Ultra-compact, broadband polarization beam splitter based on x-cut lithium-niobate-on-insulator platform using hybrid plasmonic waveguide

We propose an ultra-compact, high-performance polarization beam splitter (PBS) on the x-cut lithium-niobate-on-insulator (LNOI) platform. The device based on asymmetrical directional coupler (ADC) consists of a single-mode waveguide (SMW) and a hybrid plasmonic waveguide (HPW). Whole length of the device is only 47 μm, which is the shortest PBS on the x-cut LNOI platform due to polarization-dependent characteristic of plasmonics. When choosing proper width of coupling waveguides (WGs), the phase-matching condition can be satisfied in TE polarization while phase-mismatching exists in TM polarization at the same time. Simulation result shows that bandwidth of the device can achieve at least 200 nm with −10 dB extinction for TE polarization and at least 200 nm with less than −20 dB extinction for TM polarization, which successfully covers entire C-band and L-band. Additionally, the device exhibits large fabrication tolerance and easily fabricated characteristic.