Showing papers on "Optical switch published in 1993"

A terahertz optical asymmetric demultiplexer (TOAD)

Abstract: A device capable of demultiplexing Tb/s pulse trains that requires less than 1 pJ of switching energy and can be integrated on a chip is presented. The device consists of an optical nonlinear element asymmetrically placed in a short fiber loop. Its switching time is determined by the off-center position of the nonlinear element within the loop, and therefore it can use the strong, slow optical nonlinearities found in semiconductors, which all other fast demultiplexers seek to avoid. The switch's operation at 50 Gb/s is demonstrated, using 600-fJ control pulses. >

A Wavelength-Convertible Optical Network

Abstract: Wavelength-division multiplexing is emerging as the dominant technology in future all-optical network. To efficiently use the wavelengths, wavelength converters are employed for a circuit-switched optical network in which a circuit can change its wavelength to resolve wavelength conflicts and to reuse the wavelengths. To improve the efficiency, a few converters are provided and shared by the incoming circuits in the share-per-node or the share-per-link wavelength-convertible switch. A heuristic algorithm for dynamic routing is used to reduce the number of converters. Performance gain in call blocking probability and fairness and in the reduction of the number of converters are shown

A transport network layer based on optical network elements

Abstract: An approach to the realization of a broadband, flexible, multiwavelength transport network employing an optical network layer. The design methodology for a network demonstrator is presented, and the transmission, switching, line, and management/supervisory subsystems and components are described. >

Vanadium oxide films for optical switching and detection

Abstract: Structural, electrical, and optical properties of the polycrystalline films of VO2, V2O5, and mixtures of these two oxides are presented. Resistivity change by a factor larger than 103 accompanying the semiconductor-metal phase transition in the VO2 films is reported. A significant contrast in optical transmittance for the two phases of VO2 is observed. High temperature resistivity and optical transmittance of the V2O5 films are shown. Values of the temperature coefficient of resistance in some of the VO2 films in their semiconducting phase and in some of the V2O5 films are as high as 5.2 and 4% per degree Celsius, respectively. Phase switching properties of the VO2-V2O5 films are described. Applications of the fabricated films include optical switches and bobmetric-type light detectors.

All-Optical Switch with Switch-Off Time Unrestricted by Carrier Lifetime

Abstract: We propose a symmetric Mach-Zehnder-type all-optical switch which is based on the nonlinear refractive index change induced in semiconductors. Unlike most all-optical switches, the switch-off time, as well as the switch-on time, of this novel device is not limited by the usually slow carrier lifetime, allowing a very fast switching speed. Its switching characteristics are theoretically examined under various conditions. It is shown that the device offers a nearly square modulation characteristic that is suitable for most switching applications.

Light-triggered electrical and optical switching devices

Abstract: The functional photoswitchable systems 1–3 and 12–15 display pronounced photochromic properties; the bis-pyridinium derivative 1 represents a prototype of a switched molecular wire which may be converted from an open unconjugated form to a closed electron-conducting state.

The 'staggering switch': an electronically controlled optical packet switch

Abstract: An architecture and implementation issues for an almost-all-optical packet switch that does not rely on recirculating loops for storage implementation are presented. The architecture is based on two rearrangeably nonblocking stages interconnected by optical delay lines with different amounts of delay. The probability of loss and the switch latency as a function of link utilization and of the size of the switch are investigated. In general, with proper setting of the number of delay lines, the switch can achieve an arbitrarily low probability of loss. Growability patterns and extension of the design to the dense wavelength-division-multiplexing (WDM) case are also shown. In particular, an extension to the architecture whereby, through the use of WDM, the switch capability can be increased several times, with only minor changes to the switch design is discussed. Additionally, issues involving practical implementation of such a switch are considered. For example, a scheme that allows optical packet synchronization for the synchronously-operated switch is shown. Using this scheme, the switch can be a central component in the design of future all-optical, packet-switched networks. >

Frequency-selective optical switch employing a frequency dispersive element, polarization dispersive element and polarization modulating elements

Abstract: A liquid-crystal optical switch capable of switching separate optical signals in a physical input channel to a selected output channel. A diffraction grating spatially divides the input channel into its frequency components, which pass through different segments of a liquid-crystal modulator. The liquid-crystal modulator segments are separately controlled to rotate the polarization of the frequency channel passing therethrough or to leave it intact. The channels then pass through a polarization-dispersive element, such as calcite, which spatially separates the beams in the transverse direction according to their polarization. A second diffraction grating recombines the frequency components of the same polarization into multiple output beams.

Lightnets: Topologies for High-speed Optical Networks

Abstract: An inherent problem of conventional point to point WAN architectures is that they cannot translate optical transmis- sion bandwidth into comparable user available throughput due to the limiting electronic processing speed of the switching nodes. This paper presents a solution to WDM based WAN networks that addresses this limitation. The proposed Lightnet architecture trades the ample bandwidth obtained by using multiple wave- length for a reduction in the number of processing stages and a simplification of each switching stage, leading to substantially increased throughputs. The principle of the Lightnet architecture is the construction and use of a virtual topology network in the wavelength domain, embedded in the original network. This paper studies the em- bedding of virtual networks whose topologies are regular, using algorithms which provide bounds on the number of wavelengths, switch sizes, and average number of switching stages per packet transmission. Algorithms for the embedding of alternative regu- lar topologies are presented and their performance is evaluated. It is shown that compared to conventional network architectures, the Lightnets offer substantial performance gains in terms of increased throughput and smaller buffering requirements.

Applications of highly nonlinear chalcogenide glass fibers in ultrafast all-optical switches

Abstract: Applications of chalcogenide glass fibers in ultrafast all-optical switches have been investigated. Ultrafast all-optical switching has been accomplished in an optical Kerr shutter configuration using As/sub 2/S/sub 3/-based glass fiber. The nonlinear refractive index of the As/sub 2/S/sub 3/-based glass is estimated to be n/sub 2/=4.0*10/sup -14/ (cm/sup 2//W), which is higher by two orders of magnitude than that of silica glass fiber. Nonlinear absorption due to two-photon absorption has been revealed to be negligible, and up to a 2 pi -phase shift has been obtained. Switching speed and switching power were investigated experimentally and through calculations. A switching time of 12 ps and a switching power of 5 W can be achieved using a 10-ps gate pulse and only a 1-m chalcogenide glass fiber. However, signal transformation due to cross-phase modulation and group velocity dispersion is not negligible for shorter gate pulses. Lower switching power is possible by reducing the transmission loss and the core area and by optimizing the driving conditions. >

Wide-angle, high-speed, free-space optical communications system

Abstract: A free-space optical communications system for transmitting data between an aircraft computer system (14) and a ground-based computer system (12). The system includes a pair of corresponding optical transmitters (36) and optical receivers (38) that transmit and receive optical signals transmitted between the two computer systems. Included within each optical transmitter is one or more light-emitting diodes (42) that produce optical signals corresponding to the data to be transmitted. A beam-forming prism (44) is bonded directly to the light-emitting diodes to direct the optical signal uniformly over a target area. The optical receiver includes one or more infrared windows (50) to reduce the amount of ambient light received by the optical receiver. A compound parabolic concentrator (64) collects light transmitted from the optical transmitter and directs the light onto an avalanche photodiode (66), which includes thermal bias compensation. An AC network couples the output signal of the photodiode to a transimpedance amplifier (70). An optional optical shroud (34) surrounds the optical transmitters and receivers to further reduce the amount of ambient light that is received by the optical receivers.

Evolution of the SEED technology: bistable logic gates to optoelectronic smart pixels

Abstract: The recent evolution of quantum-well self-electrooptic effect devices (SEEDs) for application in free-space optical switching and computing systems is reviewed. Requirements of these systems have stimulated the development of devices usable in large systems of cascaded devices (the symmetric SEED), large two-dimensional arrays of these devices with improved physical performance, logically smarter extensions of these devices (logic-SEEDs), and devices integrating electronic transistors with quantum-well modulators and detectors for both reducing the required optical energies and increasing functionality. This progress and its implications for future developments are summarized. >

Polymer waveguide thermooptic switch with low electric power consumption at 1.3 mu m

Abstract: A polymer waveguide thermooptic 2*2 switch with low electric power consumption is demonstrated. The switch consists of a Mach-Zehnder interferometer with Cr thin-film heaters. The waveguides are fabricated using acrylic polymers synthesized from deuterated methacrylate and deuterated fluoromethacrylate monomers. The total insertion loss of the switch is 0.6 dB at a wavelength of 1.3 mu m, including fiber coupling losses and waveguide losses. The switching power is as low as 4.8 mW, and the rise and fall times are both 9 ms. >

Arrayed-wave guide grating multi/demultiplexer with loop-back optical paths

Abstract: An optical device is presented which is useful for optical signal transmission and switching systems by multiplexing and demultiplexing optical signals in looped optical paths, consisting of a plurality of individual loop-back optical paths. The device is essentially a multi/demultiplexer having an arrayed waveguide grating disposed between a plurality of input sections and output sections which are joined by the plurality of individual loop-back optical paths. Because the modulated signals are looped back into the same optical paths using the same devices, problems of mismatching performance introduced by using different optical devices are avoided. The device processes individual optical signals of different wavelengths, minimizes splitting losses, and reduces noise components by producing narrow bandpass signals of high signal to noise ratio. Optical signal splitting and insertion, delay line memory and delay equalization circuits can all be handled by the same circuit configuration. The device is simple in construction, reliable in performance and economical in production.

Optical processing system

Abstract: A telecommunications system comprising first and second nodes interconnected by a network transmission line. The first node comprises an optical data generator for producing an optical data signal at a first wavelength, an optical header generator for producing an optical control signal at a second wavelength, and means for multiplexing the data and control signals onto the transmission line. The second node comprises a switch and a controller responsive to signals at the second wavelength for controlling the routing of optical signals through the switch. A delay unit and associated control means are provided to ensure that sufficient delay occurs between the transmission start times of the control and data signals that the control signal completely overlaps the data signal at the second node.

Batch fabrication and operation of GaAs-Al/sub x/Ga/sub 1-x/As field-effect transistor-self-electrooptic effect device (FET-SEED) smart pixel arrays

Abstract: The structure, processing, and performance of arrays of integrated field-effect transistor-self-electrooptic effects devices (FET-SEEDs) consisting of doped-channel field-effect transistors, multiple quantum-well (MQW) modulators, and p-i-n MQW detectors are discussed. The performance of the FETs and SEEDs such as g/sub m/ and contrast, is equivalent to that obtained when they are made separately. Typical values are g/sub m/=80 mS/mm and contrast of 3. The largest arrays contain 128 circuits. The circuits operate at speeds as fast as 500 Mb/s, with optical input switching energy of approximately=400 fJ. At 170 Mb/s, the required optical input switching energy is approximately=70 fJ. This optical energy is at least a factor of 20 less than for symmetric SEEDs (S-SEEDs) with the same optical window sizes. Hence, FET-SEEDs provide superior performance compared to conventional S-SEEDs. >

Continuous-relief diffractive optical elements for two-dimensional array generation.

Abstract: Continuous surface-relief diffractive optical elements for two-dimensional array generation (fan-out) are designed and fabricated. Separable and nonseparable solutions for the two-dimensional element design are compared. The phase-grating microstructures are generated by laser-beam writing lithography in a single exposure step and converted to nickel shims by electroplating, enabling low-cost replicas to be produced by using laboratory and commercial replication processes. Results are presented for a 9 x 9 fan-out diffractive optical element with a measured efficiency of 94% and an overall uniformity within +/-8%; replicas in epoxy have the same efficiency and a uniformity of +/-15%.

Shared-memory optical packet (ATM) switch

Abstract: Previously, we determined fundamental performance limitations associated with `all-optical' packet switches, in which the packet buffering is implemented via fiber delay lines. In this work, we propose and analyze an optical packet (ATM) switch architecture that comes close to achieving the optimal performance (i.e., best possible delay-throughput performance and minimal possible buffer requirements) of a random-access, shared-memory design. The proposed Shared-Memory Optical Packet (SMOP) Switch buffers packets in recirculation delay lines of appropriately-selected lengths, and uses a novel control algorithm that: (i) keeps packets in their proper first-in, first-out sequence, (ii) supports multiple levels of priority traffic, (iii) minimizes the needed number of recirculation loops (which reduces the size of the switch fabric), and (iv) ensures that packets pass through the recirculation delay lines only a small number of times (e.g., less than 10).© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

New architectures for optical TDM switching

Abstract: A systematic theoretical study of architectures for optical TDM switching, using lithium niobate optical switches and optical fiber delay lines for storage, is undertaken. The architectures allow the bit rate and wavelength transparency of these devices to be exploited. A technique involving recursive definition and proof is used to define the networks, which are mathematically related to Benes and Waksman networks. This produces architectures that are very different from existing optical TDM networks. They exhibit economical use of components, which reaches the theoretical minimum in some cases. The use of feed-forward rather than feed-back delays give these networks superior crosstalk performance and more uniform attenuation than existing designs. >

An all-optical switch employing the cascaded second-order nonlinear effect

Abstract: A new, ultrafast, low loss, all-optical switch based on the cascaded second-order nonlinearity is proposed. The device is based on an integrated Mach-Zehnder interferometer where quasi-phase matching produces a nonlinear phase shift with a different sign in each arm of the interferometer. A full treatment of the nonlinear phase shift indicates that the proposed device, if fabricated in AlGaAs, could switch with powers around 1.3 W in a length of approximately 1 cm. >

Architecture for optical switch

Abstract: An optical switching device with switch elements (224) similar to digital micromirror devices (DMD). The switching element (224) resides in a trench (216) between two elevated areas on the substrate (214a, 214b). Sending and receiving fibers (218a, 218b) face each other across the trench (216) with the switch element (224) between them. When the switch is ON, light travels through lenses (220a, 220b) in the trench (216) from one fiber (218b) to the other (218a). When the switch is flipped OFF, the element (224) is activated and blocks the light from the sending fiber (218b) by reflecting or absorbing the light from the sending fiber (218b). The switch is activated and possibly deactivated by addressing electrodes (226a, 226b) under the element (224), which deflects through an air gap towards the activated electrode (226b). For better deflection angles the posts can be arranged closer to one end of the element than the other. An alternate hinge architecture is also provided.

Six-stage digital free-space optical switching network using symmetric self-electro-optic-effect devices

Abstract: We describe the design and demonstration of an extended generalized shuffle interconnection network, centrally controlled by a personal computer. A banyan interconnection pattern is implemented by use of computer-generated Fourier holograms and custom metallization at each 32 × 32 switching node array. Each array of electrically controlled tristate symmetric self-electro-optic-effect devices has 10,240 optical pinouts and 32 electrical pinouts, and the six-stage system occupies a 9 in. × 12.5 in. (22.9 cm × 31.7 cm) area. Details of the architecture, optical and mechanical design, and system alignment and tolerancing are presented.

Compact 40Gbit/s optical demultiplexer using a GaInAsP optical amplifier

Abstract: A polarisation insensitive GaInAsP near travelling wave semiconductor laser amplifier is used as the nonlinear element in a nonlinear optical loop mirror. With this compact configuration, the authors demonstrate a continuously tunable switching window, and report, for the first time using semiconductor materials, error ratio measurements for a demultiplexing operation from 40 to 10 Gbit/s, with a receiver sensitivity of −23 dBm.

All-optical switching based on nondegenerate phase shifts from a cascaded second-order nonlinearity.

Abstract: All-optical switching by using a nondegenerate cascaded second-order nonlinearity is described wherein a phase shift is induced at one frequency owing to the presence of intense light at a different frequency. A Mach–Zehnder waveguide device is proposed to take advantage of this process and has applications for all-optical switching and demultiplexing, potentially at power levels near 10 W by using quasi-phase matching in semiconductor waveguides.

Semiconductor laser amplifier as optical switching gate

Abstract: The properties of a semiconductor laser amplifier as optical switching gate are investigated. Particular attention is paid to gain, contrast ratio, and switching time of the device. These properties are studied experimentally and theoretically with respect to the injection current, optical input power, and cavity resonances. The experimental arrangements and the theoretical method are described. As an example of the various applications of semiconductor laser amplifier gates, packet switching experiments with self-routing, employing cascaded switching gates, are reported. In a theoretical analysis the restrictions that the properties of semiconductor laser amplifier gates impose on a larger switching system consisting of many such gates are investigated. >

Optical fiber solitons, their properties and uses

Abstract: The history and mathematical formulation of solutions are briefly reviewed. Solitons of the nonlinear Schrodinger equation are studied in greater detail because they describe nonlinear pulse propagation on dispersive optical fibers. The proposal by A. Hasegawa and the experiments of L.F. Mollenauer on long distance soliton propagation for use in repeaterless transoceanic fiber transmission cables are described. In 1986, limitations on the distance that can be spanned by a repeaterless link for a given bit rate were shown to exist. It has been shown recently that by proper design these limitations can be overcome, so that newer transoceanic cable designs are likely to utilize solitons. The special properties of solitons make them particularly suited for all optical switching and logic operations. Some recent experiments with such switches are described. >

Apparatus for switching optical signals among optical fibers and method

Abstract: An optical switch wherein mirrors move between two positions in order to transmit optical signals between input fibers and output fibers. In a first position, the optical signal is transmitted by input fibers through a one-quarter pitch of Grade Index Refractive (GRIN) lens. The light signal is then reflected by a first mirror and second mirror such that its path carries it to a focusing one-quarter GRIN lens, and to output fibers. With the mirrors in its second position, the optical signal is transmitted directly from input fibers, through one-quarter pitch of Grade Index Refractive (GRIN) lens, to a focusing one-quarter GRIN lens, and to output fibers, thereby resulting in an unreflected light signal path.

Distributed lighting system with fiber optic controls

Abstract: A vehicle lighting system includes one or more central light sources, a plurality of optical loads including headlight lenses, an optical fiber network that extends from the light sources to illuminate the headlight lenses and other optical loads, and optical switches and oscillators that include respective input fibers illuminated from the light source and output fibers to respective optical loads, and operate by enabling and disabling optical connections between their input and output fibers. The headlight assemblies switch between high and low beams by moving their fibers vertically, and control beam diffusion by moving the fibers parallel to the lens axes, including an automatic diffusion adjustment for a headlight reflection from a vehicle in front. The switches include various mechanisms for moving the input and output fibers into and out of alignment with each other, including a shaped resilient sleeve, a hinge pivotally joining the fibers, an opaque shutter with a transmissive section movable between the fibers, and also a liquid-based switch that relies upon total internal reflection. A feedback mechanism for some of the switches dims the source lamp when the switch is OFF to conserve energy. The oscillators operate by normally urging an input fiber towards an OFF position, at which it actuates a mechanism that shifts it to an ON position at which the mechanism is deactivated. A failsafe system employs multiple light sources, with each source sharing its light output with the load for another source that has failed.

Analysis of nonlinear optical switching in an erbium-doped fiber

Abstract: A mathematical model of the strong, resonantly enhanced nonlinear phase shift recently reported in Er-doped fibers which relates the phase shift and signal loss to the fiber parameters and the pump and signal wavelengths, is presented. Predictions are in fair agreement with the phase shift and loss measured in an experimental Er-doped fiber switch based on this effect. A strong, nearly wavelength independent contribution to the nonlinear phase shift is observed in the switch. The model suggests that this effect is due to the same nonlinear effect arising from one or more vacuum ultraviolet (VUV) transitions in Er/sup 3+/. >