Showing papers on "Optical switch published in 1997"

Micromachining for optical and optoelectronic systems

Abstract: Micromachining technology opens up many new opportunities for optical and optoelectronic systems It offers unprecedented capabilities in extending the functionality of optical devices and the miniaturization of optical systems Movable structures, microactuators, and microoptical elements can be monolithically integrated on the same substrate using batch processing technologies In this paper, we review the recent advances in this fast-emerging field The basic bulk- and surface-micromachining technologies applicable to optical systems are reviewed The free-space microoptical bench and the concept of optical prealignment are introduced Examples of micromachined optical devices are described, including optical switches with low loss and high contract ratio, low-cost modulators, micromechanical scanners, and the XYZ micropositioners with large travel distance and fine positioning accuracy Monolithically integrated systems such as single-chip optical disk pickup heads and a femtosecond autocorrelator have also been demonstrated

Tiny Tera: a packet switch core

Abstract: Describes Tiny Tera: a small, high-bandwidth, single-stage switch. Tiny Tera has 32 ports switching fixed-size packets, each operating at over 10 Gbps (approximately the Sonet OC-192e rate, a telecom standard for system interconnects). The switch distinguishes four classes of traffic and includes efficient support for multicasting. We aim to demonstrate that it is possible to use currently available CMOS technology to build this compact switch with an aggregate bandwidth of approximately 1 terabit per second and a central hub no larger than a can of soda. Such a switch could serve as a core for an ATM switch or an Internet router. Tiny Tera is an input-buffered switch, which makes it the highest bandwidth switch possible given a particular CMOS and memory technology. The switch consists of three logical elements: ports, a central crossbar switch, and a central scheduler. It queues packets at a port on entry and optionally prior to exit. The scheduler, which has a map of each port's queue occupancy, determines the crossbar configuration every packet time slot. Input queueing, parallelism, and tight integration are the keys to such a high-bandwidth switch. Input queueing reduces the memory bandwidth requirements: When a switch queues packets at the input, the buffer memories need run no faster than the line rate. Thus, there is no need for the speedup required in output-queued switches.

Micromechanical optical switch and flat panel display

Abstract: The invention provides an optical coupling switch and flat panel display including an array of such optical coupling switches. The optical coupling switch includes a light storage plate adapted to set up conditions for total internal reflection such that light injected into the plate is internally reflected. A light tap is disposed proximal to a coupling surface of the light storage plate for coupling internally reflected light out of the light storage plate and into the light tap when the light tap is brought into contact with the light storage plate coupling surface. The light tap is capable of movement in a direction perpendicular to the light storage plate in response to an applied electrostatic force. The optical coupling switch includes a scattering mechanism, such as a scattering surface or scattering medium, for scattering light in the light tap into a viewing volume. With this configuration, the optical coupling switch provides an elegantly uncomplicated geometry that accommodates a range of actuation schemes for efficiently producing high-speed optical switching. Also provided is an optical display in which an array of light taps are disposed proximal to a light storage plate coupling surface. Each light tap is adapted to move in response to an applied electrostatic force in a direction perpendicular to the coupling surface, and each light tap includes a scattering surface for scattering coupled light. A light source is disposed at an edge of the light storage plate for injecting light into the plate. Control circuitry is provided connected to the array of light taps for applying an electrostatic force to selected one or more of the light taps in the array.

Optical components for WDM lightwave networks

Abstract: Recently, there has been growing interest in developing optical fiber networks to support the increasing bandwidth demands of multimedia applications, such as video conferencing and World Wide Web browsing. One technique for accessing the huge bandwidth available in an optical fiber is wavelength-division multiplexing (WDM). Under WDM, the optical fiber bandwidth is divided into a number of nonoverlapping wavelength bands, each of which may be accessed at peak electronic rates by an end user. By utilizing WDM in optical networks, we can achieve link capacities on the order of 50 THz. The success of WDM networks depends heavily on the available optical device technology. This paper is intended as a tutorial on some of the optical device issues in WDM networks. It discusses the basic principles of optical transmission in fiber and reviews the current state of the art in optical device technology. It introduces some of the basic components in WDM networks, discusses various implementations of these components, and provides insights into their capabilities and limitations. Then, this paper demonstrates how various optical components can be incorporated into WDM optical networks for both local and wide-area applications. Finally, the paper provides a brief review of experimental WDM networks that have been implemented.

Scalable high performance switch element for a shared memory packet or atm cell switch fabric

Abstract: A scalable high performance ATM cell/packet switch (HiPAS) element for a shared memory switch fabric application. The switch element includes a PAC Bus (Packet/ATM Cell Bus) and the Switch Fabric Controller Bus (SC Bus). The HiPAS switch element receives and transmits the ATM cells/packets through the PAC Bus. The PAC Bus provides independent parallel datapaths for the receive port and transmit port. The PAC Bus provides a unique structural feature to the HiPAS switch element and allows expansion to the switch capacity in a manner similar to a bit-slice processor. Multiple number of HiPAS switch elements can be concatenated to expand the capacity. In the concatenated configuration, the datapaths of the receive port and transmit port are interleaved so that the interconnection remains point-to-point. As the result, all of the switch ports in the switch execute the cell transactions concurrently on the PAC Bus. In addition, each switch fabric port has a dedicated serial port to exchange status information between the switch fabric and the switch port adapter.

Wavelength conversion using semiconductor optical amplifiers

Abstract: This paper reports a detailed theoretical study of the dynamics of wavelength conversion using cross-gain and cross-phase modulation in semiconductor optical amplifiers (SOA's) involving a large signal, multisection rate equation model. Using this model, recently reported experimental results have been correctly predicted and the effects of electrical and optical pumping on the conversion speed, modulation index, and phase variation of the converted signal have been considered. The model predicts, in agreement with experimental data, that recovery rates as low as 12 ps are possible if signal and pump powers in excess of 14 dBm are used. It also indicates that conversion speeds up to 40 Gb/s may be achieved with less than 3 dB dynamic penalty. The employment of cross-phase modulation increases the speed allowing, for example, an improvement to 60 Gb/s with an excess loss penalty less than 1 dB.

Four-wave mixing in semiconductor optical amplifiers for frequency conversion and fast optical switching

Abstract: Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is an important tool for frequency conversion and fast optical switching in all-optical communication networks. We review the main applications of SOAs as nonlinear optical components. Concentrating on FWM, we define general parameters that are of relevance for signal processing applications. We show, how basic experiments and general simulation procedures can be used to determine optimum operating conditions for the intended applications. Besides a comprehensive investigation of FWM among continuous waves, we present new experimental results on FWM with picosecond optical pulses. A comparison of both reveals a different behavior and demonstrates that new optimization criteria and advanced theoretical models have to be applied for the case of short optical pulses. Moreover, we discuss the possibility to extract the dynamical SOA parameters from our experiments.

Optically nonlinear bragg diffracting nanosecond optical switches

Abstract: Monodisperse, highly charged colloidal particles in low ionic strength solutions self-assemble into bcc or fcc crystalline colloidal arrays (CCAs) due to interparticle repulsive interactions. We demonstrate that a CCA of dyed particles embedded in a poly acrylamide hydrogel acts as a nanosecond optical Bragg diffraction switching device. Under low light intensities the CCA is refractive index matched to the medium and does not diffract. However, high intensity excitation within the dye absorption band heats the spheres within nanoseconds to decrease their refractive index. The array ``pops up'' to diffract light within 2.5 ns. These intelligent CCA hydrogels may have applications in optical limiting, computing, and nanosecond fast optical switching devices, etc.

High-speed protocol for bursty traffic in optical networks

Abstract: An optical backbone network based on WDM (or OTDM) technology may become an economical choice for providing future broadband services. To achieve a balance between the coarse-grain optical circuit switching (via wavelength routing) and fine- grain optical packet/cell switching, optical burst switching is proposed. We study a one-way reservation protocol called just-enough-time (JET), which is suitable for switching bursty traffic in a high speed optical backbone network. The JET protocol has two unique, integrated features, namely, the use of delayed reservation (DR) and buffered burst multiplexers (BBM). By virtue of DR, the JET protocol not only increases the bandwidth utilization, but also facilitates intelligent buffer management in BBMs, and consequently results in a high through-put. Both analysis and simulation results show that the JET protocol can significantly outperform other one-way reservation protocols lacking one or both of these features.

Experimental study of integrated-optics microcavity resonators: Toward an all-optical switching device

Abstract: An integrated all-optical switch based on a high-Q nonlinear cylindrical microcavity resonator is proposed. The switch consists of single mode planar waveguides that allow coupling light in and out to a microresonator, exhibiting whispering gallery modes. Due to the high Q factor and the small dimensions, fast switching at low power is feasible for devices based on presently available nonlinear polymers as the active material. In this approach, the transmission of an integrated optical waveguide close to a microcavity has been measured and related to the resonances of the cylindrical microcavity.

Wavelength-selective optical add/drop switch

Abstract: A wavelength-selective optical switch having a first input port for accepting a plurality of copropagating optical channels, each of the channels having a distinct wavelength band. The optical switch includes first and second output ports. A wavelength-selective optical filter is connected to receive the copropagating optical channels from the first input port to extract a selected one of the channels while allowing the remaining channels to copropagate to the first output port. An interferometric switch is connected to receive the selected extracted channel; the interferometric switch includes a controller for controlling propagation of the selected extracted channel to either the second output port, the optical filter, or both. The optical filter is connected to receive from the interferometric switch an optical channel to be combined with the remaining copropagating channels and all directed to the first output port. In a first control state of the controller, the interferometric switch is adapted to direct the selected extracted channel to the optical filter, while in a second control state of the controller, the interferometric switch is adapted to direct the selected extracted channel to the second output port. A second input port can be provided for accepting an injected optical channel having a wavelength band corresponding to the wavelength band of the selected extracted channel. This second input port is connected to direct the injected optical channel to the interferometric switch. In this scenario, the interferometric switch is adapted, in the second control state of the controller, to direct the injected channel to the optical filter, and is adapted to direct the injected channel, in a first control state of the controller, to the second output port.

Collective switching and inversion without fluctuation of two-level atoms in confined photonic systems

Abstract: We demonstrate population inversion and sub-Poissonian excitation statistics of $N$ two-level atoms in the context of collective resonance fluorescence. This occurs within photonic band gap and other confined photonic systems that exhibit sharp features in the optical density of states. When the deviation in the photon density of states between the Mollow spectral components is considerable, the atoms switch collectively from ground to excited states at a critical value of the applied laser field. This suggests a new mechanism of sub-Poissonian pumping of lasers, fast optical switching, and optical transistor action.

Optical limiting and switching of short pulses by use of a nonlinear photonic bandgap structure with a defect

Abstract: An extension of the recently introduced nonlinear finite-difference time-domain technique [Opt. Lett.21, 1138 (1996)] for the study of electromagnetic wave propagation in a non-linear Kerr medium to include absorption is presented. The optical limiting and switching of short pulses by use of a nonlinear quarter-wave reflector (a one-dimensional photonic bandgap structure) with a defect is studied. Comparison with an optical limiter and with an optical switch with a perfect nonlinear quarter-wave reflector shows that introducing a defect can improve the performance of these devices.

Inter-ring cross-connect for survivable multi-wavelength optical communication networks

Abstract: A cross-connect (92) for a multi-ring, multi-channel telecommunications network, especially for a wavelength-division multiplexed (WDM) optical network. Each of the interconnected rings (94 and (100) is self-healing by provision of a redundant counter-rotating ring (96 and 98)) or excess capacity on pairs of counter-rotating rings. Because an interconnect between self-healing rings (90) does not need to connect working to protection fibers, or similarly redundant fibers, the complexity of the interconnect can be substantially reduced. For several important architectures, the interconnect can be decomposed into one or two 3x3 interconnects. Further, a wide-sense non-blocking 3x3 interconnect can be advantageously implemented as four 2x2 switches, which may be a basic building block of optical switches. A novel algorithm is available to add new paths through such a 3x3 interconnect. The interconnect can be decomposed into one or two 4x4 interconnects when another pair of add (102)/drop (104) lines are added. Such an architecture provides full connectivity between user nodes connected to the add (102)/drop (104) lines and user nodes attached to the rings.

Resonator modulators and wavelength routing switches

Abstract: The invention provides an optical switch and modulator which uses a closed loop optical resonator. The optical resonator is a dielectric cavity whose primary function is to store optical power. Various structures are possible, and a particularly advantageous one is a ring shaped cavity. The wavelength response at the output port of a ring resonator side coupled to two waveguides is determined by the details of the resonator, and the coupling between the resonator and the waveguides. By coupling to adjacent resonators, the modulator response can be improved over that of a single resonator. One such improvement is in modulator efficiency, which is defined as the ratio of the change in optical intensity at the output, to a change in absorption in the ring waveguides. Absorption is used for switching and modulation without incurring significant optical attenuation. Another improvement involves making the resonance insensitive to small deviations in wavelength or index change. The latter improves fabrication tolerances and compensates for possible drift of the signal wavelength. Collectively, the behavior of multiple coupled resonators yields higher order responses.

Fault-tolerant optical routing switch

Abstract: An electromagnetically controlled optical switch (100) having a plurality of optical inputs (101). An optical signal at each input (101) is spatially decomposed into two coparallel, orthogonally polarized beams by a birefringent element (130). An array (140) of field-controlled polarization rotators are positioned in the paths of the decomposed light beams so that the polarization of the emergent beam pairs are set to be at one of the orthogonal states (i.e., both beams are either vertical or horizontally polarized). A following birefringent element (150) spatially routes the light beam pairs based upon their polarization. A second array (160) of polarization rotators follows the second birefringent element (150) and is set to be in the opposite state from the first array (140), such that the emergent beams are orthogonal to their input states before they entered the first polarization rotator (140). The beams are combined by a firefringent element (170) to form a plurality of combined beams that are coupled to output ports (102, 103).

Method and apparatus providing optical input/output through the back side of an integrated circuit die

Abstract: A method and an apparatus providing optical input/output in an integrated circuit. In one embodiment, optical modulators and demodulators, which are coupled to integrated circuit input/output nodes, are disposed on or within the back side semiconductor substrate of a flip chip packaged integrated circuit. Since a flip chip packaged integrated circuit die is utilized, full access to the optical modulators and demodulators is provided from the back side of the integrated circuit die for optical input/output. In one embodiment, a heat sink including a light source and an optical assembly is thermally and optically coupled to the back side of the integrated circuit die. A light beam is directed to the optical modulators and the deflected modulated light beam is routed and directed to the optical demodulators to realize optical input/output. In one embodiment, infrared light may be utilized such that the optical modulators and demodulators are disposed within a silicon semiconductor substrate. Since silicon is partially transparent to infrared light, optical input/output is realized through the back side and through the semiconductor substrate of the flip chip packaged integrated circuit die.

Hot plug of adapters using optical switches

Abstract: A device that enables a card to be hot-plugged into a socket on a processor-base machine includes a signal bus arbitrator, a signal bus switch, a power bus switch, a cover plate switch, status signals and a controller. The controller monitors the status signals and other signals from the cover plate switch and the signal bus arbitrator to generate control signals that activate the power bus switch and the signal bus switch to control power and signal transmitting facilities at the socket.

All-optical switching in long-period fiber gratings.

Abstract: Nonlinear pulse propagation in long-period fiber gratings is studied with a mode-locked Q-switched laser pulse approximately 80 ps in duration at a wavelength of 1.05 µm. Optical switching, pulse reshaping, and optical limiting are found at intensities in the range of 1–20 GW/cm2.

Optical switching apparatus and method for use in the construction mode testing of a modular fiber administration system

Abstract: A device and method for connecting an optical switch to the optical fibers that terminate on a fiber distribution shelf within a fiber administration system. The optical switch device contains a support plate that is shaped essentially the same as the protective cover of fiber distribution shelf. As such, the support plate of the optical switch device can be joined to a specific fiber distribution shelf by substituting the support plate for the protective cover. An optical switch is affixed to the support plate, wherein the optical switch is sized not to extend beyond the peripheral boundaries of the support plate. As a result, when the support plate is placed over a fiber distribution shelf, the optical switch joined to the support plate does not obscure any other fiber distribution shelf in the fiber administration system.

Method and system for equalizing pmd using incremental delay switching

Abstract: A polarization beam splitter separates the optical data signal into first and second orthogonally polarized optical signals. A first variable time delay element provides a first incremental propagation delay for the first polarized optical signal. A second variable time delay element provides a second incremental propagation delay for the second polarized optical signal. The first and second variable time delay elements consist of a series of optical switches optically interconnected by different incremental lengths of optical fiber. For example, 2 X 2 optical switches are provided for switching between a reference fiber segment and a respective delay fiber segment to provide a relative incremental propagation delay. A controller controls optical switches in the first and second variable switching delay elements to set first and second incremental propagation delays. In particular, the first and second polarized optical signals are incrementally delayed relative to one another so as to compensate for polarization mode dispersion. A beam combiner then combines the first and second signals to form an optical output data signal which can be detected accurately by a receiver without the effects of polarization mode dispersion. In this way, optical data signals can be reliably transmitted over greater distances along a long-haul fiber optic dispersive medium at even greater bit-rates and bandwidth.

Ultrafast all-optical switch using complex refractive index changes of thin films containing photochromic dye

Abstract: An all-optical switch has been proposed based on photoinduced changes of an imaginary part of complex refractive index in a composite thin film made by silver and polymer thin films containing photochromic dye. Very fast switching on and switching off of a reading beam was demonstrated at the incident angle of guided wave mode using a photochromic spiropyran-doped polystyrene thin film and a ns pulsed laser as a writing beam. These responses were caused by the changes of an extinction coefficient due to photochromism. No applied power was required to hold the switched state.

Low loss optical switch with inducible refractive index boundary and spaced output target

Abstract: An extremely low-loss optical switch element includes a first waveguide segment having first and second regions longitudinally-adjacent with each other and having an index of refraction difference which is greater when the switch element is in an "on" state than when it is in an "off" state. The two regions have a common boundary which is oriented at an angle in the first waveguide so as to redirect optical energy through total internal reflection when the switch element is in the "on" state. The switch element further includes a second waveguide segment spaced from the first waveguide segment and disposed and oriented to guide optical energy redirected from the first waveguide segment when the switch element is in the "on" state.

Micro machined optical switch

Abstract: Optical switches utilizing electrostatically-driven actuators formed from micro machined plates are disclosed. Under an applied voltage, a movable plate moves toward a fixed plate or a conductive region of an underlying support. The switches further include a mechanical linkage from the actuator to an optical device. The displacement of the movable plate generated at the actuator is transferred, via the mechanical linkage, to the optical device. The optical device, which is positioned in close proximity to optically-aligned spaced optical fibers, is movable into and out of an optical path defined by the optical cores of the optical fibers by the action of the actuator. An "in-plane" optical switch includes an actuator having two vertically-oriented electrodes, which generates a substantially horizontally-directed displacement of the movable plate and the linked optical device. An "out-of-plane" optical switch includes an actuator having at least one horizontally-disposed suspended above a conductive region of an underlying support. The actuator generates a substantially vertically-directed displacement of the movable plate and the linked optical device.

Large-signal analysis of all-optical wavelength conversion using two-mode injection-locking in semiconductor lasers

Abstract: A large-signal analysis is presented for a DC-biased Fabry-Perot laser locked by simultaneous strong optical injection of a CW signal and a modulated signal into different modes. The model is based on the description of injection-locking by Lang (1982) which is shown to hold even under the condition of strong injection and large detuning of the input signals. The following results are obtained: the configuration allows all-optical wavelength conversion in the multigigabit range, and both logically noninverting and inverting conversion is possible. In both operation modes, the conversion mechanism is mainly attributed to dispersive switching which is shown to be very fast above threshold due to injection-locking. Operation up to data rates of 20 Gb/s is possible with reasonable output extinction ratio. The bandwidth is determined by the relaxation oscillation frequency of the laser. It will be extended by decreasing the resonator length, increasing the injected current, and increasing the injected optical power. The output signal is nearly chirp-free. The model is able to explain the main results of previously published experiments.

Optical cross-connect switch using a pin grid actuator

Abstract: An optical cross-connect switch incorporates a pin grid actuator to selectively position optical elements relative to optical beams in the switch. A high density array of aligned, optically reflective elements is attached to the ends of independently selectable and moveable pins in the pin grid actuator. The pin grid actuator is the type extensively used in dot matrix printers. Linear motion of the pins causes the reflective element attached to the pin to intercept optical beams provided by input fibers coupled to the switch. Intercepted optical beams are redirected to designated output fibers, also coupled to the switch. A staggered arrangement of the input and output fibers equalizes all of the signal pathlengths through the switch, regardless of which pin in the pin grid actuator is selected. According to an alternate preferred embodiment of the present invention, multiple optical cross-connect switches are cascaded using a staggered arrangement of interconnecting fibers.

Optical add-drop multiplexers compatible with very dense wdm optical communication systems

Abstract: The present invention provides add-drop multiplexers which are compatible with dense wavelength division multiplexed (WDM) systems having large numbers of optical channels. The add-drop multiplexers employ sets of Bragg gratings separated by an optical isolator to reliably add or drop optical channels without crosstalk. The Bragg grating sets and the optical isolator are interposed between first and second optical couplers. Optical channels to be dropped from a WDM optical signal are reflected by the first set of Bragg gratings and exit the add-drop multiplexer through the first coupler. Optical channels to be added to a WDM optical signal enter the add-drop multiplexer through the second optical coupler.

Optical node system for a ring architecture and method thereof

Abstract: An optical node system for an optical ring network reduces certain costs associated with current ring architectures by using at least a portion of the light from an incoming optical signal to transmit an outgoing optical signal. In accordance with certain embodiments, the node includes an optical multiplexer which receives optical signals having a plurality of wavelengths. The optical multiplexer can be configured to output optical signals having certain wavelengths and to route at least one optical signal from the ring of at least one particular wavelength (or wavelength band) to a corresponding optical transceiver. The optical transceiver receives the incoming optical signal of the particular wavelength routed from the optical multiplexer and transmits at least a portion of the light from the incoming optical signal having the particular wavelength. The optical transceiver can modulate user information onto the light of the particular wavelength and/or pass at least a portion of the incoming optical signal for transmission as an outgoing optical signal onto the optical ring network. Thus, the optical node system alleviates the need for nodes to have a laser tuned to the particular wavelength for transmitting an outgoing optical signal having the particular wavelength.

M input port by N output port optical switching system

Abstract: An M×N optical switching system has a plurality of M optical input ports, each of which is directs a respectively associated optical input beam along one of M spaced apart coplanar parallel input optical paths intersecting an optical coupling path. N optical output ports are installed of the input ports at spaced apart locations of the optical coupling path. Each optical output ports receives a respective optical signal along one of N spaced apart coplanar output optical paths that intersect the optical coupling path apart. M+N mirrors are alignable with a normal bisecting a common angle at a respective intersection of the M input optical paths and the N output optical paths with the optical coupling path. A plurality of actuators controllably move selected mirrors into and out of the optical coupling path, so as to cause an optical signal incident at a selected one of the M optical input ports to be coupled to a selected one of the N optical output ports.