Patent ID: 7697803

Claim:
A Return-to-Zero Differential Quadrature Phase Shift Keying (RZ-DQPSK) modulation system with single phase alignment control, comprising: a clock source; first and second phase shifters, wherein each of the first and second phase shifters are connected to the clock source; first and second logical AND gates each comprising two inputs and an output, wherein the inputs to the first logical AND gate comprise an output of the first phase shifter and a first data stream, and wherein the inputs to the second logical AND gate comprise an output of the second phase shifter and a second data stream; a DQPSK modulator comprising first and second modulator drivers, wherein the first modulator driver is driven by the output of the first logical AND gate, and wherein the second modulator driver is driven by the output of the second logical AND gate; an optical splitter connected to an output of the DQPSK modulator; a monitor and control circuit connected to the optical splitter, wherein the monitor and control circuit is configured to monitor phase alignment differences between the first and second data streams and to provide a control signal responsive to phase alignment differences; and a data precoder configured to provide the first and second data streams, wherein the control signal is connected to the data precoder and the data precoder is configured to adjust phase between the first and second data streams responsive to the control signal.