Integrated optic lithium niobate image rejection circuit giving minimum channel spacing for 622 Mbit/s CPFSK link

A minimum channel spacing of 1.2 GHz has been achieved in a 622 Mbit/s CPFSK optical heterodyne link using image rejection. The image rejection circuit, which included a lithium niobate integrated 90° optical hybrid, provided over 23 dB of rejection and resulted in a greater than threefold increase in achievable channel density.