Optical disc

Principles of work

An optical disk includes several layers. A laser beam is used to write data to the disk. The laser creates spiral tracks on the disk, which are composed of pits (depressions). The pits scatter or absorb light, and the surface reflects it.

A laser beam with a certain wavelength is also used to read the information taken from the disk. If the laser hits the pit, the intensity of the light is smaller. The variation in the intensity of the reflected light is converted into an electrical signal.

1 – Compact Disc (CD)

2 – DVD Disc (Digital Versatile Disc)

3 – Blu-ray

The more pits the disc contains, the more information can be recorded on it.

Types

CD

This type of disc was initially created to store audio recordings but later was used to store any data in the binary code. CDs are only used to read the information once written to them.

CD-RW

This type of disc has a writing layer that consists of a special chalcogenide alloy. As the alloy is heated to a certain degree, it transforms from a crystalline state to an amorphous one. This feature is the basis for rewriting, as this transition is reversible. But a CD-RW cannot withstand more than a thousand rewrite cycles.

DVD

DVD has increased the writing capacity while the disc size has remained the same. This was achieved by using a red laser with a wavelength of 650 nanometers and increasing the density of the data recorded (high number of pits).

Blu-ray

Blu-ray offers a higher density of data recording than previous generations. It operates with a shortwave blue-violet laser with a wavelength of 405 nanometers.