Double-wavelength aperture restricting filter and optical pickup apparatus using the same

摘要

A double-wavelength aperture restricting filter has a zonal part adapted to act such that one wavelength lambd1 of light keeps the quantity of light in an outer peripheral part of the luminous flux thereof whereas the other wavelength lambd2 of light apparently extinguishes this quantity of light by an interference effect. The zonal part has such a step that light supposed to pass a position corresponding to the zonal part if the zonal part does not exist and light passing a position at which the zonal part is formed if the zonal part exists generate therebetween a phase difference satisfying predetermined conditional expressions, whereas the circle formed by a step boundary has a diameter residing between two luminous flux diameters desired in two systems used for the wavelengths lambd1 and lambd2, respectively.