高性能AR膜端面を持つLDヘッドでのレンズレス光FDの信号再生特性 : レンズレス光フロッピーディスクシステム開発(3)

概要

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Anti-reflection coatings of high quality have been prepared on the facet of a semiconductor laser diode chip using the ECR sputter. We have also fabricated the optical floppy disk using the same sputter which consists of the Ge_2Sb_2Te_5 phase change layers and the SiO_2 protective films on the both side of the 70μm thickness-polyimide disk substrate. The lensless optical head which is only composed of an AR coated laser chip and a heat sink have been easily produced in our laboratory. The gap between the optical disk and the head can be controlled in the near field of a sub-micronmeter, and a small bit of a sub-micron diameter have been formed using a laser peak output of 10mW with pulses of 50 ns width. Since the reflectivity of this small pit was changed from 32% to 10%, we can confirm that the crystal phase of a optical floppy disk is changed to the amorphous phase. In our reading test of the laser diodes, having an AR coating which is used for the CD player, we understood that the laser oscillation current strongly depends on the crystal phase states on the disk and shows the big difference of a power level between a bit site and no bit site. Actually, the oscillating laser output has changed from 30μW on a non-bit site to 450μW on a bit site, if the laser current is kept constant. Thus we can easily detect the information signal recorded in our optical floppy disk using above-mentioned phenomena.
1998-03-30