Kei Shimura

The Nature of the Coupling Field in Optical Data Storage Using Solid Immersion Lenses

The field incident onto the interface between the solid immersion lens (SIL) and recording medium is decomposed into two parts that exhibit different behavior as the beam propagates through the recording layers. The homogeneous part is shown to diffract, and the inhomogeneous part decays exponentially away from the bottom of the SIL. Reflection and signal contrast are calculated for a phase-change recording medium. The dependences of the signal contrast on the gap width, the refractive index of gap and the SIL are analyzed.

Near-Field Phase Change Optical Recording Using a GaP Hemispherical Lens

A GaP solid immersion lens and a modified liquid immersion lens (MLIL) are studied. The phase change marks exhibit a diameter of approximately 200 nm when recorded by the MLIL.

Pupil-plane filtering for improved signal detection in an optical data-storage system incorporating a solid immersion lens.

A pupil-plane filtering technique is applied to data-signal detection in an optical data-storage system that uses a solid immersion lens (SIL) and a four-layered phase-change recording medium. We have confirmed by numerical calculations and experiment that the technique improves signal contrast and makes the contrast less sensitive to the gap width between the bottom surface of the SIL and the top surface of the recording medium. Light that is incident upon the objective lens that is used with the SIL is linearly polarized, and the full vectorial feature of the light is considered in the calculations.

Vector diffraction analysis by discrete-dipole approximation

The discrete-dipole approximation is applied to vector diffraction analysis in a system with large-numerical-aperture (NA) optics and subwavelength targets. Distributions of light diffracted by subwavelength dielectric targets are calculated in a solid angle that corresponds to a NA of 0.9, and their dependence on incident polarization, target shape, and target size is studied. Electric field distributions inside the target are also shown. Basic features of the vector diffraction are clearly demonstrated. This technique facilitates understanding of the vectorial effects in systems that are expected to be applied in the future to optical data storage.

Pupil Plane Filtering for Optical Pickup Heads with Effective Numerical Aperture of 1.1 and 2.0

A pupil plane filtering technique is applied to data signal detection in an optical data storage system that uses a solid immersion lens (SIL) and a quadrilayer phase change recording medium. Two systems that have the effective numerical aperture (NAEFF) of 1.1 and 2.0 are investigated. A new filter is designed for the NAEFF=2.0 system on the basis of this study. We have confirmed by numerical calculations that the technique improves signal contrast, which is defined by the ratio of the difference signal to the sum signal between the homogeneous crystalline area and the homogeneous amorphous area. We have also confirmed that the technique makes the contrast less sensitive to the gap width between the SIL and the recording medium. The vectorial feature of the light is considered in the calculations. The calculated irradiance distributions and signal levels for the system with NAEFF =1.1 are confirmed by experiments.

Performance estimation of projection display system using a diffraction-based liquid crystal spatial light modulator

The basic performance of a projection system using a diffraction-based liquid crystal spatial light modulator is studied. First, the relationship between the modulation pattern of light at the SLM and its diffraction pattern is analyzed using the scalar diffraction theory, and anew method for improving the contrast of the projected image is proposed on the basis of this analysis. Then, the optical efficiency and image contrast are estimated by numerical calculations, in which monochromatic illumination incident on the SLM at a certain angle range is assumed. Both an efficiency of 0.65 and a contrast of 200 are obtained at the same time by optimizing the modulation pattern and apertures in the projection optics. The possibility of realizing a projector delivering bright images with a high contrast is suggested.

High-density overwrite recording for a phase-change medium using a visible-light laser diode

A fast data transfer and high density recording was realized, using a 30 mw visible laser and a GeTeSb phase-change medium. Fast laser power control technique was used for suppressing the laser light power fluctuations, and a RIN of -123 dB was obtained. Using this technique, a CNR of 56 dB and an erase ratio of 25 dB was obtained with a mark pitch of 1.25 micrometers for an overwritable phase change medium.

Pupil plane filtering for improved signal detection in an optical data storage system incorporating a solid immersion lens

Solid immersion lens (SIL) technology is a promising way to increase the data density of an optical storage system by decreasing the spot size.