High-density Optical Memory Research Articles

Optical control of structural morphology in azobenzene containing polymeric liquid crystals

We present a study of photoinduced transitions occurring in a low T(G) liquid crystalline polymer containing the azobenzene group in the side chain. The structural phase of this material can be optically switched between the glassy, nematic and isotropic states. We show the equivalence of light and temperature in causing these effects, promoting this material as a tool in the investigation of structural relaxation at transitions in confined geometry and fast temperature variation as in the case of the optically induced quenching that we report. The results allow us to propose also alternative writing methods for the application of these materials to high density optical memories.

High Density Optical Memory using Nano-aperture Probe and VCSEL with Integrated Microlens Array

High Density Optical Memory using Nano-aperture Probe and VCSEL with Integrated Microlens Array

Light‐Induced Conversion of an Insulating Refractory Oxide into a Persistent Electronic Conductor.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Design window search using continuous evolutionary algorithm and clustering––its application to shape design of microelectrostatic actuator

This paper describes a search method for multi-dimensional design window (DW), which is defined as an existing area of satisfactory solutions in a design parameter space. The method consists of the following two steps: (1) direct search for satisfactory design solutions using a continuous evolutionary algorithm (CEA) from a wide area of the design parameter space in a robust manner, and (2) identification of a precise structure of DW by clustering the detected satisfactory solutions with a modified K-means algorithm. The CEA is a kind of genetic algorithms modified to deal with continuous variables. The modified K-means clustering algorithm contains an explicit procedure to determine the optimum number of clusters. The proposed DW search method was implemented to an integrated computational aided engineering system for multi-disciplinary structural design developed by the authors, and then the method was applied to shape design of a microelectrostatic actuator for next generation high-density optical memory. A DW consisting of four clusters, i.e. four sub-DWs was obtained, and the features of the representative design solutions of the four sub-DWs were compared with each other in detail, and a final design solution was determined.

Light-induced conversion of an insulating refractory oxide into a persistent electronic conductor.

Materials that are good electrical conductors are not in general optically transparent, yet a combination of high conductivity and transparency is desirable for many emerging opto-electronic applications. To this end, various transparent oxides composed of transition or post-transition metals (such as indium tin oxide) are rendered electrically conducting by ion doping. But such an approach does not work for the abundant transparent oxides of the main-group metals. Here we demonstrate a process by which the transparent insulating oxide 12CaO x 7Al(2)O(3) (refs 7-13) can be converted into an electrical conductor. H(-) ions are incorporated into the subnanometre-sized cages of the oxide by a thermal treatment in a hydrogen atmosphere; subsequent irradiation of the material with ultraviolet light results in a conductive state that persists after irradiation ceases. The photo-activated material exhibits moderate electrical conductivity (approximately 0.3 S cm(-1)) at room temperature, with visible light absorption losses of only one per cent for 200-nm-thick films. We suggest that this concept can be applied to other main-group metal oxides, for the direct optical writing of conducting wires in insulating transparent media and the formation of a high-density optical memory.

Design of a 364 nm Electrically Pumped Multi-Quantum Well Continuous Wave Nitride Vertical Cavity Surface Emitting Laser

ABSTRACTShort-wavelength vertical cavity surface emitting lasers (VCSELS) are typically important for high-density optical memory and optical imaging systems. An AlGaN/GaN multiquantum well (MQW) VCSEL was designed for operation at wavelength of 364 nm. The design process consisted of careful selection of materials and optimization of the parameters for distributed Bragg reflector (DBR) stacks, active region, and calculation of the threshold current density, external quantum efficiency, and threshold carrier concentration. InGaN/AlGaN material system was selected for constructing DBR stacks in order to minimize power dissipation and to achieve high reflectivity. A reflectivity of 99% was calculated for 33 pairs in the bottom DBR stack and 97% was calculated for 30 pairs in the top DBR stack. An external quantum efficiency of 85% has been achieved through parametric optimization. Results were comparable to that of the similar structures based on the review of recent literatures.

Polymeric nanostructured material for high-density three-dimensional optical memory storage

The unique properties of a polymer photonic crystal are examined with respect to applications as a medium for high-density three-dimensional optical data storage media. The nanocomposite material was produced from core-shell latex particles, in which the latex cores contained dye-labeled polymer. Nonfluorescent latex shells were attached to the core particles. Upon annealing, the close-packed core-shell particles formed a nanostructured material with the fluorescent particles periodically embedded into the optically inert matrix in a hexagonal close-packed structure. A two-photon laser scanning microscope was used to write bits of information into the material by photobleaching the optically sensitive particles and, under much lower fluence, read out the resulting image. Relative to conventional homogeneous storage media, the nanostructured periodic material is shown to increase the effective optical storage density by at least a factor of 2 by spatially localizing the optically active region and imposing an optically inactive barrier to cross-talk between bits. This polymer photonic crystal has the potential to dramatically improve performance further through the improved capabilities to optimize the photochemical processes and more fully exploiting the periodic nature of the information domains in the image processing.

Holographic Approach to Record and Retrieve Subwavelength-Size Objects Using Optical Near-Field

A holographic method for the storage and retrieval of subwavelength-size objects using optical near-field is proposed. Experimental results show that evanescent field components can be recorded and retrieved by our method and hence, an object whose size is smaller than the Rayleigh limit can be reconstructed. It may be an effective way of microhologram and suggests applications in biology and high-density optical memory systems.

High-Density Optical Memory using Photochromic Diarylethenes

The great interest in photochromic materials for high-density optical memory has been increased for the past decade. A super-low power readout method has been proposed to solve a problem about degradation of recorded information by readout process. About 106-time readout was demonstrated by the method. New high-density optical memory, a super-resolution disk with a photochromic mask layer, was introduced. The super-resolution method has enabled us to increase the recording density of conventional optical disks. Ultra-high density near-field photochromic memory as a new innovative storage technology was also discussed.

Electromagnetically induced transparency over spectral hole-burning temperature in a rare-earth–doped solid

We have observed electromagnetically induced transparency (EIT) in rare-earth Pr3+-doped Y2SiO5 over the spectral hole-burning temperature. The transmission of the probe laser beam is increased by a factor of exp(1.4) at 12 K when a coupling laser of 1.2 kW/cm2 is applied to the system. The observation of EIT over the spectral hole-burning temperature in a rare-earth–doped solid represents important progress toward high-density echo-based optical memories at higher temperatures.

Scanning Probe Microscopy: Present Status and New Development. Basic Performance of Near-Field Optical Microscope and Its Applications.

The principles of aperture- and scattering (apertureless)-type near-field optical microscopies (NOM), their related techniques, and their applications are summarized. In terms of a key device of the aperture-type NOM, the functional performance of an optical fiber probe with a small metal aperture is demonstrated through measurement of the photoluminescence image of single quantum dots. In the range of 50-100nm spatial resolution, the aperture-type NOM is an established and reliable technique for the spectroscopy of highly localized structures: spatially resolved spectroscopy of the surface of semiconductor materials or spectroscopic analysis of single particles, such as single molecules, single quantum dots, single metal particles, and so on. The scattering-type NOM, on the other hand, is a promising device to be applied to the surface enhanced spectroscopy, nano-manufacturing, and high density optical memory with higher spatial accuracy and higher efficiency.

Near field optics and its application to optical memory

This paper explains the principle of near field optics and lists the problem of high density optical memory for which a storage density of 1 Tbit/inch2 is expected as an application. Furthermore, the possibility of tracking avoidance is introduced in storage and read out, especially the latter, by using a planar probe array. The present status of probe array fabrication discussed. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(8): 41–48, 1998

Persistent high density spectral holeburning in CaS:Eu and CaS:Eu,Sm phosphors

Persistent spectral hole-burning has been reported for singly, Eu-doped, and doubly, Eu- and Sm-doped, CaS phosphors. Efficient photon gated holeburning in the 4f7 (8S7/2)−4f65d1 transition of Eu2+ is a result of photoionization of Eu2+ to Eu3+. These holes have a width of <5 GHz (2 K), survive thermal cycling of the phosphor up to the room temperature, 300 K, and have no detectable deterioration over more than a day of storage time at low temperature (2 K). Although self-gated holeburning is observed with the reading laser at higher powers, the photon budget for reading these holes is so small that in excess of 1000 reading cycles can be performed without destroying the optical signal. The nature of holes burned by photon-gating is found to be very different from the self-gated holes. The characteristics for the holeburning are the same in singly and doubly doped phosphors, suggesting that under the conditions of our experiments, Sm traps do not play any significant role in spectral holeburning. Possibilities of high density optical memory storage using photon-gated holeburning in this THz broad transition are discussed.

Photochromism and Its Application to a High-density Optical Memory

In order to solve problems of photochromic memory, a super-low power readout method and a crosstalk reduction method for multi-wavelength recording were proposed. In the demonstration of 2-wavelength recording using photochromic diarylethenes, the crosstalk between multiplexed channels, which is caused from broad absorption bands of compounds, was effectively reduced by the method. A new high density optical memory, a super-resolution disk with a photochromic mask layer, was also introduced. The super-resolution method has enabled us to increase the recording density of conventional optical disks.

パルスレーザー堆積法により作製したＺｎＯ系光記録膜（ＩＩ）

The 100200 nm-thick ZnO : M (M=Ga2O3, In2O3, Al2O3, Ag2O, CuO and SnO2) films in which droplet formation was suppressed have been deposited on glass substrates at room temperature by a pulsed laser deposition technique using SHG of Nd : YAG laser (λ= 532 nm). Transmittance in the as-deposited state of ZnO : Ga2O3 (2 wt%) film was the smallest among all the ZnO : M films : the film was colored with dark brown. When the films were annealed at 390°C for 50 min, the transmittance of the films increased markedly. The difference in the transmittance between the as-deposited state and the annealed state ΔT was 76% at the wavelength of 400 nm. It was found that maximal transmittance difference ΔTmax was 91% at the wavelength of 472 nm. From XRD spectra, the coloring phenomenon was explained from the fact that the Zn (100) and Zn (101) peaks were present in the as-deposited state and absent in the annealed state, and ZnO peaks such as (200), (101) and (100) were present in the annealed state and absent in the as-deposited state. It is thought that the ZnO doped with Ga2O3 films are useful as a high density optical memory due to the short wavelength (400 nm) of the next generation.

Topical Papers on Applications of Lasers to Memory. Short-Wavelength Semiconductor Lasers for Optical Memory.

Development of short-wavelength semiconductor lasers had made a large contribution to the realization of high density optical memories. For example, InGaAlP red lasers have been used as light sources for high capacity optical disc systems (DVD). The next-generation, high definition DVDs will require a furthershortning of laser oscillation wavelength into the blue-light region. This paper reviews recent developments in short-wavelength semiconductor lasers and describes some of the device characteristics related to the optical memory applications.

Polymeric Thin Films for Electro-Optic Modulator and High Density Optical Memory Applications

AbstractChromophores capable of undergoing conformational changes when exposed to ultraviolet or visible light have been synthesized with functional groups permitting attachment to polymer matrices. One class of such chromophores, containing reactive functionalities at both ends of the chromophore, are referred to as double-end crosslinkable (DEC) chromophores. These chromophores are used in the synthesis of hardened nonlinear optically active lattices and in the fabrication of buried channel nonlinear optical waveguides by photoprocessing; development of such waveguides represents a critical step in the production of polymeric electro-optic modulators. Such chromophores are also crucial to the phenomena of laser-assisted poling (also known as photochemically-induced poling). Finally, these chromophores are attached to the surface of polystyrene beads permitting the realization of room temperature spectral hole burning exploiting morphology-dependent resonances. Such resonances provide the basis of wavelength coding for the development of high density optical memories.

有機非線形光学結晶の精密研削

The laser diode has been widely used in optical memories and measurements. The laser diode having shorter wavelength is requested for achieving high density optical memories and precision measurements. The second-harmonic-generation (SHG) technology by using nonlinear optical crystals is suitable for getting short wavelength laser. The organic nonlinear optical crystals show the higher second-order-nonlinearity in comparison with conventional inorganic nonlinear crystals. However, the former crystals are very soft and very brittle, so that it is difficult to get optical surfaces by conventional polishing technology. This paper deals with the precision grinding of nonlinear optical crystal of chalcone using the ultra-precision surface grinder and also a new grinding technique named the sandwich grinding method which grinds a soft material with another material having higher grinding resistance at the same time. The ground surface of 16nm Rmax in surface roughness has been generated by the sandwich grinding method.

Surface-enhanced Raman optical data storage: A new optical memory with three-dimensional data storage

A new optical data storage technology based on the surface-enhanced Raman scattering (SERS) effect has been developed for high-density optical memory and three-dimensional data storage. With the surface-enhanced Raman optical data storage (SERODS) technology, the molecular interactions between the optical layer molecules and the substrate are modified by the writing laser, changing their SERS properties, so that they are encoded to store information as bits. Since the SERS properties are extremely sensitive to molecular microenvironments, very small ‘‘spectrochemical holes’’ approaching the diffraction limit can be produced for the writing process. The SERODS device uses a reading laser to induce the SERS emission of molecules on the disk and a photometric detector tuned to the frequency of the Raman spectrum to retrieve the stored information. The results illustrate that SERODS is capable of three-dimensional data storage.

Multiple Optical Memory using Photochromic Spiropyran Aggregates

Abstract Multiple recording technology is particularly important for the high density optical memory. Through investigating the aggregate—forming ability of the new photochromic spiropyrans, we have developed five novel spiropyrans, the aggregates of which have sharp absorption bands at different wavelengths. We have fabricated a recording medium stacked with the five kinds of aggregate layers and confirmed ten multiple optical recording characteristics by combining the five multiple frequency recording with the recording by two mutually perpendicular linear—polarized lights.