This PDF file contains the front matter associated with SPIE Proceedings Volume 6620, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Aluminum oxide single crystals doped with magnesium and carbon and having aggregate vacancy defects are proposed for volumetric fluorescent bit-wise data storage. A unique optical recording technique, which utilizes sequential two-photon absorption and incoherent confocal fluorescence detection, is utilized for nondestructive readout. The new medium is exceptionally environmentally and temporally stable and can be recorded with diode lasers. Recent static and dynamic test stand results are reported, including demonstration of 20 layers of data and random mark-length recording with a clear "eye pattern" and satisfactory carrier-to-noise ratio.

We proposed a concept of a roll-type optical advanced memory (RoCAM). RoCAM is a multilayered optical memory, in which recording layers are wound onto a shaft. Multilayered media are fabricated easily by winding a two-layered filmlm, which is composed of a photosensitive layer and a pressure-sensitive adhesive (PSA) layer. We showed certain advantages of RoCAM and also demonstrated a prototype of RoCAM and the recording and reading results for two layers.

Optical signal amplification by a homodyne detection scheme is proposed and experimentally demonstrated. We estimated that this scheme improved the signal-to-noise ratio of an 8-layer 3x read-speed Blu-ray Disc (BD) by more than 20 dB.

The special shape of the optical disk tracking grooves is proposed. These tracking grooves are similar to the blazed diffraction grating grooves. The grooves structure can be read by the standard optical disk reading equipment. The multilayer optical disk with slant tracking grooves is proposed. These grooves have different planes and angles of inclination for different data layers. This allows to direct the signals reflected from the different data layers to the different photodetectors. The optical disk capacity increases due to excluding space between tracking grooves and due to increasing the number of data layers. Sequential and parallel optical disk reading options are possible. The technique of information pits arrangement is proposed for parallel reading of information from several data layers. For protecting of the optical disk against its illegal use the disk is made partly recordable and an initialization procedure is performed at the user's recording/reproducing device. During the initialization procedure identifying parameters of the user's device are recorded onto recordable layer of the disk. Also, the unique combination of the bits pairs containing both information prerecorded on the optical disk and information about the user's recording/reproducing device is remembered in the special flash memory of the user's device.

253GB have been recorded in one of our two-photon 3-d disks. Experiments indicate a roadmap of full disk recordings from 0.5 to 1TB utilizing our very stable and efficient materials and new high-performance objective lens.

This paper reviews the analyses and the experimental results of Micro-reflector optical disc system. In Micro-reflector optical disc, data are recorded on multiple virtual planes in a monolithic holographic medium. We have demonstrated the possibility of huge capacity from our analyses of readout characteristics of the Micro-reflector. In addition, we have developed the five-axis servo control system in order to achieve precise control of two counter-propagating light spots in recording media. Using this system, we succeeded in four-layer recording/readout.

The number of layers of a micro-holographic disk is limited by wavefront aberration which is strongly dependent on the photopolymer initiation, termination and inhibition kinetics. 3D metrology is used to validate predicted index profiles.

In Lippmann photography, the interference of the image with its reflection onto a mirror in contact with the photographic emulsion allows, for each pixel of the image, the recording of Bragg gratings. Removing the mirror, processing the plate and reading out these Bragg gratings with a white light source diffracts the very colours used for recording and thus reproduces the images in colours. Using Lippmann photography as a data storage technique was proposed in the 1960th: for a given pixel, and to each recording wavelength is associated one bit of data, several bits being recorded at the same pixel. In this paper, we revisit this data storage technique and we propose and demonstrate an homodyne detection to improve the efficiency of Lippmann data storages. The proposed homodyne geometry also presents the advantage to simplify the architecture: the Lippmann mirror required for recording is kept in place for data retrieving. Such an homodyne readout could also be applied to enhance the detected signals in other holographic approaches.

A compatible optical system with high light efficiency for three optical disc systems (HD-DVD/DVD/CD) has been developed. This system is based on refraction principle and has unique shaped objective lens named 'Multi aspherical shaped compatible lens'.

A stress-induced curved \micro actuator with a grating attached at the end is demonstrated for recordable optical storage applications. The actuator and the grating were fabricated using a two-layer poly-silicon and one-layer silicon nitride micro-machining process. Three diffracted beams with equal intensity from the grating were generated when a voltage is applied to the actuator to switch its position. The single-beam and multi-beam configurations can be used for writing and reading data in the disc, respectively.

In an optical pick-up head, the objective lens actuator is a key component used to move the objective lens to the exact position for focusing the laser spot on the disc recording layer and keeping the laser spot following certain track on the disc. In order to be used in a compact pick-up head for high density drives, the objective lens actuator must be compact and controllable in focusing, tracking, and radial tilt directions. In this paper, an electromagnetic three-axis-controllable actuator with a novel structure was designed and verified. The read tests done by using a pick-up head with the actuator designed in this work proved the feasibility of this design.

The focusing objective lens is a key component in the optical pick-up head. In this paper, focused ion beam milling is used to fabricate a NA 0.65 microlens in the silicon nitride film suspended on a silicon substrate. The measured NA is 0.64 and the focused spot size is 0.64 μm.

An integrated analysis tool of optical system and media which combines system with media analysis of the discs is developed in this project. This software has been used to study the influence of disc tilt, cover layer thickness and scratches on high density recording, which show that it provides a powerful tool in practical applications.

A combination of ray-tracing and diffraction theory is used to model the diffractive optical elements used in optical data storage systems. Details of the theoretical model and some numerical simulation results are presented.

In this paper the focusing effect of flat metallic-slit array in micro-meter scale area is discussed and the role of surface plasmons waves inside slits is recognized. A proximate relationship between the equivalent focal length and slit material, slit geometrical parameters is built. The theoretically derived focal length and that from Finite Difference Time Domain (FDTD) simulation is proved to be in good agreement. Additionally, FWHM of focal point, focal depth and intensity of focal point for the slit array with invariant slit width and the slit array with variant slit width are compared as well. The slit array with varied slit width is found to have the better performance than slit array with invariant slit width.

Scaling the areal density, while maintaining a proper balance between media signal-to-noise, thermal stability and writability will soon require an alternative recording technology. Heat Assisted Magnetic Recording (HAMR) can achieve this balance by allowing high anisotropy media to be written by heating the media during the writing process (e.g. by laser light) to temporarily lower the anisotropy. Three major challenges of designing a HAMR head that tightly focuses light and collocates it with the magnetic field are discussed: 1) Magnetic Field Delivery, 2)Optical Delivery, and 3) Integration of Magnetic & Optical Field Delivery Components. Thousands of these HAMR heads were built into sliders and HGAs, and optical and scanning electron micrograph images are shown. Scanning near-field optical microscopy (SNOM) characterization of the HAMR head shows that the predicted ~λ/4 full-width half-maximum (FWHM) spot size can be achieved using 488 nm light (124 nm was achieved). SNOM images also show that wafer level fabricated apertures were able to effectively eliminate sidelobes from the focused spot intensity profile. An MFM image of HAMR media shows that Non-HAMR (laser power off) was not able to write transitions in the HAMR specific media even at very high write currents, but transitions could be written using HAMR (laser power on), even at lower write currents. A cross-track profile is shown for a fully integrated HAMR head where the magnetic pole physical width is ~350 nm, but the written track is ~200nm, which demonstrates HAMR. A HAMR optimization contour shows that there is an optimum write current and laser power and that simply going to the highest write current and laser power does not lead to the best recording. Lastly, some prospects for advancing HAMR are given and a few key problems to be solved are mentioned.

An efficient and compact method of introducing light into a magnetic recording head for use in Heat Assisted Magnetic Recording (HAMR) is proposed. The technique uses a polymer waveguide to source light into a novel metallic structure consisting of a sub-wavelength C-aperture waveguide with a 90° bend and a tapered section. The structure is modeled using Finite Difference Time Domain (FDTD) simulations and it is shown that the 90° bend allows for low loss near-field optical access into a conventional magnetic recording head while the tapered C-waveguide allows for maximum input coupling and a minimum spot size at the recording media.

The modeling for investigating the thermal effect on slider in heat assisted magnetic recording is built and its verification is conducted by comparing the simulation results and experiment results. The temperature distribution on the slider induced by locally heated media in 1Tb/in² is simulated and the results show that the effect is within a very small zone on the bottom surface. The temperature changes on other surfaces are less than 0.1°C, which can be negligible.

Optical data storage includes inexpensive, removable, easily replicated medium. Only applications requiring these will use optical storage. Multiview, multithread, imaging systems is an application that could require the next generation of optical data storage systems.

We report the new data reproducing scheme for high density over 40GB per layer with a commercial Blu-ray recordable disc. bER of 10-5 and 10-4 with 42.5GB and 45GB were experimentally obtained respectively using this new data reproducing scheme which shows the possibility of achieving 50GB with a commercial single-layer Blu-ray disc. We also propose a new evaluation parameter which is necessary for high density.

Differential phase detection (DPD) is the most popular tracking error detection method for read-only optical discs (ROM discs). However, DPD tracking-error signals deteriorate for high-density discs such as over 30-GB Blu-ray discs (BDs) where zero-cross detection becomes inaccurate. To solve this problem, we propose a new zero-cross-detection-free DPD (ZF-DPD) method by applying the least-mean-square (LMS) algorithm adaptive equalizer. We experimentally confirmed its effectiveness for a high-density (33.3 GB/layer) four-layer BD-ROM disc.

The high gain servo controller with complex zeros was proposed¹. The controller can realize a much higher gain with the same servo bandwidth. We applied the controller to Blu-ray disc drives, and confirmed decrease of servo error and improvement of resistance to vibration. On the other hand, we observed the controller increased an overshoot of an initial response. We applied the initial value compensation², and confirmed suppression of the overshoot.

High data transfer rate has been demanded for data storage devices along increasing the storage capacity. In order to increase the transfer rate, high-speed data processing techniques in read-channel devices are required. Generally, parallel architecture is utilized for the high-speed digital processing. We have developed a new architecture of Interpolated Timing Recovery (ITR) to achieve high-speed data transfer rate and wide capture-range in read-channel devices for the information storage channels. It facilitates the parallel implementation on large-scale-integration (LSI) devices.

A new rate 8/12 4-level run-length limited (2, 9) code with spaced pits/lands constraint has been constructed. The code effciency is high of 94.0%, and the density ratio is 2.0 bits per minimum recorded mark. The encoder has six states and the decoder window length is only two. This byte-oriented code is very suitable to be applied in practical multi-level read-only optical disc systems.

Inserting germanium nitride thin films between Sb-Te (for super-resolution readout) and ZnS-SiO₂ layers was effective to improve super-resolution readout durability of a super-RENS disc using a PtO_x-SiO₂ write-once recording layer. Waveform of 97-nm (that is below the resolution limit of the optics used) and 340-nm combined marks scarcely changed even after 50,000 times readout. CNR of 100 nm marks was stable (within 3 dB decrease) after 268,000 times readout.

We report the readout stability improvement results of super-resolution near field structure (Super-RENS) write-once read-many (WORM) disk at a blue laser optical system. (Laser wavelength 405nm, numerical aperture 0.85) By using diffusion barrier structure (GeSbTe sandwiched by GeN) and high transition temperature recording material (BaTiO₃), material diffusion of phase change layer and recording mark degradation were greatly improved during high power (Pr=2.0mW) readout process up to 1X10⁵ times.

Using metal/Si materials as a recording layer, we have achieved good results for a SR (super resolution) WORM (write-once read many) disc. Mainly by controlling metal composition and the ratio of metal to Si of recording layer, signal qualities were greatly enhanced. At the mark length of 75nm, the best CNR (carrier to noise) was about 45dB, write power was reduced down to 6.5mW, and minimum LFN (low frequency noise) was about 11.7dB. Jitters of single tone pattern mark for every length marks from 2T through 8T were below 10%. Readout signal was stable over 2.25×10⁵ times reading. So-called "3T-problem" was not observed.

Super-resolution near-field optical disk is one of the solutions to overcome diffraction limit and achieve high density optical recording. In this paper, a structure of super-resolution near-field phase-change optical disk with a thin thermal shield layer behind the recording layer is proposed. The optical disks with the new structure were studied theoretically and experimentally. Thermal simulation shows that the thermal shield layer can reduce the phase change layer temperature, thus improve the thermal stability of the disks. The disks with this structure were fabricated and characterized. The experiment results are in good agreement with the simulation results.

Copying speed is an important characteristic for optical read-only memory (ROM) replication systems. The copying speed of holographic ROM replication is, however, limited by small energy efficiency of the optical system due to the small diffraction efficiency of multiplexed holograms. In this paper we propose new holographic ROM replication systems with a photorefractive amplifier, and analyze the speed gain performance. We improve energy efficiency significantly and speed up replication by amplifying weak diffraction signal beams using photorefractive wave mixing. Our new theory and numerical calculations revealed that achievable speed gain can be evaluated from only a single dimensionless parameter that is the product of the three as follows: (i) the pump beam intensity ratio in the amplifier, (ii) the ratio of the photopolymer and photorefractive sensitivities, and (iii) the dynamic range per hologram of the copy medium. In current holographic recording systems, a practical copying speed gain of more than 10 is achievable with currently available photorefractive materials.

A 3D-shift multiplexing is reported with converging signal and diverging random phase coded reference beam into the Cu:Ce:Tb:CLN crystal. Shift-selectivity at first null along x,y and z-axis is measured to be 1.5, 5 and 5mm for random phase-coded reference beam. Low capacity data page with only 1-4 kbits were successfully recorded/retrieved and the achievable raw areal density of >350 Gbit/in2 will be reported.

In present holographic recording material, trade-off between the dynamic range and the shrinkage ratio after fixing causes deterioration of one of these qualities, preventing increase of storage capacity. This paper reports the evaluation results of a new holographic recording material designed for low angular distortion due to shrinkage after fixing.

Holographic Storage Characteristics of PQ/poly(methyl methacrylate) have been significantly improved by doping metallic ion Yb⁺³ and Er⁺³. The hybrid materials display significant enhancement in the holographic characteristics. The diffraction efficiency promote to 59% with Yb⁺³, to 47% with Er⁺³ from the undoped sample is 40%. The increment is up to 47% in Yb⁺³ sample; the dynamic range enhance to 2.12 and 1.58 on Yb⁺³ and Er⁺³ containing sample individually in comparison to 1.16 for the undoped copolymer. The increment of dynamic range is up to 82% for Yb⁺³ containing sample. The related mechanism of these changes is preliminary discussed with the analysis of UV-vis, FT-IR and Photoluminescence spectroscopy.

A laminated holographic recording medium based on photorefractive lithium niobate crystal is reported for the first time. The medium consists of a piece of photorefractive crystal, a data tracking layer, an intermediate dichroic mirror layer and an anti-reflection layer. Such a holographic medium is able to perform hologram recording and retrieving with compatibility with collinear and coaxial holographic recording schemes.

A control method for the angle servo of reference beam during reading recoded data images of a holographic data storage system is presented. The recording scheme with track offset is adopted in order to verify the proposed angle servo. Using only recorded data tracks the angle error signal of reference beam is generated and the angle servo is implemented. Experiments have been performed on recording and reading data images to compensate Bragg angle mismatch.

A holographic data storage simulator for the combined multiplexing method which consists of spatial shift, peristrophic, and focus-shift multiplexing has been developed. In the combined multiplexing method, wedge prisms were used to realize the focus-shift multiplexing, so we gave linear phase modulations on the reference beams to represent the effect of wedge prisms in the simulation and successfully got a good agreement between the simulated and experimental results on the diffraction efficiency characteristics. The diffraction efficiency decreases rapidly as the focal position of the reference beams are shifted, which indicates that it is possible to enlarge the capacity of the holographic data storage by the focus-shift multiplexing.

A generalized non-local polymerization driven diffusion (NPDD) model is presented, which includes the effects of absorption and inhibition. Experimentally obtained growth curves are fit using a four-harmonic numerical fitting algorithm and key material parameters are extracted.

Asymmetric shift selectivity control is studied based on the collinear holographic information storage system. Pixel patterns for asymmetric shift selectivity of holograms were designed. Characteristics of the shift selectivity were calculated and tested using a static collinear system. The shift selectivity control was performed and the asymmetric shift selectivity was proven successfully. The hologram with asymmetric shift selectivity was applied to the precision alignment process for realizing media interchangeability. Here the position sensing beam should be aligned with the holographic recording beam. It played a significant role as a calibration hologram in the demonstration of the process using a dynamic collinear system including rotating holographic recording disk media fully equipped such as the pit layer. OCIS codes: (090.0090) Holography; (090.4220) Multiplex holography; (210.0210) Optical data storage; (210.2860) Holographic and volume memories

We analyzed the effects of an external shock on a collision problem in a solid immersion lens (SIL) based near-field recording (NFR) through a shock response analysis and proposed a possible solution to this problem with adopting a protector and safety mode. With this proposed method the collision between SIL and media can be avoided. We showed possible solution for contamination problem in SIL based NFR through a numerical air flow analysis. We also introduced possible solid immersion lens designs to increase the fabrication and assembly tolerances of an optical head with replicated lens. Potentially, these research results could advance NFR technology for commercial product.

We demonstrated a high-intensity bowtie-shaped nano-aperture Vertical-cavity surface-emitting laser (VCSEL). A maximum power of 188μW is achieved from a VCSEL with an 180nm bowtie aperture at a wavelength of 970nm. Simulation shows the near-field full width at half maximum intensity spot size 20nm away from the bowtie aperture is 64×66nm². The peak near-field intensity from the bowtie-aperture VCSEL is estimated to be as high as 47mW/μm². This intensity is high enough to realize near-field optical data storage and the small spot size corresponds to storage densities up to 150Gbits/in².

An improved concept of the advanced SIL and its compensation OL of composite effective NA over 1.7 has been designed and manufactured to achieve wider assembling tolerances, higher data capacities and better signal quality. Very clear readout signals were measured from a 25 GB BD-like ROM media with 3 um cover layer and the applying feasibility of the advanced SIL system in near field optical storage was confirmed. With this novel advanced SIL system and multilayer media concept, total capacity over 500 GB per disc was expected to be accomplished.

A solid immersion lens (SIL) is described with NA = 2.64 that is fabricated from a two-step process using a large BK7 glass hemisphere and a small GaP hemisphere. The Gallium Phosphide (GaP) hemisphere has a radius 114μm, and is cemented in the center of BK7 SIL with index-matching epoxy. The BK7 SIL thickness is accommodated to have both BK7 SIL and GaP SIL in an image centric configuration. The two-step GaP SIL is tested on an induced polarization imaging system. Induced polarization pupil images, the native polarization image and induced polarization image of a DVD RW sample are given in this paper.

The media position and tilt tolerances of a high numerical aperture (NA) holographic data storage system are examined experimentally. The sources for these tolerances are explained and techniques for optimizing the drive tolerances are described.

A single meniscus aspherical lens and air-spaced spherical lenses having negative and positive powers are identified as minimum aberration configurations for page-based holographic recording systems. Further correction of pupil aberrations makes the lens system usable both for holographic and for surface recording, and the lens is realizable by using two air-spaced apsherics. Two air-spaced apsherics can attain high an imaging NA of 0.7 for holographic recording only, and an NA of 0.45 for a combination of holographic and surface recording.

We illustrate the importance of the interleaver in holographic data storage (HDS) systems affected by burst errors. We use the Gilbert-Elliott channel model to generate pages with burst errors and investigate a toroidal interleaving scheme.

We present a new class of modulation codes based on permutation coding which satisfy the channel coding constraint suitable for the digital holographic data storage, and which simultaneously provide strong error correction at high code rates. The channel decoding scheme is based on the true maximum likelihood detection realized using a newly developed efficient algorithm. The sparse permutation codes of large block sizes closely approach the information theoretic limits for the binary channel data capacity.

We have developed a single-side dual-layer rewritable HD DVD media having a larger capacity of 40 GB (20 GB per layer) for the optical system with the NA of 0.65 and the wavelength of 405 nm, and achieved the good recording characteristics. For both layers, the same track pitch of 0.34 μm as HD DVD-RAM was used. We applied more accurate thermal analysis to the dual-layer rewritable media. It was expected that the effect of the cross-erase was very small. By optimizing thermal balance of dual-layer media, the good recording characteristics were obtained for both layers with enough tilt margins. The feasibility of the dual-layer rewritable media of 40 GB user data capacity was shown for HD DVD system.

High speed HD DVD-R disc with low-to-high polarity organic dye was developed. For development of organic dye, Type A and Type B having different properties in sensitivity and read stability were examined. 4x speed recording is possible with both Type A and Type B. Furthermore, in type B, the sufficient signal characteristics were obtained at 5x speed recording for single layer disc and 2x speed recording for dual layer disc.

The relation of the local structure of the phase-change recording material and the interface layer has not been clarified while we already reported that the interface layer affects the electronic state of recording material by using the HX-PES method. It is necessary to understand more detailed physical phenomenon for crystallization mechanism of recording layer in order to develop the high-speed and higher density rewritable optical recording media. The influence of the interface layer to the local structure for atomic arrangement of a GeBiTe phase-change material was investigated by using XAFS on the actual rewritable HD DVD media. The XAFS signal and EXAFS oscillation from the actual media is obtained nondestructively. It has been shown that the interface layer influence slightly the local atomic arrangement of the recording layer, while the electronic state of recording layer is changed by the presence of the interface layer.

Phase-change wet-etching technology using GeSbTe phase-change films are developed. Selective etching between an amorphous and a crystalline phase can be carried out with an alkaline etchant of NaOH. The degree of etching was investigated by optical images using an optical microscope and the transmittance between the crystalline and amorphous films coated on transparent substrate during an etching process. Etching selectivity is dependent not only on the concentration of the alkaline etchant but also on a film structure. Specifically, metal films for a heat control cause marked effects on the etching properties of GeSbTe film. Surviving amorphous pits can be obtained with Al metal layer, however etched amorphous pits are seen with Ag metal layer. An opposite selective etching behavior can be observed between samples with two different metal layers.

Ge/Al bilayer thin films are prepared by magnetron sputtering. Thermal analysis shows that the phase change of the film occurs at 275 °C. Contrasts at 650 nm and 405 nm wavelength are 71.4% and 31.1% respectively.

This work demonstrates the feasibility of composite thin film containing nano-scale recording particles to high-density optical data storage. For an HD-DVD format "nano"-optical disk containing such a nano-composite layer, modulation higher than 0.5 was achieved when 11T and 4T signals were respectively written into the disk by using a blue-laser dynamic tester. Transmission electron microscopy (TEM) characterization attributed the recording mechanism to the grain coalescence/coarsening and crystallinity change of nano-recording particles which, in turn, results in sufficient reflectivity difference for signal readout. The utilization of nano-composite recording layers may drastically simplify the optical disk structure and thus is a promising alternative for next-generation write-once data recording.