Patent ID: 7812934

Claim:
A physical quantity measuring apparatus, comprising: an optical fiber in which fiber Bragg gratings are formed; a light source which is connected to the optical fiber, and that has a light emitting band including a band in which central reflected wavelengths of the fiber Bragg gratings change; an arrayed waveguide grating which is connected between the light source and the optical fiber via an optical branching filter, and that has output channels of which central wavelengths of at least three output channels are included in a one-tenth loss band of a reflected light by the fiber Bragg grating; light receiving devices for receiving light output from the output channels of the arrayed waveguide grating on a one-to-one basis; and a central reflected wavelength change detecting unit which is connected to the light receiving devices for estimating a change in a central reflected wavelength based on a physical quantity, by calculating a first group signal and a second group signal from light receiving signals corresponding to the at least three output channels and by calculating a differential signal between the first group signal and the second group signal, wherein: the central wavelengths of output channels comprising the first group signal are shorter than the central reflected wavelength of the fiber Bragg grating; and the central wavelengths of output channels comprising the second group signal are longer than the central reflected wavelength of the fiber Bragg grating.