Tzu-Ping Yang

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 Taguchis 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.

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.

A laser noise reduction method for holographic pickup heads

There are several methods to avoid optical feedback and reduce laser noise in optical recording systems. However, most of them utilize high cost optical components or electronics or increase the pickup head size. Furthermore, it is difficult to fit these components into in a small package like a holographic laser module. In this paper, a simple method for avoiding feedback noise in a holographic pickup head is proposed. A single wave plate is added to the optical system to rotate the polarization of the laser feedback to be orthogonal to the emitting polarization state. Experimental results show that it is feasible and practically reduces laser noise.

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.