| 摘要 |
PROBLEM TO BE SOLVED: To provide an incident-angle-dependent diffraction grating having higher performance in which the area ratio or the like of high refractive index parts of a two-dimensional relief diffraction grating is optimized. SOLUTION: The incident-angle-dependent diffraction grating is composed of a two-dimensional relief diffraction grating 1 in which high refractive index parts 2 and low refractive index parts 3 are periodically distributed in two directions, and positive and negative primary diffraction efficiencies in the respective directions monotonically vary depending on the incident angle. Normalized pitch, refractive index modulation, area ratio and normalized groove depth are set so that, under an assumption that the Bragg angle which satisfies Bragg condition is positive, the incident angle of zero degree is included between the Bragg angle and the incident angle which appears first from the Bragg angle and gives the local minimum diffraction efficiency, the condition (A) is satisfied: ä(diffraction efficiency at Bragg angle - local minimum of diffraction efficiency appearing first)×0.2+ local minimum of diffraction efficiency appearing first}≤diffraction efficiency at incident angle of zero degree, and the diffraction efficiency at Bragg angle is twice or more as large as the diffraction efficiency at the incident angle of zero degree. COPYRIGHT: (C)2008,JPO&INPIT |
