Chikara Egami

Reflection-type confocal readout for multilayered optical memory

We present a multilayered optical memory for use in reading data with a confocal reflection microscope system. We use a recording medium in which photosensitive thin films and nonphotosensitive transparent films are stacked alternately. Since the photosensitive films are thinner than the depth of focus of the recording beam, the spatial frequency distribution of the recorded bit data is extended in the axial direction. The extended distribution overlaps the coherent optical transfer function of the reflection-type confocal microscope. Urethane-urea copolymer film is used as a photosensitive material. The recording and reading of two layers are demonstrated.

Non-optically probing near-field microscopy

We present a near-field optical microscope without the use of a probe for illumination or detection or scattering of the optical fields. In our system the optical fields near specimens are converted to the topographical change of a photosensitive film, and then the topography is detected with an atomic force microscope. Urethane-urea copolymer films are used for the conversion material from the optical fields to the topography. We succeeded in imaging with a resolution higher than 50 nm.

Three-dimensional patterned media for ultrahigh-density optical memory

We report a recording medium in which a three-dimensional nanoscale structure can be photofabricated for multilayered optical memory using a two-photon process. By fabricating the structures in the medium, we can control the shape of recorded bits and, in effect, their spatial frequency distribution. We succeeded in recording bits with a 0.5μm interval in any particular plane and 2.0μm interval between successive layers. Thus, storage density of 2.0Tbits∕cm3 is achieved.

Evanescent-wave spectroscopic fiber optic pH sensor

We demonstrate a new type of fiber optic pH sensor, which is the application of evanescent-wave spectroscopic technique. A methyl red (MR)-doped-poly(methyl methacrylate) (PMMA) film that coated as part of cladding does function as a pH sensor probe. In this system MR doped in PMMA is used as indicator dye for pH measurement. The absorption spectrum shift in wavelength of indicator dye enables us to get the pH value. The sensor probe is immersed in water solution containing a small proportion of acetic acid over the wide pH range of 5.0 to 7.0. The chemical interaction between MR in sensor probe and hydrogen ion in the water solution causes a change in the dipole moment of MR, that is, the absorption spectrum macroscopically. The evanescent-wave spectroscopic technique provides the measurement of the absorption spectrum shift over a broad range of visible wavelength. The result of experiment was that MR absorption spectrum shifted by 40 nm every increase of 1.0 in pH. The small change in the pH value can be sensed as a large wavelength shift of pH indicator absorption spectrum.

Two-Stage Optical Data Storage in Azo Polymers

We have demonstrated two-stage optical memory in a photoaddressable azo polymer. The polymer serves as a data storage medium with two recording mechanisms: photoanisotropic modulation and surface-shape modulation. We can select the recording mechanism by manipulating beam energies for recording. The characteristics can be motivated to rewritable and write-once optical memories: polarization-multiplex bit memories, surface-modulated bit memories and surface-modulated holographic memories.

Polarization-multiplexed optical memory with urethane-urea copolymers.

We present a polarization-multiplexed optical memory with urethane-urea copolymers. The side chains of the urethane-urea copolymers induce cis-trans isomerization by illumination of blue or green light, and they align perpendicular to the linear polarization of the illuminated light, thus producing optical anisotropy. We found that the material showed selective anisotropy for the particular direction that was perpendicular to that of the recording beam polarization. By use of the anisotropic property three different data pages were multiplexed at the same spot of the medium. Erasure of the recorded bit data is also demonstrated.

Wide Range pH Fiber Sensor with Congo-Red- and Methyl-Red-Doped Poly (Methyl Methacrylate) Cladding

We introduce an evanescent-wave-spectroscopic fiber optic pH sensor. This sensor has part of the polymer cladding doped with either congo red (CR), which responds to pH=3 to 5, or methyl red (MR), which responds to pH=5 to 7, as the pH sensor film. In this study we succeeded in expanding the measurable pH range by using two pH sensor probes with the different pH sensitivities. In addition making the pH fiber sensor into a probe structure enabled us to achieve high pH sensitivity and to monitor the pH value easily. Reducing the quantity of doped dye made it possible to use the sensor for objects highly sensitive to pH chemical equilibrium.

Phase conjugation in methyl-orange-doped PVA films by photoinduced anisotropy

The influence of photoinduced anisotropy (dichroism and birefringence) in methyl-orange-doped polyvinyl alcohol film upon optical phase conjugation is investigated. The reflectivity of the phase-conjugate (PC) beam due to degenerate four-wave mixing (DFWM) is measured under the condition that the polarization states of a probe and two pump beams are mutually orthogonal. The more efficient PC beam generates at 515 nm rather than at 488 nm. At 515 nm, the reflectivity of the PC beam exceeds 10 percent about 30 minutes after the initiation of DFWM. It was found that birefringence rather than dichroism contributes to the generation of the PC beam at 515 nm.

High-resolution optical storage by use of minute spheres

We have developed a new optical storage system that uses minute spheres arranged upon a surface-relief grating. By using dye-doped minute spheres as recording bits we can limit a sensitive region within a spheres diameter. Using a reflection-type confocal optical system, we read out shape signals from minute spheres at high resolution. The shape signals from minute spheres are utilized as clock signals in recording and readout.

Two-way optical memory for azobenzene-containing urethane–urea copolymer films

Abstract An azobenzene-containing urethane–urea copolymer as a photochromic material has two optical properties for data storage. One is photoisomerization related to the polarization of incident beam. The other is photoablation related to the intensity of incident beam. It seemed that we could separate them with the power or wavelength of the recording beam. Therefore, we studied the characteristics of the phenomena and found that the selective use of the effects is applicable to some types of memory.