JPS57191608A - Trimming filter - Google Patents

Abstract

PURPOSE:To ensure the good separation among the red, green and blue wavelength bands and to secure the suffcient transmission at the center band, by disposing the thin film groups contanining the layers of 2lambda0/4 and 4lambda0/4 optical film thickness alternately at both ends of a layer of lambda0/4 optical thickness (lambda0: standard wavelength). CONSTITUTION:A layer 11 of 4lambda0/4 optical film thickness n1d1, a layer 12 of 2lambda0/4 thickness n2d2, a layer 13 of 4lambda0/4 thickness n3d3, a layer 14 of lambda0/4 thickness n4d4, a layer 15 of 4lambda0/4 thickness n5d5, a layer 16 of 2lambda0/4 thickness n6d6, and a layer 17 of 4lambda0/4 thickness n7d7 are laminated in that order from the side of a substrate 10. In this case, ni is the refractive index of the layer (i) and di is the geometric film thickness of the layer (i). Then a layer ZrO2 with a high refractive index and a layer containing mainly SiO2 with a low refractive index are provided to such a trimming filter at the odd and even layers counted from the side of the substrate 10. As a result, the characteristic curve has a valley parts of the transmittance at the areas near 480nm and 570nm. Thus the good transmission properties can be obtained at other visible regions.