All-silicon polarizing filters for near-infrared wavelengths

Abstract

We discuss the design and fabrication of optical filters that are transparent to a preferred linear polarization, but are partially or substantially reflective to the orthogonal linear polarization. The filters are fabricated by depositing thin films of form-birefringent silicon onto silicon wafers using the serial bideposition method. Characteristic curves that are presented for the in-plane principal refractive indices np and ns of the porous films as functions of vapor impingement angle facilitate critical aspects of the filter design. These include matching of a p principal index and an s principal index for films deposited at different angles, and realization of p and s principal indices that satisfy the antireflection condition for the silicon substrate in air.