In view of the special requirements of laser communication systems for optical mixers

this paper designs and completes a 90°mixer

with the signal light by spatial light input and the Local Oscillating（LO）light by polarization maintaining fiber input.The beam waist diameter of the spatial light introduced from the signal end of the device is 10 mm

the insertion loss of the signal light is less than 3.1dB and that of the LO less than 2.5dB.At the specified operating wavelength

the phase difference between branch I and branch Q satisfies 90°±5°.The experimental results show that this device meets the requirements of laser communication for mixer performances.