Seiichi Ohsawa

The Path from a Digital Versatile Disc (DVD) using a Red Laser to a DVD using a Blue Laser

The next generation digital versatile disc(DVD) using a blue laser is required to have 15 Gbytes capacity so that it can reproduce motion picture expert group 2(MPEG2) video stream with a main profile at a high level format for a maximum of 133 min. To achieve this goal, further improvements are necessary in both the recording and the reproducing systems. For the recording system the authors developed a super resolution recording material and an electron beam recording system. For the reproducing system the authors devised four technologies: a Viterbi decoder, a liquid crystal tilt servo system, a cross talk cancel system and a tangential adaptive equalizer. By combining these with a pick up head of 430 nm vavelength/0.6 NA lens and a 0.6-mm-thick substrate, the authors confirmed sufficient tilt margins in the case of 12.7 Gbytes (radial tilt margin: ±1.61°, tangential tilt margin: ±0.48°). Our next target is to work on the 15 Gbytes capacity.

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.

Application of the Sliding-Mode Controller to Optical Disk Drives

The Blu-ray Disc system is considered to be the next-generation optical disk system following the digital versatile disc system. The system has a high numerical aperture and a narrow track, so improved performance is needed for the servo system. A conventional pickup control based on a linear servo system is limited in the improvement of the servo performance. We have investigated a new approach to realizing high accuracy, high speed, and high robustness. One of the new servo systems is the sliding mode controller. We applied the sliding mode controller to the optical disk drive, and we proposed an effective utilization of it. We experimentally confirmed that the sliding mode controller had sufficient playability, which means trace accuracy, accessability, and defect resistance. The sliding mode controller is a promising system for realizing further playability of the high-density optical disk system.

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.

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.