| 摘要 |
PURPOSE:To obtain an optical coupler film having the transmittance which is constant over a wide wavelength range by forming a 1st layer counted from a substrate side of TiO2 and a 2nd layer of SiO2, respectively, and forming the 1st layer to have a small film thickness and the 2nd layer to have an approximately equal film thickness with respect to the thickness of 1/4 the central wavelength for designing the coupler film. CONSTITUTION:This coupler film consists of the 1st layer and 2nd layer counted from the substrate side. The 1st layer 2 is made of the TiO2 which is a high refractive index material and the 2nd layer 3 is made of the SiO2 which is a low refractive index material. The 1st layer 2 is formed to 0.42-0.44 film thickness and the 2nd layer 3 to 0.98-1.02 film thickness with respect to 1/4 the central wavelength for designing the coupler film. The respective rays of the reflected light at the boundary face are added and joined to and with the reflected light of the same phase by the interference with each other by most adequately designing the film thicknesses of the 1st layer and the 2nd layer in the above-mentioned manner. The prescribed reflectivity and transmittance are thus obtd. over the wide wavelength range.
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