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Major research directions

1. Microresonator-based photonic devices for optical interconnects

Silicon microresonators in the form of microring and microdisk possess several key merits for optical data center and networks-on-chip applications due to their small footprint, sharp resonances for wavelength selectivity, accessibility by integrated optical waveguides and tunability by means of electro-optical (EO), thermo-optical (TO), all-optical and opto-mechanical mechanisms. A myriad of silicon microresonator-based devices for data center applications has been demonstrated, including wavelength-stabilized microring resonator, all-silicon photodetectors, EO / TO switches and routers, heterogeneously integrated III-V-on-Si lasers, wavelength-division multiplexing (WDM) filters, optical delay lines and EO modulators.

2. Hybrid III-V-on-silicon photonic devices for optical interconnects

Silicon photonics that leverage the mature silicon microelectronics fabrication process offers a seamless integration of optical interconnect on silicon chips. However, silicon as an indirect-bandgap material does not efficiently emit light in the technologically important 1550-nm telecommunications wavelengths. One way to circumvent this fundamental limitation of silicon is to hybrid integrate III-V direct-bandgap semiconductors on silicon substrates.

3. Optical manipulation and biosensing

Since 1970’s, optical force has been studied and now successfully applied as optical tweezers to hold and move microscopic objects. Over the past few years, the fusion of photonics and fluidics has led to the research area of optofluidics. The on-chip optical tweezers, utilizing the fast-decaying evanescent field near the surface of the waveguide to generate an optical gradient force, can trap and transport microparticles that are located in close proximity to and spatially overlap with the evanescent field.

4. Microresonator-based nonlinear and quantum photonics

A material’s dielectric polarization can respond nonlinearly to incident electric field, converting the incoming light to other frequencies. Such frequency conversion processes arising from higher order polarizations of a medium have found its use in various applications such as frequency combs, laser spectra extension and spectroscopy. Besides these classical studies, nonlinear frequency conversion is also commonly used to generate single photons and entangled photon pairs. By confining the mixing waves in a microresonator, one can increase the nonlinear frequency conversion efficiency by orders of magnitudes due to the resonant field enhancement.