To minimize the spot size of a light focused by a lens of optical disk system, other than adoption of higher NA lens or shorter wave length laser diode, super-resolution method has been examined. It is practically used in another products, but it is rare in optical head because of its light power loss. Light power loss is essential for optical head because output light of laser diode is rather weak, Super-resolution optics up to this time uses shield which covers central part of pupil of objective lens where the peak of light power exist, so it wastes much energy. In addition to it, most of all practical use optical heads (We choose this type of head for the standard.), a part of the Gaussian beam outer than the level about 28% of its peak is shaded by pupil of the objective lens.
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