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Two different structures of n‐Si/p‐Si1−xGex/n‐Si double‐heterojunction bipolar transistors have been fabricated by molecular beam epitaxy. A common emitter current gain β of about 15 was demonstrated in one kind of structure and the β‐IC curve has been investigated. In the other structure, a novel multistep collector current IC vs collector‐emitter voltage VCE characteristic together with a strong negative resistance behavior was observed at room temperature. In this letter the basic experiments are described; a comparison and a discussion of the two kinds of devices are presented.

Subwavelength structures in silicon waveguides are presented, including practical components such as fiber-chip grating couplers, waveguide crossings, a polarization converter, a waveguide multiplexer and a Terahertz optical switch.

Low-frequency noise in cadmium-selenide (CdSe) thin-film transistors (TFTs) has been studied over a wide range of gate and drain biases, temperatures, and gate areas. The dependencies of the noise on the gate voltage and the gate length indicate that the 1/f noise originates from the bulk sources homogeneously distributed in the channel. The value of Hooge parameter α lies within the usual range 10−3

A silicon waveguide evanescent field molecular sensor interrogated by reflection from a surface grating is demonstrated. The sensor is probed by a beam of light incident at θ = 45° through the backside of the silicon-on-insulator (SOI) wafer. The reflected power shows a strong resonant feature near λ = 1532 nm, arising from resonant coupling of incident beam, guided mode, and the reflected beam. The resonant wavelength is very sensitive to molecular surface coverage. We have measured a Δλ = 1.0 nm resonance shift when a monolayer of streptavidin protein is bound to the sensor surface, or a 60% reflectivity change when measured at a fixed wavelength.

We demonstrate silicon photonic wire evanescent field sensors formed by folding long photonic wire waveguides into dense spiral paths that occupy spot sizes less than 150 mum in diameter, and are hence suitable for biochip array formats. These sensors are incorporated into both ring resonator and Mach-Zehnder interferometer (MZI) interrogation circuits, and tested by monitoring streptavidin protein adsorption. The level of detection is less than 1% of a monolayer in either configuration. Using a balanced MZI design, we show that the sensors can be insensitive to temperature and wavelength, while retaining a very high sensitivity to molecular adsorption.

We demonstrate for the first time silicon chip based instantaneous chromatic dispersion monitoring of an ultra-high bandwidth 640 Gbit/s DPSK signal. This monitoring scheme is based on cross-phase modulation in an ultra-high nonlinear silicon nano-wire.

We present several new concepts to extend the capabilities of arrayed waveguide grating spectrometers. Strong lateral mode confinement wavegaide structure in the focal plane is used to increase resolution, a Michelson-type AWG spectrometer can improve optical throughput or etendue, and we show that AWG dispersion can be magnified many times by modifying the waveguide group index.

Quasi-phase matching (QPM) employs a short period modulation or grating in the second order nonlinearity, X/sup 2/, to compensate for the phase mismatch of the pump and signal beams in a second order nonlinear process. The main challenge in implementing QPM is to incorporate this X/sup 2/ grating into the waveguide. We are investigating the use of patterned ion implantation of asymmetric quantum wells (AQWs) as a means of achieving this goal.

We demonstrate a silicon-chip-based radio-frequency spectrum analyser capable of measuring terabaud optical data. We investigate application to optical performance monitoring and show that free-carrier effects have a negligible impact on device operation.

We present a silicon-chip-based optical performance monitor, using an all-optical RF spectral analysis technique, capable of real-time performance monitoring both phase and intensity encoded signals. The device operates unimpeded by the effects of photo-generated free-carriers., OSA Topical Meeting on Photonics in Switching, July 25-28, 2010, Monterey, California

We report the first focused ion beam milled silicon-on-insulator waveguide Bragg gratings. We further demonstrate that higher order lossy modes dramatically affect the transmission spectra of surface gratings even in single-mode waveguides., IEEE International Conference on Group IV Photonics, 29 Sept.-1 Oct. 2004, Hong Kong, China

We introduce several types of new waveguide spectrometers, namely a high-resolution 50-channel AWG spectrometer, a 40-channel broadband AWG spectrometer, a Si-wire sidewall grating multiplexer, and the first planar waveguide Fourier-transform spectrometer.

Novel bidirectional negative differential resistance (NDR) phenomena have been observed at room temperature in strained base n-Si/p-Si1-x Ge x /n-Si double heterojunction bipolar transistors (DHBTs). A strong and symmetric bidirectional NDR modulated by base bias, together with a multi-step characteristic in collector current I C vs emitter-collector bias voltage V CE, was obtained in the devices with very thin base. The temperature dependence of the NDR and the multi-step I C-V CE characteristics has been measured to identify the possible transport mechanism. The physical origins of these phenomena are discussed.