METHOD AND APPARATUS FOR MEASURING REFLECTING WAVELENGTH, LIGHT LINE DISCRIMINATING METHOD AND SYSTEM

PROBLEM TO BE SOLVED: To provide technology for discriminating a light line by measuring a reflecting wavelength while excluding the influence of a background component caused by the reflection of an inspection light except a reflector. SOLUTION: The inspection light incident from a light emitting unit 8 to a light line 60 propagates in the line and arrives at a reflector 62. The inspection light is a wavelength modulation light time-varying in the wavelength by a predetermined frequency at the reference wavelength as a center. The reflector 62 reflects the light having a predetermined reflecting wavelength at high reflectivity, and reflects the light having larger wavelength deviation from the reflecting wavelength with lower reflectivity, and hence the reflected light of the inspection light reflected at the reflector 62 is periodically time-changed in intensity in response to the wavelength change of the inspection light. When the reference wavelength of the inspection light is altered while detecting the reflecting light intensity by the detector 10 and the reference wavelength is so regulated that the frequency of the time change of the reflected light intensity becomes twice as large as the wavelength change frequency of the inspection light, the reference wavelength at that time is obtained as the reflected wavelength of the reflector 62.