A photonic integrated tunable receiver/optical preamplifier in a vertical coupler filter structure

The authors propose and demonstrate a novel integrated tunable receiver which integrates a traveling-wave optical preamplifier, a two-stage passive grating-assisted codirectional coupler (GACC) filter, and a photodetector. The GACC filter has been shown to have a wavelength tunability an order of magnitude wider than that of a distributed-Bragg-reflector (DBR) filter. The transmissive style of the filter makes it possible to cascade several optical elements to achieve the high functionality of photonic integration. The device was fabricated on GaAs substrate using strained InGaAs quantum wells for optical gain and GaAs for the index tuning material operating around lambda =0.98 mu m. With zero bias applied to the filter electrodes, the receiving passband was measured to be centered at approximately 0.98 mu m with a FWHM bandwidth of approximately 3 nm. A differential signal gain of 12 dB was obtained when the amplifier current increased from 20 mA to 34 mA.