VERSATILE OBJECTIVE LENS WITH ADJUSTABLE CORRECTION FOR DIFFERENT WAVELENGTHS AND SUBSTRATE THICKNESSES FOR TESTING OPTICAL DISKS

A typical aspheric singlet used as the objective lens in optical-disk data-storage systems will not work at different wavelengths or with di fferent substrate thicknesses because of spherochromatism. Using two m icroscope objectives with adjustable collars and a pair of relay lense s, we have constructed a system in which a diffraction-limited spot of any wavelength in the range of 0.4-0.7 mu m can be moved by as much a s +/-100 mu m in both the focusing and tracking directions. We accompl ished this by simply moving an aspheric singlet mounted in an off-the- shelf optical head. The system uses the adjustable collars of the micr oscope objectives to correct for the spherochromatism of the singlet a nd to accommodate the various thicknesses of the substrates. (C) 1997 Optical Society of America.