Focusing Error Detection Method in Microholographic Data Storage System Using Polarization Characteristics

We present a disk-focusing error detection method for microholographic data storage systems using polarization characteristics. In high-speed optical storage systems, disturbances exist along the vertical direction of a disk. The diffraction efficiency of a readout signal depends on the distance bet...

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Bibliographic Details
Published inJapanese Journal of Applied Physics Vol. 50; no. 9; pp. 09ME07 - 09ME07-4
Main Authors Kim, Taeseob, Im, Chang-Hyuk, Lee, Sang-Hyuck, Kim, Nakyeong, Park, No-Cheol, Yang, Hyunseok, Park, Young-Pil, Park, Kyoung-Su
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.09.2011
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Summary:We present a disk-focusing error detection method for microholographic data storage systems using polarization characteristics. In high-speed optical storage systems, disturbances exist along the vertical direction of a disk. The diffraction efficiency of a readout signal depends on the distance between the focusing point of the reference beam and the vertical center of the microholographic grating. The proposed disk focusing error detection method uses only one laser source, unlike most existing systems, which use two laser sources. By using polarization characteristics, disk-focusing and reading beams are inserted in the media without interference, and the proposed system achieves the simultaneous reading of microholograms and disk-focusing control. By evaluating the focus error signal, we verified the reliability of the optical path and tolerable $S$-curve (FES) balance (1.8%) for the proposed system. It is possible to achieve a diffraction efficiency of over 90% at the best focus position using the proposed disk-focusing method.
Bibliography:Rate of change of readout signal obtained by simulation and experimentation with an objective with 0.55 NA and 532 nm wavelength illumination. The calculated mark height was approximately 10 μm. However, spherical aberration (SA) may occur when storage layers at different depth positions are addressed. It is expected that the signal decays slowly because of SA. Proposed disk-focusing method exploiting polarization characteristics of laser. Simulation results for focusing error signal ($S$ curve) and experimental images at PD2 (4PD). Linear motor stage module setup. Linear stage 2 is used to generate a vertical disturbance to the media. Linear stage 1 is used to compensate for the disturbance through a closed-loop feedback system. Measured disk-focusing error signal. The astigmatism method is used to detect the focusing error signal. The tolerable $S$-curve balance is 1.8%. Measured focus error signal during actuator seesaw motion along focus direction. Through the evaluation of the dynamic focus error signal, we verified the reliability of the optical path and tolerable $S$-curve (FES) balance (${<}10$%) for the proposed system. Experimental results at (a) 1 and (b) 2 Hz. The readout signal took a repetitive parabolic shape wave when linear stage 2 generated a disturbance ($\pm 50$ μm). At this point, linear stage 1 began to compensate for the disturbance, and the original readout signal was measured as a straight line, as in a static system.
ISSN:0021-4922
1347-4065
DOI:10.1143/JJAP.50.09ME07