Since the invention of the laser in the 1950’s, the impact of lasers has been felt worldwide in an innumerable amount of industries. One industry that owes a lot of its commercial success to the advent of the laser, is the entertainment industry. In the 1960’s Theodore Maiman proposed the idea of lasers capable of reading stored data, around 30 years later the compact disc and corresponding player was developed, forever changing the way the general public consumes audio and digital media.
Companies Philips and Sony were in fierce competition when developing the CD, but it was the accumulation of other important developments and discoveries that brought the compact disc and player to life.
The first optical digital recording is credited to James Russell in 1970, following other digital recording patents from Dr. David Paul Gregg in the late 1950’s. (The development of optical digital recording is a murky one, with inconsistencies in attributions.)
In 1960, Irving S. Reed and Gustave Solomon developed the Reed Solomon Code, an algebraic error connecting & detection code that helped to develop the tracking method that was instrumental in the playback function of a CD player.
The first prototype CD, the Phillips Glass Disk, initiated the race to develop the playable compact disc. After the prototype, Sony began investing in laser research, wanting to use lasers to “read” the newly created glass disks. Phillips quickly followed suit. Sony later developed the optical digital audio disk, able to play 150 minutes worth of stored information. Not wanting to be bested by their competitor, Phillips is the first to release the completed compact disc.
The first test pressing was created in Hanover, Germany, at the Polydor Pressing Operations Plant. In 1982, the first commercial CD, a recording of Claudio Arrau performing Chopin Waltzes, was released. The first popular music recording available the public on CD was ABBA’s The Visitors, in 1983. Smaller than vinyl records, greater storage space than a cassette, and affordability pushed the CD to great lengths of success, and despite the rise of digital downloads, still sustains itself as a medium to distribute and enjoy music.
As a piece of equipment found in almost every modern home and vehicle, not many stop to think about how exactly a CD player works, and by extension, what involvement lasers play in making sure the tunes keep playing, without a user’s assistance. Here’s how it works: A CD contains digitally encoded data. That CD is placed into a CD tray, that either ejects outward or is contained inside the device. The CD is then read by an internal mechanism and “scanned” by a laser beam, in a spiral track. The beam shines directly onto the disc’s surface. The lens must be able to move, with a close-range focal length, in order to focus the beam onto the disc. The beam is kept on track by a low mass lens, attached to an electromagnetic coil. The track, at only around 600 nanometers wide, is very small. The focus detection method of the CD player depends on the manufacturer, but most use the outputs of four photo diodes. Perfect focus is typically achieved when all four diodes situate themselves in circular pattern. The tracking is controlled by analogue servo amplifiers, which helps to control the output of the disk. The signal, read from the disk, is digitized, processed, and decoded into analog audio and digital control data. The “perfect focus” is used by the servo amplifier to keep the lens at proper reading distance, even in the instance that the disc is warped. This data is used by the CD player to position the playback mechanism on the correct track.
The lasers used in CD players are typically low in power, classified as Class 1 or 2 lasers. In 1996, the technology used in CD players was altered to develop the DVD player. Where in a CD player the wavelength of a laser is usually around 780 nanometers, this was reduced to 650 nanometers for the DVD player. In 2000, a 405 nanometer beam was utilized in Blu Ray players.
Despite the rise of digital downloads taking a cut of sales in CDs, DVDs, and Blu-ray, the optical CD drive is still utilized in a majority of devices and vehicles, years later. It is safe to say that the laser-based technology will stick around, and likely be improved on, for years to come.