HD/DVD compatible pick-up adapting singlet objective lens

Recently, many high-density optical disc systems using blue laser diodes have been reported and proposed as the next generation industry standard technologies. One of the technical proposals is to adapt NA 0.85 objective lenses at 405 nm and to use a 0.1 mm-thick cover layer. But, in this case, a technical challenge remains how to maintain the compatibility with current DVD/CDs. Last year at ISOM 2001, we proposed a singlet objective lens system having either an HOE (holographic optical element) or PPC (polarization phase compensator) to maintain HD and DVD compatibility. In this paper, we describe our experimental results using the compatible optical pick-up head with high density ROM and rewritable discs of 23 Gbyte and current DVD ROM discs.