Green-output diode laser reads high-density digital video disk
Researchers at Philips Research (Briarcliff Manor, NY) and 3M Photonics Research Laboratory (St. Paul, MN) have demonstrated use of a green-output (520-nm) zinc selenide (ZnSe) diode laser to retrieve information stored on a high-density digital video disk (DVD). Previously, only red-emitting semiconductor lasers had been used. Commenting on the results, Philips research team leader Diego Olego says, "We`ve illustrated the real-world applicability of blue-green semiconductor lasers by demonstrating there are no inherent problems to using them with advanced electronics products."
The shorter wavelengths of blue-green-emitting lasers mean more-densely packed "pits" of information can be recorded on the disks, thereby increasing the data storage capacity per unit disk volume. Olego notes that the next task is to extend lifetimes of ZnSe lasers. The Philips-3M device has shown a 3.5-h lifetime, and a Sony ZnSe laser has run the longest to date at 100 h. Olego sees keys to extended lifetimes as being control of defect generation in the material and improving the electrical contacts to the p-type layer of the laser structure. "Perhaps by the end of the century," he adds, "we will see low-power devices for read-only applications."
