| 摘要 |
An optical medium stores enabling information readable by a blue laser that enables the reading of content from the optical medium by a red laser. For instance, the enabling information is content protection information needed to decode the content, optical medium disc type information used to set the read parameters of the red laser or a key needed to read content. The enabling information is disposed in the optical medium to be readable by illumination of a blue laser but indistinguishable through illumination by the red laser. For instance, the enabling information is placed at the outer surface of an optical medium at which the focus point of the blue laser allows reading of marks while the red laser has insufficient precision to focus on individual marks. The marks may also be inked on the outer surface with a material that is reflective of blue light but that has inhibited reflectivity of red light. Alternatively, the enabling information is formed with pits sized to approximately one-half the wavelength of the red laser to reduce reflective energy by phase extinction. |
