Nonlinear Optical Semiconductor Micro-Ring Resonators

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In the last few years, there has been a great interest in all-optical switching devices due to the high demand on optical communication systems and networks. Unlike conventional electronic switches, photonic switching devices are ideal candidates for ultrafast data stream processing, approaching the THz regime. It is the goal of this thesis to propose, study, and demonstrate a new class of compact optical switches based on semiconductor microring resonators.

A detailed theoretical analysis of the nonlinear behavior of the microring resonator shows that, due to the resonance effect, there is an enhancement of the overall switching efficiency by up to the third power of the cavity finesse.

Two different semiconductor materials are used in fabricating these devices, GaAs and InP. Both materials are analyzed and compared in terms of switching energy requirement, nonlinear coefficients, speed limitation and ease of fabrication. In addition, two different fabrications techniques are used to realize the ring structure layout, laterally and vertically coupled.

The round trip phase of the microring resonator can be controlled by changing its refractive index. This can be accomplished by free carrier injection induced by two-photon absorption or single-photon absorption. As a result, a temporal blue shift in the resonator resonance wavelength is observed. When these carriers diffuse to the waveguide walls, the effect diminishes. A probe beam, tuned to one of the resonator resonant wavelengths, is used to capture the dynamic change in the transmission function of the resonator.  

All-optical switching is demonstrated using a single microring resonator, with few tens of picojoules switching energy and a switching window approaching 30 GHz, limited by the carrier lifetime of the guiding material. Moreover, such a device is used in time division demultiplexing a stream of data channels as well as spatial pulse routing with approximately 8~dB cross-talk noise, limited by fabrication tolerances. More complicated structures of these resonators are proposed and used to achieve a set of functionally complete photonic logic gates.