An experimental system that permits interconnection of many offices in a single video conference is described. Video images transmitted to conference participants are selected by the conference chairman and switched by a microprocessor-controlled video switch. Speakers can, at their choice, transmit their own images or images of graphics they wish to display. Users are connected to the Switching Center by optical fiber subscriber loops that carry analog video, digitized telephone, data and signaling. The same system also provides user-selectable distribution of video program and video library material. Experience in the operation of the conference system is discussed.
Fiber Optic Video Links are analyzed in terms of application, performance and cost effectiveness. Comparisons are made between coaxial cable systems and fiber optic cable systems. Fiber types and cable designs are discussed for various applications.
The considerations involved in the optimization of the design of an optical fiber for a data link for missile guidance applications are outlined. An analytical model relating spooling induced excess loss to fiber core diameter is developed. Experimental results describing the effect of fiber core diameter on spooling and coupling losses are reviewed.
The long-wavelength fiber optic transmission system described in this paper uses a two-channel optical wavelength multiplex technique to provide simultaneous bidirectional communication over a 15 km length of optical fiber. The development of molded plastic expanded-beam connectors and state-of-the-art dichroic beamsplitters has made it possible to design simple optical wavelenth multiplex components that are well suited to meet the requirements of a tactical environment.
In a mainframe computing system, the transfer of data between the processor/memory and the input/output/storage subsystems is done on the I/O channel links. With the demands for computing power increasing at above 40% per year, there is an ever increasing demand for more channel links and more performance on the link. Recent enhancements of the channel protocols make it possible to push the data transfer rate to the hardware limit due to the skew of bits on the parallel lines of the current link. The serialization of the interface with a fiber optic implementation would offer the potential of even more performance from the I/O Channel. For fiber optics to be attractive, the components must offer performance in the hundreds of Mbits/sec, with high reliability (less than 10-12 BER), low power consumption, small packaging profile, and low cost. To date, such components are not commercially available. At IBM Research, a 200 Mbit/sec, 1 km prototype serial subsystem has been built with emphasis on the development of attractive electro-optic components. Laser packaging was done using a Si chip as the substrate for both laser and fiber. A single chip, high sensitivity receiver was built with a digital IBM logic gate array chip. A monolithic dual laser chip and package were developed to enhance the availability of the transmitter. This talk will discuss the features of these developments and the possibilities for fiber optics in a large computer system.
With the growth of fiber optic technology over the last five years, numerous papers have been written on the subject of connectors. They have clearly detailed the various concepts utilized to achieve the accuracy of alignment necessary for efficient transfer of energy between optical waveguides. Intrinsic and extrinsic loss mechanisms have been defined.
A low loss, field installable, expanded beam fiber optic connector has been developed for both commercial and military use. The design includes a lens insert capable of producing losses less than 0.7 dB and can be easily installed in the field without polishing of fiber ends or use of index matching fluid at the interface between connectors. The connector has been designed for single fiber or multiple fiber applications as well as connectors with a combination of electrical and fiber optic contacts.
A review of the TRW low tolerance alignment guide principle is given as applied to the existing Optalign(R) single channel, and military six channel connector constructions. In addition, recent developments in an environmentally sealed index matched connection scheme are described which offers multimode fiber connection losses less than 0.4 dB and single mode fiber losses below 1 dB. Details of the new TRW single and multimode splice kit are also presented, along with data showing average multimode fiber insertion losses below 0.2 dB in a rapidly assembled low profile package.
The most common method of splicing low loss optical fibers is fusion splicing. To those who actually do the splicing, this technique is difficult at best. The GTE elastomeric splice is intended as an alternate solution to eliminate the difficulties encountered in field splicing. Aside from cable preparation, a splice can be completed in less than three minutes. Initial production runs show losses of 0.12 dB max and an average of 0.09 dB.
Determining insertion loss and assessing the relative quality of fiber optic connectors and splices should be a simple matter. It should be, - but it isn't. Too many other elements are being confused with the basic quality level assessment. Fiber test methods and philosophy are being applied to insertion loss testing. System budgeting concerns are causing designers to look at insertion loss specifications for guidance, but variations in system structure and com-ponents cause variations in the losses exhibited by a specific connector or splice.
Several manufacturers have been developing hermaphroditic connectors for six-fiber optical cables used in tactical military communication system applications. The specifications to which respective manufacturers have designed and tested these connectors have not been consistently the same. A test plan, as well as measurement procedures which will be uniformly applied to all connector assemblies, has been proposed. In support of the test procedures, fiber optics instrumentation that measures the insertion loss of the six-fiber hermaphroditic connectors under dynamic conditions has been developed. Special equipment to perform tests that simulate aspects of field conditions has been designed and fabricated. Selected fiber optic connectors are presently under evaluation using these procedures and instrumentation. This paper describes characteristics of the insertion loss and simulation equipment and their application to the measurement of the parameters to be tested.*
There have been rapid advances in multiplexer and demultiplexer development driven by the promises of WDM to increase the information-carrying capacity of optical fibers. The design of WDM components selected for a particular system depends on system parameters such as number of channels, direction of channels, channel loss budget, bandwidth, and source type. Multiplexers and demultiplexers can be categorized according to the optical technique used to make the couplers wavelength selective: filters or dispersive elements. Optical design examples show that filter type couplers are best for a small number of channels (3-4) while dispersive type couplers are better for larger numbers of channels. System design examples are given for three types of systems with up to eight channels. Experimental results on WDM multiplexers, 'demultiplexers, and bidirectional couplers are given. Couplers optimized for operation in a single direction have been demonstrated with channel insertion losses <2 dB and crosstalk <40 dB between channels. Couplers for bidirectional operation are shown to have higher losses. The severe effect on system crosstalk performance of out-of-band source emission is discussed.
A family of four port couplers is described which functions with 140/100pm and 230/200pm fibers. Tap ratios between 3 dB and 20 dB on the two output fibers are achieved with total throughput losses of less than 1.5 dB. A Bidirectional coupler offers a full duplex capability at a single wavelength for 140/100pm and 230/200pm fibers. Intrinsic channel isolation is in excess of 30 dB and coupled source-to-detector power throughput loss is less than 4 dB.
μA multiport branching coupler is called a star coupler. It is a passive device which is foreseen to have an extensive application. For example, it will be used for an optical fiber data bus system. A 16x16 (16 input ports and 16 output ports) star coupler was fabricated. The star coupler consists of an input fiber array and output fiber array with 16 pigtail fibers, a recutangular glass black with two perfect mirrors for mixing the input light beams uniformly and two cylindrical lenses. The glass block shape parameters were decided so as it minimize output power deviation. The star coupler characteristics are as follow, when step index fiber is 100 μm core diameter, 150 μm outer diameter and 0.25 NA (numerical aperture) Average transmission loss : 15.4 dB Average excess lass : 3.4 dB Branching power deviation : 2.0 dB The results indicate that the new star coupler is very useful for an extensive application in fiber optics data transmission.
A new optical switching component for multimode fiber-optic networks has been developed. This voltage-controlled switch is an 8-port device coupled by GRINrod lenses to four input fibers and to four output fibers (graded index, 50-μm core diameter). The matrix switches light from any input to any output, and four simultaneous input-output connections are made. There are 24 such states. Switching is done via controlled reflection from two layers of nematic liquid crystal. This switch is the first multimode, electro-ontic, fiber-optic matrix. Construction is simple and compact, using only four glass prisms and two liquid crystal layers. The matrix architecture is based on a new dual-switching-array concept that provides very low levels of optical crosstalk, more than 53 dB below the optical input level. The 5-ms on/off response time is faster than that of electro--mechanical matrices, although the 40 Vrms addressing voltage is higher. The optical insertion loss had a minimum value of 6 dB and an average value of 15 dB. The latter is due to misalignment of fibers during attachment to the switch, which can be remedied. Because the present switch does not use moving parts, it is quite reliable.
Optical switches and variable branching ratio directional couplers by moving prism have been developed. These devices have the ability of no transient switching or free branching ratio. The fluctuation loss phenomenon in switching period and insertion loss increase has not been investigated yet. This phenomenon is reported in this paper. Clockwise prism angular deviations at the assembling process are proved to be the cause of the fluctuation loss and insertion loss increase. Counterclockwise prism angular deviations at the assembling process are useful to eliminate fluctuation loss in the switching period and insertion loss increase in the prism. Details of these arguments are presented in this paper.
Recirculating delay lines have been made using loops of single mode fiber that are closed, without splices, using one or more single mode fiber directional couplers. The use of an all single mode fiber system allows the accurate storage of high frequency analog or digital signals for long delay periods. Such devices can be used as wideband transient or buffer memories. Recirculating fiber loops are also useful as transversal filters that can exhibit uniform notch and bandpass filter characteristics over a wide range of frequencies from 1 MHz to 1.3 GHz.
Acoustic sensors based on optical principles have the advantage that they are compatible with fiber optic transmission lines. Although extensive progress in the development of the optical sensors employing Mach-Zehnder fiber interferometry has been achieved, this paper will concentrate on non-interferometric sensors which have also experienced rapid development. The most promising fiber-optic acoustic sensors will be discussed, the latest results will be presented, and comparison of these sensors with the inter-ferometric sensors will be made.
The undersea environment places special demans on the design of electro-optic and fiberotic systems. Encapsulation in hermetically sealed pressure containers is one solution to the problems associated with deployment at depth. An alternative approach which avoids the inconvenience of pressure containers and pressure hull penetrators is to operate the system in a fluid-filled, pressure equalized package which. subjects the components to the ambient pressure encountered at depth. The data presented here characterize the behavior of GaAlAs, single mode, injection laser diodes under conditions of fluid immersion and hydrostatic pressure. Fluid immersion affects laser operation primarily by reducing the end facet reflectivity and thereby raising the threshold current. Elevated hydrostatic pressure also resulted in increased threshold current due, to pressure induced changes in the band structure of the active layer material. Spectral changes were particularly evident with pressure induced mode hopping being the most significant effect.
Two-way communication through a single fiber with solid-state lasers as sources is described. This system was designed to use the same optical subsystem for transmitting as for receiving at each of the two stations. Operations were performed to polarize the laser beams orthogonally to each other from the two communicating stations. A multilayer, single-mode optical fiber capable of preserving the two orthogonally polarized modes of propagation was used as transmission medium. The multilayer configuration was constructed to confine most of the energy in the fiber core to minimize losses to absorption in the cladding. Separation of the beams was made by a duplexer capable of distinguishing the difference in polarity of the two beams.
Optical systems composed of single-mode fiber are finding increasing utility as high-band-width transmission systems, interferometers, and sensors. In addition to the unique properties of single mode fibers that permit such applications, these systems have an important advantage over their conventional bulk optics equivalents - namely, a compact, lightweight, flexible, and completely guided optical path. If fiber systems are to exploit this advan-tage to the fullest, however, compatible components are needed to perform some of the basic functions (power division, polarization control and filtering, etc.) that may be required in any optical system.