Cheol-Ki Min

Solid Immersion Lens Optical Head for High-Numerical-Aperture Cover-Layered Incident Near-Field Recording

For increasing data recording density and reducing spherical aberration in cover-layered incident near-field recording (NFR) systems, a high-refractive-index cover layer is necessary and the assembly and evaluation technologies of a solid immersion lens (SIL) optical head for a high-numerical-aperture (NA) cover-layered incident NFR system are also required. To assemble a SIL optical head for the high-NA cover-layered incident NFR system, a modified Twyman–Green interferometer is developed. In this paper, we present the design and assembly results for a SIL optical head with a high-refractive-index cover-layered disk. We also compare evaluation results with those of a simulation to confirm the feasibility of the assembly. Through this research, we can improve the effective NA to 1.84, which is the highest NA reported for a cover-layered incident NFR system, and consequently, the data recording capacity per layer can be increased. # 2009 The Japan Society of Applied Physics

Micro Holographic Recording Characteristic With Defocused Micrograting

The recording of micro holographic storage is performed by the superposition of two tightly focused counter-propagating beams. The micrograting is affected by misalignment in the z -direction during the recording and read-out processes. Thus, the diffraction efficiency (DE) can be reduced by the defocusing of the micrograting. In this paper, we investigate the recording characteristics of a defocused micrograting. An optical system with a numerical aperture (NA) of 0.60 and a wavelength of 532 nm was designed for micro holographic recording. The recording tolerance was formulated by using vector diffraction theory. The recording tolerance was determined by using the Mahajans Strehl ratio (SR) of the DE. The DE was dramatically reduced at the ±0.4λ defocusing position and we determined that the ±0.4λ was the recording tolerance in the defocusing direction. In addition, we propose a precise detection method to obtain a focus error signal (FES) within the recording tolerance range. Finally, the numerical results of a defocused micrograting were experimentally verified.

Compensation Method of Mechanical Error for Micro Holographic Storage

In this paper, we experimentally investigated compensation method of the mechanical errors for the micro holographic storage. The aim of this research was overcome of disc tilt and spherical aberration problems. The proposed method was performed by using glass plate and zoom optics.