Ryuichi KATAYAMA^*

Department of Information Electronics, Faculty of Engineering, Fukuoka Institute of Technology, Fukuoka 811-0295, Japan

(Received March 31, 2014; Accepted June 23, 2014)

The effect of offsets between the focused spot positions of two recording beams used in microholographic memory in the in-plane and vertical directions of the recording medium on the readout signal was investigated through a numerical simulation. The tolerance of recording beam offsets, which was defined as the offset when the normalized signal level decreased to 0.8, was determined to be 0.092 and 0.54 μm in the in-plane and vertical directions, respectively, when the wavelength of the laser was 405 nm and the numerical aperture of the objective lenses was 0.85. These values correspond to 16% of the focused spot size. Moreover, when the recording beam offsets were within the above values and the signal-to-noise ratio of 2 was allowed, the bit intervals of 0.15 and 0.75 μm in the in-plane and vertical directions, respectively, which correspond to the recording density of 59 bit/μm³, were shown to be feasible for confocal detection.

Key words: microholographic memory, recording beam, offset, readout signal, signal-to-noise ratio, numerical simulation

^*E-mail address: r-katayama@fit.ac.jp