Optical phase detection method with orthogonal polarization and phase compensation arrangement

A method of optical phase detection, comprising the steps of:

• separating a linearly polarized signal light and a local light emitted from a local light laser light source into mutually-perpendicular P-polarized and S-polarized components by first and second polarization beam splitters;
• regulating the phases of at least one of said P-polarized and S-polarized components by first and second optical phase compensation plates so that the polarized components of said signal light are maintained in phase with each other, while the polarized components of said local light have a phase difference of 90.degree. therebetween, said step of regulating including the steps of:
• regulating the phase of the S-polarized component of said signal light by said first optical phase compensation plate, and
• regulating the phase of the P-polarized component of said local light by said second optical phase compensation plate;
• combining the polarized components of said signal light and the polarized components of said local light with each other by first and second combiners to produce an in-phase component and a quadrature component 90.degree. out of phase with said in-phase component, said step of combining including the steps of:
• combining the P-polarized components of said signal light and said local light with each other to produce said quadrature component, and
• combining the S-polarized components of said signal light and said local light with each other to produce said in-phase component;
• demodulating said in-phase component to produce an output signal;
• and
• synchronizing the phases of said signal light and the phase of said local light with each other through the use of said in-phase component and said quadrature component.

Apparatus for optical phase detection, comprising:

• laser light source means for emitting a local laser light;
• fist polarization beam splitter means for separating a linearly polarized signal light into mutually-perpendicular P-polarized and S-polarized components;
• second polarization beam splitter means for separating said local light from said light source means into mutually-perpendicular P-polarized and S-polarized components;
• combiner means for combining the polarized components of said signal light and the polarized components of said local light from said first and second polarization beam splitter means, with each other, to produce an in-phase component and a quadrature component 90.degree. out of phase with said in-phase component;
• optical phase compensation plate means, positioned between said first and second polarization beam splitter means and said combiner means, for regulating the phases of at least one of said P-polarized and S-polarized components, so that the polarized components of said signal light are maintained in phase with each other, while the polarized components of said local light have a phase difference of 90.degree. therebetween;
• demodulating means for demodulating said in-phase component to produce an output signal;
• and
• synchronizing means for synchronizing the phases of said signal light and the phase of said local light with each other through the use of said in-phase component and said quadrature component.