Micro-optics based Polarization Decoding Module for Free-Space Quantum Key Distribution

We demonstrate a compact polarization decoding module with the size of 2 cm × 2 cm × 1 cm for a free space quantum key distribution based on micro-optics. The insertion loss and polarization extinction ratio (PER) of this module are 22.8 dB, respectively, and large alignment tolerance is achieved owing to multimode fiber pigtailing. The quantum bit error rate (QBER) are measured to be 0.67% with the sifted key rate of 576 kb/s at the clock rate of 100 MHz.