Patent ID: 7957232
Filing Date: 2011-06-07
Classification: G11B

Abstract:
1. A gap controller for use in an optical information processor with an optical system that includes a solid immersion lens and that produces near-field light to be incident on an optical information storage medium, the controller comprising: a moving section for moving at least one of the solid immersion lens and the optical information storage medium so as to vary the gap between the solid immersion lens and the optical information storage medium; a gap detecting section for outputting a gap detection signal representing the magnitude of the gap between the solid immersion lens and the optical information storage medium; a gap control system for controlling the position of the solid immersion lens such that the level of the gap detection signal is maintained at a reference level Vref; and second-order difference calculating means for calculating the second-order difference of the gap detection signal with respect to the gap by getting the gap varied by the moving section and by getting the levels of the gap detection signal that change with the varying gap, wherein the gap control system determines the reference level Vref based on the second-order difference.