PROBLEM TO BE SOLVED: To precisely measure the wavelength of a light without using a reference light source.;SOLUTION: The light to be measured is branched to two by a branching means 21, and the intensity Ea of one light Pd is detected by a light receiver 22. The other light Pe is incident on a transmitting element 23 having the transmitting characteristic in that the transmittance to light is changed depending on the wavelength, and the intensity Eb of its outgoing light Pe' is detected by a light receiver 24. A transmittance calculation means 30 calculates the transmittance H of the light to be measured to the transmitting element 23 from the detected two intensities of the light. A wavelength detection means 33 determines the wavelength λx of the light Pc to be measured on the basis of the calculated transmittance H and the transmitting characteristic of the transmitting element 23.;COPYRIGHT: (C)2005,JPO&NCIPI
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