A high-voltage optoelectronic GaAs static induction transistor

Experimental realization of an optically activated, high-voltage GaAs static induction transistor (SIT) is reported. In the forward blocking state, the breakdown voltage of the device was ~200 V, while in the conduction state, on-state current densities exceeding 150 A/cm² were obtained. In the floating-gate configurations (gate open), the specific on-resistance of the device was ~50 mΩ-cm². Optical modulation of the device was achieved using a compact semiconductor laser array as the triggering source. In this mode, a gate-coupled RC network was implemented, resulting in an average switching energy gain (load energy/optical energy) of ~30. This mode of operation is applicable to series-coupled devices for pulsed switching at higher power levels     

Semiconductor devices in photonic switching

Three types of photonic switching networks have been proposed, namely, optical space-division switching, optical wavelength-division switching. Optional function devices required for each switching network are as follows: optical switch matrix for space-division switching; optical memory and optical write/read gate for time-division switching; and tunable wavelength filter and wavelength converter for wavelength-division switching. Recent progress in semiconductor functional devices such as modulators, switching devices, bistable devices, and wavelength control devices, which would be key devices to build switching networks, is reviewed     

A light-transmitting two-dimensional photodetector array using a-Sipin photodiodes and poly-Si TFT's integrated on a transparent substrate

A light-transmitting two-dimensional photodetector array (32×32 cells) using amorphous silicon (a-Si) pin photodiodes and polysilicon (poly-Si) thin film transistors (TFT's) integrated on a transparent substrate has been developed for use in a free-space optical switching network. The fabrication and the characteristics of the photodetector array are discussed. With driving circuits and sensing amplifiers, this photodetector array shows a minimum detectable power of -25 dBm and an insertion loss of 0.4 dB for an incident optical beam with a diameter of 550 μm. By monitoring the positions and the states of input optical beams, this photodetector array can be used to control the optical paths in photonic switching systems, such as a 1024-input-port optical concentrator     

Smart windows switch on the light

Optical switching devices for regulating incident solar energy that can replace traditional windows in buildings, vehicles, and aircraft are discussed. The chromogenic material in these smart windows exhibits a large change in optical properties with variation in applied electrical field, charge, light intensity, spectral composition, or temperature. The optical change transforms the material from a highly transmitting state to a partly reflecting (or absorbing) state over all or part of the visible and solar spectra. The optical switching can be activated electrically or nonelectrically. Electrically activated types, including electrochromic, liquid-crystal, and dispersed-particle (electrophoretic) devices, as well as devices based on reversible electrodeposition, and nonelectrically activated types, including devices based on photochromic and thermochromic materials, are described     

The quantum well self-electrooptic effect device: Optoelectronic bistability and oscillation, and self-linearized modulation

We report extended experimental and theoretical results for the quantum well self-electrooptic effect devices. Four modes of operation are demonstrated: 1) optical bistability, 2) electrical bistability, 3) simultaneous optical and electronic self-oscillation, and 4) self-linearized modulation and optical level shifting. All of these can be observed at room-temperature with a CW laser diode as the light source. Bistability can be observed with 18 nW of incident power, or with 30 ns switching time at 1.6 mW with a reciprocal relation between switching power and speed. We also now report bistability with low electrical bias voltages (e.g., 2 V) using a constant current load. Negative resistance self-oscillation is observed with an inductive load; this imposes a self-modulation on the transmitted optical beam. With current bias, self-linearized modulation is obtained, with absorbed optical power linearly proportional to current. This is extended to demonstrate light-by-light modulation and incoherent-to-incoherent conversion using a separate photodiode. The nature of the optoelectronic feedback underlying the operation of the devices is discussed, and the physical mechanisms which give rise to the very low optical switching energy (∼4 fJ/ μm²) are discussed.     

An 8 mm length nonblocking 4×4 optical switch array

A novel single-mode-single-slip-structure S³ optical switch using carrier-induced refractive index change is proposed as a unit cell for a small polarization-independent nonblocking N×N optical switch array. Sixteen S³ optical switches have been integrated into a nonblocking 4×4 optical switch array on an InP substrate. The 8-mm-length InGaAsP/InP 4×4 optical array has shown satisfactory switching characteristics and is suitable for larger scale integration of optical switch arrays and also for integration with other active optical devices such as laser diodes     

Wide-band guided-wave acoustooptic Bragg diffraction and devices using multiple tilted surface acoustic waves

Guided-wave acoustooptic Bragg diffraction from a single surface acoustic wave (SAW) and from two tilted SAW's has been analyzed to establish the design parameters of the related devices. Design and performance figures of the devices involving three and four tilted SAW's in single-mode Y-cut LiNbO3out-diffused waveguides are described in detail. Device bandwidth of up to 358 MHz, an optical throughput coupling efficiency of up to 25 percent, and very good optical beam quality have been realized. A bandwidth of 358 MHz enables the device to deflect a light beam of 1-cm aperture into 1000 resolvable spot diameters with a random-access switching time of 2.8 µs. A total electric drive power of 220 mW was required to diffract 50 percent of the incident light power for the unit with 245-MHz bandwidth. The development of this wide-band technique has paved the way for using such guided-wave acoustooptic devices in a number of applications in addition to those common to bulk-type acoustooptic devices.     

Characterization of a ferroelectric liquid crystal-based time delayunit for phased array antenna applications

An experimental demonstration of a photonic time delay unit (PTDU) based on ferroelectric liquid crystal devices and Thompson polarization beamsplitters (TBSs) is presented. High signal-to-noise ratios (SNRs) (>96 dB) and optical polarization extinction ratios (ER,~40 dB) are demonstrated for the PTDU using an active noise filter technique. Using a 5 V peak square wave switch drive signal, a 70 μs switching speed is demonstrated for this PTDU that can be used in fast (e.g., 5000 beam/s) beam scanning phased array systems. A shorter switching speed of 35 μs is also observed using a high 15 V peak transitional voltage driving signal     

Heterojunction InP/GaInAs phototransistors/bipolar transistorsgrown by MOVPE

Heterojunction InP/GaInAs phototransistors with base terminals have been fabricated by atmospheric pressure metal organic vapour phase epitaxy. When operated as bipolar transistors, the devices exhibit high current gain (>1600) and good junction ideality factors (1.06 for the base/emitter and 1.25 for the base/collector junction). When operated as phototransistors, the devices have large optical gain (>800) at an incident power of 1 μW, at a wavelength of 1.3 μm     

Parallel operation of a 32*16 symmetric self-electrooptic effect device array

Free-space optics for digital optical computing or for electrooptic interconnections is considered. Results of an experiment are presented in which 512 symmetric self-electrooptic effect devices (S-SEEDs) were simultaneously operated. In this experiment, simultaneous continuous bistable operation was shown for the 32*16 array of S-SEEDs, as well as simultaneously optical latching of optical data in a random access manner onto the array.<>     

Micromachined Display Device Using Sheet Waveguide and Multicantilevers Driven by Electrostatic Force

A new structure for display devices is proposed and fabricated by the microelectromechanical systems process. The device is based on physical contact and evanescent coupling between a sheet waveguide and electrostatically driven multicantilevers. When incident light is propagated into the waveguide and the cantilevers contact the waveguide by applying a dc voltage, the switched light is emitted from the side edges of the contacted multicantilevers, resulting in a display device. The device contributes to the expansion of the switching area, the removal of unnecessary scattered light, and high contrast due to the simple fabrication and structure with corner spacers for the optical separation between the cantilevers and the waveguide. Based on the experimental results with the device, a contrast of 0.9 is obtained at 170 V, and a stable drive is realized up to 1 kHz. Therefore, the device can be expected to be used for display devices by the fabrication of an array structure.     

Compact versatile thermooptical space switch based on beam steeringby a waveguide array

We present the implementation of an optical space switching concept based on thermooptic beam steering in an arrayed waveguide grating. Individual addressing of heaters on the array waveguides enables flexible switching of input signals to output waveguide channels. The switch can be used either as a 1-to-8 switch or as multiple parallel 1-to-4, 1-to-3, or 1-to-2 switches. For the implementation we used high-refractive-index SiON-SiO₂ planar waveguide technology, which allows the realization of compact devices using small bending radii. We achieved isolations of the “off'” channels with respect to the “on” channel of up to 29 dB for a 1-to-3 switch or better than 22 dB for all “off” waveguides for a 1-to-8 switch     

Field effect transistor-self electrooptic effect device (FET-SEED)differential transimpedance amplifiers for two-dimensional optical datalinks

A 4×18 two-dimensional array of GaAs FET-SEED (field effect transistor-self electrooptic effect device) differential transimpedence receivers has been fabricated for application in massively parallel optical data link board-to-board interconnections. Several FET-SEED receiver arrays were tested and displayed a mean response of ~0.7 mV/μW, and were capable of >100 Mbps per channel operation. The mean receiver sensitivity for a BER of <10^-9 was calculated from the measured noise spectrum to be -26.8 dBm at the system design rate of 40 Mbps (18 k-22 MHz bandwidth), and -23.2 dBm for a 100 Mbps rate (dc-66 MHz bandwidth). A sensitivity of approximately -25 dBm for the 40 Mbps rate was confirmed using a bit-error-rate test set. The theoretical noise is compared to measured values with good agreement assuming a FET channel noise factor of 1.4. The 1/f noise corner frequency of ~13 MHz was found to cause a ~1.2 dB degradation in sensitivity for the 100 Mbps rate. The differential amplifier mean dc output offset voltage was measured to be 10 mV, and displayed a large sigma due to parameter variations in the active devices. Two receiver arrays were successfully used in a demonstration of a fully differential parallel optical small computer system interface (SCSI) data link     

Time-Resolved Temperature Measurement of AlGaN/GaN Electronic Devices Using Micro-Raman Spectroscopy

We report on the development of time-resolved Raman thermography to measure transient temperatures in semiconductor devices with submicrometer spatial resolution. This new technique is illustrated for AlGaN/GaN HFETs and ungated devices grown on SiC and sapphire substrates. A temporal resolution of 200 ns is demonstrated. Temperature changes rapidly within sub-200 ns after switching the devices on or off, followed by a slower change in device temperature with a time constant of ~10 and ~140 mus for AlGaN/GaN devices grown on SiC and sapphire substrates, respectively. Heat diffusion into the device substrate is also demonstrated     

Description and evaluation of the FAST-Net smart pixel-basedoptical interconnection prototype

The design, packaging approach, and experimental evaluation of the free-space accelerator for switching terabit networks (FAST-Net) smart-pixel-based optical interconnection prototype are described. FAST-Net is a high-throughput data-switching concept that uses a reflective optical system to globally interconnect a multichip array of smart pixel devices. The three-dimensional optical system links each chip directly to every other with a dedicated bidirectional parallel data path. in the experiments, several prototype smart-pixel devices were packaged on a common multichip module (MCM) with interchip registration accuracies of 5-10 μm. The smart-pixel arrays (SPAs) consist of clusters of oxide-confined vertical-cavity surface-emitting lasers and photodetectors that are solder bump-bonded to Si integrated circuits. The optoelectronic elements are arranged within each cluster on a checkerboard pattern with 125-μm pitch. The experimental global optical interconnection module consists of a mirror and lens array that are precisely aligned to achieve the required interchip parallel connections between up to 16 SPAs. Five prototype SPAs were placed on the MCM to allow the evaluation of a variety of interchip links. Measurements verified the global link pattern across several devices on the MCM with high optical resolution and registration. No crosstalk between adjacent channels was observed after alignment. The I/O density and efficiency results suggest that a multi-terabit switch module that incorporates global optical interconnection to overcome conventional interconnection bottlenecks is feasible     

Picosecond optoelectronic gating of silicon bipolar transistors bylocally integrated GaAs photoconductive devices

Integration of picosecond GaAs photoconductive devices with silicon bipolar transistors to provide a high-performance optoelectronic gating element is demonstrated. GaAs photoconductive circuit elements (PCEs) with ~15-ps FWHM photocurrent transient responses have been integrated in base-drive circuit configurations. Results have demonstrated that ~70-ps FWHM pulses of >1 mA (5 V switching across 5 kΩ) are possible using ~3-4 pJ of optical input at 820 nm. Furthermore, for the silicon bipolar transistor process which has a nominal f_t > 10 GHz, gating pulses with ~50-ps rise times, limited by the input optical pulse, have been observed     

Low threshold and tunable all-optical switch using two-photon absorption in array of nonlinear ring resonators coupled to MZI

In this paper a novel structure based on Mach-Zehnder Interferometer (MZI) and an array of nonlinear ring resonators for all-optical switching including very low threshold, fast and all-optically tunable is presented. In this proposal, an array including N ring resonators is coupled to one arm of MZI to introduce the required nonlinear phase shift to switching. Also, two-photon absorption phenomenon is used and will be proposed as another alternative for manipulation of optical switching properties. The proposed idea needs small chip area (∝1/Ntraditional cases) for implementation. We show that the switching threshold intensity can be decreased with increase of N, decrease of the coupling coefficient and increase of the two-photon absorption coefficient. In this structure with traditional optical fibers with the low nonlinear index of refractions and using an array including 15 ring resonators with 6 mm diameter for each rings only 3 mW for the switching threshold power is required. Also, using erbium-doped fiber for implementation of the rings with the high nonlinear index of refractions and five ring resonators including 0.3 mm diameter, the switching threshold power can be reduced to μW level. If the nonzero two-photon absorption coefficient is considered, the switching threshold will be very smaller than the above-mentioned values. We show that with changing the optical amplifier gain the switching threshold can be tuned. So, the proposal can be used as a functional block for the integrated optical switch with very small and tunable threshold.     

Photo-injection p-i-n diode switch for high-power RF switching

The high RF power-switching properties of the photo-injection p-i-n switch (PIPINS), an optically controlled RF switch, are investigated. Proper functioning of a PIPINS as a low insertion-loss RF switch requires that it operates as a photoconductor, where the photo-injected charge is much greater than the RF sweep out charge. Insertion loss using 650-mW optical power was <0.4 dB at RF (VHF-UHF) power in excess of 200 W, and devices successfully standoff 200-W incident RF power with the series isolation being determined by the device capacitance (e.g., 225 fF). PIPINS hot-switching measurements are reported for the first time, with output RF power up to 180 W at low duty cycle, rise times of 1 ps, and fall times for a series shunt switch of ≈2.5 μs. The RF power for hot switching a PIPINS is limited by a latch-on effect, which is dependent on a variety of parameters, including duty cycle and repetition period, consistent with thermally generated carriers contributing to the latch-on effect. The switching properties of PIPINS make them a candidate for high RF power applications such as reconfigurable antennas, where electromagnetic isolation of the switch and control lines are critical     

Hybrid Integrated Cascaded 2-bit Electrooptic Digital Optical Switches (DOSs)

Hybrid integrated cascaded 1 times 4 electrooptic (EO) polymeric digital optical switches (DOSs) are proposed and demonstrated. The hybrid integration of passive polymer on the same chip with EO polymer can lower the overall device loss without affecting the EO effects. The cascaded DOS can be controlled by only two voltage signal sources without bias stabling mechanism. The device can be operated as a 2-bit reconfigurable switch. The switching voltage is around 15 V for single arm driving with reasonable extinction ratio (9~12 dB) and the loss is improved by ~2.5 dB. This device is ideal for implementing variable optical delay network     

High temperature characteristics of bipolar mode power JFET operation

The high-temperature operating characteristics of high-voltage JFET devices operated in the bipolar mode are evaluated. Good forward blocking capability with no degradation in blocking gain is observed at up to 200°C. The on-resistance and gate turnoff time of the devices was found to double from 25°C to 200°C, and the current gain was found to decrease by 30 percent. Despite the increase in gate drive requirements with increasing temperature, these devices should still be attractive for high-speed power switching applications because their on-resistance per unit area is at least 10 time lower than that of the power MOSFET.