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The possibility of an areal density over 50 Gbit/in2 was examined in near-field phase-change recording. The disk structure was optimized to maximize readout signals under the land-and-groove recording condition at a tracking pitch of 160 nm. We also evaluated the signal crosstalk from adjacent tracks. Eye diagrams of 50.4 Gbit/in2 areal density were demonstrated using 1.5 NA optics and a GaN laser diode. The track pitch and linear bit density are 160 nm and 80 nm/bit, respectively. The transmission electron microscope (TEM) micrograph of recorded amorphous marks at an areal density of 50.4 Gbit/in2 is also presented.

Land/groove recording in an MO system was demonstrated using MFM recording technology and a 690 nm wavelength diode laser. The CNR of 55 dB and cross-talk of about -35 dB were obtained at a 1.88 micrometers recorded mark length and a 0.7 micrometers yielded a 0.35 micrometers bit length and a 0.7 micrometers track pitch were 8.1% on land and 8.7% on groove. The disk tilt margins were radially +/- 0.42 deg and tangentially +/- 0.45 deg when reading out on land, and +/- 0.40 deg and +/- 0.44 deg on the groove. The recording power margins were estimated to be +/- 8.0% on land and +/- 9.0% on groove considering over-writability and cross-write characteristics.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report the results of magneto-optical (MO) detection using an optical phase shifter and a deep land/groove disk. We measured the recording characteristics in the direction of incident linear polarization and found that polarization perpendicular to the groove is best for a deep groove disk. Using perpendicular polarization, with a 693 nm wavelength diode laser and a 0.55-NA objective lens, sufficient readout and recording margins to guard against optical errors were obtained by the experiments at an area density of 3.69 Gbit/in2, which was obtained using a 0.35-µm bit length and a 0.5-µm track pitch.

We report the results of magneto-optical (MO) detection using an optical phase shifter in land/groove recording. We found that the MO detection method improves not only readout carrier level but also cross-talk characteristics against optical errors. Using this method with a 693-nm wavelength diode laser and a 0.55-NA objective lens, sufficient readout margins against optical errors were experimentally obtained at a 3.69-Gbit/in2 areal density, which yielded a 0.35-µm bit length and a 0.5-µm track pitch. Recording with a track density 1.4 times higher was achieved by introducing a 640-nm wavelength diode laser, a 0.7-NA objective lens, and a 0.258-µm bit length and yielded an areal density of 6.95 Gbit/in2.

We detected bits sized at 0.237 µm bit length and 0.85 µm track pitch recorded by magnetic field modulation on a magneto-optical disk with a 690-nm laser diode and 0.60-numerical-aperture-objective using a partial-response maximum-likelihood detection method. We confirmed that the optimum partial-response for this high linear density had four coefficients of 1 by analyzing difference metrics of error critical paths. The recorded bits with areal density of 5.6 bit/µm2 were also detected at a low error rate, which combination is 0.237-µm bit length and 0.75-µm track pitch. Its write power tolerance is limited to ±22%.