| 摘要 |
PURPOSE:To obtain fully stable spectral characteristics even when using color spectral filters by setting up an optical film thickness of a transparent protective layer, which is to be interposed between color spectral filters and the photoelectric conversion part, not less than a specific thickness. CONSTITUTION:A cyanide dichroic stripe filter 13 and a yellow dichroic stripe filter 14 are arranged so as to cross each other on a glass substrate 1 as color separation filters. While thereon interposing a transparent protective layer 3, the photoelectric conversion part 4 is formed for being incorporated in a pick-up tube. In general, the thickness t1 and the thickness t2 of both filters 13 and 14 are not equal while having different value. Accordingly, the regions A-C, where photointerference come into question have three kinds of thickness respectively while a state of wave motion of a spectral transmissivity curve is existing. Said spectral transmissivity curve shows no large change when the thickness of the layer 3 becomes not less than 2.5mum even if the thickness of the layer 3 is fluctuated, thus making it possible to obtain stable spectral characteristics. The photorefractive index of the layer 3 in case of SiO2 is 1.47 so that the optical film thickness makes 2.5X1.47 3.7mum while the thickness of the region B only requires to be set up not less than set value. |
