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Reduction of Interlayer Crosstalk in Dual-Layer Optical Disks Using Patterned Phase Plate

In dual-layer optical disks, light reflected from an adjacent layer overlaps and interferes with light reflected from the target layer on the photodetector. As a result, the signal obtained from outputs of the photodetector fluctuates. In this paper, we propose an optical head which employs a six-segment patterned phase plate in the return path to reduce interlayer crosstalk (fluctuation of a differential push–pull signal) without degrading the readout signal. The patterned phase plate weakens the intensity of the main beam from the adjacent layer which enters the sub-beam detecting sections of the photodetector and restricts the interference between sub-beams from the target layer and the main beam from the adjacent layer. Beam intensity distributions on the photodetector and push–pull signals have been investigated through numerical simulations and experiments. The results demonstrate that interlayer crosstalk can be sufficiently reduced using the patterned phase plate.