Super-resolution Near-field Structure Research Articles

Nonlinear optical properties of As2Se3 thin films

We propose As2Se3 thin film, which has large third nonlinear optical properties, as one of the candidates for super-resolution near-field structure (super-RENS) materials in the optical recording disks. As2Se3 thin film was deposited by thermal evaporation technique and surface roughness, linear/nonlinear optical properties were characterized. As2Se3 thin film shows large nonlinear optical characteristics (χR(3)=7.42×10−7 m2/W, γ=1.268×10−5 m2/W) and self-focusing phenomenon. Super-resolution effect was measured by a laser beam profiler. As a result, recording density can be enhanced by 2.3 times in case when 300 and 350 nm As2Se3 thin films are applied as a super-RENS.

Optical Properties of Metal-Oxide Films in Super-RENS

The property of the optical transmittance and reflectance induced by structural changes in AgOx, PtOx and PdOx thin films, which are materials of key layer in superresolution near-field structure (super-RENS) optical disk, is investigated by Z-scan measurements and microscopic observations. The light intensity features of the transmittance and reflectance are clarified. Laser-irradiated decomposition of the noble metal oxides in the films and their decomposition thresholds are examined. The optical properties of the films result from bubbles induced by the chemical decomposition of the oxides and the metallic nanoparticles dispersed in the bubbles. The light-induced thermal features, reversible and irreversible properties, optical responses corresponding to the decomposition of the oxides, the influence on readout stability, and the signal intensity of the metal-oxide (MeO) super-RENS disks are also discussed for MeO films.

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.

Super-RENS Disk for Blue Laser System Retrieving Signals from Polycarbonate Substrate Side

Super-resolution near-field structure (super-RENS) technology was applied to the high definition digital versatile disk (HD DVD) based system that retrieves signals from the polycarbonate substrate side using a blue laser. We used an optics with a laser wavelength (λ) of 405 nm and a numerical aperture (NA) of 0.65, and have obtained high carrier-to-noise ratios (CNRs) of 45 dB at a 100 nm mark length and 40 dB at 60 nm, which are smaller than the resolution limit (λ/4NA=156 nm). The results demonstrate that the technology can also be used in the HD DVD-based system. We discussed how well the CNR is obtained below the resolution limit when this technology is used in the DVD-, Blu-ray Disc- and HD DVD-based systems. Comparison of the best results to date strongly suggests that the difference between these systems simply comes from their λ and NA.

Enhanced Scattering of Random-Distribution Nanoparticles and Evanescent Field in Super-Resolution Near-Field Structure

This study focuses on evanescent fields induced by silver nanoparticles in the mask layer and in the interfaces in an AgOx-type super-resolution near-field structure (super-RENS). The finite-difference time-domain (FDTD) method is used to analyze the scattering fields from the localized surface plasmons of silver nanoparticles. It has been found that the spatial extension of the evanescent field is very short along the thickness direction of the layers, and the 3-dimensional coupling patterns of the evanescent fields from the individual particles are irregular. The study also found that the intensity of the evanescent fields is dependent on the silver concentration.

Properties of Super-Resolution Near-Field Structure with Platinum-Oxide Layer in Blu-ray Disc System

The super-resolution near-field structure with a platinum-oxide layer was applied to the Blu-ray Disc system. The carrier-to-noise ratios of 50.1, 46.2, and 39.2 dB were obtained at the mark lengths of 75, 50, and 37.5 nm, respectively, which are smaller than the resolution limit of 119 nm of the optics. Mark position recording with a mark length of 50 nm was also attempted, and we succeeded in retrieving recorded patterns correctly without loss of the signal.

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.

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.

Optical Property of PtOx at Elevated Temperatures Investigated by Ellipsometry

The optical properties of PtOx thin films used for the optical recording layer of super resolution near-field structures (super-RENS) are studied at high temperatures. A series of PtOx thin films for various molar oxygen fraction x were prepared using the reactive magnetron sputtering technique. From the ellipsometric studies, it is found that the complex refractive index of PtOx changes monotonically from that of metallic Pt to that of dielectric PtO2 as the molar oxygen fraction increases. When temperature increases from 30 to 700°C, all PtOx is completely decomposed at 549°C and, for the samples with x larger than 1.3, the condensation of porous Pt films is completed at 700°C. The surface roughness of PtOx thin films with x larger than 1.3 increases markedly after temperature ramping and PtOx thin films evolve into Pt metal by passing through three steps of oxidization, decomposition and condensation.

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.

Investigation on the static recording characteristic of super-resolution near-field structure with antimony mask layer

Static recording characteristic of super-resolution near-field structure with antimony (Sb) is investigated in this paper. The recording marks are observed by a scanning electron microscopy (SEM), a high-resolution optical microscopy with a CCD camera and an atomic force microscopy (AFM). The super-resolution mechanism is also analyzed based on these static recording marks. Results show that the light reaching on recording layer is composed of two parts, one is the linear transmissive light (propagating field) and the other is the nonlinear evanescent light in the optical near field. The evanescent light may be greatly enhanced in the center of the spot because Sb will transit from a semiconductor to a metal when it is melted under the high laser power irradiation. This local melted area in the spot center may be like a metal tip in the optical near field that can collect and enhance the information that is far beyond the diffraction limit, which leads to the super-resolution recording and readout.

Phase change materials in Super-RENS disk

Super-REsolution Near-field Structure (Super-RENS) is one of the most promising technologies for a subterabyte optical storage. In this paper, we will report effects of phase change material on the recording and readout characteristics of a Super-RENS disk.

Size Effects of Localized Surface Plasmon Induced by Embedded Silver Nanoparticles in Near-field Optical Disk

In this paper, we report the near-field and far-field properties of AgOx-type super-resolution near-field structure with embedded silver nanoparticles of different sizes using two-dimensional finite-difference timedomain calculations. Highly localized enhancements were found near the surface of nanoparticles, and the near-field enhancements increased with the size of nano particles. The far-field difference signals of silver nano scatters confirm the super-resolution capability, and the difference signals were stronger for larger nanoparticles. The behaviors of far-field signals indicate the correlation between the enhanced localized surface plasmons and the super-resolution capabilities.

Read/Write Mechanism for a Scattered Type Super-Resolution Near-Field Structure Using an AgOx Mask Layer and the Smallest Mark Reproduced

A working mechanism for a scattered type super-resolution near-field structure (super-RENS) disk using a silver oxide (AgOx) mask layer has been studied experimentally. The AgOx mask layer has five possible states depending on the laser power: AgOx (as-depo), uniformly dispersed Ag particles (after the initialization of 3.5 mW), Ag cluster (4–5 mW), Ag diffusion (5.5–7.5 mW), and a Ag ring structure (greater than 8 mW) for an objective lens numerical aperture of 0.5, a laser wavelength of 826 nm and a medium velocity of 2 m/s. On the other hand, the GeSbTe recording layer has the following possible states: crystal, halfway amorphous, completely amorphous, and gas bubble associated with Ag particles. For super-resolution read power (4 mW), the mask layer will have a Ag ring structure that increases both the signal carrier to noise ratio and the resolution limit. We improve the resolution limit of 413 nm to 50 nm at the duty ratio of 10% for the write optical pulse.

Enhanced resolution induced by random silver nanoparticles in near-field optical disks

The super-resolution near-field structure (super-RENS) is a high-density near-field optical data storage medium which can achieve superior spatial resolution beyond the diffraction limit. Our previous studies found that enhanced local optical intensity occurred at the near fields of super-RENS disks, and the nonlinear near-field optical enhancement is related to the localized surface plasmons of silver clusters dissociated from the AgOx layer in the super-RENS disks. In this paper, we studied the near-field and far-field properties of AgOx-type super-RENS with different distributions of silver nanoparticles using finite-difference time-domain (FDTD) simulations. Highly localized enhancements are found between adjacent silver nanoparticles in the near fields. The far-field signals of different silver nanoparticles distributions confirm the super-resolution capability of AgOx-type Super-RENS disks, and a simplified Fourier optics model is used to describe the relation between highly localized near-field distributions and enhanced resolution of far-field signals.

Static Optical Recording Properties of Super-Resolution Near-Field Structure with Bismuth Mask Layer

Super-resolution near-field structure (super-RENS) with bismuth (Bi) mask layer (Bi-super-RENS) is reported for the first time in this paper. Bi thin films with various thicknesses were studied by atomic force microscopy and grazing incident X-ray diffraction. Static optical recording tests with and without super-RENS were carried out using 650 nm semiconductor laser at recording power of 14 mW and 7 mW with pulse duration of 100 ns. The recording marks were observed by scanning electron microscopy and high-resolution optical microscopy with a CCD camera. Results showed that the Bi mask layer can also concentrate energy into the center of a laser beam at low laser power similar to the traditional Sb mask layer. Moreover, a (ZnS)80(SiO2)20 protection layer performed better than the SiN protection layer in the Bi-super-RENS. The direct observation of laser-recording marks may help better understand the working mechanism of the super-RENS, super-resolution ablation, and other nonlinear switch phenomena.

Structural Phase Transition of AgOx Sandwiched Between ZnS–SiO2 Protective Layers Under Thermal and Laser Pulse Annealing for Super-Resolution Near-Field Recording

The as-deposited AgOx prepared at an oxygen flow ratio of 0.5 consisted of Ag2O and AgO phases. During thermal annealing, the reduction of AgO into Ag2O, decomposition of Ag2O into Ag and O2, and out diffusion and aggregation of decomposed Ag would take place successively. The chemical decomposition of AgOx film sandwiched between two ZnS–SiO2 protective layers was confirmed to be an irreversible process. As being irradiated by a high power laser pulse similar to the recording process, a hollow Ag cylinder, or ring, serving as an aperture, was formed in the AgOx mask layer, and small Ag particles, serving as light-scattering centers, were precipitated in the center region. During the readout process, the small aperture can significantly reduce the readout laser spot size, while the strong near-field interaction between precipitated Ag particles and sub-wavelength marks can effectively enhance the readout signal. That elucidates the recording and readout mechanisms of super-resolution near-field structure disk with an AgOx mask layer.

Characterization of Nonlinear Optical Properties of Silver Oxide Super Resolution Near-Field Structures by Z-Scan Measurements

Femtosecond laser Z-Scan measurements are used to characterize the nonlinear optical properties of AgOx super resolution near-field structures (super-RENS). Open aperture Z-Scan measurements reveal a complex transient nonlinear optical absorption response of AgOx super-RENS under intensive laser irradiation. This is attributed to the thermal decomposition of AgOx into Ag nanoparticles in the near-field optical mask layer. A bi-compositional model is proposed to explain this complex nonlinear optical response. The threshold laser peak intensity for the phase transition and the nonlinear optical absorption coefficient of an Ag nanoparticle are determined to be Ith∼0.3 GW/cm2 and β=(-5.6±0.5)×103 cm/GW at λ=800 nm, respectively.

Effect of constituent phases of reactively sputtered AgOx film on recording and readout mechanisms of super-resolution near-field structure disk

We have studied the dependence of the constituent phases of reactively sputtered AgOx mask layer on the recording and readout mechanisms of super-resolution near-field disk. At low oxygen flow ratios, the AgOx mask layer was found to be composed of an appreciable amount of Ag particles with sizes of tens of nanometers and Ag2O phase. After recording by a high power laser pulse, a hollow Ag cylinder that had its center filled with O2 was formed in the AgOx mask layer. The hollow Ag cylinder would serve as an aperture and could effectively reduce the laser spot size during readout, leading to the super-resolution effect only. At high oxygen flow ratios, the AgOx mask layer was found to be mostly composed of Ag2O and/or AgO phases. After recording by a high power laser pulse, a hollow Ag cylinder that had its center filled with nanosized Ag particles was formed in the AgOx mask layer. The nanosized Ag precipitates would serve as light-scattering centers and could yield strong near-field interaction with the subwavelength marks, resulting in both the super-resolution and near-field effects during readout.

Super Resolution Read Only Memory Disc Using Super-Resolution Near-Field Structure Technology

Super resolution near-field structure (super-RENS) technology is one of the promising technologies for a sub-terabyte optical storage of around 200 GB capacity. We confirmed the possibility of super-RENS read only memory (ROM) media with multilayer structure using the combination of the PtOx, AgInSbTe, ZnS-SiO2 films. The carrier to noise ratio (CNR) and readout cyclability was measured for the super-RENS ROM disc in both the red laser and the blue laser systems.