Compact polarization sensors with vertically integrated photodetectors

Abstract

We describe a new method of sensing the linear polarization of light in a single mesa device structure by vertically integrating two photodetectors. The monolithic architecture eliminates the need for several discrete components, such as polarization filters and beam splitters, thus reducing critical alignment requirements and cost for various optical systems. Applications include the simplification of reading heads in magneto-optical (MO) data storage devices and constructing imaging arrays for polarization vision. In imaging, polarization sensing can extract additional information from a scene otherwise not noticeable to the human eye, facilitating remote sensing, material classification, and biological imaging. The operation principle of our vertical cavity polarization detector (VCPD) is based on a resonant cavity enhanced (RCE) photodetector, being vertically integrated with a conventional photodetector. The RCE detector is 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). For off-normal incidence of light, the reflectivity of the semiconductor-air interface and DBR are significantly different for TE (s) and TM (p) polarizations. Thus the RCE detector provides resonance enhancement for TE, capturing the TE polarized light in the top detector. For TM polarized light, both reflectivities are small, therefore, light is transmitted to and absorbed in the bottom detector. A large contrast in TE/TM response of the top and bottom detectors is achieved and the linear polarization can be computed from their relative responses. Experimental results displaying good agreement with simulation results have been recently achieved and are presented.