Etched cavity InGaAsP-InP waveguide Fabry-Perot filter tunable by current injection

A short cavity Fabry-Perot (FP) tunable filter was fabricated by chemically assisted ion beam etching (CAIBE) of an InGaAsP-InP waveguide. The FP cavity mirrors were formed by high reflectivity dielectric coatings deposited onto the two etched facets of the cavity. High-speed (less than 3 ns) wavelength-tuning of the filter was achieved by current injection. A super-linear dependence on current injection was observed in the wavelength tuning. The filter was tunable over a continuous range of 4 nm by up to 50 mA current injection. The device had a free-spectral range of 9 nm and gave a contrast ratio of about 10 dB. A theoretical simulation of the filter was developed using a beam propagation method calculation to estimate the reflection efficiency at different mirror tilt angles. The calculated contrast ratio of the filter was in good agreement with the measured result. The calculations showed that 20 dB contrast ratio should be possible by having a facet reflectivity of over 90% and ensuring that the etched facets are off-vertical by less than 1.8.