Taku Hoshizawa

1 Tbit/inch2 Recording in Angular-Multiplexing Holographic Memory with Constant Signal-to-Scatter Ratio Schedule

We developed an iterative method for optimizing the exposure schedule to obtain a constant signal-to-scatter ratio (SSR) to accommodate various recording conditions and achieve high-density recording. 192 binary images were recorded in the same location of a medium in approximately 300×300 µm2 using an experimental system embedded with a blue laser diode with a 405 nm wavelength and an objective lens with a 0.85 numerical aperture. The recording density of this multiplexing corresponds to 1 Tbit/in.2. The recording exposure time was optimized through the iteration of a three-step sequence consisting of total reproduced intensity measurement, target signal calculation, and recording energy density calculation. The SSR of pages recorded with this method was almost constant throughout the entire range of the reference beam angle. The signal-to-noise ratio of the sampled pages was over 2.9 dB, which is higher than the reproducible limit of 1.5 dB in our experimental system.

Terabyte holographic recording with monocular architecture

A Monocular architecture and high M/# media were developed for 1 TB holographic data storage system. The recording density of the high M/# media was verified in our experimental system. As the result, the recording density of 1 Tbits/inch2 which has possibility of realizing 1 TB disk was achieved.

Practical angular-multiplexing holographic data storage system with 2 terabyte capacity and 1 gigabit transfer rate

Aiming at the realization of an optical data storage system with a large disc capacity and a high transfer rate suitable for digital data archiving, we have defined the specifications of an angular-multiplexing holographic data storage system with a disc capacity of 2 TB and a transfer rate of 1 Gbps on the basis of a run-length-limited (RLL) high-density recording method using RLL modulation. To realize the specifications, RLL turbo coding, a servo system for the reference beam angle, and a servo system for book tracking were newly invented. Also, to satisfy the specifications, a holographic disc and several key components were developed in cooperation with several specialty companies. Eventually, we confirmed a high-density recording of 2.4 Tbit/in.2 achieved by the RLL high-density recording method, using evaluation equipment complying with the specifications for single book recording.

High-Density Recording Method with RLL Coding for Holographic Memory System

A high-density recoding method with RLL coding and smaller Fourier plane filter has been developed. With this method, we confirmed a holographic drive system with 667GB capacity feasible.

New optical modeling and optical compensation for mechanical instabilities on holographic data storage system using time averaged holography

Mechanical instabilities during recording and involved degradation of signal quality in high density and high data transfer rate holographic data storage system (HDSS) is one of the obstacles to prevent the technology from being a stable system. We analytically formulated effects of mechanical instabilities of a Galvano mirror and spindle motor on the HDSS by incorporating the concept of a time-averaged holography. Mechanical parameters such as amplitude and frequency of mechanical oscillation are related to optical parameters such as amplitude and phase of reference and signal beams. Especially, the analytical formulation led to a new method of optical and post compensation for mechanical instability during recording hologram. The optical post compensation method enables a robust implementation of HDSS against mechanical instabilities.

Region-Divided Adaptive Equalization for Holographic Memory

Holographic memory channels suffer from disturbances. We revealed inter-pixel interferences vary even in the same page by the disturbances. Using the newly developed region divided adaptive equalization, we can improve SNR by 3.5 dB.

Blu-ray Disc 6x read/write control LSI with an adaptive PRML detector

A 6times-speed BD and all DVD/CD read/write control LSI has been developed. It contains a PRML detector that adopts an adaptive equalizer and an adaptive Viterbi decoder to improve playback performance. As a result of BER measurements, a large margin sufficient for playing back 6times BD was obtained.

Random seed scrambling method for high density phase change optical discs

Repeatedly rewriting the same channel bit pattern at the same location on a phase-change optical disc usually causes the media to deteriorate. To prevent this, the random bit shift of 128-bit and the free polarity of NRZI-converted pulses were introduced into the DVD-RAM system. However, these measures cause difficulty in the timing control at writing starts and. complication of the control of circuits. So in this paper, a new scrambling method, the Random Seed Scrambling Method is proposed. In this method, the data is scrambled using a different seed each time the data is written, so the different data is over-written at the location each time. The method of random seed scrambling has a unique characteristic that the seed is not necessary to de-scramble the scrambled data. By using this method, the amount of the high density phase-change optical disc wear is reduced.

Adaptive signal processing method using PRML for high density optical disks

Numerous types of DVD recording equipment have emerged on the market, and there is much demand for such optical storage systems with high speed and large capacity for digital high definition broadcasts. However, it becomes difficult to maintain data reliability with increasing recording speed and density, because the signal to noise ratio degrades and recording control of the phase changed mark becomes difficult. To improve the error rate of reproduced data, PRML (partial response maximum likelihood) decoding is expected to be used. We have developed a more advanced method of PRML, where the difference of the reproduced waveform is analyzed and the PRML decoder is compensated. In this paper we report the analysis of the reproduced waveform and the effect of the developed PRML algorithm.

Lensless light-field imaging with multi-phased fresnel zone aperture

We have been proposing lensless light-field imaging with Fresnel zone aperture (FZA) in front of an image sensor in a few millimeter spacing. Synthesized shadows of real FZA with the incident light generate moiré fringes interfering with another virtual FZA in a computer and result in reconstructed images by simple Fast Fourier Transformation (FFT). In order to obtain clear images in this configuration, it is necessary to cancel several kinds of noise component in the detected image signals. We describe details of the process and discuss its effectiveness theoretically and experimentally in this paper.