设计和制作了基于晶体双折射的自由空间90°光学桥接器，用于在空间相干激光通信接收机中实现信号光束和本机振荡光束的混合并产生90°相移四通道合成光束输出，实现空间2×4 90°桥接，以进一步进行光电变换及信号解调和锁相。研制的晶体双折射2×4 90°光学桥接器由四块结构相同的双折射平板，一块相位延迟平板和一块检偏双折射平板组成。外差测量证明晶体双折射2×4 90°光学桥接器运行准确有效，性能稳定可靠，并给出了相位补偿和进一步的优化方案。晶体双折射自由空间光学桥接器适用于自由空间相干激光通信，对于未来星载激光通信终端实现小型化、轻量化、低功耗和高码率具有实际意义。

The design and fabrication of an optical 2×4 90° hybrid based on crystal birefringence for coherent receiver in free-space optical communication system are presented. The two pairs of balanced optical signals combined by the signal beam and local oscillator beam are output, which obtains the accurate phase difference of 90°, realizes 2×4 free-space hybrid, carries out photoelectric conversion and signal demodulation phase-lock. The 90° hybrid comprises two pairs of stacked birefringent plates, an analyser birefringent plate and a phase retardation plate. The testing results measured by heterodyne method verify that the 2×4 optical 90° hybrid can run accurately, effectively, stably and reliably. The phase compensation and further optimization schemes are also proposed. The free-space optical hybrid based on birefringence is particularly suitable for free-space coherent optical communication system, for intersatellite communications terminal for future compact, lightweight, low power consumption and high bit rate in the future.