Giant birefringence in multislotted silicon nanophotonic waveguides

Abstract: We demonstrate record giant birefringence, nearly twice as large as has previously been achieved (Δn group = 1.5 over more than 60 nm of bandwidth near λ = 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 optimimum 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 THz. 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