Polarization detector

A polarization detector, comprising:

• a polarization diffraction element having a substrate with two facing surfaces which are in parallel with each other, a first diffraction grating formed on one surface of the substrate, and a second diffraction grating formed on the other surface of the Substrate, light being incident upon the first diffraction grating, each grating pitch of the first diffraction grating and the second diffraction grating being nearly equal to a wavelength of the incident light;
• limiting means for limiting an incident region of the incident light with respect to the polarization diffraction element, formed on a light incident side of the first diffraction grating;
• converging means for respectively converging light transmitted through the first diffraction grating and the second diffraction grating and light diffracted by the first diffraction grating and the second diffraction grating into different beam spots;
• and
• a pair of photodetecting means for detecting each optical intensity of the two beam spots converged by the converging means,
• wherein the limiting means is formed of an aperture and limits a width of the incident light to a limit width thereof on a surface vertical with respect to a proceeding direction of the incident light, said limit width being 4t.sub.0 .multidot.tan.theta..sub.2 .multidot.sin(90.degree.-.theta..sub.1) or less, where t.sub.0, is a thickness of the substrate of the diffraction grating element, .theta..sub.1 is an incident angle of the incident light, and .theta..sub.2 is a diffraction angle of the incident light in the substrate by the first diffraction grating.

A polarization detector, comprising:

• a polarization diffraction element having a substrate with two facing surfaces which are in parallel with each other, a first diffraction grating formed on one surface of the substrate, and a second diffraction grating formed on the other surface of the substrate, light being incident upon the first diffraction grating, each grating pitch of the first diffraction grating and the second diffraction grating being nearly equal to a wavelength of the incident light, the first diffraction grating being formed with a width of 4t.sub.O .multidot.tan.theta..sub.2 or less in a vertical direction with respect to a groove direction of the first diffraction grating, where t.sub.O is a thickness of the substrate and .theta..sub.2 is a diffraction angle of the incident light in the substrate by the first diffraction grating;
• converging means for respectively converging light transmitted through the first diffraction grating and the second diffraction grating and light diffracted by the first diffraction grating and the second diffraction grating into different beam spots;
• and
• a pair of photodetecting means for detecting each optical intensity of the two beam spots converged by the converging means.

A polarization detector, comprising:

• a polarization diffraction element having a substrate with two facing surfaces which are placed in parallel with each other, a first diffraction grating formed on one surface of the substrate, and a second diffraction grating formed on the other surface of the substrate, light with a wavelength which is to fluctuate being incident upon the first diffraction grating, each grating pitch of the first diffraction grating and the second diffraction grating being nearly equal to a wavelength of the incident light, a thickness of the substrate being W.sub.0 /{4tan.theta..sub.2 .multidot.sin(90.degree.-.theta..sub.1)} or more, where W.sub.O is a width of the incident light on a surface vertical with respect to a proceeding direction of the incident light, .theta..sub.1 is an incident angle of the incident light, and .theta..sub.2 is a diffraction angle of the incident light in the substrate by the first diffraction grating;
• converging means for respectively converging light transmitted through the first diffraction grating and the second diffraction grating and light diffracted by the first diffraction grating and the second diffraction grating into different beam spots;
• and
• a pair of photodetecting means for detecting each optical intensity of the two beam spots converged by the converging means.