An optical drive is a device that uses a laser to read or write information to a disk. Although this type of equipment is often associated with computers, it can function only as a device. For example, a digital versatile disc (DVD), Blu-ray disc (BD), and compact disc (CD) player are considered optical drives even if they are not in a computer system. Many video games also use this type of device to read the game disc. Regardless of the type of disk they read or write to, all of these applications have the same basic functionality.
Optical drives use lasers.
The optical path makes an optical drive work. The optical path is made up of three components: a laser, a lens, and a photodiode. The laser writes and reads the data. The lens guides the laser across the disk surface. Finally, the photodiode detects the light reflected from the disk surface. The unit also uses two servomechanisms, or servos: one to maintain the proper distance between the puck and the laser, and the other to ensure that the laser moves in a continuous spiral path.
DVD reader.
Lasers of different wavelengths are used to read different types of media. A CD player uses a laser with a wavelength of 780nm. This is in the infrared light range. DVD players use wavelengths in the 650nm range. That is why you will see a red light when the player is working. Blu-Ray® players use a much shorter wavelength: 450nm. This places it in the violet range and explains the bluish light.
CDs and DVDs can only be read with an optical drive.
The discs that an optical drive reads and writes vary. Read-only media (ROMs), such as CD-ROMs or DVD-ROMs, do not write to the media, they just read it. These are the types of disks that the software is written to. The manufacturer will create the disc by embedding wells, called grooves, in the flat surface of the disc. Then, when a user inserts the disk into an optical drive, a reading laser shines on the disk. The light is reflected and detected by the photodiode, which then translates the data into a form that the computer or player can understand and display.
An optical drive can also write to media. This type of recording must be done on specific recordable (R) discs, such as CD-R, DVD-R, and BD-R. As you write, the engraving laser melts organic dyes into the surface of the disc and embeds grooves in the surface. As with ROMs, the read laser, which has a much shorter wavelength than the write laser, shines on the disk and reflects light. The photodiode then detects the reflection and the information is displayed.
Rewritable media can be written to rewritable (RW or RE in the case of Blu-Ray®) discs, such as CD-RW, DVD-RW, and BD-RE, repeatedly. The surface of these discs is made of a special crystalline alloy that allows data to be written to its surface repeatedly. The individual data is embedded in the disk in grooves that reflect the laser differently. The photodiode is then able to distinguish between the different reflections and display the correct information.
Many newer Macintosh computers, like the iPad, don’t have an optical drive.
