Use blue-violet wavelength laser operation 405 nm to read and write data. Respectively, the traditional CD and DVD use red in the near infrared laser at 650 nm and 780 nm.
The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD sized disc. The minimum "spot size" on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85 and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot. This allows more information to be stored in the same area. For the Blu-ray disc, diameter is 580 nm. Besides, optical characteristics of Blu-ray disc data coding, further improve the productivity.