Patent ID: 6342976
Filing Date: 2002-01-29
Classification: G02B,G11B

Abstract:
An objective lens having a variable luminous flux diameter, disposed within a luminous flux having a wavelength selectivity;said objective lens having a first region constituting a center part and a second region positioned outside said center part, said first region having no diffracting action with respect to two light beams having respective wavelengths &lgr;1, &lgr;2 different from each other, said second region being formed with a diffracting portion having a diffracting action by a diffracting grating which has a stepped cross section with respect to only one of said two light beams having respective wavelengths &lgr;1, &lgr;2; and wherein luminous flux diameter of one light of the two beams is varied and the other light beam luminous flux diameter is not varied.