| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a diffraction collimating lens which can be shared for a plurality of laser light sources having different wavelengths. <P>SOLUTION: The diffraction collimating lens 2 collimates a laser light emitted from laser light sources 1, having two or more different wavelengths λ<SB>i</SB>(i=1, 2, 3, ...), in a projection-type image display device 10 that has the laser light sources 1. At least one mirror face has a diffraction structure and the diffraction structure shows a maximum diffraction efficiency to the respective wavelengths λ<SB>i</SB>; the correction quantity of focal length generated due to a temperature variation is determined as insufficient correction for the variation (variation quantity is denoted by ΔfA) in the focal distance for a laser light source A which shows a minimum wavelength variation, with respect to the temperature variation among the laser light sources 1; and excessive correction for the variation (variation quantity is denoted by ΔfB) in the focal distance for a laser light source B which shows a maximum wavelength variation with respect to the temperature variation among the laser light sources; wherein the absolute values of the variation quantity ΔfA and the variation quantity ΔfB are substantially equal to each other. <P>COPYRIGHT: (C)2011,JPO&INPIT |
