US Patent 7859977 Optical pick-up unit

An optical pick-up including a fold mirror having an achromatic quarter-wave plate coating is provided. To allow the thin film coating to efficiently provide the quarter-wave retardation, the optical pick-up is configured such that the polarization of light incident on the fold mirror is at a predetermined angle. According to one embodiment, the predetermined angle is provided by rotating the light sources. According to another embodiment, the predetermined angle is provided by rotating a plane containing the light sources and the beam combiners. In each embodiment, the beam combiners and the fold mirror are arranged along the same axis to further improve efficiency.