Reflection Confocal Reading with Multilayered Medium

5 Reflection Confocal Reading with Multilayered Medium 

Another way to achieve the reading data with RCM is to use the multilayered recording medium in which photosensitive thin films and nonphotosensitive transparent films are alternately stacked. Since the photosensitive films are thinner than the depth of focus of the recording beam, the spatial-frequency distribution of the recorded-bit data is extended in the axial direction. The extended distribution overlaps the coherent optical transfer function of the RCM. 

The process of making the medium was as follows. The urethane-urea copolymer was dissolved in pyridine at 6.5 wt%. The mixed solution was filtered through a 0.2 fjim fiiteii and then it was spin-coated onto a glass plate at 1000 rpm for 10 s. The residual solvent was removed after heat treatment at 130°C for 12 h. Further drawing in a vacuum at 80 C for 20 h was done to remove the solvent completely. The film was gradually cooled to room temperature. The thickness was about 1 /tm. After evaporating the pyridine solvent in an oven, the PVA and PMMA films were also spin-coated on the 

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