Assembly and evaluation of a SIL optical head for cover-layered incident NFR without disk contact with the bottom surface of a SIL

In the assembly of the solid immersion lens (SIL) optical head for cover-layered incident near-field recordings (NFRs), disk contact with the bottom surface of the SIL has previously been regarded as essential. This is because SIL optical heads are designed to interface with a cover layer. However, SILs can be contaminated and damaged by this contact. We present a new SIL optical head assembly method for cover-layered incident NFRs without disk contact with the bottom surface of the SIL. To achieve this, we added zoom optics to a Twyman–Green interferometer in the measurement beam optical path. Our assembly method eliminates SIL contamination problems and the assembly procedure becomes simple because of removing the disk contact process. In addition, it is not necessary to consider the aberrations induced by disk tilt and cover-layer thickness variation. The SIL optical head assembled by the proposed method has good optical performance satisfying the optical tolerances and the measured wavefront aberration is good agreement with simulations.     

Thickness tolerance compensation of SIL first surface near-field recording with replicated lens on SIL

In this paper, we propose a novel optics design for improving the thickness tolerance of a super-hemispherical solid immersion lens (SIL) that is usually used in near-field recording for high data density. To obtain the improved thickness tolerance of a SIL and a high numerical aperture simultaneously, an aspheric replicated lens is added on the SIL. Using an additional aspheric replicated lens, spherical aberration which induces the tight thickness tolerance of the SIL is effectively reduced, therefore it was able to improve the thickness tolerance of the SIL, maintaining high NA equal to that of super-hemispherical SIL. In addition, in this paper, other various tolerances such as decenter and tilt are considered to make sure of the possibility of fabrication.     

Design of an integrated optical pickup with NA of 0.85 for small form factor optical disk drives

We design an integrated optical pickup for small form factor optical disk drives. The specifications of the pickup are compatible with those of the Blu-ray disk (BD) in terms of numerical aperture (NA) of the objective lens, the wavelength of the laser diode, and the thickness of the cover layer. The objective lens unit with NA of 0.85 consists of two aspherical refractive lenses and a diffractive optical element for compensation of the chromatic aberration. Each element of objective lens unit will be fabricated on a wafer as an array type, and the three wafers will be aligned and bonded to form an objective lens array. Therefore, elements of the objective lens unit are designed to have sufficient alignment tolerances for various directions such as de-center and tilt. The optical performances of the objective lens unit are evaluated by simulation against various disturbances such as wavelength change of emitting light from laser diode, misalignments, etc. We also design a quarter wave plate, a polarized holographic optical element, and the shape of photodiode integrated circuit array to generate focusing and tracking error signals. The entire height of the pickup including working distance is 2 mm, and the effective pupil diameter of the objective lens unit is less than 1 mm.     

Optical recording system using an integrated solid immersion lens

 Nobody doubts that the high area density recording and miniaturization of the devices in the data storage are in the general trend. What matters now is how to compact the data in a small area and how to decrease the device size. For the last decade, a lot of researchers engaged in the optical memory have expected the near-field recording (NFR) technology to be able to bring the remarkable results. However, they have been confronted with many obstacles including heat, contamination, dynamics of optical head in the unsealed environment, etc. In this paper, we propose the new concept of a solid immersion lens (SIL) with a potential to be able to resolve the critical issues on the way to the commercialization of the high areal density optical recording using the near-field recording technology. Received: 5 July 2001/Accepted: 17 October 2001     

红外连续变焦镜头的结构设计与热分析

随着红外技术的不断发展,红外连续变焦镜头的应用越来越广泛。为了避免环境温度变化影响红外连续变焦镜头的成像质量,对改变过凸轮的红外镜头进行了光机热分析。建立连续变焦红外镜头的有限元模型,通过热分析对其模型进行处理,完成对有限元模型的热分析,并求解出不同情况下凸轮槽时镜头的位移云图、不同情况下镜片的位移云图、不同角度时凸轮的位移云图和不同角度下镜片的位移云图。结果表明,热光分析方法可以模拟红外光学系统的实际使用情况,并可以预测实际使用条件下的工作条件,对光学系统的设计具有重要的指导意义。     

Improved safety mode considering external shock direction for near-field recording system using SIL

To increase the near-field coupling efficiency in a near-field recording (NFR) system, extremely small air gap (less than 100?nm) between the solid immersion lens (SIL) and media should be maintained. However, maintaining the air gap is very important and difficult. Despite various anti-shock control methods, there are physical limitations to controlling the air gap against external shock. A safety mode that moves the actuator to the initial position for large external shock is currently being used. The existing safety mode exhibits good performance for downward shocks of 6?G amplitude and 10?ms duration time, but some problems arise for upward shocks of 3?G amplitude and 10?ms duration time. To avoid collision for upward and downward shocks, we present an improved safety mode that considers the direction of the external shock for an SIL-based near-field recording system. We analyzed the upward and downward shock responses of the NFR system. The shape of the pulse input was designed to minimize the overshoot of the actuator. Through various experiments, the amplitude and duration time of the pulse input were optimized. Even with an upward shock with 8?G and 10?ms, no collision was observed between the actuator and the media by using the improved safety mode with the optimized pulse input.     

Numerical investigation of zoomable holographic projection without a zoom lens

Holographic projection is for laser displays and has the merits of being aberration free, producing high‐contrast images, having the ability of color reconstruction with one spatial light modulator, and so on. In this paper, we propose a zoomable holographic projection without using a zoom lens and verify the proposed method by using numerical simulation. Although such a system can be readily realized to use the features of holography, which is capable of recording a large image exceeding the hologram size, the required calculation is very time consuming. For acceleration, we used shifted Fresnel diffraction for setting different sampling rates on a hologram and projected image. The proposed method can project any zoom‐in and zoom‐out image between zeroth‐order and first‐order lights, and the processing time and required memory for the zoom are constant.     

Development of optical gap sensor application to near field recording

For applying near-field recording (NFR) technology to optical storage devices for the next generation, it is positively necessary to maintain a small air gap under about 100 nm. We design an apparatus to measure the air gap between the CISD type SIL [1] and the interface of dielectric substrate of the disk. And it consists of a prism, a polarizer and an analyzer. The air gap including the far-field as well as the near-field range is determined by measuring the intensity of polarized reflectance light. Through the Fresnel equation and Jones matrices, a mathematical model is established to understand the characteristics of a system according to design parameters. We can change measurement ranges/resolutions by adjusting an incident angle into the air interface. Experimental results for some specific cases are in good agreement with simulated ones and demonstrate the possiblity as a new optical gap detector.This work was funded by the Korea Science and Engineering Foundation (KOSEF) through the Center for Information Storage Device (CISD) Grant No. R11-1997-006101-0 and the Korea Sanhak Foundation.Paper presented at the 13th Annual Symposium on Information Storage and Processing Systems, Santa Clara, CA, USA, 17–18 June, 2002     

Rendering realistic spectral bokeh due to lens stops and aberrations

Creating bokeh effect in synthesized images can improve photorealism and emphasize interesting subjects. Therefore, we present a novel method for rendering realistic bokeh effects, especially chromatic effects, which are absent for existing methods. This new method refers to two key techniques: an accurate dispersive lens model and an efficient spectral rendering scheme. This lens model is implemented based on optical data of real lenses and considers wavelength dependency of physical lenses by introducing a sequential dispersive ray tracing algorithm inside this model. This spectral rendering scheme is proposed to support rendering of lens dispersion and integration between this new model and bidirectional ray tracing. The rendering experiments demonstrate that our method is able to simulate realistic spectral bokeh effects caused by lens stops and aberrations, especially chromatic aberration, and feature high rendering efficiency.     

General Spectral Camera Lens Simulation

We present a camera lens simulation model capable of producing advanced photographic phenomena in a general spectral Monte Carlo image rendering system. Our approach incorporates insights from geometrical diffraction theory, from optical engineering and from glass science. We show how to efficiently simulate all five monochromatic aberrations, spherical and coma aberration, astigmatism, field curvature and distortion. We also consider chromatic aberration, lateral colour and aperture diffraction. The inclusion of Fresnel reflection generates correct lens flares and we present an optimized sampling method for path generation.     

Numerical simulation of thermal flying height control sliders in heat-assisted magnetic recording

Heat assisted magnetic recording (HAMR) is one of the most promising techniques to extend the recording density in hard disk drives beyond 1?Tb/in². Although the diameter of the spot on the disk that is heated by the laser beam is very small, on the order of nanometers, high local temperatures on the disk and the heat dissipated in the slider during the light delivery process can cause thermal deformations of both the disk and the slider, thereby affecting the flying characteristics at the head-disk interface. In this paper, a finite element model is developed which incorporates a HAMR optical system into a thermal flying height control (TFC) slider with dual heater/insulator elements to study the effect of heat dissipation in the wave guide on the thermal deformation and flying characteristics of a HAMR-TFC slider. In addition, the power input of the laser and design parameters of the heaters are investigated.     

Application of megasonic cleaner to sub-micron particles of SIL optical flying head

 As the demand for large capacity storage drives has increased, the flying height of near-field recording (NFR) sliders becomes as small as 100 nm for super high storage density. Accordingly contamination problems have been a concern of information storage industry because it may cause a serious damage to solid immersion lens (SIL) of optical flying head. Sub-micro contaminants in air bearing of the NFR slider may affect the flyability and stability of the optical slider. In addition, the cleaning of small particles becomes more difficult as the contaminant particle size decreases because the adhesion force increases very much as the particle size decreases. Recently developed high-frequency ultrasonic (megasonic) cleaning technique have made it possible to remove sub-micron particles less than 100 nm without surface erosion and many remarkable results have been reported. In this paper, the megasonic technique is applied and tested for the cleaning of the flying head of NFR drive. 1 MHz ultrasound with maximum 100 W was used to remove polystyrene latex (PSL) particles and alumina particles deposited on the surface of the slider. Effective cleaning performance was observed without any damages on the slider surface using optical microscope and AFM at different ultrasonic energy levels and cleaning times. Received: 20 June 2002 / Accepted: 9 September 2002     

嵌入式附网刻录系统的设计与实现

设计并实现了一个基于虚拟本机刻录的嵌入式附网DVD刻录系统。详细介绍了这个系统的整体设计方案，着重介绍了基于“生产者和消费者”模型的三级缓冲结构和缓冲区管理策略，并进行了相应的实验测试和性能分析。     

Twyman-Green interferometer using virtual optics for eliminating reference wave

The Twyman-Green (TG) interferometer is widely used to evaluate optical imaging systems. It consists of an object wave and a reference wave for creating an interferogram. In this paper, we propose a simple interferometer that eliminates the actual reference wave. Instead of the piezoelectric trasnducer mirror used in the reference wave, a virtual optics was used via a numerical simulation of plane-wave illumination. A solid immersion lens of NA = 1.84 is described and fabricated for evaluating an interferogram. To verify the proposed method, the resulting interferogram with the aberration analysis was compared with those obtained using a conventional TG interferometer. The total wavefront aberration value was measured about 21 mλ_RMS and the difference between the conventional and proposed methods was approximately 3 %. Phase-shifting interferometry without mechanical and optical disturbances was demonstrated.     

Design of wafer-based NA 0.85 micro objective lens and integrated pick up module for small sized optical drive

In this paper, we propose the design of a wafer-based micro objective lens with numerical aperture (NA) 0.85 using a 405 nm blue-violet laser. The total length of the lens is 1.36 mm. The micro objective lens consists of three layers that are a hologram optical element for reducing the aberration and two grinded and polished ball for making optical power to achieve NA 0.85. The lens could be applied to an integrated optical pickup module. The approximate size of the optical pickup module is 3 mm[W] × 3 mm[D] × 3 mm[H] including the wafer-based objective lens, which is suitable for realizing a small sized optical drive based on Blu-ray Disc. The wafer-based design could offer precise alignment, easy handling and high mass productivity with micro electro mechanical system technology.     

SOM‐based projection module for mobile displays

Abstract— The development of a compact, efficient VGA projection module to be embedded in mobile devices is reported. The design incorporates laser/laser diode (LD) light sources, Schlieren optics, and a one‐dimensional diffractive spatial optical modulator (SOM). During development, the optical parameters were determined and the relationships between the parameters to optimize the optical specifications were derived. The resulting optimized specifications enable us to manufacture two types of optical modu les as compact as 13 cc and with as little as 10% speckle contrast ratio.     

Separating a color signal into illumination and surface reflectancecomponents: theory and applications

A separation algorithm for achieving color constancy and theorems concerning its accuracy are presented. The algorithm requires extra information, over and above the usual three values mapping human cone responses, from the optical system. However, with this additional information-specifically, a sampling across the visible range of the reflected, color-signal spectrum impinging on the optical sensor-the authors are able to separate the illumination spectrum from the surface reflectance spectrum contained in the color-signal spectrum which is, of course, the product of these two spectra. At the heart of the separation algorithm is a general statistical method for finding the best illumination and reflectance spectra, within a space represented by finite-dimensional linear models of statistically typical spectra, whose product closely corresponds to the spectrum of the actual color signal. Using this method, the authors are able to increase the dimensionality of the finite-dimensional linear model for surfaces to a realistic value. One method of generating the spectral samples required for the separation algorithm is to use the chromatic aberration effects of a lens. An example of this is given. The accuracy achieved in a large range of tests is detailed, and it is shown that agreement with actual surface reflectance is excellent     

Optical recording media based on nanoparticles for superhigh density information storage

The use of nanoparticles for optical strorage of information is reviewed. Several different optical recording media utilizing the nanoparticles were designed and tested. The main characteristics of the media, namely, density of recording energy needed and density of stored information start from the like ones for blu-ray disk and for the best media are far better.     

Design of compact projection lenses using double‐layered diffractive optical elements

Abstract— Based on several special properties of diffractive optical elements (DOEs) such as savings in mass and to freely modulate the wavefront of incident light, a new compact projection lens with double‐layered DOEs is presented. It is comprised of five lenses and has nearly half the weight of its original structure. The modulation transfer function (MTF) value on‐axis is 0.7 at a spatial frequency of 33 lp/mm and more than 0.3 for all off‐axis values, which satisfies the requirement of a color‐filter‐type liquid‐crystal‐on‐silicon (LCoS) 0.59‐in. display with a SVGA resolution. The maximum distortion is 0.46%.     

Simple and efficient method of calibrating a motorized zoom lens

In this work, three servo motors are used to independently control the aperture, zoom, and focus of our zoom lens. Our goal is to calibrate, efficiently, the camera parameters for all the possible configurations of lens settings. We use a calibration object suitable for zoom lens calibration to deal with the defocusing problem. Instead of calibrating the zoom lens with respect to the three lens settings simultaneously, we perform the monofocal camera calibration, adaptively, over the ranges of the zoom and focus settings while fixing the aperture setting at a preset value. Bilinear interpolation is used to provide the values of the camera parameters for those lens settings where no observations are taken. The adaptive strategy requires the monofocal camera calibration only for the lens settings where the interpolated camera parameters are not accurate enough, and is hence referred to as the calibration-on-demand method. Our experiments show that the proposed calibration-on-demand method can provide accurate camera parameters for all the lens settings of a motorized zoom lens, even though the camera calibration is performed only for a few sampled lens settings.