Masaaki Hara

Improved performance in coaxial holographic data recording

We describe a coaxial holographic recording system for achieving high recording density. We implement several techniques, such as an objective lens with high numerical aperture (NA), high capacity page data format, a random binary phase mask, and an optical noise reduction element. Our system successfully realizes a hologram recording/retrieving at a low diffraction efficiency less than 2.0 x 10(-3) and achieves a raw data density of 180 Gbit/in.(2), thus demonstrating the potential of a coaxial holographic system for high-density optical storage systems.

415 Gbit/in. 2 recording in coaxial holographic storage using low-density parity-check codes

We have applied LDPC codes into our coaxial recording system, and revealed its fundamental characteristics. In addition, by applying the E(16, 3, 8) code and optimizing optical conditions, we have successfully improved the recording density, achieving the raw data density of 415 Gbit/in.2.

Novel encryption method using multi reference patterns in coaxial holographic data storage

In this paper, we propose an encryption method, in which a multi reference pattern is used in coaxial holographic data storage. The signal data patterns are multiplexed at one spot with multi reference patterns, which are the key code for secure readout. This method is easy to implement in coaxial holographic storage drives, and provides higher security against unauthorized readout and copying of the hologram disk. We experimentally demonstrate the encryption and decryption process with the proper and improper keys. Next, we analyze the degree of security provided by this method, and demonstrate a method of increasing the security further by recording more than 10 holograms at one spot. Finally, we record multiplexed holograms to reach 50 and 100 Gbit/in.2 with this encryption method, and analyze the degradation of the error rate.

Linear Reproduction of a Holographic Storage Channel using Coherent Addition of Optical DC Components

A holographic data storage channel is normally a nonlinear channel; however, it can be made linear. Using coherent addition of DC components in the reproduction process and calculating the square root of intensity, we can retrieve a linearly reproduced signal. Our simulation results revealed that a conventional equalizer works well to suppress interpixel interference so that a higher recording density can be achieved.

High Density Recording of 270 Gbit/in.2 in a Coaxial Holographic Recording System

An improvement of the recording density in a coaxial holographic recording system is described. We employ a new optical setup into our coaxial system, where the numerical aperture (NA) of an objective lens and the data capacity in one page increase up to 0.85 and 135 kbits, respectively. The recording performances are evaluated experimentally and numerically. The obtained results demonstrate that implemented techniques successfully improve the recording density by a factor of 1.5, achieving a raw data density of 270 Gbit/in.2.

A study of the electrostatic potential on MR heads using metal powder tapes

The authors have measured the potential of electrostatic discharge using a commercial VCR drive with metal powder (MP) tapes that are widely used in business. They set up an experimental drive, which has a surface voltage meter and a magneto-resistive read (MR) head with a current-measuring circuit. Using this system, they can measure the surface voltage and current while the tape is running and can investigate how the electrostatic potential from the tape can damage the head. In their assumption that if the media surface voltage is low and current flowing into the head is lower than the sensing current of the head, the MR head can be used in a VCR. It can be not only AMR but may also be giant magnetoresistive and TMR in the future. The results of their experiments show that the peak surface voltage is low and the peak current is only about 3.6 /spl mu/A with a middle-resistance tape. The peak current is lower than the breakdown current since the sensing current is typically 10 mA. Therefore, an MR head can be used with an MP tape. The authors found that the optimum surface resistance of middle-resistance tape is 10/sup 6/ to 10/sup 7//spl middot//spl Omega/sq.

Linear Signal Processing for a Holographic Data Storage Channel Using Coherent Addition

A linear channel model and a linear signal processing technique are available for a holographic data storage channel when our proposed coherent addition technique is applied to the reproduction process. As a result, the signal-to-noise ratio (SNR) after zero-interpixel-interference (IPI) equalization is markedly improved. Moreover, we can achieve a higher transfer rate at a lower oversampling rate owing to the almost ideal linearity of the reproduced signal.

Development of a coaxial-type holographic disk system with a small drive

We have developed a coaxial-type holographic disk system with a small drive. We achieved stable operation without use of a vibration-isolating table, with a 91-Mbps data-transfer rate for recording and retrieving using LDPC code.

High-Speed Data Recording and Retrieving Using the Image-Stabilizing Technique in a Coaxial Holographic Disk System

107 Mbps and 92 Mbps data-transfer rates for recording and retrieving, respectively, have been achieved by improving the coaxial holographic disk system using the IS technique.

Experimental verification of coherent addition technique in coaxial holographic storage

We have experimentally evaluated the coherent addition technique, and revealed that the coherent addition can enhance detected data intensity and realize clear three-level data retrieving. Moreover, we have achieved great improvements in the multiplexed performance, which are the SNR gain of +3.5 dB and the data density increase with the factor of 2. We consider that this technique will strongly contribute to future holographic technologies.