| 摘要 |
PROBLEM TO BE SOLVED: To provide an incident angle-dependent diffraction grating having high performance by optimizing a duty ratio or the like of one-dimensional relief type diffraction grating. SOLUTION: The incident angle-dependent diffraction grating comprises a relief type one-dimensional diffraction grating 1 made by distributing a high refractive index part 2 and a low refractive index part 3 periodically in one direction and has±first-order diffraction efficiency monotonically changed in one direction with respect to the incident angle, wherein the normalization pitch, refractive index modulation, duty ratio and normalization groove depth are set such that Bragg angle satisfying Bragg's condition is made positive, incident angle 0°is included between the Bragg angle and the incident angle which gives the minimum diffraction efficiency appearing first from the Bragg angle, the following relation (A) is satisfied; ä(diffraction efficiency at the Bragg angle-minimum diffraction efficiency appearing first)×0.2 + minimum diffraction efficiency appearing first}≤diffraction efficiency at incident angle 0°(A), and it is satisfied that the diffraction efficiency at the Bragg angle is two times or more of the diffraction efficiency at the incident angle 0°. COPYRIGHT: (C)2008,JPO&INPIT
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