| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a variable diffraction element capable of suppressing influence of fluctuation of ambient temperature. <P>SOLUTION: The variable diffraction element is provided with transparent substrates 121 and 122, projections 13 periodically formed at a pitch P on at least one facing surface of the transparent substrates 121 and 122 and extended in a prescribed direction and a liquid crystal layer 14 interposed between the transparent substrates 121 and 122. The refractive index of the liquid crystal layer 14 to incident light of linearly polarized light in a prescribed polarization direction is changed from a first refractive index n<SB>1</SB>to a second refractive index n<SB>2</SB>(n<SB>1</SB><n<SB>2</SB>) by voltage application. The projection 13 is composed of a transparent material having a refractive index n<SB>s</SB>equal to the first refractive index n<SB>1</SB>or the second refractive index n<SB>2</SB>and has a height d represented by ä(0.5+m)×λ/Δn} (wherein Δn=¾n<SB>2</SB>-n<SB>1</SB>¾, m denotes a natural number including zero and λ denotes a wavelength of the incident light) and a duty ratio D=w/P which is a ratio of the width w of the projection 13 to the pitch P of 0.05 to 0.35 or 0.65 to 0.95. <P>COPYRIGHT: (C)2009,JPO&INPIT |
