Giant birefringence in multi-slotted silicon nanophotonic waveguides

Abstract

We demonstrate record giant birefringence, nearly twice as large as has previously been achieved (Delta n(group) = 1.5 over more than 60 nm of bandwidth near lambda= 1550 nm) using a multi-slotted silicon nanophotonic waveguide. The birefringence is optimized by the use of materials with high refractive index contrast to create a compact single-mode waveguide, and the etching of deeply sub-wavelength channels within the waveguide, which are strongly coupled in the near field and separated by narrow air channels of optimum lateral width. When used as a polarization-selective delay element, the delay-bandwidth product per unit length is 46.6/mm over a bandwidth of 8.74 T Hz. We also design and demonstrate mode shaping of both the TE and TM polarizations to achieve near-identical coupling to a macroscopic external object, such as a lensed fiber or detector.