Jau-Jiu Ju

Magnetocurrent in a bipolar spin transistor at room temperature

A spin transistor which consists of a metallic giant magnetoresistance emitter, a copper base, and a p-n junction was prepared on a Si(100) wafer. The emitter current changes from 1mA at a magnetically parallel state to 0.968mA at a magnetically antiparallel state. At the same states the base currents were 29.3μA and 333nA, respectively, which gave a magnetocurrent ratio of ∼8600% and a transfer ratio of 3×10−2 at room temperature for a common collector configuration. The sensitivity of this spin device is higher than 4000%∕Oe. The memory effect and the high performance make it possible for practical usage. The working principle of this kind of three-terminal spin device can be simply described by circuit theory.

New Write-Once Medium with NiOx Film Using Blue Laser

Both a new write-once medium with a sputtered NiOx film and a write-once optical disk using a blue laser has been fabricated. The optical constant of sputtered NiOx films for different ratios of O2/Ar was determined, and showed little dependence on sputtering ratios of O2/Ar and wavelength. The X-ray photoelectron spectra (XPS) data indicated those films have two major components, NiO and Ni2O3. Most NiOx films released oxygen gradually below 300°C. Over 300°C, there was an apparent transition due to the decomposition of the Ni2O3. At a writing power of 12 mW and a reading power of 0.5 mW under conditions of a numerical aperature (NA) of 0.65 and a wavelength of 405 nm, the carrier to noise ratio (CNR) was more than 47 dB and jitter was less than 13%. The recording principle depends primarily on the explosive pressure of the O2 released due to laser heating of the NiOx film.

An automatic pin identification method for the three-phase dc brushless motor

The pin identification is to find the definition of each connecting pin of a three-phase brushless motor. The 11 pins of the motor can be distinguished into three groups by a simple resistance measurement method. An automatic method has two steps. In the first step, the motor is in an open-circuited mode; and the individual pins of the windings are identified by comparing back electromotive forces. A special integral is defined and used to match Hall signal pins with the Hall sensors. The polarity of each pair of the Hall signal pins is determined by the second step of a standstill method. The proposed method is illustrated and verified by an experiment.

New optical storage formats developed in Taiwan

Two new optical storage formats, forward versatile disk (FVD) and blue high-definition digital versatile disk (HD-DVD), developed in Taiwan, are introduced. Some major technologies, including new modulation code and multilayer technology, are adopted in these formats to differentiate from current optical disc formats. For the further HD storage, several advanced technologies have been developed.

LCD diffractive element design to handle multiple disk thicknesses

We describe the design of a single diffractive LCD element placed adjacent to the objective lens that can be addressed to provide the required spherical aberration (SA) compensation for a plurality of disk substrate thicknesses. It is now commonplace that optical disk drives must be able to handle disks of more than one substrate thickness. The major problem is compensating for the SA introduced when the highly corrected objective lens is used with a disk substrate thickness other than that which it was specifically designed for. An abundance of methods for solving this problem in the specific case of CD/DVD backward compatibility exist in the literature; we use an active device to extend this to include HD-DVD as well.

A Novel Pickup Head Design for DVD-Multi System

This paper introduces a novel holographic optical element (HOE) pattern design to generate focusing and tracking signal for using in digital versatile disc DVD-multi pickup heads. The digital verstile disk (DVD) multi drive will be able to read disks written in the DVD-ROM, DVD-video, DVD-audio, DVD-R/W, and DVD-R formats. DVD multi drive will also be able to write disks in the DVD-RAM and DVD-RW/R formats. The HOE design provides the focusing error signal and both differential phase detection (DPD) and pushpull tracking signals for DVD-ROM disks and rewritable land-groove disks. The HOE pattern is divided into two main regions. The inner region is for focus detection and the outer region is for DPD and Pushpull tracking detection. In this study, a rotary actuator is used to reduce the tilt angle of the objective lens in the DVD-multi pickup head. The finite element method of the actuator is studied to analyze the resonance of the structure and the magnetic field of the voice coil motor.

Polarized diffractive optical element design for a multibeam optical pickup head

This paper addresses the design and construction of an interesting polarization-switched diffractive optical element (DOE) that generates multiple beams incident on the disk and acts as a beamsplitter and servo-generating element for light returning from the disk. In this way, data speed is increased proportional to the number of beams on the disk, and, by combining three functions into a single optical element, allows a more compact and lightweight pickup to be realized. The polarization-switched DOE is constructed as a sandwich of two pieces of some birefringent material, with one rotated by 90 degrees relative to the other so that the ordinary and extraordinary axes are interchanged, and with a common index-match layer between them. A diffractive pattern is etched into each of the two birefringent pieces. Linearly polarized light traveling from the laser towards the disk is diffracted into multiple beams by one of the diffractive patterns while experiencing no diffraction from the other. Travelling the roundtrip from the DOE to the disk and back to the DOE, the light traverses a quarter-wave retarder two times thereby rotating its polarization direction by 90 degrees. It now experiences no diffraction from the multiple beam diffraction layer, but is diffracted by the second diffraction layer, which steers it onto the photodetectors and alters the beam to create useful focus and tracking error signals. This design is important in that it provides a way for two diffractive surfaces, each acting independently with high efficiency on orthogonal polarizations of light, to be combined into a single element. Implementation and application to a multiple-beam holographic pickup head module are presented.

Optimization of the Lens Holder and Yoke for a Near-Field Optical Pickup Actuator to Enhance Frequency Response

A four-wire voice-coil actuator is designed and optimized for use in a near-field optical drive. The first objective was to design a lens holder which could accommodate a large-size lens module while possessing a strong mechanical structure. The second objective was to optimize the yoke so that the magnetic field would be uniform within the stroke range of the voice coils. These improvements eventually helped to improve the bandwidth of the frequency response of the actuator

Storage density expansion by off-track recording

We have delivered an idea, based on multiple level coding, to read and write with the multiple level tracking system. By utilizing off-track recording and multi-level coding, we may increase the track density to expand the optical disc density. Off-track recording is a design using LC diffractive optical element (LCDOE) to control the recording beam in desired angle. Another beam is for reading and tracking.

Holographic Optical Element with High Assembly Tolerance for the Optical Module of Digital Versatile Disc Pickup-Heads

The astigmatic focus detection method and differential phase detection (DPD) tracking method are now widely used in a digital versatile disk (DVD) pickup head. The DPD tracking method requires the returning spot to remain centered in a quad detector and therefore makes the optical alignment very critical. In this paper, a novel holographic optical element (HOE) pattern design to relax the alignment tolerance and achieve a stable DPD tracking servo property is described. Simulations show that the servo signals are insensitive to photo-detector (PD) misalignment when compared to that of a conventional HOE design.