Juil Lee

Development of an air gap servo system for high data transfer rate near field optical recording

This paper describes development of a bi-axial actuator-based air gap servo system for a near field optical recording system using a blue laser and a solid immersion lens (SIL). We first present a new pull-in procedure ensuring smooth air gap servo start-up without lens-disc collision. Furthermore, a memory-loop control technique has been employed to realize a high-speed air gap servo system guaranteeing a high data transfer rate.

A novel approach to control of nonminimum-phase nonlinear systems

We present an approach to control of nonminimum-phase multiple-input-multiple-output (MIMO) nonlinear systems based on a singular perturbation-like technique. First, we show that a MIMO nonlinear system can be converted into a singularly perturbed system through magnitude and time-scaling transformation. In particular, the proposed transformation technique can make the hidden or internal dynamics behave like a fast subsystem. However, the fast subsystem takes a weakly controllable form, which implies that a small positive low-gain parameter multiplies the control input in the fast subsystem. For this reason, the well-known integral manifold approach is then utilized to decompose the resulting singularly perturbed system into two subsystems in separate timescales, each of which is of a lower dimension and, more importantly, controllable in the sense that the control input will explicitly appear in the boundary-layer system. The proposed method is particularly useful to make the input-output dynamic characteristics of a decouplable nonminimum-phase nonlinear system decoupled and linear.

Near-Field Recording with a Solid Immersion Lens on Polymer Cover-layer Protected Discs

Recent demonstrations have shown that near-field optical recording with a solid immersion lens in a conventional actuator is a strong candidate for optical storage beyond Blu-ray Disc. All results published so far were obtained with so-called first-surface configurations, in which the data layer is not protected by a cover-layer. In this paper we demonstrate a next step towards creating a system suitable for a commercial product with removable discs. First results are presented for read-out of discs with a few µm protective polymer cover-layer and a solid immersion lens with NA=1.45 and λ=405 nm.

Near Field Recording on First-Surface Write-Once Media with a NA=1.9 Solid Immersion Lens

We present a single-wavelength near field recording set-up with a blue laser and a NA=1.9 solid immersion lens in a conventional focus and tracking actuator. The most important aspects to realize such a near field recording system are discussed, in particular, gap error signal normalization and correction of chromatic aberration of the objective lens. First recording results demonstrate that the set-up is fully operational.

Improved Near-Field Recording System for First-Surface Media with an NA=1.9 Solid Immersion Lens

Near-field optical recording using a solid immersion lens is quickly becoming an attractive technology for use in commercial optical data drives. Calculations and experiments show that Near-field optical recording has the potential to enable data storage capacities of more than 150 GB per side on a compact disc (CD)-sized disc, which may prove sufficient to continue the optical recording roadmap beyond Blu-ray Disc. Compared to alternative approaches that aim to achieve high storage densities, near-field recording requires a minimum change in drive architecture and media technology. In this paper we present our progress on the development of a near-field optical recording system with an NA=1.9 Solid Immersion Lens in a conventional actuator, using a single blue laser diode.