Takayuki Sano

YBCO superconducting coils operated at nitrogen temperature

Trial coils of YBa2Cu3Ox superconductor were prepared from oxide superconducting powder and binder mixtures. The critical temperature of the wire was more than 86 K in the four-probe measurement. Magnetic fields, 21.1 gauss, and 350 gauss were generated by dc operations at 77 K and 4.2 K, respectively. A critical current density in the coil was of 1,330 A/cm2, corresponding to a level of 77 K and zero magnetic field. Experimental results show that an oxide superconducting magnet with an appropriate protection circuit is feasible and stable at liquid nitrogen temperature.

Secure holographic memory by two-wave encryption method with a photorefractive crystal

We propose a new all-optical encryption technique, which is a two-wave encryption method, and discuss security and holographic memory using this technique. Unlike the DRPE method, this technique is characterized by its ability to reduce output intensity for unauthorized memory access, along with the property to output a recorded white-noise image. Thus, the monitoring of output intensity achieves easy detection of unauthorized access. According to our numerical simulation, a particularly significant difference can be found in output intensity, with a correlation coefficient of 20% or under between a key using unauthorized access and a compatible key to find detection sensitivity of unauthorized access. Robustness can be readily improved by increasing key length, and the probability was observed to be 10−6 or under on identifying a randomly generated key with a key length of about 32× 32 for the compatible key, even though the key length is too small. It is shown experimentally that the use of a compatible key reproduced a clear original image, but unauthorized key-based reproduction reduced output strength to approximately 1/20.

Image cross-connector using a photorefractive polymer

We propose an image cross-connector using an organic photorefractive polymer. With this device, it is possible to perform a reconfigurable connection between multiple input–output image ports by setting the incident angle of individual control beams to minute levels. The use of a polymer can reduce the thickness of the index grating to be induced inside the medium, which can also reduce the distortion of the output image and bring about high precise image connection without an additional optical system. We conduct an experiment with a hole-transport polymer PATPD to verify the operations of an image cross-connector, in which different images from a vertical array of input images would be connected separately to two output ports by two control beams that were injected at different angles.

Experiment on selective erasure for multiplexed holograms by using photorefractive phase-shift

We propose a method of the selective erasure for multiplexed holograms by using photorefractive phase-shift. This method realizes the complete selective erasure with simple operation. We conduct an experiment on selective erasure with two LiNbO3:Fe.

Proposal of New Rewritable Printing Media Using Electrophoresis and Confirmation of Its Mechanism

A new rewritable printing media using electrophoresis and selective heating is proposed to contribute to the reduction in paper consumption by printers. The mechanism is that when a heated part of the rewritable media is melted, white particles in that part of the media are able to move by electrophoresis. The media is initialized by heating its entire surface under the condition of voltage application and imaging is carried out by selective heating under the condition of an applied reversed-polarity voltage. Using a mixture system of carnauba wax and particles coated with titanium oxide (TiO2), the feasibility of the mechanism is confirmed.

Security Assessment of Two-Wave Encryption

To determine the degree of security in two-wave encryption under practical conditions, we present a novel numerical technique for simulating the recording and readout of two-wave encryption. The calculation results of the retrieval characteristics show that the diffraction efficiency in an incorrect decryption is 10 times as low as that in correct decryption key and that the output data with an incorrect key is a white noise image. We estimate the necessary key correlation to decrypt an encrypted data is 0.2 when the length of an encryption key is 2313. This means that the decoding probability of the encryption key in two-wave encryption is less than 10-6 even if such a short key is used.

Noise reduction strategy in high-speed replication of holographic memories using photorefractive amplification

We propose a high-speed replication system using photorefractive amplification for holographic memories. Also, we show a noise reduction strategy that enables to ensure a high signal-to-noise ratio of replicated holograms by using a transient gain of photorefractive amplification.

High-Speed Holographic Read-Only Memory Replication Systems with Two-Wave and Four-Wave Photorefractive Amplifier

Copying speed is an important characteristic for optical read-only memory (ROM) replication systems. The copying speed of holographic ROM replication is, however, limited by small energy efficiency of the optical system due to the small diffraction efficiency of multiplexed holograms. In this paper we propose new holographic ROM replication systems with a photorefractive amplifier, and analyze the speed gain performance. We improve energy efficiency significantly and speed up replication by amplifying weak diffraction signal beams using photorefractive wave mixing. Our new theory and numerical calculations revealed that achievable speed gain can be evaluated from only a single dimensionless parameter that is the product of the three as follows: (i) the pump beam intensity ratio in the amplifier, (ii) the ratio of the photopolymer and photorefractive sensitivities, and (iii) the dynamic range per hologram of the copy medium. In current holographic recording systems, a practical copying speed gain of more than 10 is achievable with currently available photorefractive materials.

Selective Erasure for Multiplexed Holograms in Photorefractive Crystal Using Phase Conjugator

A novel selective erasure method for multiplexed holograms in a photorefractive crystal using a phase conjugator is presented. In this method, the π-phase shift effect on the diffracted beam due to the photorefractive effect is used. There is a π-phase shift between the interference pattern formed by the reading and diffraction beams, and that formed in the recording process. By returning the reading and reconstructed beams to a recording medium with a phase conjugator, the hologram can be selectively erased in parallel with the readout. Therefore, a dynamic selective erasure can be realized without requiring the accurate alignment of the selective erasure beams. The calculations using coupled-wave equations and experiment results demonstrate the implementability of our method. Furthermore, we analytically determine the requisite conditions of incident beams in the selective erasure process for the reduction of the decay of other multiplexed holograms.

Selective erasure for multiplexed holograms by using photorefractive phase-shift

In this paper, we propose a method of the selective erasure for multiplexed holograms using photorefractive phase-shift. By using this method, we can achieve the more simple selective erasure system than the conventional one. The multiplexed holograms in the photorefractive crystal can be selectively erased by overwriting with the index grating induced by the /spl pi/-phase shifted reference beam and the object beam identical with that used in the recording process.