Polarization-independent reflectometry and polarization-independent reflectometer

A polarization independent reflectometer, comprising:

• a light source for generating low-coherence light having a polarization degree of 0.3 or less;
• an interferometer adapted to hold the polarization degree of propagation light and including a light branch section for separating a low-coherence light from said light source into two parts;
• a optical measurement block for entering one of the branch parts in a measured optical circuit as measurement light and taking out reflected light signal provided by reflecting the measurement light at each point responsive to a propagation distance of the measured optical circuit;
• a variable optical delay circuit for giving the other a group delay that can be changed arbitrarily as local light signal;
• and a lightwave combining section for combining the local light signal from the variable optical delay circuit and the reflected light signal from the optical measurement block and causing the local light signal and the reflected light signal to interfere with each other;
• a detection system for detecting the intensity of the interference light output from said interferometer, in which a reflection intensity at each point responsive to the propagation distance of the measured optical circuit is measured as a function of the group delay from the intensity of the interference light detected;
• a polarizer composed on one of a path from the variable optical delay circuit to the lightwave combining section and a path from the optical measurement block to said lightwave combining section except light reciprocating parts;
• a polarization rotation device for arbitrarily rotating the polarization state of propagation light 0 degrees and 90 degrees, said polarization rotation device composed on one of the path from the variable optical delay circuit to said lightwave combining section and the path from the optical measurement block to said lightwave combining section except light reciprocating parts;
• and
• a signal processing system provided for detecting the intensities of interference light by said detection system when the polarization state is rotated 0 degrees and 90 degrees by said polarization rotation device with a predetermined group delay given by the variable optical delay circuit and adding the intensities of interference light, to measure the reflection intensity at the point responsive to the propagation distance of the measured optical circuit corresponding to the predetermined group delay.