2-[formula omitted] Ultra-broadband polarization beam splitter with tunable transmissions based on silicon-Ge[formula omitted]Sb[formula omitted]Se[formula omitted]Te[formula omitted] hybrid subwavelength gratings

Abstract

Recently, integrated optical devices working at 2-μm wavelengths have attracted considerable attention. Among such devices, a polarization beam splitter is an essential building block for constructing the on-chip circuit. Here, we have proposed an ultra-broadband polarization beam splitter with tunable transmissions working at 2-μm waveband. Coupled-mode based directional coupler is utilized for the device design. Subwavelength grating structures provide efficient dispersion control, which endows broad optical bandwidths. In addition, a rear-bent coupler is cascaded at the output of the device to furtherly suppress the crosstalk. The silicon-Ge2Sb2Se4Te1 hybrid materials provide tunable transmissions. When the Ge2Sb2Se4Te1 is in the amorphous state, with high extinction ratios more than 20 dB, the bandwidths exceed 200 nm (1900∼2100 nm) and 130 nm (1925∼2055 nm) for TE0 and TM0, respectively. Furthermore, the insertion losses are less than 0.24 dB (1900∼2100 nm) and 0.56 dB (1925∼2055 nm) for TE0 and TM0, respectively. When being in the crystalline state, the device works as an absorber that fully attenuates the input energy. In different intermediate amorphous–crystalline​ hybrid states, it is also possible to achieve tunable transmissions.