Polarisation sensing with resonant cavity enhanced photodetectors

The authors describe a new method of polarisation sensing using resonant cavity enhanced (RCE) photodetectors. The RCE detectors are constructed by integrating a thin absorption region into an asymmetric Fabry-Perot cavity formed by a bottom mirror composed of a distributed Bragg Reflector and the semiconductor air interface. 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) polarisations. A pair of monolithically integrated RCE photodetectors with cavity lengths tuned for resonance and anti-resonance provide a large contrast in response to TE and TM polarisations. The device formed by this technique eliminates the need for external polarisation filters and beam splitters, thus alleviating the problems associated with the bulkiness of the polarisation sensors in many applications