Patent ID: 7805085

Claim:
An optical reception apparatus for receiving to process a signal light which is differential phase shift keying modulated using a quadrature-phase component, comprising: a splitter that splits said signal light input thereto into two lights; first and second delay interferometers respectively arranged on optical paths through which the respective lights split in said splitter are propagated; first and second photoelectric converters that receive the respective lights output from said first and second delay interferometers to convert the two lights into electric signals, and output respectively first and second data signals corresponding to the quadrature-phase component of said signal light; a clock recovery circuit configured to recover a clock signal based on the data signal output from one of said first and second photoelectric converters; a multiplexer that outputs a third data signal which is obtained by multiplexing the first and second data signals output from said first and second photoelectric converters, in accordance with timing of the clock signal recovered by said clock recovery circuit; a framer configured to frame the third data signal output from said multiplexer in accordance with a predetermined communication method and also to generate a frame synchronizing signal indicating whether or not a frame synchronization is achieved; and a delay interferometer controller that, when the frame synchronization is not achieved, performs a control of resetting operating conditions of said first and second delay interferometers according to the frame synchronizing signal generated by said framer, and repetitively performs said control until the frame synchronization is achieved, wherein the resetting control of said delay interferometer controller is performed by temporarily blocking input of said signal light to each of said first and second delay interferometers to suspend the operations thereof.