super-RENS Disk Research Articles

High-density channel model and detection method for signal readout from super-resolution near-field structure discs

Although a readout method using the super-resolution near-field structure (super-RENS) effect can overcome diffraction limits, readout characteristics for greatly surpassed high-density conditions do not become clear, because a high-density channel function having a differential response property is superimposed on a normal readout function. We propose a high-density channel model to indicate the properties of the super-RENS effect directly. This model can be expressed as a differential response function using the finite impulse response (FIR) filter model. It expresses the super-RENS readout process, which is divided on the basis of recording densities such as high and normal Blu-ray Disc™ densities. We estimated the properties of super-RENS readout signals by comparison between theoretical expressions and experiments. Results show that good signal quality require readout signals having sharp peaks and smaller offsets. We also evaluated the channel model by adding an adaptive FIR filter and a Viterbi decoder by simulations. Results show that the super-RENS disc can achieve a fourfold higher recording density if the signal-to-noise ratio (S/N) is improved to 6 dB in the case of partial response (PR) (1 + D + D2).

Sparse modeling of super-resolution near-field structure read-out signals

In this study, super-RENS disc read-out signals were modeled with various nonlinear models. In the results of modeling the nonlinearity, DC offset, and domain bloom phenomena of the super-RENS channel with a second-order Volterra filter, it was identified that the number of significant quadratic coefficients was relatively small. Therefore, a sparse Volterra model and a truncated Volterra model are applied to effectively model the nonlinear channel. In addition, the Hammerstein-type asymmetric conversion model is employed to model the nonlinear channel for the purpose of comparison. The results demonstrate that the sparse model of a simplified polynomial form achieves good modeling performance for the super-RENS disc read-out signals.

Nonlinear Equalization for Super-Resolution Near-Field Structure Discs Using a Simplicial Canonical Piecewise-Linear Model

In this paper, we propose a simplicial canonical piecewise-linear (SCPWL) model-based equalizer to mitigate nonlinear distortion resulting in inter symbol interference (ISI) in a super-resolution near-field structure (super-RENS) disc system. The proposed equalizer consists of the linear part represented by a finite impulse response (FIR) filter and the nonlinear part implemented using a SCPWL function. Its validity is tested using radio frequency (RF) signal samples obtained from a super-RENS disc. The raw bit error rate (BER) performance with the proposed equalizer is measured for various key parameters of the SCPWL model. The simulation results demonstrate that the proposed equalizer achieves outstanding raw BER performance improvement by effectively compensating for the nonlinear distortion introducing the ISI.

Simple Readout Channel Model of Super-Resolution Near-Field Structure Disk System

The readout channel response of super-resolution near-field structure (super-RENS) disks have been experimentally investigated using a 63-bit pseudorandom sequence and the autocorrelation of the readout sequence. The time domain analysis reveals that the super-RENS disk has two responses: one is the response of the normal readout beam and the other is the sharp differentiated response of the super-RENS effect. The numerical analysis proves that the sharp differentiated response offers an excellent spatial resolution of the super-RENS disks.

Simple Readout Channel Model of Super-Resolution Near-Field Structure Disk System

The readout channel response of super-resolution near-field structure (super-RENS) disks have been experimentally investigated using a 63-bit pseudorandom sequence and the autocorrelation of the readout sequence. The time domain analysis reveals that the super-RENS disk has two responses: one is the response of the normal readout beam and the other is the sharp differentiated response of the super-RENS effect. The numerical analysis proves that the sharp differentiated response offers an excellent spatial resolution of the super-RENS disks.

Nonlinear Modeling for Super-RENS Disc Using a Simplicial Canonical Piecewise-Linear Adaptive Filter

A correct and accurate model of an optical storage system is very important in the development and performance evaluation of various data detection algorithms. In this paper, we present a nonlinear modeling of a super-resolution near-field structure (super-RENS) read-out signal using the simplicial canonical piecewise-linear (SCPWL) model. The validity of this model is tested using radio frequency (RF) signal samples obtained from a super-RENS disc. The experiment results on modeling indicate that the SCPWL model can be efficiently utilized for the nonlinear modeling of the super-RENS systems.

A Compressed Sensing Approach for Modeling the Super-Resolution Near-Field Structure Disc System With a Sparse Volterra Filter

In this paper, we investigate the compressed sensing (CS) algorithms for modeling a super-resolution near-field structure (super-RENS) disc system with a sparse Volterra filter. It is well known that the super-RENS disc system has severe nonlinear inter-symbol interference (ISI). A nonlinear system with memory can be well described with the Volterra series. Furthermore, CS can restore sparse or compressed signals from measurements. For these reasons, we employ the CS algorithms to estimate a sparse super-RENS read-out channel. The evaluation results show that the CS algorithms can efficiently construct a sparse Volterra model for the super-RENS read-out channel and that observable nonlinear interactions take place among restricted components in the read-out channel.

Bit-Error-Rate Evaluation of Super-Resolution Near-Field Structure Read-Only Memory Discs with Semiconductive Material InSb

Bit-error-rate (bER) evaluation using hardware (H/W) evaluation system is described for super-resolution near-field structure (super-RENS) read-only-memory (ROM) discs fabricated with a semiconductor material, In–Sb, as the super-resolution active layer. bER on the order of 10-5 below a criterion of 3.0×10-4 is obtained with the super-RENS ROM discs having random pattern data including a minimum pit length of 80 nm in partial response maximum likelihood of the (1,2,2,1) type. The disc tilt, focus offset, and read power offset margins based on bER of readout signals are measured for the super-RENS ROM discs and are almost acceptable for practical use. Significant improvement of read stability up to 40,000 cycles realized by introducing the ZrO2 interface layer is confirmed using the H/W evaluation system.

First Playback of High-Definition Video Contents from Super-Resolution Near-Field Structure Optical Disc

A super-resolution near-field structure (super-RENS) read-only-memory disc with an In–Sb thin film as a super-resolution active layer corresponding to a 50 Gbyte capacity per layer was fabricated. The carrier-to-noise ratio at a pit length of 75 nm exceeded 40 dB and a bit error rate (bER) of the order of 10-5 satisfying the 3.0×10-4 criterion was obtained. To the best of our knowledge, this is the first report on the successful and seamless playback performance of a high-definition video content from the super-RENS disc at a data transfer rate of either 36 or 72 Mbps. The bER results of fixed and adaptive partial response maximum likelihood detections are described.

Nonlinear Modeling and Equalization of Super-Resolution Near-Field Structure Discs Using a Canonical Piecewise-Linear Model

In this study, we apply the canonical piecewise-linear (PWL) model to the modeling of super-resolution near-field structure (super-RENS) read-out signals because reliable and accurate channel modeling is essential for performance analysis and development of equalizers for super-RENS disc systems. To mitigate the nonlinear inter symbol interference (ISI), furthermore, we propose a canonical PWL model-based equalizer (PWLEQ) for super-RENS discs. The validity of the model and the equalizer is tested using radio frequency (RF) signal samples obtained from a super-RENS disc. The modeling experiment results verified that the canonical PWL model can be efficiently utilized for the nonlinear modeling of super-RENS systems. The raw bit error rate (BER) performance with the proposed equalizer is measured for various delays and step sizes of the canonical PWL model. We observe a marked improvement in raw BER when using the proposed equlaizer.

Optically High Spatial Resolution Obtained Using Super-Resolution Near-Field Structure Disk System

Super-resolution near-field structure (Super-RENS) disks with AgInSbTe (AIST) mask layers with varying thicknesses were prepared and their spatial resolutions were experimentally evaluated. The thickness of each AIST mask layer was changed from 6.5 to 18.6 nm. A Super-RENS disk with a mask layer thickness of 18.6 nm was recorded and retrieved at a small mark length of 23 nm, which is far beyond the diffraction limit. By the third-harmonic spectrum analysis of read signals, a readout spatial resolution of 19.3 nm was obtained. This spatial resolution can be used for optical disks with capacities of more than 1 TB.

Effect of Recorded-Dot Size on Readout Signal in Nano-Optical Storage

In this paper, we study the features on transmittance and reflectance for different diameter and height of recorded bubble dot in a PtOx super-RENS disk, by means of a simulating calculation. Some interesting conclusions are shown, and difference between model adopted in our study and actual structure is also discussed.

Nonlinear Equalization for Super-Resolution Near-Field Structure Discs

In this paper, we present a neural network-based equalizer (NNEQ) for super-resolution near-field structure (super-RENS) discs. In order to investigate the presence of nonlinear interactions, we employ the bicoherence test, which is based on higher-order statistics. This test reveals that a super-RENS disc experiences severe nonlinear inter symbol interference (ISI). To mitigate the nonlinear ISI, we apply the NNEQ, which relies on the nonlinear autoregressive network with an exogenous input (NARX) model. Its validity is tested with radio frequency (RF) signal samples obtained from a super-RENS disc. The performance of the proposed equalizer is superior to that of the case without equalization and that of the case with limit-EQ in terms of bit error rate.

Blu-ray Type Super-Resolution Near-Field Phase Change Disk with In2Ge8Sb85Te5 Mask Layer

A new mask layer of In2Ge8Sb85Te5 was developed and used on super-resolution near-field phase change optical disks (super-RENS). The thermal and optical properties of the mask layer were investigated. Thermal analysis showed higher crystallization temperature and activation energy but lower melting temperature than Ge2Sb2Te5 phase change material. Ultra-fast crystallization within 30 ns was obtainable using a pulsed high-power laser beam of 405 nm wavelength. The recording performance of the new structure was evaluated on an optical recording system with a numerical aperture of 0.85 and a 405 nm blue-violet laser diode. Carrier-to-noise ratio (CNR) of 32, 25, 15, and 10 dB were obtained for 80, 50, 40, and 30 nm mark trains, respectively. Readout thermal stability of 20,000 cycles was realized for 80 nm mark trains. These performances were by far the highest obtainable for blu-ray aperture-type super-RENS disk.

Study on readout durability of super-RENS disk

Characteristics essential for the readout durability of a superresolution near-field structure (super-RENS) disk are studied experimentally by using a home-built optical measuring setup and atomic force microscope, based on a simplified PtOx super-RENS disk. The experimental results show that for a super-RENS disk with constant structure and materials, readout signals including transmittance and reflectance vary with changes in bubble shape and size, indicating that the readout durability of the disk has a strong dependence on bubble stability, which is closely related to the thickness of the cover layer, the recording power and readout power, and the mechanical properties of the dielectric layer. Based on our experimental results, the main direction for improving readout durability is also proposed.

Capacity Increase in Radial Direction of Super-Resolution Near-Field Structure Read-Only-Memory Disc

We propose a novel super-resolution near-field structure (super-RENS) read-only-memory (ROM) disc with a narrow track pitch using a group tracking technique. The group tracking technique enables the tracking control of an optical disc because it consists of track pitch sizes that are less than the diffraction limit. The group tracking technique to increases capacity in the radial direction of the super-RENS ROM disc. By using this technique, carrier-to-noise ratio (CNR) was obtained at 33 dB and the minimum crosstalk level was -23 dB at the 100 nm pit length. A readout track was selected by controlling the offset level of the tracking error signal in a high definition digital versatile disc (HD-DVD) system. It was confirmed that the capacity of the super-RENS ROM disc with the group tracking structure was improved in the radial direction.

Effect of SiO2 Addition to PtOx Recording Layer of Super-Resolution Near-Field Structure Disc

A dielectric material (SiO2) was added to the PtOx recording layer of a recently developed super-resolution near-field structure (super-RENS) disc to enhance the readout durability. The PtOx–SiO2 (Pt8.4Si21.1O70.5) composite layer was prepared by a chip-on-target sputtering method. The recorded mark became significantly solid-filled when the prepared layer was used to replace the PtOx layer of the original disc. The carrier-to-noise ratio obtained for the 100 nm marks (laser wavelength: 405 nm, numerical aperture: 0.65) was 44 dB. It was possible to readout 7.5×104 times until the initial carrier-to-noise ratio (CNR) decreases by 3 dB; this is a more than one-order-of-magnitude enhancement compared with at in the simple PtOx case. Readout laser power was not reduced. This enhancement is achieved as a result of improving the recording layer of the super-RENS disc.

Phase-change optical recording: Past, present, future

We discuss specific features of Te-based compounds that made them the best materials for the phase-change data storage. It is demonstrated that the phase-change recording is due to a switch of Ge atoms between octahedral and tetrahedral symmetry positions within the Te face-centered cubic lattice. It is this nature of the transition that makes the Te-based media fast and stable. The driving force for this transition is also discussed. The chapter is concluded by introduction of a concept of the super-resolution near-field structure (super-RENS) disc that allows to reduce a bit size well below the diffraction limit and makes 100 GB/disc storage a reality.

Optothermal Property and Decomposition Characteristics of PtOx Ultrathin Film Sandwiched Between ZnS–SiO2 for Super-Resolution Near-Field Recording

We have investigated the optothermal property and decomposition characteristics of PtO(x) ultrathin film protected by ZnS-SiO2 layers and effects of the constituent phases of PtO(x) on super-resolution capability and read stability of the super-RENS disk. All the ZnS-SiO2/PtO(x)/ZnS-SiO2 multilayers exhibited a steep reflectivity drop at the temperature range between 265 and 350 degrees C, corresponding to the decomposition of PtO(x). The decomposition temperature of the 4-nm-thick PtO(x) ultrathin film protected by ZnS-SiO2 layers was much lower than those obtained in thick PtO(x) films without protection. The activation energy for thermal decomposition was approximately 1.3 eV. Both the decomposition temperature and activation energy for thermal decomposition were unaffected by the constituent phases of PtO(x). Carrier to noise ratios (CNR) of over 40 dB for mark size of 150 nm were achieved in all super-resolution near-field structure (super-RENS) disks, while the super-resolution readout was limited to 2.5 x 10(3) approximately 4.5 x 10(4) cycles. The effect of constituent phases of PtO(x) on the super-resolution capability of super-RENS disk with a PtO(x) mask layer was minimal. However, as the constituent phases of PtO(x) mask layer transformed from a mixture of Pt and PtO, to pure PtO, and then to a mixture of PtO and PtO2, the readout stability of super-RENS disk increased dramatically since less heat was absorbed by the PtO(x) mask layer composed of PtO and PtO2 during the readout process, prohibiting the diffusion of materials inside the bubble to the GeSbTe phase change layer.

Numerical Analysis and Comparison of Three Metal-Oxide-TypeSuper-Resolution Near Field Structures

Based on the Fresnel–Kirchhoff diffraction theory, webuild up a Gaussian diffraction model of metal-oxide-type super-resolution nearfield structure (super-RENS), which can describe far field optical properties. Thespectral contrast induced by refractive index and the structural changes inAgOx, PtOx and PdOx thin films, which are the key functional layersin super-RENS, are studied by using this model. Comparison results indicate that thespectral contrast depends intensively on the laser-induced distribution and changeof the refractive index in the metal-oxide films. The readout mechanism of themetal-oxide-type super-RENS optical disc is further clarified. This Gaussiandiffraction model can be used as a simple and effective method for choosing properactive materials in super-RENS.