Seiji Nishino

Two-photon absorption recording in photochromic diarylethenes using laser diode for three-dimensional optical memory

We have studied two-photon absorption (TPA) recording in photochromic diarylethenes for a three-dimensional (3D) optical memory, and demonstrated the TPA recording for the first time using a laser diode with a pulse width of 2 ns without a thermal influence. In comparison with the recording sensitivity by a femtosecond fiber laser, it was found that the peak power can be greatly reduced and the TPA sensitivity has squared characteristics depending on the pulse width range from 94 fs to 2 ns. Finite difference time domain (FDTD) analysis of optical intensity through refractive pits suggests that 3D recording in multilayered medium is more suitable, because optical aberrations induced by the lens effect of refractive pits are greatly reduced and the reflectance from a pit is improved, in comparison with that in a bulk medium.

Dual focus optical head with a hologram-integrated lens

A dual focus optical head with a holographic optical element (HOE) that can read both 0.6 mm disks and 1.2 mm disks has been developed. To ensure practicality and mass-producibility of the head, we examined servo-signal characteristics and evaluated allowable ranges for the misalignment of the HOE, the wavelength deviation, the disk tilt angle and the defocus distance. It was found that stable servo operation can be obtained and that except for the issue of coma aberration, the allowable ranges are wide enough for mass-production. When an objective lens having initial coma aberration is used with a plane-type HOE, coma aberration still remains for the 1.2 mm disk after performing skew adjustment for the 0.6 mm disk. We found that the aberration can be reduced by integrating an HOE with the objective lens on its first surface.

Dual Focus Optical Head for 0.6 mm and 1.2 mm Disks

We propose a dual focus optical head with a holographic optical element (HOE) which corrects spherical aberrations in order to read both 0.6 mm disks and 1.2 mm disks. The thin disks are read using transmitted light and the thick disks are read using +1st order diffracted light of the blazed HOE. The good quality of the focused spots and the focusing error signals was experimentally confirmed. No influence of unnecessary diffracted light was observed.

Microexplosion recording in spin-coated polymer films including ZnO nanoparticles for three-dimensional optical memory

As a microexplosion recording material, we propose polymer films including ZnO nanoparticles (ZnO polyester composite) for write-once multilayered recording media. These media with the ZnO composite material can be fabricated by a spin-coating method and can be read at the violet wavelength of 0.405 µm. By the electromagnetic analysis of diffraction loss, we clarified the pit design and the optical performance for void formation recording. From the results of experiments performed using three kinds of mode-locked pulsed lasers (pulse widths of 150 fs, 16 ps and 6 ns), with a clear reflection microscope image of submicrometer pits, the microexplosion sensitivity was confirmed to be greatly improved by 14, 38 and 50 times, respectively.

Application of a Polarizing Holographic Optical Element to a Recordable Optical Head

A polarizing holographic optical element (HOE) with compensating grooves on the surface of a LiNbO 3 substrate has good polarizing beam-splitter characteristics. This polarizing HOE was applied to a recordable optical head with an integrated laser and photodetector unit. In the optical head, a correct far-field tracking method is constructed by setting the polarizing HOE and a quarter-wave plate right under the objective lens, which can be moved with the objective lens. A holographic pattern of the polarizing HOE is divided into 20 portions along a disc track direction for spot size focus error detection and far field tracking detection. With this optical head, conventional CD play-back and recording signals on phase change discs were performed. Then the tracking offset caused by objective lens shift was measured and determined to be markedly decreased. Signal degradation by the ±1st light diffracted by a polarizing HOE was not observed. Good characteristics of recording and play-back for phase change discs were also obtained. This recordable optical head was found to have desirable characteristics and high productivity.

Dual focus optical head for 0.6 mm and 1.2 mm disks

We propose a dual focus optical head with a holographic optical element (HOE) which corrects spherical aberrations in order to read both 0.6 mm disks and 1.2 mm disks. The thin disks are read using transmitted light and the thick disks are read using +1st order diffracted light of the blazed HOE. The good quality of the focused spots and the focusing error signals was experimentally confirmed. No influence of unnecessary diffracted light was observed.

Dual focus optical head for 0.6-mm and 1.2-mm disks

We propose a dual focus optical head with a holographic optical element (HOE) which compensates for spherical aberration, allowing it to read both 0.6 mm disks and 1.2 mm disks. The thin disk is read using transmitted light and the thick disk is read using +1st order diffracted light of the blazed HOE. The characteristics of the focused spot, the servo signal detection and the signal of the Compact Disc indicate that both disks can be read by the dual focus optical head.

A very small holographic optical pick-up head with a movable single-assembly optical system

A very small holographic optical pick-up head with a movable single-assembly optical system was proposed. The optical system measures 11 mm(W)×4 mm(D)×4 mm(H) and weighs only 0.34 grams. The basic performance of the optical system mounted on a conventional actuator was demonstrated experimentally.

Efficient planar-type butt coupling of a proton-exchanged waveguide on a Z-cut LiTaO3 substrate

A half-wave thin film was formed on the facet of a proton-exchanged waveguide by the oblique deposition of Ta2O5. Planar-type butt coupling of the waveguide on the z-cut LiTaO3 substrate to the AlGaAs laser diode in transverse electric mode oscillation was realized with coupling efficiency as high as 53%.