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A silicon polarizing beam splitter is designed and fabricated based on an asymmetric slot waveguide structure without adopting additional strip-slot waveguide mode converters. The asymmetric slot waveguide consists of a 150-nm-wide and a 350-nm-wide nanowires with a slot of 100 nm, which can realize a transverse magnetic light cross-coupling with a 392-nm-wide strip waveguide, while little transverse electric light coupling can happen. The fabricated device has a coupling length of ~18 μm with a coupling gap spacing of 450 nm, which can achieve a polarization extinction ratio (PER) of ~14 and 25 dB at the bar and cross ports, respectively. Low insertion loss is realized, while more than 10-dB PER can be obtained over the wavelength range of 1520-1576 nm. The device performance could be further improved with the fine optimization of device structure parameters and fabrication process.
Feng et al. (Thu,) studied this question.