Numerical investigations of an ultra-compact polarization beam splitter based on augmented low-index guiding and subwavelength grating structures

We report the design of an ultra-compact polarization beam splitter with high performance that is based on augmented low-index guiding and subwavelength grating (SWG) structures. The transverse-electric (TE) and transverse-magnetic (TM) modes are confined in high-index silicon (Si) and low-index silicon nitride (Si(3)N(4)), respectively. They are separated by using, respectively, a gradually curved Si waveguide and a Si(3)N(4) SWG structure with optimal grating-element. The footprint of the proposed polarization beam splitters (PBS) is 2.9 × 2.25 μm(2). The device offers high polarization extinction ratios (PERs) of ~18 dB for the two polarizations, with low insertion losses of ~0.22 dB (~0.71 dB) for the TE (TM) mode at the wavelength of 1550 nm. Over the broad band from λ = 1500–1650 nm, the PERs of the TE and TM modes are above 17 and 16 dB, respectively. By narrowing the operating band to the range from λ = 1500 to 1600 nm, the proposed PBS provides PERs of >17 dB for both polarizations. Finally, the fabrication tolerance of the designed PBS is also addressed and discussed in detail.