| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a diffraction grating capable of suppressing light quantity loss. <P>SOLUTION: The diffraction grating is provided with first and second diffraction grating parts 5 and 6 which are formed on both principal surfaces of a transparent base material 2 and wherein a low refractive index material 3a and a high refractive index material 4a are alternately disposed. In the first diffraction grating part 5, grating depths of the low refractive index material 3a and the high refractive index material 4a are respectively set so that phase difference between the low refractive index material 3a and the high refractive index material 4a is 2π with respect to a second wavelength and the ratio of a width dimension of the low refractive index material 3a to a period of the diffraction grating part is set to be a value except 0.5 so that diffraction efficiency is made to be a prescribed value with respect to a first wavelength. In the second diffraction grating part 6, grating depths of the low refractive index material 3b and the high refractive index material 4b are respectively set so that phase difference between the low refractive index material 3b and the high refractive index material 4b is 2π with respect to the first wavelength and the ratio of the width dimension of the low refractive index material 3b to a period of the diffraction grating part is set to be a value except 0.5 so that diffraction efficiency is made to be a prescribed value with respect to the second wavelength. <P>COPYRIGHT: (C)2008,JPO&INPIT |
