Jeong Kyo Seo

Improved Antishock Air-Gap Control Algorithm with Acceleration Feedforward Control for High-Numerical Aperture Near-Field Storage System Using Solid Immersion Lens

A near-field storage system using a solid immersion lens (SIL) has been studied as a high-density optical disc drive system. The major goal of this research is to improve the robustness of the air-gap controller for a SIL-based near-field recording (NFR) system against dynamic disturbances, such as external shocks. The servo system is essential in near-field (NF) technology because the nanogap distance between the SIL and the disc is 50 nm or less. Also, the air-gap distance must be maintained without collision between the SIL and the disc to detect a stable gap error and read-out signals when an external shock is applied. Therefore, we propose an improved air-gap control algorithm using only an acceleration feedforward controller (AFC) to maintain the air-gap distance without contact for a 4.48 G at 10 ms shock. Thus, the antishock control performance for the SIL-based NF storage system in the presence of external shocks is markedly improved. Furthermore, to enhance the performance of the antishock air-gap control, we use the AFC with a double disturbance observer and a dead-zone nonlinear controller. As a result, the air-gap distance is maintained without contact for a 6.56 G@10 ms shock.

The Small-Sized Optical Module and the Sled Moving Method of a Gap Servo Near-Field Recording

We present two viewpoints of small-sized optical module of a gap servo NFR. One is experimental results on the adjustment system and the other is the sled moving way mounted on the deck mechanism.

Cross-Talk Effects between Gap Error and Track Error Signals in a Gap Servo Near Field Optical Storage System

We presented experimental results including 50 GB capacity RF signals in a gap servo NFR system. Considerable cross-talk effects have been observed between gap and track error signals and the origins of them have been investigated

Numerical Simulations on a Stepped Solid Immersion Lens Suggested from the Experimental Consideration of the Backflow

When the air flows round the conical solid immersion lens (SIL) due to the disk rotation, the air climbs up along the lateral surface of the conical SIL at the downstream of the SIL. The existence of this backflow, which has opposite direction of the disk rotation, is confirmed numerically and experimentally. The backflow exists below one-quarter of the gap between the rotating disk and the lateral surface of the SIL and it is known to be one of major sources which carries contaminant particles to the SIL top. A step, 40 µm in height and 25 µm below the rotating disk, is fabricated on the lateral surface of the SIL to prevent the backflow. Numerical simulation shows the step reduces the pressure difference between the bottom and the top of the SIL so that the backflow is reduced dramatically.

Readout characteristics of an advanced SIL system of high NA for the near field optical storage with cover layer media

An improved concept of the advanced SIL and its compensation OL of composite effective NA over 1.7 has been designed and manufactured to achieve wider assembling tolerances, higher data capacities and better signal quality. Very clear readout signals were measured from a 25 GB BD-like ROM media with 3 um cover layer and the applying feasibility of the advanced SIL system in near field optical storage was confirmed. With this novel advanced SIL system and multilayer media concept, total capacity over 500 GB per disc was expected to be accomplished.