Takahiro KUROKAWA^1*, Tatsuro IDE¹, Yukinobu TANAKA², and Koichi WATANABE¹

¹Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo 185-8601, Japan
²Yokohama Research Laboratory, Hitachi, Ltd., Yokohama 244-0817, Japan

(Received November 30, 2013; Revised December 27, 2013; Accepted January 14, 2014)

A write/read system using high-productivity multilayer optical discs was developed. The recording medium used in the system consists of planar recording layers and a separated guide layer, and is fabricated by web coating and lamination process. The recording layers in the medium are made of one-photon-absorption material, on which data can be recorded with a normal laser diode. The developed system is capable of focusing and tracking on the medium and amplifying readout signals by using phase-diversity homodyne detection. A highly layer-selective focusing method using homodyne detection was also proposed. This method obtains stable focus-error signals with clearly separated S-shaped curves even when layer spacing is quite narrow, causing large interlayer crosstalk. Writing on the medium and reading with the signal amplification effect of homodyne detection was demonstrated. In addition, the effectiveness of the method was experimentally evaluated.

Key words: optical memory, multilayer optical discs, phase-diversity homodyne detection, optical interference, focus error signal, interlayer crosstalk reduction

^*E-mail address: takahiro.kurokawa.nb@hitachi.com