Ultra-compact polarization beam splitter utilizing a graphene-based asymmetrical directional coupler

A novel ultra-compact polarization beam splitter (PBS) utilizing an asymmetrical directional coupler with a combination of a silicon waveguide (SW) and a graphene multilayer embedded silicon waveguide (GMESW) has been proposed and investigated. The modal characteristics of the GMESW for the TM mode varies significantly, whereas that for the TE mode changes slightly with respect to the SW, inducing the launched TM mode to directly pass through the SW with little influence from the GMESW, while the TE mode undergoes a strong coupling and is transferred to the GMESW. A designed PBS with an 8.3 μm-long coupler and 200 nm-wide gap separation offers high extinction ratios (18.2 and 21.2 dB) and low insertion losses (0.16 and 0.36 dB) for the thru and cross ports, respectively. The presented PBS also presents the ability to work with variable splitting ratio power for the TM mode by varying the chemical potential of graphene, implying various applications in signal processing on a chip.