| 摘要 |
A diffraction grating has incident and emitting side gratings respectively formed on front and rear faces of a diffraction substrate composed of a transparent plane-parallel plate. A pitch LAMBDA 1 of the incident side grating, a pitch LAMBDA 2 of the emitting side grating, a refractive index n1 of the diffraction substrate, a thickness t of the diffraction substrate, and incident angle theta 1 of light incident to the incident side grating, an angle theta 2 of diffraction within the diffraction substrate, an emission angle theta 3 of light emitted from the emitting side grating, a distance T from the emitting side grating to a face for receiving the emitted and diffracted light, and a wavelength lambda of the light are set to satisfy the following conditions. <IMAGE> <IMAGE> and <IMAGE>
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