Super-resolution Near-field Structure Disk Research Articles

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.

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.

超分辨近场结构光盘的传统以及差分读出方法研究

超分辨近场结构光盘的传统以及差分读出方法研究

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.

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.

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.

Error Rate Reduction of Super-Resolution Near-Field Structure Disc

We report the error rate improvement of super-resolution near-field structure (super-RENS) write-once read-many (WORM) and read-only-memory (ROM) discs in a blue laser optical system [laser wavelength (λ), 405 nm; numerical aperture (NA), 0.85]. We prepared samples of higher carrier level WORM discs and wider pit width ROM discs. Using controlled equalization (EQ) characteristics and an adaptive write strategy and an advanced adaptive partial response maximum likelihood (PRML) technique, we obtained a bit error rate (bER) of 10-4 level. This result shows the high feasibility of super-RENS technology for practical use.

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.

On a thermally induced readout mechanism in super-resolution optical disks

We have simultaneously measured the carrier-to-noise ratio (CNR) as well as the transmitted and reflected light intensities from platinum oxide based super-resolution near-field structure (PtOx super-RENS) disks. The the reflected and transmitted light intensities were found to decrease and increase, respectively, as the CNR value increased. The phase-change material AgInSbTe (AIST) used in PtOx super-RENS disks was found to exhibit a strong optical nonlinearity with respect to readout laser power. AIST becomes transparent at higher laser powers. To ascertain whether the presence of Pt nanoparticles is important to the readout mechanism, a super-RENS disk was fabricated in which the PtOx layer was replaced with a metal-free phthalocyanine (H2Pc) layer and the CNR of the H2Pc disk was measured. From the observation that the CNR value was equivalent to that of a disk made using PtOx, we conclude that the presence of nanoparticles does not play an important role in the super-RENS readout mechanism. Finally, we also investigated the use of Si and the alloy Ge2Sb2Te5 in lieu of AIST in a super-RENS disk and simple three layer structure disks. The super-resolution effect was observed for all disk types. Based upon these observations, we discuss the possibility of a thermal origin for the super-resolution effect in all super-resolution disks.

High-Speed Fabrication of Super-Resolution Near-Field Structure Read-Only Memory Master Disc using PtOx Thermal Decomposition Lithography

We propose a new lithography technique using thermal decomposition of platinum oxide (PtOx) for high-throughput master disc fabrication. The smallest pit size was evaluated to be 50 nm using a laser wavelength of 405 nm and a numerical aperture (NA) of 0.65; hence, it is one-twelfth the optical spot size. In addition, fabrication of pits with different shapes was examined, and its effects on super-resolution near-field structure (super-RENS) disc properties were studied. The readout signal characteristic evaluated on the basis of carrier-to-noise ratio (CNR) with an elliptical pit was 7 dB larger than that of the round one. The results demonstrated that this high-throughput fabrication technique is also useful for controling the pit shape for CNR improvement of super-resolution readout.

Near-Field Characteristics and Signal Enhancement of Super-Resolution Near-Field Structure Disk with Metal Nanoparticles

In this study, we focus on near-field characteristics and surface plasmon (SP) induced by uniform- and nonuniform-size Ag nanoparticles in the mask layers of super-resolution near-field structure (super-RENS). The finite-difference time-domain (FDTD) method is used to analyze scattering fields from the localized SPs of Ag nanoparticles. It has been found that the spatial extension of the evanescent field is very short along the thickness direction of the mask layers, and the three-dimensional coupling patterns of the evanescent fields from the nonuniform-size particles are the most irregular. The signal enhancement mechanism of a super-RENS disk is discussed.

Carrier-to-noise ratio enhancement of super-resolution near-field structure disks by Ag nanostructure

The recording and retrieval characteristics of super-resolution near-field structure disks have been evaluated before and after the fabrication of a Ag-nanostructured film on the top dielectric layer, using a 405nm wavelength laser and a 0.65 numerical aperture lens system. The carrier-to-noise ratio for 100nm mark signals is significantly improved by applying the Ag-nanostructured film. The underlying mechanism for the enhancement depends on the top dielectric layer thickness. A simulation based on Mie theory shows good agreement with the measured reflectance spectrum for the Ag-nanostructured film.

Super-resolution and frequency-dependent efficiency of near-field optical disks with silver nanoparticles

The super-resolution capability of the AgOx-type super-resolution near-field structure disk with silver nanoparticles was studied using finite-difference time-domain method at different incident light frequencies. The near fields exhibited strongly local field enhancement around silver nanoparticles in the AgOx layer due to localized surface plasmon. The subwavelength recording marks smaller than lambda/10 were distinguishable since the metallic nanoparticles with high localized fields transferred evanescent waves to detectable signals in the far field. The far-field signals from random silver nanoparticles displayed similar behaviors as those from single nanoparticle and red-shifts of peak frequencies from particle-particle interaction.

Enhanced readout signal of superresolution near-field structure disks by control of the size and distribution of metal nanoclusters

We present a study in which we enhance the carrier-to-noise ratio of a superresolution near-field structure (super-RENS) disk to read below 100-nm marks by implementing a mask layer comprising a Au nanocluster-embedded dielectric film. Various Au nanocluster-embedded mask layers are fabricated by a radio-frequency cosputtering process, and the size and distribution of Au nanoclusters are controlled. To verify the enhancement of the various films for super-RENS disk applications, the sensitivity enhancement of plasmonic gas sensing is demonstrated.

Improvement of Noise Characteristics in Super-Resolution Near-Field Structure Disc

The research interest in super-resolution near-field structure (Super-RENS) technology is shifting from the signal intensity (carrier-to-noise ratio, CNR) to the signal uniformity (jitter or bER). To achieve uniform signal characteristics, it is important to reduce signal fluctuation in the super-RENS disc. In this study, we investigated the relationship between signal fluctuation and low-frequency noise (LFN), and analyzed the LFN increase in recording and readout processes. It was found that signal fluctuation had a close relationship with LFN. It was also found that certain recorded mark shapes, such a bubble shape, and high readout power increased the LFN during recording and readout processes of a super-RENS disc. Therefore, using non bubble-type recording material and low super-resolution readout material, we markedly improved the LFN of a super-RENS disc.

Readout Power Dependence of Signal Distribution Observed in Fourier Plane of Focus Spot

We describe the readout-power dependence of the properties optical readout signals, and discuss the super-resolution mechanism in platinum-oxide super-resolution near-field structure (super-RENS) disks. From the Fourier analysis of a focused spot, it is clear that a low-reflectivity region within the beam spot during readout above the threshold readout power is generated in a special-temperature region, which, in turn, is associated with the readout mechanism. These phenomena suggest that such readout is related to a large change in the optical properties of a phase change layer, as proposed in the ferroelectric catastrophe model.

Signal Characteristics of Super-Resolution Near-Field Structure Disks with 100 GB Capacity

We report the basic characteristics of super resolution near-field structure (Super-RENS) media at a blue laser optical system (laser wavelength 405 nm, numerical aperture 0.85). Using a novel write once read many (WORM) structure for a blue laser system, we obtained a carrier-to-noise ratio (CNR) above 33 dB from the signal of the 37.5 nm mark length, which is equivalent to a 100 GB capacity with a 0.32 micrometer track pitch, and an eye pattern for 50 GB (2T: 75 nm) capacity using a patterned signal. Using a novel super-resolution material (tellurium, Te) with low super-resolution readout power, we also improved the read stability.