Patent ID: 7253943

Claim:
A phase optimization apparatus comprising: a first arm having a first semiconductor optical amplifier that is operated with a first predetermined current and amplifies a pump signal and a probe signal; a second arm having a second semiconductor optical amplifier that is operated with a second predetermined current and amplifies the probe signal, and a π phase shifter that controls the phase of the amplified probe signal; an optical band-pass filter that filters optical signals output from the first and second arms, which have interfered and have been mixed with each other, and outputs the probe signal that has been modulated in a same manner as the pump signal has been modulated; and a phase control unit that receives as feedback a portion of the output signal of the band-pass filter and outputs a phase control signal, which controls a phase difference between the first and second arms to increase or decrease an optical power of the band-pass filter depending on the phase difference, to the it phase shifter of the second arm; wherein the phase control unit comprises: a splitter that separates a portion of the optical output signal of the optical band-pass filter from the output signal; a first converter that converts the separated optical signal into a current signal; a second converter that converts the current signal into a voltage signal; a low-pass filter that low-pass-filters the voltage signal; and a phase controller that determines the phase difference between the first and second arms from the output signal of the low-pass filter, and outputs to the second arm a phase control signal that controls the phase difference to increase or decrease the optical power of the optical band-pass filter according to the phase difference.