Mid-infrared polarization beam splitter based on square/circular hybrid air holes with wide bandwidth and ultrashort length

A novel mid-infrared polarization beam splitter (PBS) based on GaS is proposed. The high birefringence is achieved by using the cladding structure of alternating arrangement of square and circular air holes as well as introducing double elliptical air holes. The finite element method (FEM) is utilized to investigate the mode coupling characteristics in the proposed PBS. The results show that the highest extinction ratio of 115 dB and shortest length of only 40 μm can be realized at a wavelength of 4 μm. A wide bandwidth of 200 nm ranging from 3.9 to 4.1 μm is obtained.