Multi-layer recording method has been studied and developed since dual layer disk of DVD-ROM and the studied disk type has expanded from ROM to Rewritable disk. Multi-layer disk has new problems different from a single layer disk. One is an inter-layer cross-talk, which a component of a signal from adjacent layer leaks into a detected signal when the information data is reproduced from a target layer. Second is a recording power fluctuation, which the light power reached a target layer changes by marks on intermediate layers. There were many works that solve this problem. This causes severe problem for signal processing and recording performance. There was work that was proposed to design the structure of a multi-layer disk and an optical head. In this paper, we reported the consideration of a code in order to solve the problems.
A performance comparison between a rate 8 / 14 asymmetrical run-length-limited (RLL) code and the EFMPlus code for optical disks is described. The limited condition of the rate 8 / 14 asymmetrical code is. This code has a better detection window size than the EFMPlus code because of the 14.3 percent greater efficiency of its coding rate. We describe the bit error rate (BER) performance and the tilt and defocus tolerance of the rate 8 / 14 ARL code. Compared to the EFMPlus code, the rate 8 / 14 ARL code has a 0.7-dB gain in the required S / N at a BER of 10-4. The rate 8 / 14 ARL code is also more robust against tilt and defocus.
In high-density optical disc systems that use high-NA objective lenses and multi-layered discs, it is important to reduce spherical aberration (SA). With high-NA lenses, SA is induced by errors in substrate thickness. The distance between layers in multi-layered discs also leads to SA. To use a type of phase-shifting device as a dynamic compensator for SA, a method of differential focus-error detection has been proposed for the real-time measurement of SA as a spherical aberration signal (SAS). The derivation of an equivalent substrate-thickness variation from the SAS with an accuracy of up to 0.8 mm is demonstrated in this paper. Using the SAS to drive a liquid-crystal phase-shifter, the fluctuation of the SAS caused by the substrate thickness error has been suppressed successfully during real-time disc rotation.
To make higher density on optical disk, a new recording method- 2D recording-which can increase the track-density rather than the linear density was proposed. The performance of this method on increasing density is estimated by the simulation and confirmed by measuring the read-out signal. Consequently, it is clarified that this method can attain more than twice the areal density independently and realize the density of 2.2Gbit/in2 which is 8 times as large as that of first generation using 680 nm laser diode.
KEYWORDS: Optical discs, Edge detection, Modulation, Signal detection, Signal processing, Clocks, Optical storage, Data storage, Data archive systems, Process control
A large size optical disk (for example, in 300 mm diameter) has been applied to document files and archived coded data files. Recently, demands for larger capacity and higher speed are growing greatly. Therefore, we developed a write once optical disk (300 mm in diameter), which adopts the pit-edge recording method and the MCAV (modified constant angular velocity) method to achieve higher linear density. On optical disk system combining the above two methods has yet been developed. In addition, new techniques must still be developed to satisfy the requirements of large capacity and high speed using these two methods. In this paper, new techniques were have developed are discussed.
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