This paper presents theoretical and experimental results for wavelength-multiplexed holographic recording. Analytical formula for calculating diffraction efficiency is derived by modified coupled-wave equations. Recording medium characteristics and recording conditions for high diffraction efficiency are clarified by the formula. Crosstalk between hologram pages is also calculated by the formula. Experimental data agree well with the theoretical results. In addition, Two-dimensional character images were recorded in SBN single crystal using a tunable LD, and successfully reconstructed with our experimental system. The theoretical results predict that a few hundred multiplexed holograms can be recorded with little crosstalk using the proposed system. This multiplexed holographic recording technique will enable high data-transfer rates and high-density recording

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We found that in weakly-coupled giant magnetoresistive (GMR) sandwich the small-field response's slope is dependent on its past magnetic history. Based on this storage mechanism, we designed a μ binary solid state memory element. Simulation results show that it operates on the general principle of storing a biary digit in hard component and sensing nondestructively its remanent state by switching the soft component in such a way that the magnetic state of the hard component unaltered and thereby causing a dramatic GMR polar readout. So far one-bit experimental apparatus has been realized.

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A computer simulation of recording magnetization in metal evaporated tapes was carried out, and a difference of magnetization between surface region and bulk region of the tapes was obtained. This phenomenon cannot be explained by the conventional theory determining magnetization at the trailing edge of ring heads. A new magnetization model determining magnetization at the leading edge of ring heads was established. This model proved to be effective, since recording experiment results using some ring heads show that the recording magnetization was determined at the leading edge of the heads.

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The recording performance in terms of signal-to-noise ratio can be effectively improved by equalizing the inter-track orthogonal coding for a new coding method which has been recently proposed to remove inter-track interference. When PR4 is used, low bit error rate is obtained at high linear densities. On the other hand, when integrated equalization is used, much larger signal-to-noise ratio is obtained than that in conventional NRZ coding. Furthermore, we showed that besides the code sequences of Hadamard matrix, nearly orthogonal code sequences are also capable to remove inter-track interference. Code expansion for more channels is also described.

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PRML (Partial Response Maximum-Likelihood) systems which attract much attention as an efficient signal processing method in high-density digital magnetic recording are obtained by utilizing an ISI canceller. And the bit-error rate performance is evaluated by computer simulation. The required SNR at the reading point to achieve a given bit-error rate is compared with conventional PRML systems. The results show that our system exhibits a good performance.

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Nonlinear distortion in digital magnetic recording increases with the increase of linear recording density, which causes the degradation of signal-to-noise ratio (SNR) performance. The relationship between nonlinear bit shift and normalized linear density is obtained and a nonlinear channel model based on this relationship is given. The nonlinear equalization of PR4 partial response channel using a three-layered feedforward neural network is assumed and the equalization and SNR performances are obtained by computer simulation based on the nonlinear channel model. They are compared with that of conventional Nyquist equalization. The result shows that the neural network equalizer attains large improvement in SNR. The partial response maximum-likelihood (PRML) system with a neural network equalizer is also studied.

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