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.

In order to reduce the pantograph noise that greatly contributes to overall noise, we have developed two types of low-noise pantograph. Further noise reduction was realized by the effects of attenuation of the pantograph noise insulation plate and by using only one pantograph per trainset. A multi-segment slider was also developed to increase the performance of following the overhead contact wire, which is imperative when running with only one pantograph per trainset. These countermeasures for pantograph noise have been installed on FASTECH 360 (high-speed test trains of East Japan Railway Company). The results measured by use of a microphone array show that the pantograph peak noise level is reduced by more than 2 dB compared to that of the series E2 trains now in operation.

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 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.

No abstract