Post-trimming of photonic crystal nanobeam cavities by controlled electron beam exposure.

We theoretically and experimentally demonstrated that the resonant wavelength of photonic crystal (PhC) nanobeam cavities can be individually post tuned by selective electron beam exposure and development. By exposing the SU-8 cladding with different doses, the thickness of the SU-8 can be precisely and individually controlled from 150 nm to 650 nm. The phenomenon is employed in the localized control of the cladding layer from above the cavity region, thereby modifying the resonant wavelengths. The transmission spectrums of the PhC nanobeam cavities are measured before exposure, after exposure and after development, respectively. Utilizing the proposed method, the resonant wavelengths of the PhC nanobeam cavities can be post-tuned as large as 30 nm. This method is applicable to the post-trimming adjustment of the frequency response of the silicon-photonic filters.