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 cavi ty mirrors were formed by high reflectivity dielectric coatings deposited o nto the two etched facets of the cavity, High-speed (less than 3 ns) wavele ngth-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 eff iciency at different mirror tilt angles. The calculated contrast ratio of t he filter was in good agreement with the measured result, The calculations showed that 20 dB contrast ratio should be possible by having a facet refle ctivity of over 90% and ensuring that the etched facets are off-vertical by less than 1.8 degrees.