Fig. 1. Transmission of polarization states. (a) Orthogonal polarization fundamental mode propagating in ideal fiber; (b) orthogonal polarization mode propagating in the case of PMD

Fig. 2. Basic model of WDM-type polarization compensation

Fig. 3. Schematic diagram of a real-time polarization state compensation system based on WDM

Fig. 4. Preparation structure of conjugate polarization state

Fig. 5. Standard orientation of polarization-maintaining fibers on a four-port polarizing beam splitter

Fig. 6. Flowchart of polarization control program

Fig. 7. Results of polarization test for 30 minutes without and with compensation. (a) Without compensation; (b) with compensation

Fig. 8. Change graph of Stokes parameter at polarization of 0°

Fig. 9. Structure diagram of the PDM-DQPSK system

Fig. 10. Polarization-division multiplexing system based on non-orthogonal polarization

Fig. 11. Polarization compensation QKD system over optical fibers based on WDM

Fig. 12. Evolution of quantum bit error rate in fiber polarization-encoded QKD within 8 hours

Fig. 13. Count evolution of single photon detector within 8 hours