Apparatus for receiving optical signal and method of controlling phase offset for differential quadrature phase shift keying

A method of controlling a phase offset in receiving optical signals for differential quadrature phase shift keying (DQPSK), the method comprising:nreceiving an original optical signal modulated in DQPSK;delaying the original optical signal by one bit to make a delay optical signal and performing an interference on the original optical signal and the delay optical signal;generating a control signal by use of an interference result between the original optical signal and the delay optical signal; andcontrolling a phase offset for the interference between the original optical signal and the delay optical signal by use of the generated control signal;wherein the generating of the control signal includes determining a variation, according to the phase offset, of a constructive interference signal and a destructive interference signal corresponding to the original optical signal and the delay optical signal.

An apparatus of receiving optical signals for differential quadrature phase shift keying (DQPSK), comprising:na delay interference unit configured to delay an original optical signal modulated in DQPSK by one bit to make a delay optical signal and perform an interference on the original optical signal and the delay optical signal; anda phase offset control unit configured to generate a control signal by use of an interference result between the original optical signal and the delay optical signal, and control a phase offset for the interference between the original optical signal and the delay optical signal by use of the generated control signal;wherein the phase offset control unit is configured to generate the control signal at least in part by determining a variation, according to the phase offset, associated with a constructive interference signal and a destructive interference signal corresponding to the original optical signal and the delay optical signal.