The optical hybrid is mainly used to split and combine the signal beam and the local oscillator beam from two inputs, thereby generating four mixed beams with a relative phase difference of 90°. 90º optical hybrid is suitable for coherent signal demodulation for either homodyne or heterodyne detection. The device accepts the two optical signals (S & L) and generates four output signals: S+L, S-L, S+jL, and S-jL.