Y. Gu’s research while affiliated with University of Maryland, Baltimore County and other places

InGaAs APDs with improved photon counting characteristics were designed and fabricated and their performance improvements were observed. Following the results, a 4times4 individually addressable APD array was designed, fabricated, and results are reported

Dense wavelength-division multiplexing (DWDM) technology offers tremendous transmission capacity in optical fiber communications. However, switching and routing capacity lags behind the transmission capacity, since most of today's packet switches and routers are implemented using slower electronic components. Optical packet switches are one of the potential candidates to improve switching capacity to be comparable with optical transmission capacity. In this paper, we present an optically transparent asynchronous transfer mode (OPATM) switch that consists of a photonic front-end processor and a WDM switching fabric. A WDM loop memory is deployed as a multiported shared memory in the switching fabric. The photonic front-end processor performs the cell delineation, VPI/VCI overwriting, and cell synchronization functions in the optical domain under the control of electronic signals. The WDM switching fabric stores and forwards cells from each input port to one or more specific output ports determined by the electronic route controller. We have demonstrated with experiments the functions and capabilities of the front-end processor and the switching fabric at the header-processing rate of 2.5 Gb/s. Other than ATM, the switching architecture can be easily modified to apply to other types of fixed-length payload formats with different bit rates. Using this kind of photonic switch to route information, an optical network has the advantages of bit rate, wavelength, and signal-format transparencies. Within the transparency distance, the network is capable of handling a widely heterogeneous mix of traffic, including even analog signals.

In this work, we study a high efficient four-junction solar cells using AlAsSb(1.91eV), AlInAs(1.46eV), ALGaInAs(1.0eV) and InGaAs(0.75eV) materials. The >35% efficiency is calculated under AM0, and the thickness of each layer is adjusted to equalize the short circuit current. We also experimentally fabricated a 1.0eV cell and studied its characteristics.

The structure of Avalanche photodiodes (APD), which achieved high gain, high speed and low noise operation, was discussed. By utilizing a combination of the (hetro-junction) band discontinuity and high doping, electrons and holes reached their ionization thresholds in the small bandgap materials. The device had two large band discontinuities, where the deterministic impact ionization took place. It was suggested that an accurate control of doping profiles was required to successfully demonstrate the device and with the possibility of the well-controlled high p-doping using carbon and high n-doping techniques, this high performance device can be obtained.

In this paper, we simulated and calculated expected efficiency of proposed four-junction solar cells. The InGaAs, AlAsSb, AlInAs and AlGalnAs four-junction solar cells system has a potential to achieve high efficiencies, and can be manufacturable. We fabricated and tested an AlInGaAs(1.0 eV) solar cell.

Avalanche photodiodes (APDs) are attractive for use in large capacity long distance optical communication systems. They provide an advantage over p-i-n detectors because of their internal gains. A gain-bandwidth product of ∼300 GHz has been achievable using an APD with a