Hsi-Fu Shih

Design of optical head with holographic optical element for small form factor drive systems

An optical head composed of an optical module and a biaxial actuator is designed for small form factor drives. This system adopts a finite-conjugate objective lens with numerical aperture 0.65 for 654-nm wavelength. A holographic optical element is used for simplifying the optical configuration which provides a better approach for alignment. The actuator is of a spider-like suspension for the focusing and is of a swing arm for the tracking.

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.

Realization of free-space optical pickup head with stacked Si-based phase elements

We have developed a novel stacked silicon-based microoptical system, which is optical-on-axis and transmissible in both visible and infrared ranges. By using the new microoptical system techniques, we fabricated a miniaturized optical pickup head module. This optical pickup head consisted of a 650-nm laser diode, a 45/spl deg/ silicon reflector, a grating, a holographic optical element, and some aspherical Fresnel lenses. These optical phase elements fabricated on a SiN/sub x/ membrane were suspended on Si chips. Each element was then stacked by chip bonding. We could obtain a circular focusing spot on the optical disc as small as 3.1 /spl mu/m.

Design and Fabrication of a Small-Form-Factor Optical Pickup Head

This paper presents the design and fabrication of a small-form-factor optical pickup head (OPH) for both red and blue wavelength. A holographic optical element (HOE) is used for beam splitting, aberration correction, and servo-signal generation to reduce the number of components and simplify the assembly procedure. In addition to demonstrating this OPH by using existing discrete components, several key components and processes are developed to use micro-electro-mechanical system (MEMS) technology to facilitate batch fabrication and wafer level assembly of the micro OPU.

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.

Improvement of the light-trapping effect using a subwavelength-structured optical disk

The subwavelength structures formed by data tracks in an optical disk are applied to improve the light-trapping effect for thin-film amorphous silicon (a-Si) solar cell applications. An antireflection coating (ARC) consisting of at least two dielectric layers (SiO2 and ZnS-SiO2) is designed for the top planar surface of the disk. The a-Si thin-film solar cell layer is deposited below the bottom surface of the disk. Finally, a reflective metal coating is attached to the a-Si layer to fully reflect the incident light and extend the round-trip light path. With the proposed configuration, the reflectance and absorptance can be effectively decreased and enhanced by more than 10% compared with those without ARC and structured surfaces.

Micro objective lens with NA 0.65 for the blue-light small-form-factor optical pickup head.

A micro objective lens with the numerical aperture (NA) of 0.65 and clear aperture of 1.1mm was designed, fabricated, and tested for the proposed blue-light small-form-factor optical pickup head system. It adopted the finite optical conjugation and could be produced by using the glass molding technique. The experimental results verify the optical performance near the diffraction-limited focus spot for the applications of high-density portable optical storage systems.

Fabrication and Verification of a Small-Form-Factor Blue-Light Optical Pickup Head With Holographic Optical Element

A small-form-factor (SFF) blue-light optical pickup head (OPH) with holographic optical element (HOE) has been fabricated and assembled. The assembly and alignment of various components in the pickup head were facilitated by using a flip chip bonder. Experimental results indicated that the focusing error signal (FES) of the assembled OPH with the wavelength of 405 nm could be successfully detected. The linear range of the FES was about than 4 μm. The gauge repeatability and reproducibility (GR&R) of the assembly process was tested and found to be acceptable.

Optical Head with Two Wavelengths in Single Path Using Holographic Optical Element

In this paper, we review a number of digital versatile disk (DVD) pickup designs and present a new structure with two wavelengths using a 780 nm integrated optical unit (IOU) and a 650 nm laser diode (LD) in a single optical path. The 780 nm IOU acts as a sensor for the 650 nm system. Two returned beams of different wavelengths are diffracted by a holographic optical element (HOE) to the same detector. With this construction, the number of components is reduced and alignment is effectively simplified.

Multiple-Beam Liquid Crystal Grating for the Recordable Optical Pickup Head

By combining the technology of a liquid crystal diffractive optical element with that of a multiple-beam grating, a novel multiple-beam liquid crystal grating is proposed for the application of recordable optical pickup heads. This grating has the function of generating seven diffracted beams with equal intensity in each order while applying a voltage to the device. It provides the switching ability between the single beam and multiple beams for writing data and reproducing data, respectively.