High-Density Magneto-Optical Recording with DWDD and DTE
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High-Density Magneto-Optical Recording with DWDD and DTE Toshimori Miyakoshi*, Tsutomu Shiratori, Yasuyuki Miyaoka and Yasushi Hozumi Advanced Device Technology Development Center, Core Technology Development Headquarters Canon Inc., 3-30-2 Shimomaruko, Ohta-ku, Tokyo, 146-8501, Japan ABSTRACT We have developed a new light intensity modulation recording method called Domain Tail Erasing (DTE). This new recording method enables high-density recording far beyond the optical resolution limit with a medium combining the layer structure of Domain Wall Displacement Detection (DWDD) with that of Light Intensity Modulation Direct Overwrite (LIMDOW). Recording performance nearly identical to that with Magnetic Field Modulation (MFM) was confirmed with this method, using conventional optics with a wavelength of 660 nm and an NA of 0.60. However, the DTE method still requires a bias magnet, which remains a disadvantage in cases in which a thinner drive apparatus is required. We have therefore also made the bias magnets unnecessary by introducing a device to generate a magnetic field as a magnetic film included inside the medium. INTRODUCTION A technique has already been developed [1,2] that can attain a recording density of 15 Gbit/in2 (80 nm/bit, 540 nm/track) with the existing optical parameters of DVD, in which the signals are recorded by Magnetic Field Modulation (MFM) and reproduced by Domain Wall Displacement Detection (DWDD) [3]. If this technique could be employed in a DVD, a capacity of more than 20 GB per layer would be achieved. However, in order to perform such high-density recording, it has so far been necessary to place a magnetic field modulation head close to the recording film. This has made it difficult to apply the reproduction technology to a DVD type optical disk, which has a sandwiched-film structure, or to a Blu-ray type disk system, which has an optical head placed on the film side of the disk. In order to overcome this difficulty, we proposed a new recording method named Domain Tail Erasing (DTE), with which minute marks much smaller than a spot size can be written by light intensity modulation, as can be done with MFM. This new recording method enables high-density recording far beyond the optical resolution limit with a medium combining the layer structure of DWDD with that of Light Intensity Modulation Direct Overwrite (LIMDOW). A recording performance nearly identical to that using MFM was confirmed with this method, using conventional optics with a wavelength of 660 nm and an NA of 0.60. However, the DTE method still requires a bias magnet, which remains a disadvantage in cases in which a thinner drive apparatus is required. We have therefore also made the bias magnets unnecessary by introducing a device to generate a magnetic field as a magnetic film included inside the medium. In order to obtain a sufficiently strong bias field to perform recording with a bias layer introduced into the DTE medium, the stray field distribution during the recording process was studied by simulation. A stra
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