Patent ID: 7308204

Claim:
A noise suppressing method comprising: dividing an input light including a signal light and noise light within a signal wavelength band of the signal light into a first component with a first polarization direction parallel to a polarization direction of the signal light and a second component with a polarization direction orthogonal to the first polarization and applying the first component to a first arm and the second component to a second arm; shifting an optical phase of the second component in the second arm so that the optical phase of the second component in the second arm differs by π from the first component in the first arm; combining the first component output from the first arm and the second component output from the second arm to cause the noise lights included in the first and second components interfere with each other; and adjusting the polarization of the second component in the second arm to maximize a SNR of the combined light by the combining step, wherein the adjusting the polarization of the second component in the second arm measures a degree of polarization of the combined light and adjusts the polarization direction of the second component in the second arm to maximize the degree of polarization.