Patent ID: 6794625
Filing Date: 2004-09-21
Classification: G02B,G03F,G11B

Abstract:
An optical apparatus for determining a position of an article, the apparatus comprising an illumination unit, focusing optics and a focus detection unit, wherein:the illumination unit is operable to generate incident light and illuminate an elongated region of the article for producing light returned from the illuminated region; the focusing optics directs the incident light towards the article and directs at least a portion of the returned light toward the focus detection unit; and the focus detection unit comprises an optical system and a detector, the optical system being operable to collect the directed portion of the returned light and create at least two images on a sensing surface of the detector in the form of at least two interference patterns, respectively, wherein at least one pattern is created by interference between: light components of the collected light that propagated within a first periphery region of an optical axis of the focusing optics; and light components of the collected light that propagated within a paraxial region of said optical axis, and wherein at least one other interference pattern is created by interference between: light components of the collected light that propagated within a second periphery region of said optical axis, substantially symmetrical to said first periphery region with respect to said optical axis; and light components of the collected light that propagated within the paraxial region of said optical axis; and wherein data representative of a relation between intensity profiles in the at least two interference patterns is indicative of the position of the article relative to a focal plane of said focusing optics.