Compact all-optical bypass-exchange switch

An electronically or optically addressed compact optical bypass-exchange switch is investigated and experimentally demonstrated.The switch is polarization based and consists of a controllable λ/2 platesandwiched between two polarizing beam displacers. The input and the output signals propagate normal to the switching array, which makes the switch extremely attractive for cascading switching arrays, as found in multistage interconnect networks. A complete, all-optical interconnection network is suggested.     

Switching kinetics of a Cu2S-based gap-type atomic switch

The switching time of a Cu(2)S-based gap-type atomic switch is investigated as a function of temperature, bias voltage, and initial off-resistance. The gap-type atomic switch is realized using a scanning tunneling microscope (STM), in which the formation and annihilation of a Cu-atom bridge in the vacuum gap between the Cu(2)S electrode and the Pt tip of the STM are controlled by a solid-electrochemical reaction. Increasing the temperature decreases the switching time exponentially with an activation energy of about 1.38 eV. Increasing the bias voltage also shortens the switching time exponentially, exhibiting a greater exponent for the lower bias than for the higher bias. Furthermore, faster switching has been achieved by decreasing the initial off-resistance between the Cu(2)S electrode and STM tip. On the basis of these results, we suggest that, in addition to the chemical reaction, the electric field in the vacuum gap plays a significant role in the operation of a gap-type atomic switch. This investigation advances our understanding of the operating mechanism of an atomic switch, which is a new concept for future electronic devices.     

Analytical model of a bubble switch

A model is presented for a bubble switch based on the Y-bar propagation element. Good correlation of the predictions of the model with experimental results is found for 8 μ bubbles. The heuristically derived scaling law, which predicts that the switching current must remain constant as the bubble diameter decreases, is confirmed by direct calculation with the model. The model shows that it will be increasingly difficult to design switches as the bubble diameter is reduced below 1 μ.     

Free-space optical cross-connect switch by use of electroholography

An electrically controlled holographic switch is proposed as a building block for a free-space optical interconnection network. The switch is based on the voltage-controlled photorefractive effect in KLTN crystals at the paraelectric phase. It is built of electrically controlled Bragg gratings stored in the volume of the crystal. A compact switch that connects four high-speed fiber-optic communication channels with high efficiency is demonstrated experimentally. The switch performance is investigated and optimized. This switch is extremely attractive for cascaded switching arrays such as those found in multistage interconnect networks.     

Three-dimensional broadband polymer optical waveguide switch matrix

A 1 x 4 3D broadband polymer optical waveguide switch matrix is demonstrated. The fabricated device, which contains four vertically coupled thermo-optic switches, has a compact construction (only 9 mm in length) and a power consumption of 45 mW. Compared with the corresponding planar ones, this 3D switch matrix has two distinct features. First, the light signal can be easily switched to any output port by operating only a single switch unit. Second, the switching extinction ratio, cross talk, and insertion loss of this matrix are practically wavelength independent over the whole C band. We also show that this structure can be extended quite simply to an M x M nonblocking switch matrix.     

Design of polarisation-independent bidirectional optical switch

Optical switching plays a vital role in all optical communication and network. Various optical switchings have been developed in recent years as a way to improve reliability problems and to build small size, robust integrated devices. A novel low crosstalk, high switching speed, compact in structure, efficient in performance, polarisation independent, and reversible 2 × 2 optical switching is proposed using a phase spatial light modulator (PSLM), a polarising beam-splitter (PBS), a mirror, a half-wave plate (HWP) and a quarter-wave plate (QWP). The optical switching should be helpful in the design of a large-scale switch matrix, and show considerable promise in the future of fibre optic networks.     

A surface-anchored molecular four-level conductance switch based on single proton transfer

The development of a variety of nanoscale applications requires the fabrication and control of atomic or molecular switches that can be reversibly operated by light, a short-range force, electric current or other external stimuli. For such molecules to be used as electronic components, they should be directly coupled to a metallic support and the switching unit should be easily connected to other molecular species without suppressing switching performance. Here, we show that a free-base tetraphenyl-porphyrin molecule, which is anchored to a silver surface, can function as a molecular conductance switch. The saddle-shaped molecule has two hydrogen atoms in its inner cavity that can be flipped between two states with different local conductance levels using the electron current through the tip of a scanning tunnelling microscope. Moreover, by deliberately removing one of the hydrogens, a four-level conductance switch can be created. The resulting device, which could be controllably integrated into the surrounding nanoscale environment, relies on the transfer of a single proton and therefore contains the smallest possible atomistic switching unit.     

A nonvolatile plasmonic switch employing photochromic molecules

We demonstrate a surface plasmon-polariton (SPP) waveguide all-optical switch that combines the unique physical properties of small molecules and metallic (plasmonic) nanostructures. The switch consists of a pair of gratings defined in an aluminum film coated with a 65 nm thick layer of photochromic (PC) molecules. The first grating couples a signal beam consisting of free space photons to SPPs that interact effectively with the PC molecules. These molecules can reversibly be switched between transparent and absorbing states using a free space optical pump. In the transparent (signal "on") state, the SPPs freely propagate through the molecular layer, and in the absorbing (signal "off") state, the SPPs are strongly attenuated. The second grating serves to decouple the SPPs back into a free space optical beam, enabling measurement of the modulated signal with a far-field detector. In a preliminary study, the switching behavior of the PC molecules themselves was confirmed and quantified by surface plasmon resonance spectroscopy. The excellent (16%) overlap of the SPP mode profile with the thin layer of switching molecules enabled efficient switching with power densities of approximately 6.0 mW/cm2 in 1.5 microm x 8 microm devices, resulting in plasmonic switching powers of 0.72 nW per device. Calculations further showed that modulation depths in access of 20 dB can easily be attained in optimized designs. The quantitative experimental and theoretical analysis of the nonvolatile switching behavior in this letter guides the design of future nanoscale optically or electrically pumped optical switches.     

Low-temperature-GaAs device used simultaneously as a mode-locking device and as a photoconductive switch

We present a low-temperature-grown GaAs device that combines the features of mode locking and photoconductive switching. The mode-locking mechanism is based on intensity-dependent defocusing. Additionally, the generated carriers produce an electrical signal in the biased switch geometry. This technique allows for simultaneous generation of synchronized optical and electrical pulse trains with a single device.     

A resistive superconducting power switch with a switching power of 40 MW at 47 kV

After a short review of the state of the art in superconducting and conventional switch technology, the experimental results for a resistive superconducting switch are described. All components of the experiment were designed and constructed after the requirements of the high voltage technique. Fibreglass reinforced epoxy manufactured by different techniques was the preferred insulation material. For fast-current induced triggering of large wire switches, a useful solution is given. The switching process was investigated and compared with an existing theory. The rapid increase of the hot spot temperature of the high resistive switch material could be controlled. Some unexpected properties concerning the stability and quench propagation of the superconducting cable use are described and an attempt is made to give an explanation.     

Polarization-controlled multistage switch based on polarization-selective computer-generated holograms

We describe a polarization-controlled free-space optical multistage interconnection network based on polarization-selective computer-generated holograms: optical elements that are capable of imposing arbitrary, independent phase functions on horizontally and vertically polarized monochromatic light. We investigate the design of a novel nonblocking space-division photonic switch architecture. The multistage-switch architecture uses a fan-out stage, a single stage of 2 x 2 switching elements, and a fan-in stage. The architecture is compatible with several control strategies that use 1 x 2 and 2 x 2 polarization-controlled switches to route the input light beams. One application of the switch is in a passive optical network in which data is optically transmitted through the switch with a time-of-flight delay but without optical-to-electrical conversions at each stage. We have built and characterized a proof-of-principle 4 x 4 free-space switching network using three cascaded stages of arrayed birefringent computer-generated holographic elements. Data modulated at 20 MHz/channel were transmitted through the network to demonstrate transparent operation.     

Analysis of a digital microstrip optical switch: a novel method

A time domain analysis of an optically controlled digital microstrip switch for microwave integrated circuits on Si substrates is studied. A new model for high-frequency pulse propagation on a microstrip optical switch for different optical parameters is presented. A frequency-dependent macromodel for a microstrip line with a gap is implemented in Spice 3, taking into consideration high-frequency pulse dispersion, conductor and dielectric losses, metallization thickness, gap length, and different optical parameters such as optical energy, surface recombination velocities, and diffusion of generated carriers. In addition, the developed model has been used to optimize the switching frequency, gap length, level of optical power, and suitable substrate material parameters.     

Nonequilibrium quantum transport properties of a silver atomic switch

Combining nonequilibrium Green's function technique with density functional theory, electron transport, and structural properties of an Ag atomic switch through Ag2S have been investigated. We have found that an Ag atomic conductance channel in Ag2S is generated after structure optimization, resulting in large enhancement of the electron transmission coefficient at the Fermi level and metallic behavior of the Ag-Ag2S-Ag system. Such spontaneous metallization at the Ag-Ag2S interface may play an important role in fast switching of the Ag-Ag2S atomic switch.     

An automatic low temperature heat switch

A heat switch for use at cryogenic temperatures is described. It utilizes the pressure-dependence of thermal conductivity of gases and the decrease of vapour pressure with temperature. The switching temperature can be varied widely by changing the working gas. Due to the absence of mechanically moving parts, lifetime and reliability are high. A thermal conductivity on/off ratio of 500 can easily be achieved.     

Vertically oriented carbon nanofiber based nanoelectromechanical switch

We present a proof-of-principle study of a vertically aligned carbon nanofiber switch and study relevant parameters via a model for a static switch. Vertically aligned freestanding carbon nanofibers are produced by plasma-enhanced chemical vapor deposition (PECVD) and their deflection under applied voltage is measured using an optical microscope. The deflection is compared with a static force balance model, which successfully predicts the switching behavior assuming a nanofiber modulus of 40 GPa, which is consistent with independent modulus measurements made in our laboratory. The model is then extended to explore constraints for implementing a vertically aligned nanotube switch into present CMOS process flow. Carbon nanofibers of less than 40 nm in diameter, which may be grown by current PECVD technology, are shown to be acceptable for device integration for current and future CMOS scaling. To accommodate varying tube sizes and architectures, a basic scaling relationship is developed to relate CMOS via parameters and nanofiber characteristics to programming voltage.     

Compact carrier-injection photonic crystal switch for on-chip communications

Performances and metrics of an electro-optical wavelength switch in silicon?on- insulator technology using a 20 μm long photonic crystal directional coupler structure are theoretically studied using both electrical and finite difference time domain simulations. The possibility of photonic switching through carrier injection using a forward-biased PIN diode configuration is evaluated. It is shown that wavelength routing near λ=1550 nm with optical insertion loss of 1 dB and an electrical cut-off frequency of 60 MHz can be achieved with a bias voltage of 1 V and a dissipated electrical power of 700 μW. Integration of the device could be applied to active routing of light in silicon chips for the realisation of on-chip switching networks.     

Interferometric optical switch enhanced by a multi-resonance ring resonator structure

We propose a novel configuration for optical switches by the use of two coupled ring resonators acting as a phase-shifting element in a Mach–Zehnder interferometer. Because the ring structure is multi-resonant within one period of its phase response, light at any frequency within the period can be addressed by tuning the device across a small frequency interval. This enables the use of low voltages for electro-optic control of the switch, allowing for a tunable photonic switching device that operates at 1?V voltage levels.     

Tuning the conductance of a molecular switch

The ability to control the conductance of single molecules will have a major impact in nanoscale electronics. Azobenzene, a molecule that changes conformation as a result of a trans/cis transition when exposed to radiation, could form the basis of a light-driven molecular switch. It is therefore crucial to clarify the electrical transport characteristics of this molecule. Here, we investigate, theoretically, charge transport in a system in which a single azobenzene molecule is attached to two carbon nanotubes. In clear contrast to gold electrodes, the nanotubes can act as true nanoscale electrodes and we show that the low-energy conduction properties of the junction may be dramatically modified by changing the topology of the contacts between the nanotubes and the molecules, and/or the chirality of the nanotubes (that is, zigzag or armchair). We propose experiments to demonstrate controlled electrical switching with nanotube electrodes.     

Switching transient analysis of a metal/ferroelectric/semiconductor switch diode with high speed response to infrared light

A thin PbTiO(3)-n-p(+) silicon switch diode has been developed, in which the switching voltage (the turned-on voltage) changes in proportion to the infrared light power. The diode has a rapid response time of 0.65 mus compared with other conventional infrared sensors. It is attributed to the rapid switching device structure and the smaller pyroelectric layer thickness, 50 nm. In this paper, we have analyzed the rapid switching transient response by using heat conduction and switching theory successfully. The experimental results are in agreement with the theoretical analysis.     

A remotely controlled coaxial switch for impedance standard calibration

A switch which permits the connection, in sequence, of a couple of four-terminal-pair impedance standards to an automatic RLC bridge, is presented. The purpose of the switch is to automate the process of impedance calibration by 1:1 substitution. The switch is capable of engaging four coaxial lines at a time (switching both the internal conductor and the screen of each line); the electrical contacts are British Post Office MUSA connector. The switch, in the closed position, adds 2 m/spl Omega/ of resistance to each coaxial line in the electrical path. The switch is moved by pneumatic actuators to avoid any electrical interference, and is remotely controlled via RS-232 interface. Measurement examples are shown.