Stanley Cheung

CMOS-compatible, athermal silicon ring modulators clad with titanium dioxide

We present the design, fabrication and characterization of athermal nano-photonic silicon ring modulators. The athermalization method employs compensation of the silicon core thermo-optic contribution with that from the amorphous titanium dioxide (a-TiO(2)) overcladding with a negative thermo-optic coefficient. We developed a new CMOS-compatible fabrication process involving low temperature RF magnetron sputtering of high-density and low-loss a-TiO(2) that can withstand subsequent elevated-temperature CMOS processes. Silicon ring resonators with 275 nm wide rib waveguide clad with a-TiO(2) showed near complete athermalization and moderate optical losses. Small-signal testing of the micro-resonator modulators showed high extinction ratio and gigahertz bandwidth.

Ultra-Compact Silicon Photonic 512 × 512 25 GHz Arrayed Waveguide Grating Router

This paper discusses design, fabrication, and characterization of a 512 × 512 arrayed waveguide grating router (AWGR) with a channel spacing of 25 GHz. The dimensions of the AWGR is 16 mm × 11 mm and is fabricated on a 250 nm silicon-on-insulator platform. The measured channel crosstalk is approximately -4 dB without any compensation for the phase errors in the arrayed waveguides. The AWGR spectrum in the arrayed waveguide grating arms were characterized by using an optical vector network analyzer. Fabrication details of obtaining low loss silicon ridge waveguides are also discussed.

Demonstration of a fast-reconfigurable silicon CMOS optical lattice filter

We demonstrate a fully-reconfigurable fourth-order optical lattice filter built by cascading identical unit cells consisting of a Mach-Zehnder interferometer (MZI) and a ring resonator. The filter is fabricated using a commercial silicon complementary metal oxide semiconductor (CMOS) process and reconfigured by current injection into p-i-n diodes with a reconfiguration time of less than 10 ns. The experimental results show full control over the single unit cell pole and zero, switching the unit cell transfer function between a notch filter and a bandpass filter, narrowing the notch width down to 400 MHz, and tuning the center wavelength over the full free spectral range (FSR) of 10 GHz. Theoretical and experimental results show tuning dynamics and associated optical losses in the reconfigurable filters. The full-control of each of the four cascaded single unit cells resulted in demonstrations of a number of fourth-order transfer functions. The multimedia experimental data show live tuning and reconfiguration of optical lattice filters.

Monolithic InP 100-Channel

We demonstrate monolithic integration of a 100-channel arrayed-waveguide grating (AWG) with 10-GHz channel spacing and 100 optically controlled Michelson-interferometer-based phase and amplitude modulators. The high-resolution AWG showed better than -15-dB crosstalk, and the modulator extinction ratio was better than 20 dB with either electrical or optical modulation control. The twin-integrated devices comprise a 50-mm diameter InP wafer with 1200 independent optoelectronic components.

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This paper discusses the architecture and provides performance studies of a silicon photonic chip-scale optical switch for scalable interconnect network in high performance computing systems. The proposed switch exploits optical wavelength parallelism and wavelength routing characteristics of an Arrayed Waveguide Grating Router (AWGR) to allow contention resolution in the wavelength domain. Simulation results from a cycle-accurate network simulator indicate that, even with only two transmitter/receiver pairs per node, the switch exhibits lower end-to-end latency and higher throughput at high (>90%) input loads compared with electronic switches. On the device integration level, we propose to integrate all the components (ring modulators, photodetectors and AWGR) on a CMOS-compatible silicon photonic platform to ensure a compact, energy efficient and cost-effective device. We successfully demonstrate proof-of-concept routing functions on an 8 × 8 prototype fabricated using foundry services provided by OpSIS-IME.

10-GHz Device for Optical Arbitrary Waveform Generation

We present a fully-reconfigurable CMOS-compatible silicon-photonic lattice-filter with four cascaded unit cells consisting of resonant rings and Mach-Zehnder interferometers. The measurements show high-quality filter responses including IIR and FIR filter characteristics matching theoretical predictions.

A scalable silicon photonic chip-scale optical switch for high performance computing systems

This letter demonstrates a 1-GHz hybrid mode-locked monolithic semiconductor laser fabricated on indium phosphide. Its operating regimes are explored and optical pulses as short as 36 ps were measured. The linear cavity is 41 mm long with integrated active quantum well and passive waveguide structures. To our knowledge, this is the lowest reported repetition rate for a monolithically integrated mode-locked semiconductor laser. We further describe optimization steps of the saturable absorber reverse bias, driving RF frequency, and the semiconductor optical amplifier gain current for minimal output pulsewidth.

Fully reconfigurable silicon photonic lattice filters with four cascaded unit cells

We report high-extinction and low-loss 40-channel × 100-GHz arrayed waveguide grating (AWG) fabricated on silicon-on-insulator using high quality etching condition resulting in <; 0.8 dB/cm loss and low phase errors.

1-GHz Monolithically Integrated Hybrid Mode-Locked InP Laser

This paper discusses optimum design strategies for high-efficiency hybrid semiconductor optical amplifiers (SOA). A comprehensive model is presented to determine the width, composition, and number of quantum wells for a hydrophobic bonded SOA with In s-x-y)Ga (x)Al (y) As quantum-wells (QW). Optimizing the interfacial bonding layer, III-V wafer stack design, straight hybrid amplifier dimensions and flared amplifier configurations leads to a design for up to 35% wall-plug efficiency at 2 mW input and 10 dB gain. Likewise, optimized dimensions also lead to 15% wall-plug efficiency (WPE) at 0.1 mW input and 10 dB gain. Thermal effects due to the effect of the buried oxide layer (BOX) is presented and methods of improved thermal extraction is discussed.

Low-loss and high contrast silicon-on-insulator (SOI) arrayed waveguide grating

Group-IV materials for monolithic integration with silicon optoelectronic systems are being extensively studied. As a part of efforts, light emission from germanium has been pursued with the objective of evolving germanium into an efficient light source for optical communication systems. In this study, we demonstrate room-temperature electroluminescence from germanium in an Al(0.3)Ga(0.7)As/Ge heterojunction light-emitting diode without any complicated manipulation for alternating material properties of germanium. Electroluminescence peaks were observed near 1550 nm and the energy around this wavelength corresponds to that emitted from direct recombination at the Γ-valley of germanium.