• Tilted gratings effectively modulate mode dispersion, increasing the bandwidth of polarizing beam splitters and reducing coupling lengths. • Shallowly etched tilted gratings can avoid the impact of excessively narrow ridge width on fabrication accuracy. • The tilted gratings cause radiation loss in the TE mode of the cross port and increases the extinction ratio. By utilizing the anisotropy of tilted gratings, a broadband and high manufacturing tolerance silicon polarizing beam splitter is demonstrated based on shallowly etched gratings. The tilt angle causes the grating wave vector to produce different components in the transverse and longitudinal directions. The transverse momentum component is strongly coupled only with the transverse electric (TE) mode, resulting in its radiation leakage at the cross port and almost lossless transmission at the through port; while the transverse magnetic (TM) mode is almost unaffected by the longitudinal electric field distribution and maintains low-loss transmission at the cross port. TE or TM light can theoretically achieve an extinction ratio of 39.96 or 27.61 dB at a wavelength of 1550 nm, respectively. The fabricated device with a coupling length of 25.34 μm can achieve an extinction ratio of 25.41 dB for TM light or 25.07 dB for TE light with a low excess loss. An extinction ratio of more than 20 dB can be realized in the wavelength range from 1525 to 1610 nm for both polarizations, which is beneficial for applications in coherent optical communications, sensing or quantum information processing.
Feng et al. (Wed,) studied this question.