Verification of tracking servo signal simulation from scanning tunneling microscope surface profiles

Abstract

Well-defined track crossing signals are essential for the laser tracking servo systems to follow radial runout. An approach has been developed to verify Fourier optics calculation of the track crossing signals from 3-D surface profiles measured by scanning tunneling microscopy (STM) and also by measuring the actual tracking servo groove signals from the substrate on an optical disk tester. Nearly quantitative agreement between the tracking signals calculated from the measured STM profiles and those measured by the optical disk tester was demonstrated on grooved glass disk substrates with a 1.6 μm pitch and nominal groove depths of 20, 40, and 70 nm, and on photopolymer on glass substrates with track pitches of 1.6, 1.4, 1.2, 1.0, 0.8 and 0.6 μm and a groove depth of 67 nm. Injection molded polycarbonate substrates made with high and low mold temperature showed poor replication at the lower mold temperature. The servo signals reflected the degraded servo groove performance due to the poor servo groove replication at the lower mold temperature.