An 8:1, 5 Gb/s, time division multiplexer has been implemented using optoelectronic or metal-semiconductor-metal switches for sampling. The device was fabricated on InP and the switches activated via optical fiber delay lines by pulses from a GaAlAs laser diode array. This device concept is applicable to chip and to board level computer multiplexing. Time division multiplexing (TDM), serializing parallel data for high speed transmission, is an important element in most concepts and implementations in computer networking as well as other areas of communications. An optoelectronic TDM (OE-TDM) approach is advantageous in speed, power, and signal-control isolation. It was conceived initially to offer serial transmission off VLSI chips and recently has shown promise as a stand alone multiplexing technique. We report an improved multiplexer in InP giving an 8:1 multiplex ratio, a 26 dB signal-to-noise ratio, and a 5 Gb/s serial data rate while using a realistic parallel data level of 2 volts instead of the earlier 15 V.
Guided-wave optical interconnections for interchip data transmissions and clock distributions are demonstrated. The optical interconnection circuit consists of a silica-based guided-wave circuit, laser diodes and photodiodes. The interconnection topology adopts the star coupler network used in Local Area Networks as a model. The laser diodes and photodiodes are integrated with the guided-wave circuit. Preliminary experiments on a 4-chip interconnection circuit yielded a 340 Mbps data rate and a 250 MHz clock frequency.
In this paper we discuss the electrical and physical properties of interconnection structures that impact the performance of computer systems. These considerations are illustrated with three examples of such devices found in a typical main-frame. The requirements for the future are then presented. The ability of new technologies, electrical and optical for satisfying these requirements are discussed.
A laboratory model of a hybrid optical interconnect for board to board communication in a multiple broadcast topology has been built. The hybrid structure contains both free space and guided elements. The device is able to connect 9 processing elements each with a 64 bits output word. So 576 parallel output channels are fanned out to 5184 parallel channels. More processors can be interconnected by stacking these units or by making an adaption of the dimensions and lay-out. The fan-out is provided by multiple imaging of the fiber tips in the input plane by an objective lens and a facet mirror. The crosstalk between two neighbouring 250 μm diameter fiber channels with a pitch of 375μm is as good as -28 dB. The performance of this first non-optimized model showed some image distortion and a mismatch in numerical aperture of the fibers and the imaging optics.
The use of optical wavelength division multiplexing (WDM) for the simultaneous transmission of clock and data signals has possible application in the interconnection of communications equipment. This paper presents experimental results from transmitting clock and data signals through a single-mode optical fibre using WDM and highlights a technique to overcome phase mis-alignment between the clock and data signals at the point of retiming.
In synchronous systems, clock signals are used to maintain the order of occurance of events as well as defining the time frame in which logic is performed. Clock skew, the variance in arrival times of the same state of the clock signal to various parts in the system, is being identified as one of the main limitations to system performance. In this paper, we analyze an optical alternative for clock distribution. To demonstrate the feasibility of optical clock distribution, an experimental system has been designed and implemented to achieve a clock skew less than 200 psec.
Optical communications technology has seen highly successful implementations in telecommunications and local area networks and is now being explored for data, control, and clock applications within digital systems, such as computers and signal processors. The requirements for optical interconnections within these systems are significantly different from those applications where optical communications are used today. Digital systems require short high-speed interconnections with miniature transmit/receive modules that dissipate little power. These interconnections must also be compatible with standard digital packaging, power supply voltages, and environmental conditions. This paper explores insertion opportunities for optical interconnections within digital systems, the implementation issues, and specific examples of this technology.
An example of requirements to jitter budget and LED spectrum width, based on experimental data, is presented. Analytical expression for LED spectrum width is derived. Method of experimental evaluating of the transmission system performance is discussed.
In November '87, the Accredited Standards Committee X3, "Information Processing Systems," approved a project for FDDI support of singlemode fiber (SMF) as an alternative to the current multimode fiber (MMF). This paper describes: why it will be important for FDDI to support token-ring networks made of any combination of MMF and SMF; the status, the organization and the content of the draft standard document (SM-PMD); possible future plans for the evolution of the PMD standards.
A high performance truncated ridge ELED transmitter is described. It features high launched power, narrow spectral linewidth, and very high reliability. The MOVPE process and a straightforward design provides a high chip yield to provide for a cost-effective ELED transmitter optimized for FDDI applications.
The concept for using a duplex connector for the Fiber Distributed Data Interface (FDDI) was formalized in late 1983. The duplex requirements were driven by both the token ring topology and by the need to simplify connectivity between stations. Though most users speak in terms of a duplex connector or Medium Interface Connector (MIC), the FDDI Physical Medium Dependent (PMD) document only defines the physical parameters for a duplex receptacle. The receptacle is the boundary between the station and the cable plant of an FDDI network and hence the only location at which station conformance can be verified. The duplex connector or plug is therefore part of the FDDI cable plant.
FDDI promises to herald a new era in high speed communication among computers and peripherals. It also imposes stringent requirements at both the network interface and the interconnection between nodes. The aim of the paper is to provide the FDDI user with an understanding of the various implementation considerations and tradeoffs involved in hooking up the FDDI physical link.
Measuring equipment which can be used to test components and systems for the PMD (Physical Medium Dependent) and PHY (Physical Layer Protocol) layers of FDDI will be described. An overview will be given of test procedures in Appendix A of the PMD document. Emphasis will be placed on Bit Error Rate Testing and various optical test sets will also be discussed.
An automated test system was developed to test and characterize high-speed, fiber-optic transmit/receive (T/R) modules in a high-volume production environment. This tester is designed to test the Fiber Distributed Data Interface (FDDI), Physical Media Dependent (PMD) specifications and various other parameters to 200 MBd and higher. At this time, the PMD specifications are still evolving and various test methods are being employed to test the same parameters. The results from these test methods may yield components giving sub-par system performance. In order to guarantee the interoperability of these modules from various suppliers, consistency in test methodology must be established. This consistency will aid in the acceptance and success of the FDDI standard.
A Local Area Network (LAN) designed to a standard commercial interface, the Institute of Electrical and Electronics Engineers (IEEE) 802.3 or Ethernet, has been developed using fiber optics as the physical medium. The LAN, WhisperNet, operates in an active ring and thus has an inherent low cost migration path to a Fiber Distributed Data Interface (FDDI) implementation.
With the telephone trunk lines in place, the telephone operating companies and CATV corporations are intending to bring fiber optic technology directly to the home using a singlemode bidirectional fiber network. The obvious advantages are the enhanced services that could be provided by the enormous information capacity available using optical fiber.
Details of the development of asymmetric plastic fiber couplers and large port number star couplers are presented. Both coupler types have been fabricated with relatively high performance at a low cost. These devices are manufactured by direct bonding of the plastic optical fibers while heating. Results are given for 2x2, 3x3 and 4x4 asymmetric couplers utilizing 250μm, 500μm, 750μm and 1000μm diameter fibers and for 16x16, 32x32 and 64x64 star couplers using 250μm diameter fiber.
Optical fiber line systems operating in the first window (0.854μm) are longer experimental systems. Such systems have been installed and put into traffic in numerous places all over the Brazil as well as the world. They are used primarily in urban areas and in combination with digital switches. The optoelectronic technology is now advancing very fast. According to the multimode system consideration, the application to short haul routes, including interoffice trunks, appears to be most attractive today. In particular, non-repeatered systems between offices are of benefit to solve anticipated construction and maintenance problems in an urban area. We have developed a very compact 8 Mbps system to be used in interoffice trunks where special properties of optical fiber systems are required for such as the possibility for nonmetallic cables for interconnection of power plants to the public network, high electromagnetic disturbances which rule out conventional systems and others.
Three alternative architectures for an optical fiber to the home delivery system are analyzed: an all digital switched video and voice/data system; an analog broadcast video, digital voice/data system; and an analog switched video, digital voice/data system. These architectures are studied with respect to a potential application in a representative telephone serving area in terms of cost and technical feasibility. Four distribution topologies are considered. These are a one fiber star, a two fiber star, a ring, and a bus/star topology. The three architectures are integrated with the four distribution topologies to create five feasible fiber to the home models. Each model has been analyzed in terms of costs and practicality. The bus-star broadcast analog video, digital voice system is the least expensive alternative at present. However, it is not clear that this topology is a good choice for future growth. Issues such as privacy, reliability, and the potential lack of expandability of this architecture may mitigate this result.
The importance and complexity of interconnections in computers increase tremendously if one considers the von Neumann digital computer in connection with parallel computers with many tightly coupled processors. There is an indication that processing and interconnecting aspects will merge in future computer architecture. Parallel computers are able to perform a myriad of processing tasks such as "computational seismics", chemical reaction and aerodynamic simulation, dynamic imaging and robot vision. Such systems, comprised of many tightly coupled processors can meet the computational performance goals, required for these processing tasks. However a major problem is the construction of a suitable interconnection network which provides fast and flexible interprocessor communications at a reasonable cost. The cost-effectiveness of any arbitrary network design is governed by factors such as the number of processors applied, the computational tasks to be performed, the required speed of the interprocessor data transfers, the complexity of the actual hardware topology of the network and any cost constraints on its construction. The Delft Parallel Processor [DPP], which has been operational since 1981, is a modest size MIMD computer with a powerful interprocessor interconnection topology. (MIMD = Multiple-Instruction stream, Multiple-Data stream). In the DPP architecture, multiple data streams are realized by means of plural parallel data channels (one per data stream), with a branch-off per channel to each Processing Element [PE] to fetch the data on which to operate. A fast and efficient exchange of information within the DPP is performed by this 'full interconnectivity' Multiple-Broadcast [MB] interconnection topology. In the case of many processors, this MB interconnect has to be realized by means of Optical Interconnects [01's], to validate at several levels the quality and flexibility of communication systems for both interconnection topologies and data flow protocols. Conventional Electrical Interconnects [Us] and switching technologies are now becoming an insuperable bottleneck at several levels. The implementation of high speed, multi-pin, silicon and GaAs VLSI/VHSI circuits is one extreme; the choice of a massively reconfigurable parallel interconnection scheme is another. Optimum routing methods are hard to define. The application of wired Ors for the board-to-board interconnects and Local Area Networks [LAN's] is the most promising. Structured optical waveguide techniques, image mapping optics, optical starcouplers and free space holographic for the inner- and interchip communication may be the future, although coupling between opto-electronic components and/or waveguides still requires critical alignment.
A universal information multiplexer (UNIMUX) is capable of simultanously supporting a multitude of heterogenous interfaces such as RS-232, V.35, IBM 3270 coaxial links, T-1, 802.5 token-ring LANs, telephones and other devices over one fiberoptic backbone within a campus environment. As such, the UNIMUX is capable of providing economical alternatives for on-premises data distribution without sacrificing performance.
This paper will describe the physical medium for a fiber optic local area network which utilizes the intrinsically simple, fiber efficient, linear bus topology. The implementation relies on three unique fiber optic components - an active WDM coupler, hard plastic clad silica fiber, and a low loss tap for the HCS fiber. In fiber optics, bus topology has fallen out of favor because of the well known difficulty in tapping fiber, as well as cumulative fiber losses from relatively high loss taps. The existence of a low loss (.05dB) tap which can be installed at arbitrary locations on a fiber (without breaking the fiber), allows reconsideration of -the bus. Another benefit of this tap is that the ratios are tunable between -13dB and -35dB during installation. The active WDM further simplifies the architecture by allowing bidirectional transmission on a single fiber bus; halving the amount of taps, connectors, and fiber that would otherwise be required. Short wavelength emitters and detectors are used in the WDM which enhance reliability and reduce cost. Results from a 30 tap bus will be presented and will include off/on tap ratios, bit error rate tests, power budget considerations and receiver considerations.
Computer data links are evolving from copper cable systems to fiber optics simply because the optical fiber itself offers the advantages of higher data rates and longer distances. The Compact Disc (CD) laser is suitable as the light source because it satisfies the computer system requirements for low cost, high data rate, miniaturized package, and high reliability.
Computers have revolutionized the factory floor as well as the office environment. As a result, there has been a dramatic increase in the amount of information constantly exchanged between shop-floor computers that control and monitor plant equipment and among myriad office workers with individual desk-top computers. This widespread use of distributed processing has naturally led to the need for reliable data communication links. A unique approach has been developed which permits the networking of broadband data over optical fiber. This Local Area Network is a broadband network which utilizes analog techniques for communications. Analog methods allow for the use of multiple carrier frequencies and thus multiple services. For example, multiple networks such as the Manufacturing Automation Protocol, Broadband Ethernet, and the PC Network can coexist on the same optical fiber in addition to other broadband services such as video.
Recent improvements in plastic optical fiber properties and increasing availability of optical components designed for this fiber suggest that POF based local area network (LAN) systems may represent an increasing fraction of installed optical fiber systems. POF based systems can satisfy one of the major driving forces in the marketplace: low cost. The plastic fiber is lower in cost than competing silica based optical fiber and most coaxial or twisted pair media options. Optical interconnect components such as LEDs, detectors, and optical connectors can be similarly low in cost for POF based systems. Of course, POF retains the advantages of glass fiber cabling systems such as noise immunity, high bandwidth and ease of cabling.
Ethernet, and the closely related IEEE 802.3 CSMA/CD standard (Carrier Sense Multiple Access with Collision Detection), is probably the widest used method for high speed Local Area Networks (LANs). The original Ethernet medium was baseband coax but the wide acceptance of the system necessitated the ability to use Ethernet on a variety of media. So far the use of Ethernet on Thin Coax (CheaperNet), Twisted Pair (StarLan) and Broadband Coax has been standardized. Recently, an increased interest in Fiber Optic based LANs resulted in a formation of an IEEE group whose charter is to recommend approaches for Active and Passive Fiber Optic Ethernet systems. The various approaches which are being considered are described in this paper with an emphasis on Active Star based systems.
An asynchronous high-speed fiber optic local area network is described that simultaneously supports packet data traffic with synchronous T1 voice traffic over a standard asynchronous FDDI token ring channel. A voice interface module (VIM) was developed that parses, buffers, and resynchronizes the voice data to the packet network. The technique is general, however, and can be applied to any deterministic class of networks, including multi-tier backbones. In addition, the higher layer packet data protocols may operate independently of those for the voice thereby permitting great flexibility in reconfiguring the network. Voice call setup and switching functions are performed external to the network with PABX equipment.
A Tactical Multichannel Fiber Optic Transmission Link system developed by GTE, replaces multiwire copper cables used to interconnect military communication shelters. The full duplex system employs an asynchronous design for multiplexing twenty six channels over nine kilometers of tactical optical cables . The savings in cable weight and deployment time as well as improved performance and distance make the system attractive to the military users. Successful field testing has proven the superiority of optical fiber over copper cable.