High extinction ratio and low loss polarization beam splitter based on multimode interference for PICs.

A polarization beam splitter (PBS) with a high extinction ratio that is based on multimode interference (MMI) is proposed and experimentally demonstrated on a silicon-on-insulator platform. The PBS is designed using cascaded MMI to enhance the extinction ratio (ER) and minimize insertion loss (IL) compared to a conventional MMI structure. The proposed device has a high extinction ratio (22.3 dB for TE and 25.6 dB for TM) and a low insertion loss (0.7 dB for TE and 0.1 dB for TM) at a wavelength of 1550 nm while the device supports a broad bandwidth of 60 nm (${\rm ER} \gt {16};{\rm dB}$ER>16dB) for both polarizations over a wavelength between 1520-1580 nm. Moreover, the eigenmode expansion method shows that the device has a large fabrication tolerance of an MMI width ${\pm} 40; {\rm nm}$±40nm and a length ${\pm} 1500; {\rm nm}$±1500nm. The proposed PBS can be used in on-chip silicon photonic integrated circuits for polarization division multiplexing.