Development of micro-ring resonator-based optical bandpass filter using SU-8 polymer and optical lithography

Laterally-coupled SU-8 ridge waveguide-based micro-ring resonator was designed, fabricated and characterized for optical filtering applications. Fabrication was done by optical lithography using a patterned chrome mask of SU-8 ridge waveguide and micro-ring resonator structures, which was replicated onto a plasma enhanced chemical vapour deposited (PECVD) silicon-dioxide layer on a silicon wafer. Optical characterization showed that the fabricated micro-ring resonator had a free spectral range (FSR) of ∼16 nm for a ring radius of 15 μm in TE polarization. A simple semiconductor laser diode and a monochromator were used for the characterization of the device. The measured through port and drop port light output for different wavelengths indicate that the device can be used as an optical filter around 1565 nm centre wavelength, with a 3 dB bandwidth of 5.3 nm and an extinction ratio of ∼10.5 dB.