Simulative Experiment on Precise Tracking for High-Density Optical Storage Using a Scanning Near-field Optical Microscopy Tip

Abstract

This paper describes simulative experiment of sub-micron region tracking control for a near-field optical disk storage, utilizing a scanning near-field optical microscopy (SNOM) tip as a highly sensitive head. A continuous tracking error detection model was introduced, and evaluated its equivalent tracking performance experimentally. Sub-sub-micron aperture head's tracking error arising from an electrical and an optical noises could be suppressed to several nanometers assuming that head operating spacing is maintained less than 50 nm and tracking control bandwidth is limited to 5kHz. The results showed that we could estimate the tracking error due to the noise derived mainly from the opto-electonic conversion system. In this simulative experiment, the optical efficiency of the head was relatively small compared with that of the planer or tapered type aperture; thus, the result should be regarded as an under-estimation. The optimization of the sensor location for more efficient data detection, and the more practical evaluation of a tracking control system considering the actuator characteristics are problems that remain to be studied in future.