Three-dimensional Optical Data Storage Research Articles

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.

Singlebeam two-photon three-dimensional optical storage in a pyrryl-substituted fulgide photochromic material

We introduce a high-density three-dimensional optical data storage approach by using a pyrryl-substituted fulgide photochromic material with a method of single-beam two-photon recording and fluorescence confocal readout. The detailed information about the photochromic material and the experimental setup are presented. The experiments about multi-layered recording and readout are carried out with a 100-μm-thick transparent photochromic material film. The results show that the lateral resolution is better than 1 μm, and the longitudinal resolution is about 3 μm. Besides, the readout times for the recorded data are desirable when using a readout laser power smaller than 5 mW.

Three-dimensional optical data storage using three-dimensional optics

Three-dimensional optical memory with photorefractive mate- rials is discussed for ultra-high density/capacity memory exceeding the classical limit of a conventional optical recording system. Bit data are recorded as highly localized refractive index variations in three- dimensional volume using a focused laser beam. We show recording and reading results using a multilayered recording medium with a pho- toisomerization polymer and transparent films. Two-photon recording is also demonstrated. We also discuss the spherical aberration corrections using a volume holographic device, and compact confocal configuration using a semiconductor laser. © 2001 Society of Photo-Optical Instrumentation En- gineers. (DOI: 10.1117/1.1402123)

Effect of saturable response to two-photon absorption on the readout signal level of three-dimensional bit optical data storage in a photochromic polymer

We observe a saturable change in the refractive index induced by two-photon absorption in a photochromic polymer, while the erasable nature of the polymer is maintained. As a result, the support region of spatial frequencies of the recorded data bits caused by the refractive index change in the polymer is enlarged. This feature leads to the significant enhancement of the signal level in a reflection confocal microscope readout system for three-dimensional photochromic bit optical data storage.

Rewritable 3D Bit Optical Data Storage in a PMMA-Based Photorefractive Polymer

3D bit optical data storage has the ability to reach Tbytes on a recording medium no larger than a compact disc using two-photon excitation and multi-layer recording. The introduction of a poly-vinyl carbazole (PVK) based photorefractive polymer as the recording material allows the system to rewrite the recorded information via the photorefractive effect.[1,2] In this paper, we demonstrate the use of continuous wave illumination for three-dimensional (3D) bit optical data storage under two-photon excitation in a new poly(methylmethacrylate)-based (PMMA) photorefractive polymer. This achievement makes it possible to develop a cheap, compact, sub Tbyte rewritable optical data storage system to further extend the capabilities of compact disc and digital versatile disc technology.

Nondestructive readout of photochromic optical memory using photocurrent detection

We proposed and demonstrated a nondestructive readout method using photocurrent detection for photon-mode photochromic memory. The principle of this readout method, which utilized the ionization potential change according to photoisomerzation reaction, was confirmed by using a medium with a photochromic diarylethene layer and phthalocyanine photoabsorbing layer, and by using a near-infrared readout light. We demonstrated perfect nondestructive readout operations over 106 times.

Feasibility of Femtosecond Laser Writing Multi-Layered BitPlanes in Fused Silica for Three-Dimensional Optical Data Storage

The ultrashort pulse laser writing multi-layered data bits in fusedsilica for three-dimensional optical data storage through the mechanismof optical damage induced by multi-photon absorption is demonstrated.The 800 nm, 120 fs Ti:Sapphire laser beam is focused intocubic samples with a 0.65 NA commercial microscope objective. The sizeof the recorded bits can be smaller than 0.5×0.5×2.5 µmas the laser pulse energy is lower than 300 nJ and thecorresponding bit data storage density is 0.2×1012 Tbits/cm3. Due to the aberration produced by themismatch of the refractive indices between the recording material andits immersion medium, the longitudinal size of the recorded bitincreases and the contrast of the bit to the surrounding uninfected zonedecreases asthe bit plane gets deeper. Hence, a relatively lower storage density of0.05×1012 Tbits/cm3 is realized.

Optical Memory Effect by Interference of Multiple-Scattered Light in a Fluorescent Fulgide Derivative

We report an observation of a new wavelength- and angle-selective optical memory effect caused by interference of multiple-scattered light in polystyrene powder doped with a fluorescent fulgide derivative. This effect is applicable to three-dimensional optical data storage.

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.

Three-Dimensional Optical Data Storage Using Photochromic Materials.

Three-Dimensional Optical Data Storage Using Photochromic Materials.

Three-dimensional optical data storage in a fluorescent dye-doped photopolymer

We propose a new, to our knowledge, monolithic multilayer optical storage medium in which data may be stored through the diffusional redistribution of fluorescent molecules within a polymer host. The active portion of the medium consists of a photopolymer doped with a fluorescent dye that is polymerized at the focal point of a high-numerical-aperture lens. We believe that as fluorescent molecules bond to the polymer matrix they become more highly concentrated in the polymerized regions, resulting in the modulated data pattern. Since data readout is based on detection of fluorescence rather than index modulation as in other photopolymer-based memories, the problems of media shrinkage and optical scatter are of less concern. An intensity threshold observed in the recording response of this material due to the presence of inhibitor molecules in the photopolymer allows for the three-dimensional confinement of recorded bits and therefore multilayer recording. The nonlinear recording characteristics of this material were investigated through a simple model of photopolymerization and diffusion and verified experimentally. Both single-layer and multilayer recordings were demonstrated.

Lack of association between volumetric hippocampal measurements and episodic memory in schizophrenia but not in healthy controls

Lack of association between volumetric hippocampal measurements and episodic memory in schizophrenia but not in healthy controls

Biomolecular Electronics: Protein-Based Associative Processors and Volumetric Memories

The promise of new architectures and more cost-effective miniaturization has prompted interest in molecular and biomolecular electronics. Bioelectronics offers valuable near-term potential, because evolution and natural selection have optimized many biological molecules to perform tasks that are required for device applications. The light-transducing protein bacteriorhodopsin provides not only an efficient photonic material, but also a versatile template for device creation and optimization via both chemical modification and genetic engineering. We examine here the use of this protein as the active component in holographic associative memories as well as branched-photocycle three-dimensional optical memories. The associative memory is based on a Fourier transform optical loop and utilizes the real-time holographic properties of the protein thin films. The three-dimensional memory utilizes an unusual branching reaction that creates a long-lived photoproduct. By using a sequential multiphoton process, parallel write, read, and erase processes can be carried out without disturbing data outside of the doubly irradiated volume elements. The methods and procedures of prototyping these bioelectronic devices are discussed. We also examine current efforts to optimize the protein memory medium by using chemical and genetic methods.

Theoretical study of signal-to-noise ratio on near-field photochromic memory with fluorescence readout

The signal-to-noise ratio (SNR) on the fluorescence readout of a near-field photochromic memory was theoretically studied. Under various conditions the shot-noise-limited SNR was analyzed. SNR by bright spot recording (BSR) that was better than that by dark spot recording (DSR) was obtained under the condition of low writing power or wide bandwidth. Under the condition of bandwidth W = 1 MHz and P(write) = 10(-8) W only BSR can attain sufficiently high SNR, and the SNR was greater by as much as 30 dB than that of DSR. It was concluded that BSR is a promising method for high-density near-field photochromic memory with a fluorescence readout.

Use of two-photon excitation for erasable–rewritable three-dimensional bit optical data storage in a photorefractive polymer

We report what is believed to be the first use of a photorefractive polymer in erasable-rewritable three-dimensional bit optical data storage under two-photon excitation. We successfully demonstrate writing, erasing, and rewriting of multilayered information in a photorefractive polymer consisting of 2,5-dimethyl-4-(p-nitrophenylazo)anisole, 2,4,7-trinitro-9-fluorenone, 9-ethylcarbazole, and poly(N-vinylcarbazole). A three-dimensional bit density of 5 Gbits/cm(3) is achieved by two-photon absorption under pulsed beam illumination at an infrared wavelength of 800 nm in the recording process. Complete erasing of the recording information is achieved by use of ultraviolet illumination.

Theoretical Study on Data Transfer Rate of Near-Field Photochromic Memory

The data transfer rate of near-field photochromic memory was theoretically studied. The data transfer rate for the medium with the sensitivity εB=104 and φBA=0.1 in the recording process was about 1 kilo bps (bits per second) at the light power density of 102 W/cm2, but it increased to over 1 Mbps at 105 W/cm2. Fluorescence and reflectance detection readout methods of a near-field photochromic optical memory were also theoretically studied. The data transfer rate at the light power of 10-6 W in the readout process was around 1–10 Mbps. When the average reflectance is high, there is a benefit of using a fluorescence detection method for obtaining a high data transfer rate.

Use of continuous-wave illumination for two-photon three-dimensional optical bit data storage in a photobleaching polymer

We show that a continuous-wave laser beam at an infrared wavelength of 800 nm can be used for two-photon three-dimensional bit data storage in a photobleaching polymer. We successfully demonstrate recording and reading of six layers of data bits with a transverse bit separation of 4.3microm and an axial layer separation of 20microm . This result leads to a three-dimensional bit density of approximately 3Gbits/cm(3) .

High-density three-dimensional optical data storage in a stacked compact disk format with two-photon writing and single photon readout

Using a polymer block doped with a highly efficient two-photon dye, we have achieved a high density data storage with gray-scale control in multiple planes as stacked compact disks at a separation of 10 μm. The absorption and fluorescence of the dye at the written spot shift to a longer wavelength, permitting an easy fluorescence mode readout with a linear excitation using an inexpensive laser source. The storage capacity in this case is estimated to be 1012 bits/cm3.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging1, optical data storage2,3 and lithographic microfabrication4,5,6. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures7.

Confocal readout of three-dimensional data bits recorded by the photorefractive effect under single-photon and two-photon excitation

In three-dimensional optical bit data storage, data bits can be recorded as a result of the change in refractive index in photorefractive and photochromic materials under single-photon and two-photon excitation by a high numerical-aperture objective. In principle, these recorded data bits can be read out using reflection confocal microscopy because such a microscope exhibits an optical sectioning property for three-dimensional imaging. In this article, the conditions are described under which three-dimensional data bits recorded by the photorefractive effect under single-photon and two-photon excitation in these materials can be read in reflection confocal microscopy. The effect of the refractive-index mismatch between a volume recording medium and its immersion medium on these conditions is also considered.