US Patent 7561803 Bi-directional signal interface using photonic coupler

A signal interface comprises a non-reciprocal device having a first port that accepts a first electrical signal and a second port that accepts a second electrical signal. The non-reciprocal device passes the second electrical signal through the first port without a phase shift and passes the first electrical signal through the second port with a 180 degrees phase shift. An optical modulator receives an optical signal at an optical input port, a second signal at a first and a second electrical input port, the first electrical signal at a third electrical input port, and the phase-shifted first electrical signal from the non-reciprocal device at a fourth electrical input port. The optical modulator transmits the second electrical signal to the first port of the non-reciprocal device without a phase shift and modulates the first electrical signal on the optical signal and providing the modulated optical signal at an optical output port of the optical modulator.