Near-Field Optical Recording on a Pre-Grooved Phase-Change Disk in the Blue-Violet

Near-field optical recording was implemented on a pre-grooved phase-change disk by using a φ1 mm superhemispherical solid immersion lens (SIL) of 1.5 numerical aperture. The SIL unit was mounted on a two-axis actuator for enabling both gap-height and tracking controls. The gap height was precisely adjusted with a capacitance formed between the SIL and disk materials. Groove structures were fabricated on a glass substrate by a reactive-ion-etching (RIE) process and flattened with spin-on-glass (SOG) coating for obtaining reliable push-pull tracking error signals. The phase-change layer stack was optimized by a vector diffraction analysis in order to maximize evanescent coupling at the gap height as small as 50 nm. A bit density of 80 nm was demonstrated on the land of a pre-grooved disk at the wavelength of 407 nm.