Design of a promising silicon slot waveguide-based ultra-short low loss efficient polarization rotator for the mid-IR

We propose design of a promising ultra-short and highly efficient mid-IR polarization rotator (PR) on silicon-on-calcium-fluoride (SOCF) platform, whose rotation section is formed from an asymmetric slot waveguide for the working wavelength of 4.47 mu m by exploiting mode coupling scheme. Numerical results demonstrate that within a conversion length of just similar to 18 mu m, the maximum achievable polarization conversion efficiency (PCE) for both the polarizations (TE-TM and TM-TE) is as high as similar to 100% with significantly low loss of similar to 0.15 dB. Achieved polarization extinction ratios (PERs) are as high as 43.3 dB and 34.9 dB for TE-TM and TM-TE polarizations, respectively. Furthermore, over a large bandwidth of 360 nm (4.29-4.65 mu m), our designed PR exhibits very high PCE (> 98%) for both the TE-TM and vice versa with an appreciable PER of similar to 18 dB and relatively low loss of similar to 0.26 dB. Study on fabrication tolerances reveals that designed PR is robust to potential imperfections in fabrication. To the best of our knowledge, our designed PR is the shortest PR reported to date for the mid-IR wavelength regime with a healthy balance/compromise between PCE, PER, bandwidth, loss and fabrication tolerance.