Patent ID: 8922789

Claim:
A displacement measuring device, comprising: an irradiation system for irradiating irradiation light; a first fiber Bragg grating that has first transmittance distribution or first reflectance distribution with respect to a wavelength of transmitted light or reflected light; a second fiber Bragg grating that has second transmittance distribution or second reflectance distribution with respect to a wavelength of transmitted light or reflected light; and a detecting system that detects amplitude of the irradiation light that has passed through the first fiber Bragg grating and the second fiber Bragg grating of which at least one of the first transmittance distribution and the second transmittance distribution changes in a wavelength direction with a change amount different from that of the other, according to a displacement amount of an object, or amplitude of the irradiation light that passes through the first fiber Bragg grating and second fiber Bragg grating of which at least one of the first reflectance distribution and the second reflectance distribution changes in the wavelength direction with a change amount different from that of the other, according to the displacement amount of the object, and acquires an index to indicate the displacement amount based on the amplitude that changes according to the change amount of at least one of the first transmittance distribution and the second transmittance distribution, or the change amount of at least one of the first reflectance distribution and the second reflectance distribution.