Patent ID: 8570509

Claim:
A spectrometry apparatus comprising: a transmissive diffraction grating that transmits incident light having an operating wavelength λ, wherein the transmissive diffraction grating has inclined surfaces made of a first dielectric material, the inclined surfaces are inclined relative to a reference line, if an angle of incidence of light incident on the transmissive diffraction grating with respect to the reference line is defined as an angle α, and an angle of diffraction of diffracted light with respect to the reference line is defined as an angle β: the angle of incidence α is smaller than a Bragg angle θ defined with respect to the inclined surfaces, and the angle of diffraction β is greater than the Bragg angle θ, if an inclination angle of the inclined surfaces with respect to the reference line is deflned as an angle φ: the inclined surfaces are arranged at a period P/cosφ in a direction perpendicular to the reference line, and the incident light is linearly polarized parallel to a flat surface perpendicular to the reference line and perpendicular to the direction in which the inclined surfaces are arranged, and 1.0<λ/ P< 2.0.