Guided optical communications using glass optical fiber waveguides is a rapidly growing field. In this paper a discussion of the transmission characteristics of the optical fiber will be given. This will include first a description of rays and modes in the waveguide. Attenuation, long the benchmark for judging fibers has its sources broadly grouped into two categories, absorption and scattering. These will be further subdivided into their contributing factors and discussed, giving a summary of the current status of attenuation reduction. The information carrying capacity is potentially limited by two things, differing group velocity for each mode and finite spectral width of the transmitted light. These will be discussed, showing the effect that material properties and the radial index gradient have on information bandwidth. In the multimode waveguide energy may be transferred between modes during transmission. This can be beneficial by causing the information capacity to decrease only as the (fiber length)12 rather than directly as the fiber length as in the case of no mode coupling. It can also be detrimental since there is an additional attenuation associated with mode coupling. This effect will have an impact on fiber parameters as well as on fiber packaging and will be discussed.

Several methods of fabricating optical waveguides which are currently being studied will be described. This will include a discussion of the doped deposited silica techniques being used in the preparation of commercially available low-loss fibers, and other techniques presently being developed, such as double crucible melting techniques, plastic-clad glass fibers, and rod-in-tube techniques. The impact of the fabrication technique on such fiber performance parameters as peak refractive index difference, index gradients, dispersion, attenuation and durability will be explored. The economics of the various process will be superficially examined in terms of raw materials costs and availability, as well as their purity requirements.

This paper reviews in a tutorial fashion the coupling of radiation from electrolumi-nescent sources into fiber waveguide transmission lines. A brief discussion of the splice coupling and data distribution components is also presented.

This paper is divided into four subsections: 1) LED Source Components, 2) Source Modulation Electronics, 3) Photodetector Components, and 4) Receiver Electronics. The important characteristics of LED source components are discussed, both qualitatively and quantitatively. Edge, dome, flat, Burrus, and miniature-lensed Burrus LED types are identified, and performance parameters available from each are comparatively tabularized. The source modulation electronics discussion is divided into analog and digital categories. Two practical linear IM driver configurations are presented (low and high frequency), and practical, digital low and high bit rate driver configurations are presented. The design considerations underlying each circuit are discussed. Solid-state optoelectronic detectors of interest in fiber optics communications fall into the two general categories of avalanching and nonavalanching (PN/PIN). Available performance in several key parameter areas is quantified for both types. The receiver electronic configuration discussion begins with examination of a general block diagram and brief description of each function. Focus is then concentrated on the transresistance preamplifier function, with the presentation and parameter comparison of four practical preamplifier configurations (including two hybrid preamplifiers). A graph showing the available system NEP performance versus avalanche gain with one of the best available avalanche detectors is presented.

Guided Optical Cable System design methodology is developed by considering the application criteria and the interactive process of performing system-level conceptual design trades. The design impact of user performance requirements and other user considerations are identified, and practical examples of user evaluation criteria are presented. The cyclic process of interacting component hardware capabilities with system-level design implementations is presented by defining the interaction of spatial and electronic multi-plexing, frequency-division multiplexing and time-division multiplexing, and baseband analog and digital modulation base trades. Optical link budgets for these implementation concepts are presented to show the effects of source power, source line width, optical cable losses and dispersions, and receiver sensitivities. The paper is concluded with an example that shows the use of guided optical communications systems is best optimized when inherent characteristics are exploited by the conceptual designer.

Optical fiber waveguides are being employed in several communication systems of moderate bandwidth and length. For example, Nippon Electric Company(I) has reported on a 7.6 Mb/s system operating over 2.3 km using SELFOC fiber waveguide while U. S. Naval Electronics Laboratory Center (2) has installed a 44 MHz closed circuit TV system and a 108 kHz, 6 telephone system both several hundred feet long. GTE Labs(3) reported on a short length T-2 (6. 3 Mb/s) system. Others will be described in this conference. (4) The full potential afforded by the characteristics of optical fiber waveguide transmission such as wide bandwidth, noise immunity, small size and weight has not been reached as yet. More studies of its feasibility in various applications are required, and here the suitability of wide-band signal transmission over optical fiber waveguides is examined.

Due to rapid progress in optical fiber transmission, application in many long distance communication systems is within the scope of demonstrated technology. This paper summarizes the important technical factors which make up a large portion of the system trade-offs. Such items as required repeater power and repeater spacing versus bit rate for PCM are presented.

This paper discusses the most important factors involved in the design of an optical fiber communications link. The system signal-to-noise ratio is determined by many factors, including source power, source-fiber coupling efficiency, and fiber losses. Noise arising in such links, especially that related to detection, is treated in some detail. In addition to signal-to-noise considerations, system components must be chosen to provide the necessary fidelity of information transmission. Sources and detectors have limited frequency responses, and various dispersive effects are associated with light propagation in fibers. A representative link design is made to illustrate these various factors. Although many things must be considered in optimizing the design of a practical fiber link, an understanding of those treated above permits a realistic estimate of the characteristics and potentialities of optical links to be made for any given system requirement.

Information systems using optical waveguides consist of electro/optical and opto/ electrical converters, the fiber optic cable and connectors. The paper describes the application requirements determining the scheme of a signal transmission link via optical waveguides, as e.g. kind of transmission, bandwidth, transmission length and number of channels. All the fiber optic components are developed as parts of a construction kit. Corresponding to the application requirements these components can be combined to different signal transmission links. In detail the realization of one fiber optic link in the field of non telephone application is given. For the electro/optical control of thyristors in a high voltage direct current transmission plant, especially the undisturbed signal transmission at high potential differences is required. A digital transmission system up to 1 Mbit/s is re-alized with available LEDs and PHDs and with fiber optic bundles having a transmission loss of 1 dB/km.

This paper presents a comparison of the performance of optical communication links employing analog pulse-position modulation and analog intensity modulation. In particular, the theoretical output signal-to-noise ratios for the two types of modulation are compared assuming "equivalent" optical links. Analog pulse-position modulation offers signal-to-noise ratio improvement over intensity modulation at the expense of increased system complexity and expanded transmission band-width. The effect of timing errors on the signal-to-noise ratio of the pulse-position modulation receiver is considered, and it is shown that these errors can degrade performance significantly from theoretical .

A review of Light Emitting Diodes (LEDs) and Injection Lasers (ILs), which are suited as signal sources in Fiber Optic Communication Systems is presented. LED and IL structures and their important operational characteristics, such as efficiency, power out, radiance,spectral emission, and lifetime are discussed.

The basic design principles of radiation emitting diodes are discussed. Theoretical and experimental values of radiant power, radiant intensity, and radiance of GaAs and GaAlAs infrared surface emitting sources are reviewed. A comparison of various device geometries shows that small-area, high-radiance, etched-well emitters are the optimum design for coupling to individual optical fibers but that high-radiant-intensity shaped emitters are the optimum design for coupling to larger diameter fiber bundles. Improved linearity can be achieved with GaAlAs planar emitters incorporating a buried-junction structure to minimize non-radiative surface recombination.

High-speed data links using laser-like LED's, single fiber graded index multimode waveguides, and avalanche photodiodes are described. We describe a new stripe-geometry laser/LED source in which lateral current confinement is achieved by selective diffusion of the n-type substrate prior to the epitaxial growth of the GaAs/GaAlAs layers. Using an H.-P. 3760A/3761A Bit Error Rate system, we observed no errors in a psuedo-random sequence of 1011 bits over a half kilometer fiber at 150 Mbits/sec., the bit rate limit of the H.-P. system. Satisfactory eye diagrams were observed at somewhat higher bit rates. A measurement of the broadening of single laser pulses set an upper limit to the pulse dispersion, for this particular h km fiber, of h nsec/km, which compares to 5 to 25 nsec/km for step-index fibers of similar diameters and index differences. A status report will be presented on an experiment to install a 360 meter cable with six independent waveguide channels thru buried conduit between two laboratory buildings.

Before optical systems are fully operational, repeatable multi-channel quick-disconnect couplings must be a reality. This paper describes the performance and characteristics achieved with a connector for medium loss optical waveguides, "medium loss" being taken to mean 1000 to 100 dB/km and having a numerical aperature of around 0.50. The connectors described are conventional MIL-C-83723, modified to accept optical ferrules in lieu of the standard electrical contacts.

The individual loss mechanisms contributing to the insertion loss of an optical waveguide joint are described and quantified. Losses attributable to the characteristics of individual waveguides as well as losses due to coupling technique are included. The identification and understanding of these loss mechanisms has led to the design of optical waveguide alignment and retention techniques that minimize or avoid these effects. To make a connector useful in field applications of optical cables utilizing these techniques, the hardware must be reliable, stable, low cost, quick, and fully intermateable, as well as providing low insertion loss. Experimental results are given that indicate extrinsic insertion loss as low as 0.3 dB is routinely attainable in each channel of multifiber connections utilizing low-loss optical waveguides.

Optical "T" and Multiple "T" access couplers designed for tapped trunk line multi-terminal communication systems which use bundles of multimode fibers as the transmission media have been investigated. The particular coupler designs tested used bent pyrex rods for bifurcation and scrambling. Coupler throughput losses (not counting packing fraction losses) are 1.5 - 2.5 dB. The bent rod optical "T" and multiple "T" access couplers must be used with high N.A., low packing fraction loss fibers.

Appropriate components have been produced for the conception of communications systems with optical fiber bundles of low active diameter ( (.0500 /um), high numerical aperture (0.5) and medium losses (e?,100 dB/Km). All the components are detachable and terminated with subminiature male connectors. The series include : - Emitter and detector units including LED's, PIN silicon photodiodes and optical couplers enclosed in BNC adapter or with flange mounting. -Complete transmitter and receiver modules with analogic, TTL or ECL compatible ouput/input. - Bundle to bundle mixing connectors permitting standardization of cable terminals and reducing random coupling variations due to fiber breakage and positionning.

The use of fiber optic communications in a modern computing system is investigated. The scope of this paper is limited to intraunit interconnection and the inplant network. The inherent properties (e.g., electromagnetic compatibility, ground level dependence, volume reduction, data rate, delay, etc.) are discussed in relation to the area of usage within a computing system. The evaluation of these properties indicates that the initial usage of fiber optics will probably occur for interunit inplant network interconnection. It is shown that the associated signal delay of a fiber optic link as well as the dissimilar materials technologies will preclude the initial use of fiber optics for intraprocessor interconnection. A representative local inplant data network is analyzed with respect to data requirements and equipment complement. This configuration is used as a basis for implementation of a fiber optic data communication network. Various fiber optic interconnection configurations (e.g., point-to-point, star, multidrop and bus) are investigated. The advantages/disadvantages of these configurations are analyzed and com-parisons made with respect to total cable length and optical loss. This analysis indicates that point-to-point Space Division Multiplexed and Star data configurations are viable in fiber optics interconnection techniques.

A broad class of army communication applications are contemplated for optical waveguides. Of principal interest is the multimode low-loss fiber. A few potential applications include: (a) long haul TDM cable, (b) local distribution cable used to connect telephone users to central switches within a command post, (c) antenna remoting via fiber optic guide, (d) computer interconnections. The cost effectiveness of these cables vs. conventional cable is a critical issue that will be treated in detail within this paper. Exploratory developmental models that utilized a low-loss Corning Fiber within a tactical ruggedized cable are presented. The use of both a LED source and double hetrojunction GaAlAs Lasers is discussed. Also treated is the design of cable modems, interfaces and repeaters.

Fiber optics technology promises to have a substantial impact on Navy communications of the future, eventually superceding electrical cables in many systems. Advantages of fiber optics in military communications include immunity from electromagnetic interference, crosstalk, and signal leakage; large bandwidth for size and weight; ground isolation of terminals; and survivability at high temperatures. Improvements during the past decade in optical transmission lines, transmitters, and receivers have made it possible to consider fiber optics for use in aircraft, ships, land lines, undersea cables, missiles, and satellites. Fiber optics are expected to be utilized in both point-to-point links and multiterminal busses on aircraft, ships, and submarines. The relatively short distances on aircraft make it possible to use high-loss (500-1000 dB/km) fiber bundles for point-to-point links; somewhat lower losses will be needed for data busses. Length and cost considerations indicate the use of low-loss (20-100 dB/km) fibers, with each fiber representing a single communications channel, for most shipboard applications. Some undersea cables, with lengths well in excess of one kilometer, will require very low-loss (<10 dB/km) fibers. Several systems which have been developed or are under development by NELC for use in each of these environments will be described. In each case, the advantages of using fiber optics in comparison with conventional technology will be discussed.

Low loss Fiber Optic Cable is being evaluated as a potential future replacement for Kennedy Space Center's 13,000 mile Wideband cable system. In order to make economical use of the wide bandwidth characteristic of glass fibers, a Frequency Division Multiplexing (FDM) scheme has been devised to stack many analog and digital data channels on a single fiber. The Multiplexed Optical Transmission System (MOTS) will offer a unique flexibility of plug-in modularity to meet changing data and bandwidth requirements in addition to the standard "goodies" of immunity to lightning and other RFI type interferences. and of smaller size and lighter weight.

A lightning instrumentation system was designed to record current magnitudes of light-ning strikes that hit a launch pad service structure at NASA'S Kennedy Space Center. The instrumentation system consists of a lightning ground rod with a current sensor coil, an optical transmitter, an optical fiber cable link, a detector receiver, and a recording system. The transmitter is a wideband pulse transformer driving an IR LED emitter. The transmitter operates linearly as a transducer. A low loss fiber bundle provides isolation of the recorder system from the electromagnetic field of the lightning strike. The output of an optical detector receiver module is sampled and recorded in digital format. The significant factors considered in the design were dynamic range, linearity, mechanical configuration, electromagnetic isolation, and temperature compensation.

A fiber optic delay line system consisting of 10 Corning multimode low loss optical fibers with 60 ns time delay increments has been designed and tested for potential application to a space object imaging system (SOI)*. A brief overview of the optical imaging system application is given followed by the details of delay line design and tests. Both pulsed ruby laser and cw helium neon measurement techniques are discussed and the results are presented. A pseudo attenuation phenomenon observed during the pulsed laser tests and attributed to cladding mode propagation is reported along with techniques for cladding mode suppression. Possible alternative applications of this system are also given.

The recent development of low loss optical fibers has made possible simplified de-livery of visible and near infrared laser light for medical and industrial applications. This paper will discuss several of these applications and the fiber assembly used.