Shigeo Terashima

Magnetic super-resolution

Magnetically induced super-resolution (MSR) disks have been proposed to overcome the diffraction limit. This paper reports an MSR disk which has exchange-coupled magnetic double layers. An in-plane magnetization film is used as a readout layer in the magnetic double layers. The MSR disk can be overwritten by a magnetic field modulation recording method. An areal density of 2.2 Gbit/in/sup 2/ was obtained with a currently available optical head having a 680 nm wavelength laser. Besides, the disk had high recorded-data-stability in continuous readout of 5/spl times/10/sup 5/ revolutions with a laser power of 2.5 mW, and it also kept a high signal quality after a continuous erasing test of 2/spl times/10/sup 5/ revolutions with a recording laser power of 6.5 mW.

Magnetically induced superresolution using domain stability

Two types of magnetically induced superresolution (MSR) readout methods were investigated. In one MSR method, triple-layered films in which the readout layer was coupled magnetostatically with the recording layer were used. In another MSR method, exchange-coupled triple-layered magnetic films were used. We utilized the phenomena of domain nucleation and domain collapse in readout layers in these MSR readout methods, and obtained a short rise time with domain nucleation and a short fall time with domain collapse in their readout layers.

New disc format for land/groove recording on magnetically induced super-resolution disc

We developed a new disc format for land/groove recording. The new disc had grooves wobbled on one side to obtain address information. We examined characteristics of signals reproduced from the wobbled grooves and a suitable groove shape for a double-layered magnetically induced super-resolution disc. By the use of the new disc format, good signal quality of address information is obtained on both lands and grooves. At a groove shape with 40 nm depth and 0.7 µm track pitch, a CNR of 47 dB and a crosstalk of -32 dB were obtained at the recorded mark length of 0.55 µm in magnetic field modulation recording.

New magnetically induced super resolution disk by using exchange-coupled magnetic layers

Readout process of a new type of magnetically induced super resolution (MSR) disk was analyzed by calculating a domain shape in exchange-coupled ferrimagnetic layers. Analysis revealed that a suitable wall energy density at an interface between the layers existed for improving readout characteristics. This result obtained from calculation was confirmed by experiments. An areal recording density of 2.4 Gb/in/sup 2/ was achieved by using an 830 nm wavelength laser.

High density recording with a super resolution magneto-optical disk using magnetic field modulation method

Abstract We have improved the recording magnetic field sensitivity of a magnetic super resolution (MSR) disk consisting of double magnetic layers and examined the magnetic field modulation recording properties. An areal density of 2.2 Gbit/in 2 was obtained with a currently available condition. The experimental optical pickup system had a 680 nm wavelength laser diode and an objective lens of a 0.55 numerical aperture. The MSR disk had 0.7μm-width lands and grooves. The crosstalk values between the land and its adjacent grooves were less than −28 dB. The areal density in the improved MSR disk was accomplished by recording in both lands and grooves and using mark edge recording with a (1,7) run-length-limited coding. Also, if a signaling technique called ‘PRML’ is used, an areal density of 3.1 Gbit/in 2 could be realized.

Readout of Optical Disk Recorded by Pit Edge and Depth Modulation

We report a Read-only (ROM) disc which is recorded by pit edge and depth modulation (PEDM). The information recorded by pit edge modulation is read out through an RF signal channel, and that recorded by pit depth modulation is read out through a tangential push-pull signal channel by detecting signal polarity at the pit edge. Each signal is sliced with a single level and is combined with another signal so that a multi-value recording is realized without multiple level slicing. The information recorded and read out using tangential push-pull signal polarity can never be copied onto recordable discs. Thus, not only a larger recording density and a higher transfer rate but also secure information storage are achieved with no change of the current optical and mechanical systems.