A method of optical phase detection, in which a signal light polarized linearly and a local light emitted from a local light laser light source are combined with each other so that an in-phase component and a quadrature component, which is 90 degrees behind the local light in phase and is combined with the signal light, are taken out; and the in-phase component is demodulated while the phase of the signal light and that of the local light are synchronized with each other through the use of the in-phase component and the quadrature component, in which the signal light and the local light are separated into mutually-perpendicular P-polarized and S-polarized components by first and second polarization beam splitters; the phases of the P-polarized or S-polarized components are regulated by first and second optical phase compensation plates so that the polarized components of the signal light are kept in phase with each other, but the polarized components of the local light have a phase difference of 90 degrees between themselves; and the polarized components of the signal light and those of the local light are combined with each other by a first and a second combiner so that the in-phase component and the quadrature component are obtained. Therefore, a method having a low demodulation error can be easily provided to be widely used for high-capacity coherent optical communication.
Optical phase detection method with orthogonal polarization and phase compensation arrangement