光记录装置的记录密度是用焦点的衍射极限来控制的。焦点直径与光源的波长成正比,与物镜的数值孔径成反比,但是若将数值孔径增大,则因为记录盘基板的厚度变化而产生的球面像差的增加与数值孔径的4次方成正比。本文叙述利用物镜和基板之间设 The recording density of the optical recording device is controlled by the diffraction limit of the focal point. The focal spot diameter is proportional to the wavelength of the light source and inversely proportional to the numerical aperture of the objective lens. However, if the numerical aperture is increased, the spherical aberration due to the variation of the thickness of the recording disc substrate increases in proportion to the fourth power of the numerical aperture . This article describes the use of the lens and the substrate set up between