Design and fabrication of polarization and phase modulated beam splitter

Polarization and phase controlled beam splitter is an indispensable optical element in free space quantum communication system. Its performance directly affects the communication quality and determines the communication error rate. Based on the theory of equivalent layer design, the special film structure of ''dielectric+metal+dielectric'' is adopted, and Ag metal material and SiO₂, Al₂O₃, Ta₂O₅ dielectric material are selected to realize 45° incident angle on quartz substrate, and the average transmittance/reflectance ratio is 8.5: 91.5 in the wavelength range from 1500 nm to 1600 nm. Phase is controlled at 1530, 1540, 1550, 1560 nm. By optimizing the deposition process, the splitter film samples are prepared by electron beam evaporation with ion assisted technology. The test results show that the average transmittance/reflectance ratio is 8.53: 91.47 in the wavelength range of 1500-1600 nm under the condition of 45° incidence. The transmitted phase difference controlled within 5.02° and the reflected phase controlled with 8.05° in the range of 1530, 1540, 1550, 1560 nm, which meets the requirements of spectral energy splitting ratio and phase control of communication system. In addition, the film passed the corresponding environmental test, which meets the reliability requirements.