Rohit Grover

Optical signal processing using nonlinear semiconductor microring resonators

Recent fabrication advances have enabled compact semiconductor microring resonators to be fabricated with high-finesse values and picosecond cavity lifetimes. These devices have potential applications in optical signal processing as all-optical switches, multiplexers and logic gates. Theoretical analysis shows a maximum reduction in the switching power proportional to the fourth power of the field enhancement in the microring. An enhancement in the wavelength conversion efficiency by four-wave mixing which is proportional to the eighth power of the field enhancement is also predicted and experimentally confirmed. Experimental results demonstrating bistability, picosecond switching using pump and probe excitation, optical time-division demultiplexing, spatial pulse routing and four-wave mixing in GaAs-AlGaAs microring resonators are reported. Apart from the bistable response, which was thermally induced, the nonlinear effects observed in the microrings were caused by the two-photon absorption process. Applications of microrings to realize all-optical logic gates are also proposed.

A tunable GaInAsP-InP optical microring notch filter

The authors demonstrate an ultracompact tunable GaInAsP-InP microring notch filter. The core of the device is a quantum-well superlattice and forms the intrinsic region in a p-n structure. The device has curved sections of radius 2.25 /spl mu/m and straight sections of length 1 /spl mu/m, making it the smallest microring filter ever reported. They obtain 0.8 nm (100 GHz) of tuning by reverse-biasing the diode structure over 8 V using the quadratic electrooptic effect.

High-finesse laterally coupled single-mode benzocyclobutene microring resonators

We demonstrate benzocyclobutene microring resonators. These devices, made of a readily available polymer and fabricated with a simple process, are among the smallest radius (10 /spl mu/m) of polymer microrings. They feature the widest free-spectral range (23.7 nm) as well as highest finesse (192) in any single-ring polymer devices reported to date.

III‐V Semiconductor Optical Micro‐Ring Resonators

We describe the theory of optical ring resonators, and our work on GaAs‐AlGaAs and GaInAsP‐InP optical micro‐ring resonators. These devices are promising building blocks for future all‐optical signal processing and photonic logic circuits. Their versatility allows the fabrication of ultra‐compact multiplexers/demultiplexers, optical channel dropping filters, lasers, amplifiers, and logic gates (to name a few), which will enable large‐scale monolithic integration for optics.

Nonlinear and active optical III-V semiconductor micro-resonators

We review our work on GaAs-AlGaAs and GaInAsP-InP optical micro-ring resonators. We have demonstrated passive linear filters and wavelength multiplexers/demultiplexers. Nonlinear rings demonstrated include logic gates and time-domain demultiplexers. Active rings demonstrated include tunable filters using the quadratic electro-optic effect, and ring amplifiers and lasers. The latter, when reverse biased, become modulators by the electro-absorption effect.

Electrically pumped InGaAsP/InP microring optical amplifiers and lasers with surface passivation

InGaAsP/InP microring lasers and optical amplifiers providing gain at 1550 nm are demonstrated. The microrings provide about 10 dB of gain in pulsed mode. Sulfur passivation is used to reduce carrier loss to surface recombination.

Vertically coupled GaAs-AlGaAs and GaInAsP-InP microring resonators

Single transverse mode vertically coupled semiconductor microring resonators were made using a novel fabrication technique without regrowth. GaAs-AlGaAs and GaInAsP-InP devices are demonstrated.

Photonic AND/NAND logic gates using semiconductor microresonators

This study demonstrates and characterizes the performance of all-optical AND and NAND logic gates using InP and GaAs micro-racetrack resonators. Since the switching energy of the device scales down by field enhancement (FE), subpico joule switching energy is predicted, which is required to operate the logic gate at 100 GHz assuming a carrier lifetime of 10 ps and that the microresonator has a moderate FE of 4.

A tunable micro-ring notch filter

This paper demonstrates electro-optic tuning of a laterally-coupled GaInAsP-InP micro-ring resonators. The device is a p-i-n diode, with the intrinsic region of forming the waveguide core. The intrinsic region is composed of a superlattice of quantum wells. By applying a reverse bias, the resonance wavelength is tuned by 0.8 nm (100 GHz) over 8 V using the quadratic electro-optic effect. The quadratic electro-optic coefficient is estimated to be 4.9 /spl times/ 10/sup -15/ cm/sup 2//V/sup 2/. Independent measurements of the electro-optic characteristics of the wafer is also presented.

Periodically-coupled GaAs-AlGaAs and GaInAsP-InP microring resonators with high-order, wide-FSR response

Summary form only given. Our work on periodically-coupled, triple-microring-resonator channel dropping filters in GaAs-AlGaAs and GaInAsP-InP is based on our prior fabrication efforts in these systems We demonstrate high-order filtering, bandpass flattening and improved free spectral range. Their behavior is consistent with theoretical analysis of such devices we have demonstrated vernier effect, and high-order filtering in triple-ring parallel cascaded filters.