Light wavelength measuring apparatus and method for measuring wavelength of subject light with high speed by using two-beam interferometer

A light wavelength measuring apparatus comprising:

• a two-beam interferometer which splits an incident light in two optical paths, combines and outputs split lights together again, the two-beam interferometer being configured to generate at least one or more combined light made from two beams having polarization states different from each other;
• a polarization state detector which detects a variation in the polarization state of the combined light generated by the two-beam interferometer;
• and
• an electric circuit which calculates a wavelength of the incident light based on the variation in the polarization state of the combined light detected by the polarization state detector,
• wherein a difference in length between the two optical paths of the two-beam interferometer of a point of splitting the incident light and a point of combining the split lights is fixed, for a detection of polarization variation in the combined light according to a wavelength variation of the incident light by the polarization state detector.