How does blue-ray DVD work?

Answer

Blueray DVDs work on the same principle as CDs and DVDs.
The discs contain a mirror layer. The information is provided on a disc by making pits in this mirror layer at specific locations that break the reflection.

By scanning the surface of the disk with a laser beam, a reader can detect where the pits were made and thus reconstruct the information on the disk.

The difference between the different types of disks is mainly the wavelength of the laser beam used to read the disks. For CDs and DVDs, a red laser beam is used (with wavelengths of 780 nanometers and 650 nanometers, respectively). For Blue-ray DVDs, a blue laser beam (with a wavelength of 405 nanometers) is used. The shorter wavelength of this laser beam makes it possible to see smaller pits on the disc that can also be placed closer together.
Because smaller pits can be used, it is possible to place more information on the same disk surface.