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 AE1 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.

A Multilayered Blu-Ray Disc readout technique with an optical longitudinal filter for reducing interlayer crosstalk in a three-beam optical system

“…On the other hand, the DPP method, which is the most commonly used method for TES detection, is much more susceptible to interlayer crosstalk because two weak sub beams are fluctuated by strong stray light of the main beam. To suppress the DPP signal fluctuation, we previously proposed a novel optical-readout technique (named "optical longitudinal filter (OLF)"), which uses a grating on the optical axis [6] . The key feature of this technique is to reduce the interlayer crosstalk by diffracting only the stray light from the adjacent layers selectively according to the difference of their focal points.…”

Reducing Interlayer Crosstalk in Reading Multilayer Disc for Compact Optical Pickup Using Polarizing Filter

“…Several suppression techniques for the crosstalk have been reported. [1][2][3] We chose the method able to separate the reflection by a target layer from those by multilayers with polarization 1) and are trying to apply this method for an optical pickup in an astigmatic aberration system, with the aim of keeping the pickup size small.…”