Polarizers in an Asymmetric Twin Waveguide Based on Resonant Coupling

A polarization filter based on resonant coupling in an asymmetric twin waveguide (ATG) is demonstrated for the first time. A special taper design of the upper waveguide cladding enables power transfer from the fundamental input to the first higher order mode and causes mode beating. A power extinction ratio (PER) of the TE-relative to the TM-polarization of (3.1 ± 0.4) dB is measured at 1610 nm for two consecutive TM-pass polarizers. A TM/TE-PER of (1.4±0.4) dB is observed for a second device with a similar configuration also at 1610 nm. A single polarizer has a length of only 372 μm. Multiple polarizers can be easily placed in series to increase the PER. In addition, the input waveguide acts as a spot size converter to enable improved coupling to a lensed fiber.