Patent ID: 7577076

Claim:
A tilt sensor for determining information related to a tilt of an object to a reference plane, comprising: a diffraction element disposed at a position on an optical path of a light beam from the object, the light beam entering the diffraction element at an incident angle, the position of the diffraction element determined in accordance with a positional relation with the object, wherein the diffraction element diffracts diffraction light at a diffraction efficiency that varies in accordance with the incident angle of the light beam; and a photo detector that receives the diffraction light diffracted by said diffraction element and outputs a photoelectric signal, wherein the diffraction element has a Q-factor described by a first equation: Q =2 πλT /( nP 2 )≧0.5, wherein λ indicates a wavelength of an incident light, T indicates a groove depth of a grooved grating of the diffraction element, n indicates a refractive index of the diffraction element, and P indicates a groove pitch of the grooved grating of the diffraction element.