Optical reception apparatus compatible with DQPSK polarization multiplexing format

An optical reception apparatus compatible with DQPSK polarization multiplexing format, for receiving to process a DQPSK polarization multiplexed signal light obtained by polarization multiplexing a set of DQPSK modulated signal lights of which polarization states are different from each other, comprising:

• a polarization splitting section that splits the DQPSK polarization multiplexed signal light input thereto into a horizontally polarized DQPSK modulated signal light and a vertically polarized DQPSK modulated signal light;
• a first branching section that branches the horizontally polarized DQPSK modulated signal light split by the polarization splitting section into two, to generate a first horizontally polarized signal light and a second horizontally polarized signal light;
• a second branching section that branches the vertically polarized DQPSK modulated signal light split by the polarized splitting section into two, to generate a first vertically polarized signal light and a second vertically polarized signal light;
• a first branch through which the first horizontally polarized signal light and the first vertically polarized signal light are propagated;
• a second branch through which the second horizontally polarized signal light and the second vertically polarized signal light are propagated;
• a first delay interfering section arranged on the first branch;
• a second delay interfering section arranged on the second branch;
• a signal light input/output section that supplies to the first delay interfering section the first horizontally polarized signal light and the first vertically polarized signal light so that propagation directions thereof are opposite to each other, and supplies to the second delay interfering section the second horizontally polarized signal light and the second vertically polarized signal light so that propagation directions thereof are opposite to each other, and also, extracts the first horizontally polarized signal light and the first vertically polarized signal light which have been propagated through the first delay interfering section, and extracts the second horizontally polarized signal light and the second vertically polarized signal light which have been propagated through the second delay interfering section;
• first to fourth photoelectric converting sections that receive, respectively, the first horizontally polarized signal light, the first vertically polarized signal light, the second horizontally polarized signal light and the second vertically polarized signal light, which have been extracted by the signal light input/output section, to convert them into electric signals;
• a reception processing section that processes the electric signals output from the first to fourth photoelectric converting sections, to regenerate reception data obtained by demodulating the horizontally polarized DQPSK modulated signal light and reception data obtained by demodulating the vertically polarized DQPSK modulated signal light;
• and
• a control section that feedback controls the first and second delay interfering sections based on the process result in the reception processing section.