Pickup Head Research Articles

Data Detection using Pattern Recognition for Multi-level Optical Recording

An optical disc system using multi-level (ML) amplitude-modulation can achieve higher data capacity and transfer rates than previous systems without changing the drive or pick-up head except to add a new chip set to the ML. The ML system can provide a bit error rate (BER) that is fully correctable around the order of 10-5 with sigma to dynamic range (SDR) < 2%. We improved the margin of SDR using a new data detection method that uses pattern recognition and evaluated its performance.

4-axis optical head lens actuator for disc tilt compensation

As the track density and disc rotational speed of digital versatile disc (DVD) increase rapidly, a lens actuator in the optical pickup head with better performance is required. In this paper, a four-axis magnetic suspension type lens actuator is developed for use at a high information bit rate and high density recording. Except for tracking and focusing, the actuator can compensate the tilt angle of the disc. The prototype of the actuator is fabricated, and the experimental results compared with the analysis results show that the new actuator can achieve small tilt angle and the tilt angle is linear with the current of the coils.

Pick-up head for an electronic stethoscope

The pick-up head (1) with an acousto-electrical transducer (4) for converting sound vibrations to electrical signals, comprises as characterizing features a sound influencing bell (2) arranged around a slender peg (3) bonded directly to the transducer (4), and the sound influencing bell (2) delimits a listening area on a body surface and influences to a predetermined degree and in a predetermined manner, by means of internal reflection and/or absorption, the direct sound picked up by the slender center peg (3). The bell (2) is acoustically decoupled from the center peg (3).

Development trends in Taiwan's opto-electronics industry

With a fast growing market in multimedia and internet industries, the demand for corresponding key optical electronic devices in optical communication systems, optical input/output, optical storage, and liquid crystal displays has been rising, thus spurring the development of related industries. Not only does the Taiwanese opto-electronics industry have a bright future, but huge investments in the area have also boosted the industries of LED (laser emitting diode), scanners, and CD-ROM in Taiwan, which are now ranked in the top three worldwide in terms of their revenues. However, the cost of CD-ROM production cannot be easily reduced due to the high cost of imported key components (e.g. pick-up head and IC components mainly from Japan), which seriously affect the competitiveness of the industry. It is estimated that the opto electronics industry in Taiwan is about 3–4 years behind that of Japan technology-wise with the revenue also far below that of Japan. In recent years, many huge investment projects in Taiwan have attracted attention from domestic and overseas Taiwanese professionals, who have been aggressively devoting themselves into development of new technology. It is therefore easy to be very optimistic about the enormous potential development in the Taiwanese opto-electronic industry which has a solid foundation and is under-developed. This article analyzes the current situation of the opto-electronics industry, using the Delphi method to forecast future developments of the Taiwanese opto-electronic industry up to the year 2010. The simulated results will be a reference to those who are interested in studying the future of the opto-electronics industry in Taiwan.

Development of a low-cost autofocusing probe for profilemeasurement

In this research, a low-cost and precision autofocus laser probe system was developed.Modified from the pickup head of a commercially available DVD as a basis, it can detect the focuserror signal (FES) of the object with a built-in four-quadrant photodiode. The FES will feed backto the developed controller, through which the objective lens can be adjusted in positionautomatically to remain in focus, driven by a voice coil motor (VCM). The driving current(converted from servo-FES) of the VCM and the objective lens displacement are one to onelinearly related within several hundred micrometres. Because of this relationship, the surfaceprofile and the surface roughness of the tested object can be realized. Calibrated results showedthat the designed probe has 200 µm linearity range, 0.2 µm accuracy, 0.1 µm resolution andstandard deviation of 0.2 µm on average. Some examples are given to show the applicability of thisprobe system.

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.

Fast switching liquid crystal lenses for a dual focus digital versatile disc pickup

We investigated two types of liquid crystal (LC) lenses, the convex LC lens and the adaptive LC lens. Both lens types were designed and fabricated for integration in a novel pickup head for dual layer digital versatile discs (DVDs). The polarization dependent focal length of LC lenses was used to read both DVD information layers simultaneously. For fast and near diffraction limited performance, a new circular electrode structure with 64 ring electrodes was studied. Short response times of 50 ms for blazed Fresnel lens profiles and less than 10 ms for binary lens profiles could be realized using the transient nematic effect. Both lens types were characterized in terms of diffraction limited operation, focus efficiency and switching time.

Dual-axis driving and interference forces analysis for high sensitivity objective lens actuator

As the mechanical and electrical device adjusting the objective lens, driven by dual-axis forces, the lens actuator must provide a precise means of accurately following the disk displacement in the focusing and tracking directions in a digital DVD pickup head. To study the driving and interference forces and improve the driving sensitivity of the lens actuator, we put forward a new calculation method in this paper. Compared with the traditional finite element method, the new method can be conveniently used to obtain the most exact result on the dual-axis driving and interference forces, which cannot be easily dealt with using the finite element method. Important conclusions are given and a typical experiment verifies the validity of the-new method.

Digital Versatile Disc/Compact Disc-Compatible Pickup Head with Dual-Lens Lever Actuator for Next-Generation Applications

As the track density and disc rotational speed of digital versatile disc (DVD) increase rapidly, an optical pickup head with better performance is required. In this paper, the design requirements of pickup heads aiming at high speed and high recording density are discussed. A new pickup head with a dual-lens lever actuator is proposed. The prototype of the lever actuator is fabricated, and the measurement results are compared with the analysis results. The experimental results show that the new pickup head can be used for the DVD system, and satisfies the requirements of high-density and high-speed.

Photo-Polymer Objective Lens for Red Blue Lasers

The authors designed a photo-polymer objective lens which can be used for both red and blue lasers. The following two conditions were set to facilitate this lens production process. 1) We chose photo-polymer resin as one of the doublet lens materials. 2) One surface of the photo-polymer lens was designed to be flat. We installed this lens in pickup heads and played back some disks. Its performance was almost as good as that of a noncompatible glass lens.

Tilt Servo Using Modal Wavefront Actuator

In this paper, a new approach of disk tilt servo by using piezoelectric modal wavefront actuator is proposed. A compatible configuration of commerical optical pickup head (PUH) is presented with a piezoelectric folding mirror. Based on this device, the innovation has the advantages of high bandwidth, linear control, simple drive line and high spatial wavefront resolution.

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.

Lens Shift Correction in Tracking Servo System for Digital Versatile Rewritable Disc

In this paper the development of tracking offset correction for playback of a digital versatile rewritable disc (so called DVD-RAM), is described. The slim drive, having a small optical pick-up head with a small objective lens, is easily influenced by the deviation of the push-pull tracking error signal due to lens shift. The DVD-RAM disk format provides information not only on the amount of lens shift using the push-pull tracking error signal of address marks to correct tracking deviation, but also an opportunity to determine the optimum initial lens position using the differential phase tracking error signal.

A design of the load routing problem in a tandem AGV system

Automated guided vehicles are commonly employed in modern automated material handling systems or flexible manufacturing systems. In a tandem AGV system, all stations are properly divided into several nonoverlaping closed loops according to the flow among stations. The transit area located between two adjacent loops serves as an interface and allows loads to be transferred from one loop to another. Material flow that is not located within the same loop will start from the pick-up station and head for its destination via the transit station. The load routing problem of a tandem AGV system has been a major factor affecting the performance of the material handling system. Under the objective of transporting all loads to their destinations in minimum traveling time, the routes for all loads in a tandem AGV system are planned in this paper.

The development of a low-cost focusing probe for profile measurement

A high-precision optical probe based on the principle of focusing-range detection is developed in this research. The probe adopted for use was directly taken from the pick-up head of a CD player. Because its principle is similar to that of the autofocusing probe, the characteristics of each component of the head were investigated and its conversion into a focusing probe was attempted. The S-curve within the focusing range can be analysed, revealing the linear relationship between the normalized focus-error signal (FES) and the measured distance. The system accuracy of the probe was found. Within the measurement range of 10 µm the linearity error was about 1%, the standard deviation was about 34 nm and the frequency response was about 8 kHz. Some practical applications were carried out, namely profile measurements of a step height, a CD surface and a silicon-wafer grating. All results were highly consistent with the nominal values.

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.

Holographic Laser Module with Dual Wavelength for Digital Versatile Disc Optical Heads

Backward compatibility with CD-R necessitates having two laser sources in the digital versatile disc (DVD) pickup head. The dual-wavelength optical head complicates pickup design and enlarges the volume of the head. Moreover, it increases the number of components and assembly cost. In this paper, we present a new design for a dual-wavelength holographic pickup-head module. Packaged together in the module are two laser diodes, photodiodes and a holographic optical element (HOE) for diffracting reflected light from the disk onto the corresponding photodetectors. This module can be used as the core of an optical head capable of reading DVD, CD and CD-R.

Robust Focus and Tracking Detection for Holographic Digital Versatile Disc Optical Pickup-Head Modules

This paper introduces a robust focus and tracking detection method for use in holographic pickup heads. The method, which we call split-aperture servo detection, provides the focus error signal and both differential phase detection (DPD) and pushpull tracking signals but requires one less axis of alignment than the commonly used quad detector with astigmatic focus detection. A set of simulations designed according to Taguchi's method is presented comparing the manufacturability of holographic modules using the split-aperture approach and the astigmatic approach. The split-aperture approach is seen to have strong advantages. Experimental verification of a prototype digital versatile disc (DVD) pickup is also presented.

Preventing Coma Aberration by Annular Apodizer for Optical Disk Tilting

This research was carried out to determine the optimum parameters for an optical apodizer, applicable to a pick-up head for higher recording density optical disks. The coma aberration generated by tilting a disk increases the side-lobe intensity of the beam waist spot, and the increased side-lobe portion of the beam waist spot mainly deteriorates crosstalk from an adjacent track. Calculations were made to estimate coma aberration, in which the author adopted the annular radius of the apodizer and the side-lobe intensity of the beam waist spot as parameters. The result, which was confirmed experimentally, is that an annular apodizer whose radius is half the pupil radius effectively prevents coma aberration.

Prediction of a large optical bistability in hybrid-cavity surface-emitting lasers

We propose that optical bistability with a large on/off ratio should be achievable in a hybrid-cavity surface-emitting laser (RCSEL), where the active region of the surface-emitting laser is pumped by an integrated edge-emitting laser. The pumping scheme of the HCSEL is very similar to that in a conventional multi-segment edge-emitting laser, where optical bistability has been widely demonstrated. We use the two-mode rate equations to show that if the edge-emitter on and off output levels lie, respectively, above and below the vertical-cavity threshold condition, then a very large on/off ratio can be obtained from the HCSEL. Calculations show that the lower limit of the bistable current range is determined primarily by the effective absorption characteristics of the vertical-cavity region, with the upper limit influenced by the relative sizes of the vertical cavity and edge-emitting segments. The enhanced on/off ratio makes the HCSEL a very attractive candidate for such applications as efficient optical pickup heads, optical triggers or memory cells.