Yukio Kurata

Fabrication Method of Double-Microlens Array Using Self-Alignment Technology

A fabrication method for double-microlens arrays with self-alignment technology (SAT) is proposed. To satisfy the tolerance of the alignment of a two-layer-lens array, we developed a new fabrication method without an alignment process. Using SAT, we achieved a brightness increase of 30% compared with the conventional single-layer microlens array.

Water Purification Using the Adsorption Characteristics of Microbubbles

Recently, technology using microbubbles has been studied for water purification. However, the mechanism and physical parameters of the purification process have not yet been sufficiently clarified. The purpose of this study is to clarify the physical parameters of microbubbles that influence water purification. Firstly, we measured and analyzed the purifying performance using various millimeter-sized bubbles, and we obtained the equilibrium constant of the pollutant adsorbed on the bubble surface from the experimental results. Secondly, we experimented with purifying the polluted water using microbubbles and clarified that the purification performance of microbubbles agreed with that theoretically expected using the equilibrium constant obtained in the preparatory experiment. We assume that an important parameter affecting adsorption on the surface of microbubbles is the equilibrium constant in the chemical potential. Because the equilibrium constant is derived from the surface chemical potential, it is equal to the bulk chemical potential of the liquid. In the microbubbles diameter (70 µm) range in this study, we have found that the most significant factor determining the adsorption is the surface area. The surface tension of microbubbles is not significant factor.

Optical Pickup Employing a Hologram-Laser-Photodiode Unit

In this paper we review the holographic optical element technology applied to compact disc (CD), digital versatile disc (DVD) and mini disc (MD) pickups. Using this technology, the number of optical components and the size and weight of a CD pickup are successfully reduced and its reliability is improved, because many functions of the optical components are integrated into a hologram-laser-photodiode unit. For DVD application, the focus detection for a dual-layer disk and the differential phase detection (DPD) method are realized by the hologram technology. Our unique two-segment DPD method shows more stable characteristics than the conventional DPD method. An integrated MD hologram pickup is also developed with an optical waveguide device that functions in magneto optical (MO) signal detection.

Three-beam CD optical pickup using a holographic optical element

A three beam CD optical pickup has been developed with a holographic optical element (HOE). The HOE has a hologram for beam splitting and servo signal generation on one side of a glass substrate, and a grating for tracking-beam generation on the other side. The hologram pattern is divided into two regions. The grating periods of these regions are different from each other, so that the focus error signal is detected by Foucault knife-edge method. And also the radial error signal is detected by the twin-spot method. The HOE is cemented at the top of a package in which a laser diode and a photodiode for signal detection are mounted. The HOE offers a improvement of environmental stability of the pickup too. In spite of the usage of a plastic housing, the optical pickup shows superior characteristics of environmental stability.

Multiplexing method with noncoaxial spherical waves for holographic data storage

Holographic data storage capacity is proportional to the thickness of a photopolymer recording medium. To maximize the use of the performance of a photopolymer recording medium, a multiplexing technique that can record holograms in the thickness direction of such a medium is demanded. To this end, we propose a new multiplexing method that combines shift, peristrophic, and focus-shift multiplexings, and successfully records holograms in the thickness direction of the medium by controlling the incidence angle of the reference beams. We confirm that the holograms recorded are well spatially separated in the thickness direction of the medium, and that up to 50 holograms can be recorded.

Optical Pickup using Integrated Optical Unit for Blu-ray Disc

This paper reports the developed optical pickup for blu-ray disc which uses the integrated optical unit to detect the spherical aberration error signal. This study has obtained the prospect of the high efficiency for detection using the segmented wave plate by the photonic crystal structure

Method Combining Focus-Shift and Angle Multiplexing Method for Holographic Data Storage

Holographic data storage capacity is proportional to the thickness of a photopolymer recording medium. To maximize the performance of a photopolymer recording medium, it is necessary to develop a multiplexing technique that has sensitivity in the vertical direction of the medium. As a method to achieve this, we suggest the focus-shift multiplexing method by which holograms are recorded in the vertical direction of the medium. By combining angle multiplexing and this focus-shift multiplexing, we confirm that the multiplexed holograms that are recorded by angle multiplexing are well spatially separated in the vertical direction of the medium, and these holograms can be reconstructed without crosstalk noise.

New Tracking Servomechanism Using Phase-Shift Differential Push-Pull Method for Recordable Optical Disks

We have improved the phase-shift differential push-pull (PS-DPP) tracking method with a multidivision phase-shift grating, which is applicable to various optical disks with different track pitches and does not require the accurate alignment of the three-spot position on a disk. In this paper we presented the properties of this method in recordable optical disks such as phase-change or dye media in which reflectivity greatly changes after recording. In particular, we found the cause of a radial tracking error signal offset occurring at the boundary between recorded and unrecorded tracks. To resolve this issue, we proposed two solutions: one is the optimum calculation procedure for the PS-DPP signal, and another is a newly designed phase-shift grating for recordable disks. We demonstrated the offset cancellation effect of this improved PS-DPP method using a new hologram laser unit for various types of digital versatile discs (DVDs) and showed its applicability to the Blu-ray Disc (BD).

A Novel Tracking Servo System for Multitypes of Digital Versatile Disks Using Phase-Shift Differential Push-Pull Method

We have developed the phase-shift differential push-pull (PS-DPP) tracking system with a phase-shift grating, which is independent of sub-beam position alignment. In this paper we propose an improved PS-DPP method using the latest inclined multidivision phase-shift grating, which enables the easy assembly of an optical pickup for digital versatile disks (DVDs) with different track pitches. Simulation and experimental results using a DVD hologram laser show that the sub-beam can detect only those lens-shift signals unaffected by track-cross signals.

Spherical aberration error detection for blu-ray disc optical pickups

For a high-numerical-aperture (NA) optical pickup system, the spherical aberration (SA) caused by cover layer thickness error should be corrected. We detected the SA error signal using a newly designed hologram optical element (HOE). The HOE has both sufficient signal sensitivity and constant signal level independent of objective lens shift. In addition, we fabricated on SA servo for a dual-layer Blu-ray disc.