All-optical flip-flops based on DFB laser diodes and DFB-arrays

We present numerical and experimental results on a number of different all-optical flip-flops which are based on DFB laser diodes or DFB-arrays. All these flip-flop concepts show potential for fast switching with low switching energy and high extinction ratio. They are moreover very robust in the sense that the switching pulses (and the injected CW beam in some cases) can be of arbitrary wavelength and that the bistability characteristics can be tuned by simple variation of the current injected into the devices. Two different designs for all-optical flip-flop operation will be discussed in detail. The first one is a DFB or DBR laser diode coupled to a semiconductor optical amplifier, in which the bidirectional coupling between laser and amplifier causes the bistability. The second concept is based on bistable behaviour in a single AR-coated DFB laser, with low coupling coefficient and in which a CW signal is injected. These all-optical flip-flops can easily be extended to optically switchable multistate devices with any number of stable states. Such multistate devices are briefly discussed at the end.     

Opto-electronic Bistable Devices for Image Processing

Several opto-electronic bistable devices with twisted nematic liquid crystals are designed and used for image processing. The optical bistability characteristics of liquid crystals are used for two types of light valve, those with array structure and parallel operation and those with single cell with sequential operation. Experimental studies demonstrate the application of these opto-electronic bistable devices in important operations currently used in image processors, such as intensity limiting for contrast improvement and noise elimination, contour accentuation for pattern recognition, linear and nonlinear optical filtering (in spatial and spectral domains), incoherent-to-coherent image conversion and logic operations.     

InGaAsP/InP有源时分光子交换器件

自行设计并研制成功了两种有源时分光子交换器件：ＩｎＧａＡｓＰ／ＩｎＰ ＥＭＰＢＨ双稳激光器ＩｎＧａＡｓＰ／ＩｎＰ ＭＱＷ ＤＣＰＢＨ双稳激光器，对这两种器件的部分性能作了简要报道。     

An optical system for bilateral recombination-radiation diagnosticsof the carrier redistribution in switching power devices

An optical scanning system is developed for the detection of recombination radiation from power devices. The instrument facilitates two-dimensional characterization of the excess-carrier content in a device. A bilateral technique enables measurements along various perpendicular surfaces of the devices under investigation. Hence, measurements of processes not present, or less dominant, in one direction may be observed in another. Examples taken from gate turn-off (GTO)-thyristor investigations are presented. All stages of the switching cycles as well as during the ON-state can be investigated with the instrument. Detailed three-dimensional carrier maps are produced for the visualization of measurement results, and sequences of maps are used to observe time-dependent phenomena involved in the transient operation of a device. Features associated with placement of the optical focus are explained, and possibilities of tomographic mapping of power devices are discussed     

Optical switching and normal mode splitting in hybrid semiconductor microcavity containing quantum well and Kerr medium driven by amplitude-modulated field

ABSTRACT

We theoretically investigate optical bistability/multistability for all optical switching signature in a hybrid semiconductor microcavity system comprising a quantum well and a Kerr nonlinear substrate. The system is essentially two optically coupled microcavities with one of the microcavity being driven by an external amplitude-modulated pump laser. We show that the switching between bistable and multistable behaviour is influenced by the modulated pump laser, Kerr nonlinearity and the optical coupling between the two microcavities. We further investigate the intracavity spectrum of quantum fluctuations which exhibit the well-known normal mode splitting (NMS). The NMS behaviour is also found to be influenced by the system parameters. These results demonstrate that the present hybrid nonlinear system can be used in designing sensitive optical devices.     

All-optical bistable switching based on photonic crystal slab nanocavity using nonlinear Kerr effect

In this paper, we propose all-optical bistable switching based on a two-dimensional (2D) photonic crystal slab nanocavity using the nonlinear Kerr effect with improved optical properties such as on/off ratio and switching power. The nonlinear properties of different kinds of nanocavity-based L3 structures are characterized. Using the 2D finite-difference time-domain method, we present a new structure of nanocavities for all-optical switching. The device has on/off ratio greater than 15?dB and power smaller than 375?mW for input optical pulses in the range of picoseconds.     

Switching process between bistable positions of multiquantum flux tubes in a thin-film type I superconductor

A superconducting memory device based on a bistable vortex position represents an interesting storage medium for future Josephson computers. In order to study the operational mode of such a single-flux quantum memory cell, we use as a model system multiquantum flux tubes in a thin-film type I superconductor (Pb). By employing high-resolution stroboscopic magnetooptical flux detection, we are able to globally visualize both spatial and temporal behavior of rapidly switching individual flux tubes. All experimental results agree reasonably well with theoretical model considerations of the energy balance during the elementary switching process.Supported by a grant from the Deutsche Forschungsgemeinschaft.     

nu-Si:H-FLC: ferroelectric liquid-crystal-amorphous silicon novelty filter

Presented is a ferroelectric liquid-crystal-amorphous silicon (alpha-Si:H) optical novelty-filter sensor. It uses the bistable switching property of the ferroelectric liquid crystal to store an inverted image, which is used to optically filter a subsequent image by means of an intrinsic pleochroic-dye-based polarizing scheme. The resulting novelty signal, encoded as transmitted intensity, is then detected by the use of an integrated interdigitated detector that monitors the photocurrent generated in the alpha-Si:H. Each aspect of the device functionality is covered, and the optimum device configuration and operation is discussed. System demonstrations through the use of the device are reported, and alternative applications discussed.     

Optical bistability and multistability driven by external magnetic field in a dielectric slab doped with nanodiamond nitrogen vacancy centres

Abstract

The theoretical investigation of controlling the optical bistability (OB) and optical multistability (OM) in a dielectric medium doped with nanodiamond nitrogen vacancy centres under optical excitation are reported. The shape of the OB curve from dielectric slab can be tuned by changing the external magnetic field and polarization of the control beam. The effect of the intensity of the control laser field and the frequency detuning of probe laser field on the OB and OM behaviour are also discussed in this paper. The results obtained can be used for realizing an all-optical bistable switching or development of nanoelectronic devices.     

High-speed free-space interconnect based on optical ring topology: experimental demonstration

The design and implementation of a high-speed optical-ring-topology-based free-space optical interconnect is described. This interconnect system operates at 500 MHz and consists of 16 laser transmitters, a four-channel free-space interconnect, and a high-speed receiver. A nearest-neighbor interconnect is demonstrated. At the data rate of 500 MHz the total system throughput is 8 Gbits/s. The system can easily be operated at much higher data rates since the rate is limited only by the electronic circuitry. A discussion is given about device issues such as optical switching devices, and practical system-design issues such as integration and interface with current electronic systems are considered. This interconnect is promising to the implementation of ultrafast massively parallel single-instruction multiple-data machines.     

Memory effect of sol–gel derived V-doped SrZrO3 thin films

V-doped SrZrO₃ (SZO) thin films on LaNiO₃/SiO₂/Si substrate are synthesized by sol–gel method to form metal–insulator–metal (MIM) sandwich structure. The physical and electrical properties of the MIM device are studied. The structure and surface morphology of the SZO films are also characterized by X-ray diffraction and scanning electron microscopy. Such a device has the bistable switching properties of current–voltage characteristics. The resistive switching between high state and low state can also be operated with voltage pulses. The device with the properties of long retention time and non-destructive readout is expected to be suitable for nonvolatile memory application.     

Field-programmable logic devices with optical input-output

A field-programmable logic device (FPLD) with optical I/O is described. FPLD's with optical I/O can have their functionality specified in the field by means of downloading a control-bit stream and can be used in a wide range of applications, such as optical signal processing, optical image processing, and optical interconnects. Our device implements six state-of-the-art dynamically programmable logic arrays (PLA's) on a 2 mm x 2 mm die. The devices were fabricated through the Lucent Technologies-Advanced Research Projects Agency-Consortium for Optical and Optoelectronic Technologies in Computing (Lucent/ARPA/COOP) workshop by use of 0.5-mum complementary metal-oxide semiconductor-self-electro-optic device technology and were delivered in 1998. All devices are fully functional: The electronic data paths have been verified at 200 MHz, and optical tests are pending. The device has been programmed to implement a two-stage optical switching network with six 4 x 4 crossbar switches, which can realize more than 190 x 10(6) unique programmable input-output permutations. The same device scaled to a 2 cm x 2 cm substrate could support as many as 4000 optical I/O and 1 Tbit/s of optical I/O bandwidth and offer fully programmable digital functionality with approximately 110,000 programmable logic gates. The proposed optoelectronic FPLD is also ideally suited to realizing dense, statically reconfigurable crossbar switches. We describe an attractive application area for such devices: a rearrangeable three-stage optical switch for a wide-area-network backbone, switching 1000 traffic streams at the OC-48 data rate and supporting several terabits of traffic.     

Towards an optimal model for a bistable nematic liquid crystal display device

Bistable liquid crystal displays offer the potential for considerable power savings compared with conventional (monostable) LCDs. The existence of two stable field-free states that are optically distinct means that contrast can be maintained in a display without an externally applied electric field. An applied field is required only to switch the device from one state to the other, as needed. In this paper we examine a theoretical model of a possible bistable device, originally proposed by Cummings and Richardson (Euro J Appl Math 17:435–463 2006), and explore means by which it may be optimized, in terms of optical contrast, manufacturing considerations, switching field strength, and switching times. The compromises inherent in these conflicting design criteria are discussed.     

Low-switching power (<45 mW) optical bistability based on optical nonlinearity of ytterbium-doped fiber with a fiber Bragg grating pair

We propose a new optical bistable device (OBD), which is constructed by connecting two symmetrical fiber Bragg gratings with a ytterbium-doped fiber to form a nonlinear Fabry–Perot cavity. The principle of this new OBD is described using the transfer-matrix method, and the two groups of transmitted and reflected optical bistability loops under different parameters are investigated symmetrically. Compared with single fiber Bragg grating switching, whose switching power is greater than 2?kW, this new device has evident merits in reducing the switching power to less than 45?mW.     

In-Plane Integration of Polymer Microfluidic Channels With Optical Waveguides– A Preliminary Investigation

The next major challenges for lab-on-a-chip (LoC) technology are 1) the integration of microfluidics with optical detection technologies and 2) the large-scale production of devices at a low cost. In this paper the fabrication and characterisation of a simple optical LoC platform comprising integrated multimode waveguides and microfluidic channels based on a photo-patternable acrylate based polymer is reported. The polymer can be patterned into both waveguides and microfluidic channels using photolithography. Devices are therefore both quick and cost-effective to fabricate, resulting in chips that are potentially disposable. The devices are designed to be highly sensitive, using an in-plane direct excitation configuration in which waveguides intersect the microfluidic channel orthogonally. The waveguides are used both to guide the excitation light and to collect the fluorescence signal from the analyte. The potential of the device to be used for fluorescence measurements is demonstrated using an aqueous solution of sodium fluorescein. A detection limit of 7 nM is achieved. The possibilities offered by such a device design, in providing a cost-effective and disposable measurement system based on the integration of optical waveguides with LoC technology is discussed.     

Designing bistable [2]rotaxanes for molecular electronic devices

The development of molecular electronic components has been accelerated by the promise of increased circuit densities and reduced power consumption. Bistable rotaxanes have been assembled into nanowire crossbar devices, where they may be switched between low- and high-conductivity states, forming the basis for a molecular memory. These memory devices have been scaled to densities of 10(11) bits cm(-2), the 2020 node for memory of the International Technology Roadmap for Semiconductors. Investigations of the kinetics and thermodynamics associated with the electromechanical switching processes of several bistable [2]rotaxane derivatives in solution, self-assembled monolayers on gold, polymer electrolyte gels and in molecular switch tunnel junction devices are consistent with a single, universal switching mechanism whose speed is dependent largely on the environment, as well as on the structure of the switching molecule. X-ray reflectometry studies of the bistable rotaxanes assembled into Langmuir monolayers also lend support to an oxidatively driven mechanical switching process. Structural information obtained from Fourier transform reflection absorption infrared spectroscopy of rotaxane monolayers taken before and after evaporation of a Ti top electrode confirmed that the functionality responsible for switching is not affected by the metal deposition process. All the considerable experimental data, taken together with detailed computational work, support the hypothesis that the tunnelling current hysteresis, which forms the basis of memory operation, is a direct result of the electromechanical switching of the bistable rotaxanes.     

Comparison of Sagnac and Mach-Zehnder ultrafast all-optical interferometric switches based on a semiconductor resonant optical nonlinearity

We present a theoretical analysis of recently demonstrated ultrafast all-optical interferometric switching devices (based on Sagnac and Mach-Zehnder interferometers) that use a large optical nonlinearity in a resonant regime. These devices achieve ~10-ps switching windows and do not require high-energy optical control pulses. We theoretically analyze and compare one Sagnac and two Mach-Zehnder switching configurations.     

Optical Bistability and Reversed Switching Effect in a Three-photon Resonant Medium

We have developed, ab initio, a theory for the interaction of coherent laser light in three-photon resonance with two effective levels of a multilevel atom. The theory is developed to consider the optical bistability of homogeneously broadened, three-photon, resonant multilevel atoms inside a ring cavity. It is shown that optical bistable behaviour in the fundamental and the generated third harmonic can be obtained using, for example, Na atoms. The device may be useful in constructing two-channel, optical bistable switches. In certain nonlinear regimes it may be possible to obtain reversed switching between the fundamental and the third harmonic bistability.     

Optical bistability in vertical-cavity semiconductor optical amplifiers

We present an overview of the properties and applications of optical bistability in vertical-cavity semiconductor optical amplifiers (VCSOAs). The basic physics and analytical models of this optical nonlinearity are discussed. Experimental results obtained from a VCSOA operated in the 850 nm wavelength region are presented. Counterclockwise hysteresis loops are obtained over a range of initial phase detuning and bias currents. One hysteresis loop is observed experimentally with an input power as low as 2 muW when the device is biased at 98% of its lasing threshold. Numerical simulations based on the Fabry-Perot resonator model and rate equations we developed show good agreement with our experimental observations. In addition, a low input intensity high contrast (10:1) optical and gate and 2R regeneration are demonstrated. We believe that bistable VCSOAs can significantly advance the prospect of a dense two-dimensional array of low-switching-intensity all-optical logic and memory elements.     

Sliding-banyan network performance analysis

The sliding-banyan (SB) network employs an interleaved multistage shuffle-exchange topology, implemented with a three-dimensional free-space interconnection architecture that connects a multichip backplane to itself. Surface-normal emitters and detectors, which compose the stages' input-output, are spatially multiplexed within the same chip location, along with electronic control and switching resources. A simple deflection self-routing scheme minimizes internal contention, providing efficient use of switching and interconnection resources. The blocking performance of the SB is quantified through simulations based on realistic nonuniform traffic patterns. Results show that the SB architecture requires significantly fewer resources than other self-routing banyan-based networks. The multistage-switching and interconnection-resource requirements are close to the theoretical minimum for nonblocking networks, and the SB's distributed self-routing control resources grow only approximately linearly with the number of nodes, providing good scalability.