Near-field Recording Research Articles

Design and Evaluation of a Solid Immersion Mirror Using a Dielectric Layer Stack for Near-Field Optical Recording

A new solid immersion mirror (SIM) with high optical efficiency utilizing angular dependence of a dielectric layer stack for near-field optical recording is proposed. The new SIM with a dielectric layer stack was designed, fabricated, and evaluated. The SIM had both convex and aspherical surfaces with a dielectric multilayer stack on one surface and an aluminum reflection coating on the other. The front and rear surface error rms values of the fabricated SIM were 43 mλ (λ=405 nm) and 90 mλ, respectively. The rms error of the wavefront aberration of the SIM was 150 mλ.

Thermal simulation for a two-dimensional near-field optical recording system using a vertical-cavity surface-emitting laser

An optical recording method with high throughput is required to create a two-dimensional near-field optical memory system using a vertical-cavity surface-emitting laser (VCSEL). Optical recording is possible with the combination of a near-field probe and patterned medium. A patterned medium consisting of 40 nm periodic dots with phase change medium and silver nanoparticles were used for plasmon resonance induced by an electromagnetic wave. The electric field power density at the silver nanoparticles was increased about 87 000 times over that with a structure without patterned medium. Heat from this structure is effectively used by thermal conduction out of a silver nanoparticle and by concentrating the heat on a particle. When the 1 mW optical intensity from a VCSEL is used, near-field optical recording is achieved. The recorded feature size was estimated at 40 nm. In this letter, a recording method is described using plasmon resonance and thermal conduction effects.

Optical flying head mounted on four-wire type actuator

A new actuator structure applicable for the near field recording (NFR) system is studied. In the structure, the optical flying head (OFH) is coupled to a conventional four-wire type actuator generally found in CD and DVD. The major purposes of the design of the actuator structure are the application of active focusing, the elimination of ramp-load mechanism and the tracking performance enhancement in the NFR system. The OFH with a magneto-optical (MO) coil to provide the necessary magnetic field for MO recording, an air bearing slider having a transparent optical section to provide optical path through the slider, and a solid immersion lens (SIL) for the use of near field is integrated with the bobbin and the voice coil assembly of the four-wire type voice coil motor (VCM) actuator through suspension. With a view to the realization of the suggested actuator, the flying characteristics of the designed OFH are evaluated by computer simulation. In addition, the flying stability of the OFH during the focusing and tracking motion of the actuator is experimentally evaluated.

Novel Nondestructive Readout Methods For Near-field Optical Recording with Large Refractive Index Modulation in Amorphous Diarylethene Layer

Novel nondestructive readout methods for near-field optical recording has been demonstrated with an amorphous photochromic film. Large refractive index change of an amorphous photochromic layer of 1,2-bis(5-(2,4-diphenylphenyl)-2,4-dimethyl-3-thienyl) perfluorocyclopentene induced by the photochromic reactions is detected by the use of a guided-wave mode and a substrate radiation mode with near-IR laser light. The modulation amplitude in the reflected light intensity before and after the photo-bleaching reaction was as high as 20%.

An Optical Configuration Based on Flying Head Structure for Near-Field Recording

We report an optical configuration with a flying head for a near-field recording system. The configuration consists of a fixed optical unit and condensing optics based on the flying head structure. While the fixed optical unit includes a light source and a signal-detection unit, the condensing optics include a solid immersion lens (SIL) embedded in the flying slider and infinite objective lens arranged on the flying slider. Free-space propagation using a collimated beam is employed to optically connect these two units. After we investigated the head structure and its fabrication process, we evaluated the fabricated optical flying head, both as an optical head and a flying head. The jitter was 8.87% when the shortest mark length was 0.364 µm. The C/N ratio was 49.53 dB for 0.2 µm of the mark length. The tolerances of relative tilt and decenter between the two optical axes of the fixed optical unit and the condensing optics which were derived experimentally were ±0.3 deg and ±150 µm. These results suggest that the optical configuration is adequately practical even for use in mass production.

Highly efficient probe with a wedge-shaped metallic plate for high density near-field optical recording

The distribution of the optical near-field generated by a probe with a wedge-shaped metallic plate was calculated using a finite difference time domain method. The dependence of the distribution on the size and the material of the metallic plate was calculated, and it was shown that a strong optical near-field was generated at the apex of the metallic plate when the size and the material were optimized so that a surface plasmon was excited in the metallic plate. The influence of the recording medium was also calculated. The resonance wavelength shifted toward a longer wavelength and the decay length of the optical near-field increased when the recording medium was placed near the probe. The spot size calculated on the surface of the recording medium was 30 nm, and the efficiency (defined as the ratio between the power of the optical near-field at the surface of the recording medium and that of the incident light) was about 20% when the spacing between the probe and the recording medium was 10 nm. The near-field distribution for a probe with two metallic plates was also calculated, and it was shown that a strong optical near-field was generated between the apices of the metallic plates when the plasmon was excited in the metallic plates.

Analysis of the aperture formation mechanism in the fabrication process of nano-aperture arrays

The fabrication of nano-aperture arrays has attracted much interest for its potential application in near-field optical recording, one of the most probable candidates for high-density storage devices. A parallel-processing technique based on nano-aperture arrays has been investigated in order to achieve fast scan rate. In this work, the fabrication process of nano-aperture arrays and the analysis on the aperture opening mechanism will be presented. A series of oxide pyramid arrays have been fabricated by generating inverted pyramid array followed by stress-dependent oxidation on inner surfaces and backside Si etching. Nano-apertures have been opened at the apexes of pyramids by diluted HF solution. The relation between aperture diameters and etch time showed good linearity with proper aperture opening rate. The variation of opening rate upon HF concentration was examined and measured to be ∼23 nm/min for 50:1 HF solution. Investigations on the parameters determining aperture-opening rate will be discussed.

MO 근접장 기록을 위한 광학 갭 센서

This paper proposes a new method of measuring an air interface distance between a solid immersion lens (SIL) applied magneto-optic technology and the disk surface. For applying near-field recording (NFR) technology to the magneto-optic storage devices for the next generation, it is positively necessary to maintain the small air gap under about 100nm. We design an apparatus that consists of some optical components such as a prism, a polarizer and an analyzer. By using the Fresnel reflection coefficient equation, Jones matrices calculation and Malus's law, we establish a mathematical model for understanding the characteristics of the system. The simulations are based on the mathematical model and through the simulation results which is made with various cases we can estimate the performance of the new optical gap sensor system. Experimental results, which are also based on the mathematical model for specific cases, are in good agreement with simulated ones and demonstrate the possibility as the new optical gap sensor.

近接型光記憶へ向けた負圧利用型フレキシブル光ヘッドスライダの浮上設計(情報機器コンピュータメカニクス2 -機構・制御,IIP2004 情報・知能・精密機器部門講演会)

近接型光記憶へ向けた負圧利用型フレキシブル光ヘッドスライダの浮上設計(情報機器コンピュータメカニクス2 -機構・制御,IIP2004 情報・知能・精密機器部門講演会)

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.

Advanced optical and magneto-optical recording techniques: a review

Optical data storage is advancing rapidly as we move forward in the 21st Century. Most people today are familiar with CDR and CD-RW as forms of optical data storage, but DVD-R, with considerably higher capacity, will challenge CD-R as the preferred storage medium soon. This review paper looks at the current state of optical recording and some of the current techniques which offer increased magneto-optical storage density, such as Magnetic Super Resolution (MSR), which is already on the market as the GIGAMO disk, and other methods under development. The latter includes Magnetically AMplified Magneto-Optical System (MAMMOS) and Domain Wall Displacement Detection (DWDD). To complement these technologies are a variety of optical techniques, such as near-field recording, which will enable higher storage densities by overcoming the diffraction limit. Holographic storage has promised much over the years, and has largely remained in the research domain. However, new materials and multiplexing techniques show considerable promise for this volumetric storage medium. The overlapping optical and magneto-optical technologies have yielded the concept of hybrid recording and this will also be addressed in this paper. The paper concludes with a look at alternative storage mechanisms, which utilise electronic, as opposed to thermal transitions, to offer improved data rates and improved storage efficiency, and this may dramatically change the way data is stored.

근접장 기록을 위한 부상형 광학 헤드의 최적설계

This paper presents an approach to optimally design the air-hearing surface (ABS) of the optical flying head for near-field recording technology (NFR) NFR is an optical recording technology using very small beam spot size by overcoming the limit of beam diffraction. One of the most important problems in NFR Is a head disk interface (HDI) issue over the recording band during the operation. A multi-criteria optimization problem is formulated to enhance the flying performances over the entire recording band during the steady state. The optimal solution of the slider, whose target flying height is 50 nm, is automatically obtained. The flying height during the steady state operation becomes closer to the target values than those for the Initial one. The pitch and roll angles are also kept within suitable ranges over the recording band. Especially. all of the all-hearing stiffness are drastically increased by the optimized geometry of the air hearing surface.

Novel suspension structure for near-field optical recording system

A suspension structure for a near-field optical flying head is proposed. This structure is designed to attain a stable flying attitude and high structural resonance of the optical head, which has a larger mass and high centre of gravity compared with that of a hard-disc head. The width-to-length aspect ratio of loadbeam and flexure hinges were designed using numerical simulation to optimise the structural resonance by controlling their bending and torsional stiffness. Experimental results show that this suspension structure achieves both remarkably high structural resonance characteristics and a stable flying attitude against roll acceleration.

Amorphous Photochromic Films for Near-field Optical Recording

A dithienylethene derivative having bulky substituents, 1,2-bis(5-(2,4-diphenylphenyl)-2,4-dimethyl-3-thienyl)perfluorocyclopentene (1a) was synthesized in an attempt to prepare photochromic amorphous films. 1a formed a stable bulk amorphous state at room temperature and the glass transition temperature was observed at 82°C. The conversion ratio from 1a to the closed-ring isomer (1b) upon irradiation with 303 nm light was as high as 73% in the amorphous film. Rewritable photon-mode near-field optical recording was demonstrated with the amorphous thin film of 1b.

Head-Disk Interface in Near-Field Recording Disks

The tribological properties of a near-field optical disk with diamond-like carbon (DLC) protective and lubricant films were evaluated. DLC protective films were prepared under different sputtering conditions and their mechanical and optical properties were investigated. Near-field recording (NFR) disks were prepared on several different substrates, and the substrate material effects on a head-disk interface (HDI) were measured by a tribological test. The heat-treated NFR disks with a glass substrate showed the best durability.

Readout characteristics of flexible monolithic optical head slider combined with visible laser light guide

Optical near-field recording is a candidate technology for overcoming the diffraction limit of conventional optical recording. In our previous work, we proposed a novel optical head slider for near-field recording that we call a flexible optical head slider. An air-bearing pad pattern is formed on the apex of a cantilever-like polymeric waveguide so that, by using the cantilever itself as the slider suspension, a single body structure incorporates the functions of the flying slider, suspension, and waveguide. This structure can be expected to provide several important advantages by miniaturizing head assemblies; simplifying the assembly and optical trimming processes; and producing a lighter head, thus allowing a wider tracking bandwidth. In this paper, we report the read-out signal evaluation of the flexible optical head slider. Using a slider with a sub-micron sized aperture, read-out of a test metal-patterned ROM (Read Only Memory) disk was successfully demonstrated down to a 0.2 μm linewidth line and space pattern.

Effect of substrate and protective coating on the tribological characteristics of optical recording media

To develop a flying-type optical head mounted on a slider with flying height below 100 nm for Near Field Recording (NFR) application where removability of the media is required, plastic media is preferred because of their manufacturing cost effectiveness. In this work the effects of substrate material, carbon protective coating, and lubricant on the tribological characteristics of the slider/media interface were investigated. For the substrate, glass, engineering plastic (PEEK), and polycarbonate (PC) were used. A thin carbon protective layer and a lubricant layer were deposited on the substrates. The tribological characteristics of carbon and lubricant layers were evaluated using an Atomic Force Microscopy (AFM). Also, the flyability test, drag test, Contact-Start-Stop (CSS) test, and load/unload test were performed for each substrate while monitoring the friction as well as acoustic emission signals. It was found that the flyability was the key factor that affected the durability of the disks. As for the carbon coating, better performance was observed in the order of a-C, a-C:H, and a-C:N. Finally, 5 nm lubricant thickness was better than 2 nm lubricant thickness in terms of durability. The results of this work are expected to serve as the basis for developing an optical media with high durability in NFR application using a flying slider.

반복 학습 제어를 이용한 NFR 디스크 드라이브의 2단 서보 시스템

Recently, near-field recording (NFR) disk drive schemes have been proposed with a view to increasing recording densities of hard disk drives. Compared with hard disk drives. NFR disk drives have narrower track pitches and are exposed to more severe periodic disturbances resulting from eccentric rotation of the disk. It is difficult to meet servo system design specifications for NFR disk drives with conventional VCM actuators in that the servo system for an NFR disk drive generally requires a feater gain and higher bandwidth. To tackle the problem various dual-stage actuator systems composed of a microactuator mounted on top of a conventional VCM actuator have been proposed. This article deals with the problem of designing a tracking servo system far an NFR disk drive adopting a dual-stage actuator. We summarize design constraints pertaining to the dual-stage servo system and present a new servo scheme using iterative teaming control. We design feedback compensators and an iterative teaming controller for a target plant and verify the validity of the proposed control scheme through a computer simulation.

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.

근접장 광기록용 슬라이더의 동특성 분석

Dynamic analysis using impulse responses is formulated to estimate effect of slider rail shape on dynamic responses in near-field optical recording drive. Impulse responses are obtained on numerical nonlinear model including rigid motion of a slider and fluid motion of an air bearing under the slider. Dynamic characteristics of slider motion are evaluated by utilizing the decay ratio of impulse responses and modal frequencies from frequency response functions. The dynamic characteristics of the designed NFR slider are checked by comparing those of a HDD slider(Nutcracker). Also, sensitivities of slider Position conditions and rotation speed on the dynamic characteristics are investigated.