Design and analysis of wide-frequency-band germanium-based terahertz subwavelength grating polarizer

Terahertz (THz) polarization detection is of great significance in fields like biomedicine, atmospheric monitoring and astronomical observation. The Germanium (Ge)-based detector with high sensitivity and wide detection frequency band of 2~8 THz, can achieve THz polarization detection by combining it with the micropolarizers oriented in different directions. In this paper, a single layer Ge-based THz subwavelength grating polarizer array is designed and analyzed for the Ge-based detector, based on the equivalent medium theory and leaky mode resonance effect of the subwavelength grating. The grating structure parameters are designed and optimized using the finite difference time domain (FDTD) method. The simulation results show that the polarizer can obtain nearly transverse magnetic (TM) polarized wave on the transmission side and nearly transverse electric (TE) polarized wave on the reflection side in the wide THz frequency range under the condition of normal incidence, which shows it has good polarization beam splitting characteristic. At the frequency of 6 THz, the reflectivity of the grating polarizer for TE polarized wave is 99.995%, while the transmittivity of the grating polarizer for TM polarized wave is 98.88%. The polarization extinction ratio (PER) of the polarizer for reflected wave is 19.5 dB and that for transmitted wave is up to 43.1 dB. Besides, the angle characteristics and preparation tolerances of the polarizer are discussed. The calculation results show that the polarizer has large angle and preparation tolerances.