Polarization sensing with resonant cavity enhanced photodetectors

We describe a new method of sensing the linear polarization of light using resonant cavity enhanced (RCE) photodetectors. The RCE detectors are constructed by integrating a thin absorption region into an asymmetric Fabry-Perot cavity. The top reflector is formed by the semiconductor air interface while the bottom mirror is a distributed Bragg reflector (DBR). Quantum efficiency of these RCE devices can be controlled by tuning the cavity length by recessing the top surface of the detector for off-normal incidence of light the reflectivity of the semiconductor-air interface can be significantly different for TE(s) and TM(p) polarizations. A pair of monolithically integrated RCE photodetectors with cavity lengths tuned for resonance and antiresonance provide a large contrast in response to TE and TM polarizations. An alternative polarization sensor can be formed by vertically integrating a conventional and a RCE photodetector. We show that a large contrast in the TE/TM responsivities of the vertical cavity polarization detectors (VCPD) can be achieved, thus combining detection and polarization sensing in a single mesa semiconductor device. These devices alleviate the problems associated with the bulkiness and critical alignment constraints of the conventional sensors based on polarizing filters or splitters and have potential for fabrication of monolithic smart pixels and imaging arrays