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A new method for time interval measurement is described. It consists of an externally triggered triangular waveform generator together with an analogue-to-digital converter to form a time-to-amplitude conversion chain (TACC). It features high resolution, large measurement range, improved linearity and simplicity: only one amplitude-to-time conversion and concise calculation.

Land/groove recording was conducted on the trilayer double-mask MSR media. A CNR of 47 dB was obtained for a mark length of 0.33 µ m and track pitch of 0.7 µ m. The crosstalk was negligibly low when the readout magnetic field was applied in the writing direction. Random jitter was 10%, even when the data were recorded on the adjacent tracks, assuming (1, 7)-RLL encoding. This implies that an areal density of 3.69 Gbits/inch2 is possible. The crosstalk changed drastically depending on the readout magnetic field direction. It was found that the area of the front mask was larger when the readout field was applied in the writing direction, compared to the readout field in the erasing direction. This explains the big difference in crosstalk due to the readout field direction.

We obtained a high carrier-to-noise ratio (CNR) of 47 dB and a low jitter of 8% for 0.33 µm mark length ( 0.66 µm mark pitch) on exchange-coupled trilayer magnetically induced super resolution (MSR) media. This media is composed of a readout layer, an intermediate layer, and a writing layer. The magneto-optical signal is read through an aperture at the focal point between a front mask and a rear mask. The double mask can be formed by applying a readout magnetic field smaller than 300 Oe.

We have studied the write power margin for an magnetically induced super resolution (MSR) by front aperture detection (FAD) disk system and investigated a method for evaluating jitter which uses XY-mapping visualization. Using this method, we evaluated the effect of conventional write compensation on the shifts of the leading and trailing edges and developed a new write compensation pulse that is optimized for a high density system such as the ISO 8X. We confirmed the advantages of using the new write compensation pulse for MSR.

Techniques of dosage control for scanning exposure are introduced and the accuracy of exposure dose achieved by these techniques are discussed. Analytical formulation of the dosage accuracy is performed for the first time under consideration of both pulsed energy fluctuation and exposed position jitter. Actual dosage accuracy was measured by adopting the simplest method. Experimental data from the exposure apparatus are shown and the effectiveness of derived formula for dosage error estimation is confirmed. Application for the exposure system is also discussed.

Quadrupled compact disk-read only-memory (CD-ROM) mastering processes with a 363.8 nm UV light source have been developed. The UV light source exposure power for pit formation is less than that for the 457.9 nm conventional light source, because the photoresist exposure characteristic depends on light source wavelength. The fabricated disk exposed by EFM signals with doubled-linear-density CD format has a 0.8 µm track pitch and about 0.25 µm pit width. Under optimum fabrication exposure power for reduced crosstalk and better modulation amplitude, an excellent jitter value, 10 ns, is achieved for the quadrupled CD-ROM.

Read/write technologies for the second-generation magneto-optical disk are developed. A large capacity of 1 GB on a 130-mm-diameter disk and high transfer rate of 2∼4 MB/s are attained by mark length recording and the zoned constant angular velocity (zoned CAV) method. Read technologies such as slice level adjustment in the direct slice detection method, the independent edge detection and resync patterns for DC free are combined with the (1-7) run-length limited (RLL) code to provide sufficient edge jitter margin of over 60% of the detection window.

Precise mark-edge recording on a high signal-to-noise ratio (S/N) exchange-coupled direct overwrite magneto-optical (MO) disk provides 2 GB capacity on a 130 mm disk with a sufficient edge jitter margin. Write compensation technology was proven to be effective for both non- and direct-overwrite MO disks.

Aiming to obtain a rewritable compact disc (CD-rewritable) with high performance at both CD-velocity (CD1X) and double CD-velocity (CD2X), the phase change optical disc with the Ag-In-Sb-Te system has been developed. In the one-pass overwriting mode with eight-to-fourteen modulation, high carrier-to-noise ratio, wide power margin and high erase ratio have been obtained at both velocities. As for stability, we acquired a satisfactory result in the read-out test of 106 cycles with read power of 1.5 mW. We conclude that the phase change optical disc with the Ag-In-Sb-Te system is suitable for use at both CD1X and CD2X. Furthermore, the phase change process of the Ag-In-Sb-Te system has also been investigated. The chemical structure of the Ag-In-Sb-Te system in its ordered state was found to be (Ag-Sb-Te) x (In1-y Sb y )1-x .

Write/erase cyclability for mark-edge recording is studied using rare-earth element[RE]-rich TbFeCo media. Mark-edge jitter for the (1-7) random pattern is small enough even after millions of cycles of data writing and erasing.

High-density recording characteristics of phase-change optical disks were studied using 2-7 pulse-position-modulation (ppm) in-groove recording. Carrier-to-noise-ratio (CNR) was over 50 dB at a mark length of 0.60 µm and the crosstalk at the track pitch of 1.10 µm was less than -30 dB. In addition, a 256 MB 90 mm overwritable PC optical disk system having read/write compatibility with the ISO 128 MB MO disk has been developed based on the acquired results. The drive is based on the 90 mm MO drive at a wavelength of 780 nm and NA of 0.53. The user capacity of 256 MB was achieved using a mark length of 0.63 µm, track pitch of 1.25 µm, 2-7 ppm in-groove recording, and MCAV with 10 zones. The number of sectors per track was varied from 31 to 49.

This paper describes improvement in jitter characteristics in mark edge recording (MER) for phase change media at a high linear velocity. Jitter of the mark edge position, usually caused by thermal and/or intersymbol interference, can also increase due to overwrite when MER is used with phase change media. We have found that the main cause of jitter increase due to overwrite is the difference in absorptivity between the amorphous and the crystalline states. We were able to reduce jitter significantly by controlling absorptivity through the use of a Si reflective layer. It was also confirmed that this improvement in jitter characteristics can achieve high recording density of 0.59 µm/bit.

The effects of independent detection of leading edge / trailing edge on edge-shift and jitter are investigated for typical heat-mode recording processes using read-out pulse width, recording timing measurements and thermal simulation. In addition, in order to investigate the edge-shift reduction limit for this new method, a method is proposed to analyze what causes the edge-shifts; it statistically evaluates the relative edge intervals between adjacent edges of a particular worst-case recording pattern. Our results clarify that the new method is effective for reducing edge-shifts and jitter.