Integrated MMI Optical Couplers and Optical Switches in Silicon-on-Insulator Technology

Integrated multimode interference (MMI) coupler based on silicon-on-insulator(SOI) has been becoming a kind of more and more attractive device in optical systems. SiO2thin cladding layers (＜1.0 μm) can be usedin SOI waveguide due to the large index step be-tween Si and SiO2, making them compatible with VLSI technology. The design and fabrica-tion of MMI optical couplers and optical switches in SOI technology are presented in thepa-per. We demonstrated the switching time of 2 × 2 MMI-MZI thermo-optical switch is less than 20 μs:

Fiber Optic Coupling of CW Linear Laser Diode Array

Based on a set of microoptics the output radiation from a continuous wave (CW) linear laser diode array is coupled into a multi-mode optical fiber of 400 ptm diameter. The CW linear laser diode array is a 1 cm laser diode bar with 19 stripes with 100 fxm aperture spaced on 500 (xm centers. The coupling system contains packaged laser diode bar, fast axis collimator, slow axis collimation array, beam transformation system and focusing system. The high brightness, high power density and single fiber output of a laser diode bar is achieved. The coupling efficiency is 65% and the power density is up to 1.03 * 10~4 W/cm~2.

Co—Design of Monolithically Integrated Photo—Detectorand Optical—Receiver

A behavioral model of the photodiode is presented．The model describes the relationship between photocurrent and incident optical power，and it also illustrates the impact of the reverse bias to the variation of the junction capacitance．According to this model，the photodiode and a CMOS receiver circuit are simulated and designed simultaneously under a universal circuit simulation environment．

Characteristics of AlGaN/GaN HEMTs Grown by Plasma-Assisted Molecular Beam Epitaxy

AlGaN/GaN high electron mobility transistor (HEMT) materials are grown by RF plasma-assisted molecular beam epitaxy (RF-MBE) and HEMT devices are fabricated and characterized. The HEMT materials have a mobility of 1035cm~2/(V ? s) at sheet electron concentration of 1.0 * 10~(13)cm~(-2) at room temperature. For the de-vices fabricated using the malt-rials,a maximum saturation drain-current density of 925mA/mm and a peak extrinsic iransecmductance of IHfimS/mm are obtained on devices with gate length and width of l/-im and 80/im respectively. The f_t, unit-current-gain frequency of the devices,is about 18. 8GHz.

Design and Fabrication of Ultracompact 3-dB MMI Coupler in Silicon-on-Insulator

An ultracompact 3-dB coupler is designed and fabricated in silicon-on-insulator,based on 12 line tapered multimode interference(MMI) coupler.Comparing with the conventional straigth MMI coupler,the device is-40% shorter in length.The device exhibits uniformity of 1.3dB and excess loss of 2.5dB

Micromechanical Tunable Optical Filter

A micromachined vertical cavity tunable filter with AlGaAs/GaAs distributed Bragg reflector is presented. This filter can be electrostatic tuning over a range of 28nm with an applied voltage of 7V.

Modulation of Photonic Bandgap and Localized States by Dielectric Constant Contrast and Filling Factor in Photonic Crystals

The band structure of 2D photonic crystals (PCs) and localized states resulting from defects are analyzed by finite-difference time-domain (FDTD) technique and Pade approximation. The effect of dielectric constant contrast and filling factor on photonic bandgap (PBG) for perfect PCs and localized states in PCs with point defects are investigated. The resonant frequencies and quality factors are calculated for PCs with different defects. The numerical results show that it is possible to modulate the location, width and number of PBGs and frequencies of the localized states only by changing the dielectric constant contrast and filling factor.

SOI Waveguides Fabricated by Wet-Etching Method

SOI waveguides fabricated by wet-etching method are demonstrated. The single mode waveguide and 1×2 3dB BBI splitter are analyzed and designed by three dimensional beam propagation method to correct the error of effective index method and guided mode method. The devices are fabricated. Excellent performances, such as low propagation loss of -1.37dB/cm, low excess of -2.2dB, and good uniformity of 0.3dB, are achieved.

Optimization of InGaAs Quantum Dots for Optoelectronic Applications

Self-assembled In_0.35Ga_0.65As/GaAs quantum dots with low indium content are grown under different growth temperature and investigated using contact atomic force microscopy(AFM). In order to obtain high density and high uniformityu of quantum dots, optimized conditions are concluded for MBE growth. Optimized growth condi-tions also compared with these of InAs/GaAs quantum dots. This will be very useful for InGaAs/GaAs QDs opto-electronic applications, such as quantum dots lasers and quantum dots infrared photodetectors.

Measurement of Cavity Loss and Quasi-Fermi-Level Separation for Fabry-Perot Semiconductor Lasers

A fitting process is used to measure the cavity loss and the quasi-Fermi-level separation for Fabry- Perot semiconductor lasers. From the amplified spontaneous emission (ASE) spectrum, the gain spectrum and single-pass ASE obtained by the Cassidy method are applied in the fitting process. For a 1550nm quantum well InGaAsP ridge waveguide laser, the cavity loss of about ～24cm~(-1) is obtained.

Heteroepitaxial Growth and Heterojunction Characteristics of Voids-Free n-3C-SiC on p-Si(100)

Highly oriented voids-free 3C-SiC heteroepitaxial layers are grown on φ50mm Si (100) substrates by low pressure chemical vapor deposition (LPCVD). The initial stage of carbonization and the surface morphology of carbonization layers of Si(100) are studied using reflection high energy electron diffraction (RHEED) and scanning electron microscopy (SEM). It is shown that the optimized carbonization temperature for the growth of voids-free 3S-SiC on Si (100) substrates is 1100 ℃. The electrical properties of SiC layers are characterized using Van der Pauw method. The I-V, C-V, and the temperature dependence of I-V characteristics in n-3C-SiC-p-Si heterojunctions with AuGeNi and Al electrical pads are investigated. It is shown that the maximum reverse breakdown voltage of the n-3C-SiC-p-Si heterojunction diodes reaches to 220V at room temperature. These results indicate that the SiC/Si heterojunction diode can be used to fabricate the wide bandgap emitter SiC/Si heterojunction bipolar transistors (HBT's).

Raman Investigatins of 3C-SiC Films Grown on Si (100) and Sapphire (0001) by LPCVD

The Raman measurements have been performed with the back-scattering geometry on the SiC films grown on Si(100) and sapphire (0001) by LPCVD. Typical TO and LO phonon peaks of 3C-SiC were observed for all the samples grown on Si and apphire substrates, indicating the epilayers are 3C-SiC polytype. Using a free-standing 3C-SiC film removed from Si(100) as a free-stress sample, the stresses of 3C-SiC on Si(100) and sapphire (0001) were estimated according to the shift of TO and LO phonons.

The Incident Angle Dependence of Quantum Efficiency of GaAs Based RCE Photodetectors

The theoretical analysis and experimental measurement on the incident angle dependence of quantum efficiency of GaAs based resonant cavity enhanced (RCE) photodetector is presented. By changing the angle of incoming light, about 40 nm wavelength variation of peak quantum efficiency is obtained. The peak quantum efficiency and optical bandwidth at different mode corresponding to different angle incidence is characterized with different absorption dependence on wavelength. The convenient angle tuning of resonant mode will be helpful to relax the strict constraint of RCE photodetector to light source with narrow emission spectrum such applications in space optical detections and communications.

Array for 980nm Vertical Cavity Surface Emitting Diodes and Detectors

Both the vertical cavity surface emitting diodes and detectors are fabricated by using the epitaxial wafer with resonant cavity structure. Their characteristics are analyzed. The light emitters have high spectral purity of 4.8nm and high electroluminescence intensity of 0.7mW while injection current is 50mA. A 1*16 array of surface emitting light device is tested on line by probes and then used for module. The light detectors have wavelength selectivity and space selectivity. The required difference in input mirror reflectivity between emitters and detectors can easily be achieved though varying the numbers of top DBR period by etching.

3μm GaInNAs/GasAs Quantum Well Resonant Cavity Enhanced Photodetector

A 1.3μm GaInNAs resonant cavity enhanced (RCE) photodetector (PD) has been grown by molecular beam epitaxy (MBE) monolithically on (100) GaAs substrate using a home-made ion-removed dc-plasma cell as nitrogen source. A transfer matrix method was used to optimize the device structure. The absorption region is composed of three GaInNAs quantum wells separated by GaAs layers. Devices were isolated by etching 130μm-diameter mesas and filling polyamide into grooves. The maximal quantum efficiency of the device is about 12% at 1.293μm. Full width at half maximum (FWHM) is 5.8nm and 3dB bandwidth is 304MHz. Dark current is 2 * 10~(-11) A at zero bias voltage. Further improvement of the performance of the RCE PD can be obtained by optimizing of the structure design and MBE growth conditions.