Active Controlled Fiber Optical 90 Hybrid for Coherent Communications

This letter presents the realization of an active controlled fiber optical 90" hybrid, for use in phase diversity receivers. The four output signals are proportional E1 2 Ez and E, f E2.exp (j90°), where E, and Ez are the complex amplitudes of the two input signals. A hybrid comprising four 3-dB monomode fiber couplers and two phase shifters was designed for the 1.5 pm wavelength range. The principle of operation is described and experimental results are presented. The maximum phase error is smaller than 0.5".