Dual Wavelength Optical Head for 0.6 mm and 1.2 mm Substrate Thicknesses

A dual wavelength optical head for 0.6 mm and 1.2 mm substrate thicknesses, containing 635 nm and 785 nm laser diodes, has been developed. Holographic optical element (HOE) type optics and variable magnification type optics are described. For both types of optics, high light power efficiency is obtained, which is suitable for random access memory (RAM) applications. Moreover, the use of 785 nm light makes it possible to read compact disc-recordable (CD-R). A readout operation for a quadruple density CD and a conventional CD has been successfully demonstrated.