Use of Grating in Reading Multilayer Discs to Reduce Amount of Interlayer Crosstalk

Abstract

Crosstalk from adjacent layers affects the tracking error signal of conventional optical pickups when a multilayered disc is read. The tracking error signal fluctuates and makes precise tracking difficult. We propose the use of a grating in the return path to reduce the amount of crosstalk. Using a grating with an uneven plane on the optical axis reduces the amount of stray light causing the crosstalk and allows the target light to pass through. We show that using a grating with an appropriate pitch prevents diffracted light higher than an order of ±1 from going back to detectors. As the shape and depth of the grating are important factors for the zeroth-order light, we chose a deep triangular grating. We measured the distribution of the transmitted intensity through the grating as a focused beam position was scanned and found that the grating can reduce the amount of crosstalk.