MEMS focus control and spherical aberration correction for multilayer optical discs

Abstract

We present the use of a large-stroke deformable membrane mirror at 45° incidence to achieve a very compact optical system capable of fast multi-layer focusing in an optical disc unit. The MEMS mirror replaces a lens translation mechanism and liquid crystal compensator, resulting in a single optical element to control both focus depth and compensation of attendant focus-dependent spherical aberration. We outline the membrane optical requirements in terms of stroke and aberration compensation required for multi-layer focusing for current DVD and BD standards. We demonstrate an adjustable range of at least 1.6 μm peak wavefront spherical aberration correction at a membrane displacement of 7 μm, which should be sufficient capability for quadruple layer BDXL™ discs.