The key technology behind both HD DVD and Blu-ray is the blue laser, an evolutionary development of the infrared and red lasers used in CD and DVD players. The wavelength of the light coming from the blue lasers in both high-def disc formats is 405 nanometers (billionths of a meter), which is shorter than the DVD wavelength of 650 nanometers (a pure red) and nearly half the CD wavelength of 780 nanometers (in the near-visible infrared). Using a shorter laser wavelength allows a much smaller spot to be focused onto the reflective data layer (see “Laser spot sizes” in the diagram below).
Top, the red and blue laser spots used to read the four optical-disc formats are shown to scale, though greatly enlarged. Middle, the data surfaces are shown to scale in simulations of atomic-force-microscope scans of the pit layers. Bottom, vertically to-scale renditions of the disc layers used by the four formats.
No comments:
Post a Comment