Fiber Bus Research Articles

The fair distributed queue (FDQ) protocol for high-speed metropolitan-area networks

A new protocol, fair distributed queue (FDQ), suitable for very high-speed metropolitan-area networks (MANs), is presented. FDQ is a slotted system implemented on a unidirectional fiber bus. It has similarities to distributed queue dual bus (DQDB), the IEEE 802.6 Standard for MANs, including the bus topology and same nodal hardware. Like DQDB, FDQ achieves full throughput efficiency independent of the bus length, the transmission speed, and the number of nodes. Unlike DQDB, FDQ allocates equal bandwidth under heavy load to all active users in a time period less than or equal to the round-trip propagation delay without wasting bandwidth. Its delay characteristics are studied via simulation and compared to DQDB. FDQ has lower average delays under Poisson load than DQDB with or without the bandwidth balancing (BWB) mechanism. Two distinct implementations of priority levels are given and their characteristics are discussed. It is shown that FDQ's delay and throughput characteristics are little affected with increasing distances or transmission rates. Thus, FDQ possesses excellent scalability properties which allow its total length to extend over 100 km and transmission rate well above 1 Gb/s.

Design and application of double amplified recirculating ring structure for hybrid fibre buses

The design of a double-parallel amplified recirculating optical delay line utilizing an erbium-doped fibre amplifier for a fibre optical bus is described. This structure is used for amplifying, equalizing and filtering multicarrier signals coming from optoelectronic units attached to fibre couplers. The use of this structure for a hybrid multimode-singlemode fibre bus that includes optoelectronic units for sensors is also demonstrated.

Fibre-based local area network with priority access

A new-local area network based on a multiaccess unidirectional fibre bus is described. Communication between network stations is by means of objects and can be point-to-point, multicast or broadcast: Each communication object is unique, with an inherent priority embedded in its frame structure. It is impossible for objects of the same priority to attempt media access at the same time, and collisions between objects of different priority are always resolved in favour of the highest-ranked object without the need for a backoff interval. The access protocol is simple, robust and fair in as much as the physical position of stations does not adversely affect their probability of accessing the media or the station queueing delays. The network is ideal for real-time applications and electrically hostile environments, which are characteristic of manufacturing cells. Similar networks are briefly reviewed and the new distributed access protocol is described. It is shown that throughput is high, irrespective of the number of active nodes or the physical length of the media.

An overview of the Solar Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission

The scientific objectives of the NASA small-class explorer mission SAMPEX are summarized. A brief history of the Small Explorer Program is provided along with a description of the SAMPEX project development and structure. The spacecraft and scientific instrument configuration is presented. The orbit of SAMPEX has an altitude of 520 by 670 km and an 82 degrees inclination. Maximum possible power is provided by articulated solar arrays that point continuously toward the sun. Highly sensitive scientific instruments point generally toward the local zenith, especially over the terrestrial poles, in order to measure optimally the galactic and solar cosmic ray flux. Energetic magnetospheric particle precipitation is monitored at lower geomagnetic latitudes. The spacecraft uses several innovative approaches including an optical fiber bus, powerful onboard computers, and large solid state memories (instead of tape recorders). Spacecraft communication and data acquisition are discussed and the space- and ground-segment data flows are summarized. >

Application of an Excimer Laser Machining Technique in the Construction of an Optical Fiber Bus

An excimer laser technique was developed to machine precision tap openings in a polymer‐clad silica optical fiber for use in the construction of an optical backplane. In this technique, a telescope was used to image the laser beam onto the surface of the fiber at the desired tap location. The cladding then was removed using a prescribed number of pulses from the excimer laser. Single optical fiber taps were constructed using an ultraviolet‐curable acralate to attach a tap fiber to a laser‐machined opening in a central fiber. Tap measurements were made on single taps constructed from 650 × 350 micron elliptical openings and 250 micron diameter circular openings. Tap measurements also were made on a triple tap assembly which was fabricated using elliptical tap openings. The elliptical openings, with the major axis oriented along the longitudinal axis of the fiber, were determined to be more suitable for tap construction. The results of this study indicate that excimer laser machining is a promising technique for construction of a linear tapped bus for optical backplanes.

Optical interconnect based on a fibre bus

A technology which may form a powerful optical interconnection scheme based on a bus architecture is presented. It is shown that the fibre array connectors involved require alignment tolerances comparable to those of present electrical connectors. Further system flexibility can be obtained by tailoring the connector wavelength characteristics. Results of an experiment, where distributed amplification within the backplane of an optical bus was used to compensate for the power removed at the access points, are also presented. This allows a significantly higher number of output ports to be served than would be possible using a passive bus. As an example application, the feasibility of using the technology as the backplane interconnection in a card and rack system is demonstrated. Extension to a switching scheme using the multi-dimensional optical network concept is described.

Multi-gigabit networking based on DTM

Abstract A new TDM technique, DTM-Programmable Synchronous Transfer Mode, is presented. DTM is a hybrid between STM and ATM with more dynamic bandwidth allocation than STM and without the performance degrading need to process a header in each cell as is necessary in ATM. Some basic ideas are: • - preallocate bandwidth (time-slots) to all network nodes to avoid competiton for a common resource when it is most harmful, and provide a mechanism for fast background reallocation; • - use circuits to concentrate all processing in a connection establishment phase and make the data transfer phase extremely simple; • - connect each node to more than one fiber and provide switching; • - use wavelength multiplexing to increase the usage of each node. A network is outlined based on these ideas. Each node connects to up to three dual fiber buses. The addressing scheme allows cubic mesh networks. The proposed scheme does not, in contrast to e.g. DQDB, require optical termination in each node. This means, in combination with wavelength multiplexing and switching, that, although the fiber media carry traffic in the Terabit/s range, the nodes can still operate in the Gigabit/s range.

Fiber optic frequency hopping multiple access communication system

A network architecture is presented for a fiber optic frequency hopping multiple access (FO-FHMA) communication system. It is shown that the network, in addition to providing an independent (from other users) and asynchronous access to the optical fiber channel for the network subscribers, effectively utilizes the available bandwidth when the optical channel is sparsely utilized. In this arrangement the network users employ pseudorandom codes to frequency modulate the optical signal on the fiber bus using an optical pulse modulator. A balanced optical phase discriminator followed by a standard frequency dehopping receiver are used to decode the user provided information at a desired point on the fiber bus. It is demonstrated that the system may easily be implemented with the aid of a number of available optical components and standard frequency hopping transmitter and receive.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transmissive serial interferometric fiber sensor array

A transmissive serial array architecture for multiplexed interferometric fiber-optic sensors based on time division addressing is discussed. The configuration gives rise to intrinsic optical crosstalk between sensor elements of the system due to multiple cross-coupling of pulses between the series of sensor elements and the output fiber bus. This crosstalk is theoretically analyzed in detail, and compared to experimental results obtained with both three- and eight-sensor networks. Phase detection sensitivities as low as approximately 10 mu rad/ square root Hz at a signal frequency of 1 kHz are reported. >

Implementational Considerations in Fibre Optic Bus Network

For local area networks, bus topologies are the most preferred ones because of the reliability and the simplicity offered by them. However, it is difficult to construct a fibre optic bus network due to two main reasons (i) non availability of high impedance bidirectional taps and (ii) unidirectional nature of light propagation in fibres. This paper examines in detail the issues involved in implementation of optical fibre bus networks. It evaluates various major schemes that have been proposed towards this end and finds out the optimum implementation for each one of them. Every implementation has certain constraints on the number of nodes that can be supported for the available power budget. Other pertinent issues like the required dynamic range, reliability, expansion capabilities and the protocols supported are also discussed. Amongst the various implementations examined, the one using star couplers and linear bus with asymmetric coupler appear to be superior to the others.

Optical phase division multiplexing for local communications applications

A local fiber bus system is described wherein many users sequentially phase-modulate the output of a single light source. Since the modulated signal has a constant envelope, optical amplifiers can be used to boost the signal power along the bus to a level sufficient for reliable detection. Also, since a single laser source is used, a higher quality device (for example, with small linewidth) is more readily affordable. This system is analyzed to determine the limits of performance due to noise. The analysis indicates that many wideband signals could be accommodated if noise sources only, rather than signal distortions caused by nonideal optical devices, were the limiting factor. For example, with optical amplifiers distributed along the bus, this system can support 1000 10-MHz users.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Loop distribution using coherent detection (fiber optic networks)

A novel architecture is described for point-to-multipoint distribution using coherent detection and a totally passive fiber bus. Coherent technology is used initially to provide transmission at rates of a few hundred Mb/s without the need for a local oscillator at each station. It is expected that this architecture can then be expanded via WDM (wavelength-division multiplexing) to transport multiple wavelengths as coherent technology matures. The performance of the proposed topology is analyzed and compared to that of previous bus structures using variable and fixed taps with direct-detection receivers. This performance analysis consists essentially of a loss budget calculation intended to determine the relative numbers of stations which each of the architectures could support. Because the rates and loop lengths are modest and the spectral width of the sources associated with coherent communication are very small, dispersion (or rise-time budgeting) is not expected to present any real limitation for the systems considered here. A performance analysis and comparison of three tree structures is presented. Engineering issues and open questions are discussed. >

Optical Amplifier Applications in Fiber Optic Local Networks

The number of waveguide taps N that a passive optical fiber bus can accommodate is typically quite low, due to significant attenuation of the signal in the taps and splices. In an effort to increase N substantially, this paper investigates the potential use of optical amplifiers to boost the signal along the bus. An analysis is performed for both direct detection and heterodyne detection. Values of N are determined for a wide range of system and device parameters, such as signal duration, amplifier noise bandwidth, and amplifier saturation power. It is found that the use of optical amplifiers can increase N by at least an order of magnitude, and by as much as two orders of magnitude under many circumstances.

Wave Coupling Between Parallel Single-Mode and Multimode Optical Fibers

A directional coupler composed of a single-mode optical fiber and a multimode optical fiber has been considered to be capable of serving as a drop/insert device of a node in optical fiber Iocal area networks. It should couple almost all the local transmitter power into the multimode fiber bus, while removing only a small fraction of the optical power from the bus through the single-mode fiber. In this paper, the underlying fundamental process of the power transfer between two such optical fibers is analyzed utilizing a coupled-mode theory. Numerical calculations show that wave coupling among the guided modes on the fibers is quite complicated and that the wave amplitude variations along the propagation direction are different from the sinusoidal types resulting from two-mode coupling. The theoretical results do support the expected performance of the proposed couplers and provide an important guide for the design of such devices.

Lightwave system using microwave subcarrier multiplexing

We present a demonstration of subcarrier multiplexing in a lightwave multiple-access network. Three 44 Mbit/s digital signals are transmitted along a single-mode fibre bus by intensity-modulating two 1.3 μ-wavelength, multimode laser diodes with FSK subcarriers, at frequencics between 3.5 and 4.0 GHz. Intermodulation distotion, generated when two or more subcarriers are transmitted by the same laser, does not degrade the tranmission quality.