Independent phase matching for TE and TM polarization in directional couplers with tilted subwavelength structures

Tilted subwavelength gratings (SWGs) are promising structures for birefringence control and polarization management in integrated photonic waveguides. Here we show how tilted SWGs can be used to design a directional coupler based polarization beam splitter which is symmetric for TM polarization but asymmetric for TE polarization. Using this approach, we develop a polarization beam splitter with calculated insertion loss below 1 dB and an extinction ratio better than 20 dB over a bandwidth of 86 nm. The fabricated device shows negligible insertion loss and an extinction ratio over 15 dB over a bandwidth of 72 nm.