Aligning microcavity resonances in silicon photonic-crystal slabs using laser-pumped thermal tuning

We report the postfabrication alignment of multiple microcavity resonances in silicon photonic-crystal (PhC) slabs using laser-pumped thermal tuning. The thermal gradient resulting from a focused laser spot was used to differentially tune the resonant wavelengths of two microcavities spaced about 50μm apart. The resonant wavelengths could be brought closer together, over a tunable range of more than 5nm. A cross over in the resonant wavelengths was demonstrated, showing that two microcavities can be tuned to the identical wavelength. The results show that differential thermal tuning can be used to remove slight fabrication differences in nominally identical microcavities, relaxing the fabrication tolerances that will be required to realize coupled-resonator structures in PhCs.