UC San Diego

Microresonators are widely used in the creation of optical devices which exploit their unique properties and characteristics such as spectral selectivity and field localization. We investigate two applications for microresonator devices that integrate multiple functionalities into the same volume through application specific design optimization. The first application is in free-space optical communications, where we develop a bandpass filter and an optical receiver which are integrated together. The second is in the guided wave application, where we develop a waveguide polarizer and a waveguide bandpass filter. For the first free-space communication application, we examine how the functionalities of a flat-top passband and a wide angular bandwidth can be integrated with a photodetector by exploiting properties of 1-D photonic crystals with multiple defects. In the first part of the research, we achieve a thin-film bandpass filter by optimally choosing the optical thickness ratio of high to low refractive- index materials in dispersive mirrors and experimentally characterize the fabricated device, demonstrating a bandwidth of 65 nm and field of view of 50⁰. In the second part, we integrate a photodetector into the resonator using the dispersive mirrors to achieve these functionalities. We fabricate and characterize the resulting device: a back-illuminated In0.47Ga0.53As-based resonant-cavity-enhanced PIN photodiode, showing 0.80 peak quantum efficiency, 35.96nm spectral bandwidth and 30⁰ angular bandwidth. For our second application involving guided wave components, we develop two devices, a waveguide polarizer and a waveguide bandpass filter. The waveguide polarizer device uses nanostructures to realize highly birefringent waveguides. With an appropriately sized nanostructure, a waveguide can be fashioned that allows only TM-like modes to propagate through the waveguide. We create such a polarizer using nanostructures of 26 μm lengths in a GaAs/AlAs ridge waveguide, providing an insertion loss of 0.54 dB and an extinction ratio of 20 dB. In the waveguide bandpass filter device, the methodology used to design thin-film filters in our first free-space application is extended and optimized for designs using microcavities in a photonic bandgap monorail waveguide. We present a square waveguide filter centered at 1554 nm with a maximum transmission of 0.88 and a FWHM of 13.6 nm