Patent ID: 6487148
Filing Date: 2002-11-26
Classification: B82Y,G11B

Abstract:
An edge detection system for detecting a pre-formatted mark on a disk surface by detecting a beam reflected from the disk surface, comprising:an optical head configured to provide evanescent coupling for operation under a near-field configuration, where a spacing variation between the head and the disk surface is high, by receiving and focusing the beam onto the disk surface at a distance less than one wavelength of said beam; a light detector operatively coupled with said optical head to receive the reflected beam, said light detector having a first input element that receives a first spatial half of a reflected beam from the disk surface having pre-formatted marks to produce a first signal, and a second input element that receives a second spatial half of said reflected beam to produce a second signal; and an edge detection analyzer coupled to said first and second input elements to produce a difference of said first and second signals to indicate a location with respect to a pre-formatted mark on the disk surface, where the difference of said first and second signals substantially reduce the dependence of so generated edge signal on said spacing variation.