Design and numerical study of a compact, broadband and low-loss TE-pass polarizer using transparent conducting oxides

A compact, broadband, and low-loss TE-pass polarizer using transparent conducting oxides (TCOs) embedded in the center of the strip waveguide and deposited on its top is proposed and analyzed in detail. With the tunable permittivity of TCO, epsilon-near-zero (ENZ) of its real part and significant increase of its imaginary part can be achieved around the wavelength of 1.55 μm under a certain electron concentration. By introducing this ENZ material into the strip waveguide, huge polarization dependence can be realized, that is, the TE mode is almost not affected due to its quite weak interaction with TCOs, while the TM mode is extremely confined in the accumulation layers of TCO with high absorption loss, leading to a great reduction in length for the present polarizer. Moreover, the top TCO layer is applied to further enhance the polarizer performance. Results show that a polarizer of only 4.5 μm in length with an extinction ratio (ER) of 25.26 dB and an insertion loss of 0.21 dB is achieved at 1.55 μm, and its bandwidth can be extended to ~140 nm for an ER>20 dB. In addition, the ER can also be increased only by enlarging the length of the TCO-based polarizer.