Ultra-compact broadband polarizing beam splitter a using tilted nano-grating-based bridge waveguide

An ultra-compact broadband silicon polarizing beam splitter is demonstrated with the assistance of a tilted nano-grating-based bridge waveguide. By tilting the grating elements to gain polarization control over the anisotropy of the equivalent medium, a new design freedom to engineer the effective mode index and circumvent small variable duty cycles can be adopted to benefit the device fabrication. The transverse magnetic (TM) light can be resonantly coupled to the cross port, while the transverse-electric (TE) light can almost completely output from the through port. The length of the coupling region is only 13.6 µm, which can realize an extinction ratio of 30.57 dB for TM light or 31.15 dB for TE light at a 1550-nm wavelength theoretically. The fabricated device can achieve an extinction ratio of 29.35 dB for TM or 22.6 dB for TE light with a low excess loss, and an extinction ratio of more than 20 dB can be realized in the wavelength range from 1525 to 1610 nm for both polarizations. The presented device also shows a good fabrication tolerance, which would facilitate its practical applications in commercial photonic integrated circuits.