Terahertz achromatic quarter wave plate: Design, fabrication, and characterization

The terahertz achromatic quarter wave plate is realized for the first time in the frequency band of 1.3-1.8 THz via design, fabrication, and characterization. The wave plate is made from 9 pieces of birefringent crystalline quartz plates with different thickness, which are precisely stacked together with different rotation angles. The designed quarter wave plate shows phase retardance of 90°±3° with a stable optical axis. Experimental results show that the linearly polarized terahertz wave converts into circularly polarized when transmitting through the fabricated quarter wave plate placed at 45°. The quarter wave plate is also used to measure the known input state of polarization. The optimization method introduced in this paper is applicable to design the wave plates in the other frequency bands as well.