuitry is used to drive the LED and to regenerate the received optical signal at the PIN. The optical interfacing hardware is designed to provide simultaneous transmission of the optical and electrical signals, making the optical data link compatible with mainframe hardware and providing relocatability and reduced installation costs. The data link has met the various performance specifications for point-of-sale (POS) terminals in the laboratory, and it is presently being evaluated more extensively.
Fiber optic inertial frame rotation sensors based upon the Sagnac Effect offer the possibility of advantages in production cost, operating lifetime and performance over traditional spun mass and non-waveguide laser gyro's. A number of design approaches are possible which fall broadly into the two categories of single and dual-frequency inter ferometers. A feature in common to all is the need to control the relative phase of the counter-propagating waves at certain points within the sensors by introducing a nonreciprocal phase bias. This paper discusses the family of possible design approaches.
To overcome the hazards of electrical sensors in explosive environments, passive optical sensors using fiber-optic communication to a remote monitoring station are being seriously studied. Development of three passive optical sensors to measure liquid-level, pressure, and temperature in cryogenic propellant tanks is described. Characteristics together with results obtained from an experimental model incorporating those sensors and operating with liquid nitrogen as the test fluid are identified.
The rapid advances in fiber optic communications over the past few years have generated increased interest in the computer industry to evaluate and use this technology. A number of prototype links for the interconnection of data processing equipment have been fabricated and successfully tested in data transmission applications. The features of fiber optic links utilized in these applications have primarily been freedom from electromagnetic interference and smaller, lighter cables. Future applications are also likely to take advantage of fiber link features such as high bandwidth and low attenuation. This paper reviews the status of fiber link component and application activity as it relates to today's local data network environment and then suggests how new system designs might take more significant advantage of fiber optic technology.
The steadily increasing number of microprocessor controlled devices such as intelligent terminals, numerically controlled machines, etc. created the need for new approaches to the problems associated with distributing processing functions. Optical communication devices could be used in order to develop new methods to facilitate the distribution of tasks and programs among a large number of small and relatively slow machines. The essence of the approach should be to find means "to pay with bandwidth and low self induced noise" for simpler and more flexible implementation of task and program distribution. An analysis has been conducted leading to the formulation of the relationship between bandwidth, protocols, and topologies. It appears that ring and common bus topologies are the most suitable for implementation utilizing optical communication channels. An experimental fiber optic based loop system has been designed and constructed. The current realization operates at 20 Mb/sec and affords a 255 unit addressing space. The addressing space can be arbitrarily divided into physical and functional addresses. Mechanism for controllerless operation has been developed and tested. The current data rate can be increased to about 200 Mb/sec without major design changes. Measurement, simulation and analytical results are reported.
Optical multiplex technology, presently in vogue in many segments of industry, is now under scrutiny at General Motors. We are evaluating this technology as a means of simplifying the vehicle harness, reducing weight, eliminating electromagnetic interference, and providing drastically new interior styling options. Door, seat, steering column, forward and rear harness vehicle assemblies, are replaced with a single fiber optic cable in each area. A four bit microprocessor at the top of the steering column, and in each door, multiplexes control console button commands over fiber optic cables. A microprocessor at the other end of the cables decodes the optical signals and operates seats, windows, windshield wipers, etc.
The unique requirements placed on an optical fiber data system in space are briefly reviewed in this paper. These include temperature extremes, particle radiation, and, in some cases, a stringent electrical power budget. An overriding need is for the best possible reliability. Results related to the power consumption of a fiber terminal pair are reported, with the conclusion that a 32-port transmission star bus configuration could be operated error-free at 10 Mbits/s on 1/8 watt per transmitting terminal. The design of a transmitter terminal optimized for low idling power consumption is discussed. Although the electronic elements on a spacecraft are protected, the fiber cable may be subjected to large temperature extremes. Measured effects of temperature on fibers and cables are discussed and related to bus design. Radiation effects are briefly reviewed, with special reference to the long-duration low dose rate environment of a spacecraft.
To increase the signal carrying capacity of a transmission system, it is customary to multiplex input signals into the system. At the receiving end of the transmission system, the signals are separated from one another and processed into their original form. There is a limit to the amount of information that can be transmitted in this manner in a single transmission system channel.
This paper presents a review of recent research and development in high radiance LEDs intended for use as sources in optical fiber communications systems. Development in the last decade has resulted in reliable devices for use in the 0.8 to 0.9 μm wavelength region based on the AlxGal-xAs-GaAs double heterostructure material system. Both high-power and wide-bandwidth LEDs have been produced. Near-optimum performance of small area surface emitters (Burrus diodes) as well as edge emitters has been obtained. The paper will describe new trends in improving LED-to-fiber coupling efficiency, methods for reducing the nonlinearity of LEDs for analog applications, degradation mechanisms and device life. Recent achievement in long wavelength LEDs and PIN photodiodes has led to the development of a second generation of LED-fiber systems for operation at 1.3 μm wavelength, with data rates as high as a few hundred Mb/s and repeater spacings (or data link spans) of many kilometers.
The major types-of AlGaAs laser structures that operate single-mode in cw operation are reviewed. The principles of spatial-mode stabilization are presented. The laser structures are divided into two categories according to their output powers for safe, reliable operation:. low-power (1-7 mW/facet) devices and high-power (15-30 mW/facet) devices. The performances of typical structures are described and experimental results relevant to single-mode operation are displayed. Finally, the devices' dynamic behavior, as related to their use in optical communication systems, is briefly discussed.
The advantages and properties of InGaAsP laser diodes in the 1.0 - 1.7 μm spectral region are discussed. The structure, growth (both vapor and liquid phase epitaxy) and operating principles of these devices are briefly reviewed. State of the art device results from 1.3 and 1.55 μm devices are then presented. The modal, thermal and reliability properties of these devices, as well as their commercial availability, are also discussed and possible directions for future applications are considered.
The current state of the art of photodetectors, both PIN and avalanche, for 1.1-1.6μm operation is reviewed. The devices are compared as components of optical receivers using several different types of amplifiers. GaInAsP/InP PIN and APD detectors are shown to be clearly superior to Ge devices with respect to dark current and potentially so with respect to other sources of noise. Receivers with performance within a few dB of the quantum limit appear to be possible with current technology.
A central advantage of optical communication over cable technology is the potential for long distance transmission at very high data rates. Above 200 Mb/s the modulation capability of the laser source becomes a significant factor in establishing system performance. We review here the current understanding of phenomena which limit laser diode performance at high data rates in fiber optical systems.
Significant improvements have been achieved in recent years in the transmission characteristics and the mechanical performance and environmental performance of optical fibers and cables which have broadened the applications of fiber optic systems. Fiber optic cables are finding increasing acceptance in a wide variety of applications such as tactical field (military), computer interconnect, telecommunications, antisubmarine warfare, submarine, airborne, and missile guidance. This paper describes the mechanical and environmental design considerations in order to meet the multitudinous requirements for fiber optic cable installation in ducts, plowed-in and aerially strung.
Improvements in optical waveguide manufacturing processes have reduced the attenuation rate to approximately the material limit imposed by Rayleigh scattering. Today there is a need to develop measurement techniques or Procedures which can be used to predict the overall system insertion loss and bandwidth. Multimode propagation in graded waveguides makes it difficult to define the attenuation rate and bandwidth without referencing the particular source Power distribution used in making the measurement. This paper will discuss the problems in making these measurements and will present a recent model and results which can be used to predict system performance.
The emergence of optical fibers as an important communications medium has created the need for standardized test procedures for evaluating fiber transmission characteristics. In this paper we will review some of the standardization efforts aimed at improving the agreement between optical fiber measurements made at different locations. We will also outline the characteristics that a standardized test procedure should have to be useful to the fiber optics industry. In addition, the procedures followed in an industry wide round robin measurement study will be described to illustrate the current status of standardized fiber optic loss measurements.
The technology of telecommunications via optical cables is reaching a first stage of maturity. One indication of this is the emergence of standards relating to the construction, materials, performance and testing of cables. The purpose of such standards is to provide assistance and guidance to both users and manufacturers in the generation and interpretation of cable specifications. In this paper we have attempted to illustrate with examples the type of standards which are emerging for telecommunications cables. Primarily the standards activities have concentrated on two areas: 1) the construction of cables, and 2) the performance testing of cables. The content of this paper is based primarily on the standards work of two particular groups but can be considered representative of the overall activities.
An unofficial discussion of the status of interconnect standardization is presented. It includes an over-view of U.S. and international status in such groups as the EIA P-6 and IEC SC-46E committees. The rationale for choosing the 4 tier system is explained, along with a table showing the structure of the system, as Basic, Generic, Sectional and Detail specifications. The implications of the recent OMB Circular A-119 on Federal Participation in the Development and Use of Voluntary Standards is discussed, particularly as it amplifies the already pressing question of adequate level of resource commitment to the standards question activity.