Takuma Yanagisawa

Multilayer 500 Gbyte Optical Disk

To confirm the feasibility of realizing subterabyte or terabyte optical memories, we evaluated a multilayer read-only disk having 20 information layers. We propose a new disk structure, which is an alternative structure to reduce interlayer crosstalk, optimized by computer simulations. We fabricated multilayer read-only optical disks using a conventional manufacturing process for Blu-ray disk (BD) dual-layer media. Moreover, we improved the reproduction system to compensate for the large spherical aberration. From the experimental results, we obtained sufficiently low jitter values reproduced from a 20-layer disk. We confirmed the feasibility of the multilayer read-only disk with a capacity of 500 Gbytes.

Signal Simulation of 25 Gbytes Read-Only Optical Disk System using a High Numerical Aperture Objective Lens

We have already developed and reported the high-definition digital-versatile-disk read-only-memory system of capacity 15 Gbytes using a blue laser and new signal processing technique. On the other hand, a high numerical-aperture system has been reported of numerical-aperture 0.85 and cover layer thickness 0.1 mm. In this paper, we examined the increase in capacity on application of our signal processing technique to the high numerical-aperture system using computer simulation. As a result, we found that a 25 Gbytes read-only-memory disk system had sufficient system margins on applying the limit equalizer and the adaptive tangential equalizer. Furthermore, if the crosstalk canceler is applied, we may achieve a system of capacity larger than 25 Gbytes.

Superresolution in optical disk systems with a non-linear refractive layer

We derived the optical transfer function in scanning optical microscopy which has the same properties as optical disk read-out systems, in the case where we observed an object coated with a non-linear refractive layer whose amplitude transmissivity depends on the incident light intensity, and showed that this cutoff frequency is higher than that of the case where we observed the object without the aid of a non-linear refractive layer.

Jitter Analysis for Land/Groove Phase Change Disk

A 22 GB optical video recording system with an objective lens of high numerical aperture (NA), a blue laser and a thin cover layer is proposed. We classify the jitter which increased by aberrations into three components for this system. We analyze the dependence of jitter components on the groove depth in detail. Furthermore, we confirm advantages of the limit equalizer (Limit-EQ) and the two-dimensional adaptive equalizer for the land/groove (L/G) phase change disk.

Analysis of prediction level setting in PRML decoding on Blu-ray disc system

In the application of the PRML decoding to the optical disk system, an asymmetry of a reproduced signal deteriorates the decoding performance. We investigated the relation of the prediction level setting and the PRML decoding performance. When the average level of the input signal was adjusted to the center of the prediction level, the margins was deteriorated little, even if there is a signal asymmetry. We found that the PRML decoding has a good tolerance to the signal asymmetry by using a simple circuit structure.

Cross-talk Canceller for Wobbling Signal

We have developed a cross-talk canceller for a wobbling signal (WCTC). The WCTC cancels cross-talk in the wobbling signal using three push-pull signals reproduced from three adjacent tracks. Furthermore, push-pull tracking offset, caused by a shift of an objective lens, is detected from a balance between cross-talk from an inner track and that from an outer track. It is experimentally confirmed that the WCTC effectively reduces cross-talk and can detect the tracking offset.

Analysis of the Crosstalk in a High-Density Optical Disc System

A crosstalk canceler has been proposed in order to readout a signal from a high-density optical disc. We have confirmed by the computer simulations that a crosstalk canceler is highly useful technology. Furthermore, we have calculated the readout margins of the high-density optical disk system applying a blue laser, a crosstalk canceler and some other signal processing methods.