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World's First Red Laser Capable of Continuous Oscillation at Room Temperature

After developing the world’s first red laser capable of continuous oscillation at room temperature, Toshiba again became a global pioneer the following year by developing the transverse mode control structure for application to optical discs.

World's First Red Laser Capable of Continuous Oscillation at Room Temperature

U.S. physicist Theodore Maiman invented the world's first ruby laser in 1960. In 1962, pulse oscillation of a semiconductor laser was reported. Then, in 1970, continuous oscillation at room temperature was achieved by a galliumaluminum- arsenide (GaAlAs) infrared semiconductor laser. Inspired by these leading-edge technological developments, Toshiba’s Research and Development Center (currently the Corporate Research & Development Center) also started research on semiconductor lasers and, in 1973, succeeded in the recording and reproduction of holograms by semiconductor laser for the first time in the world.

After that, aiming at the application of semiconductor lasers to the optical communications field, our company participated in a large-scale project for the research and development of optical measurement control systems sponsored by what was then the Ministry of International Trade and Industry. Under this project, we conducted research on an integrated-wavelength semiconductor laser in which lasers with different oscillation wavelengths were integrated on the same substrate. A device achieving the integration of five wavelengths was developed in 1983 as a light source for wavelength-division multiplexing (WDM) optical communications, and received high evaluations worldwide.

On the other hand, with the objective of realizing optical discs with higher capacity, Toshiba was independently working on the development of an indium-galliumaluminum- phosphide (InGaAlP) red semiconductor laser. Although the GaAlAs infrared semiconductor laser was widely used at that time for conventional music CDs, optical discs required a semiconductor laser that could oscillate in the visible light region. For this purpose, we concentrated first on laser semiconductor crystal growth technology and in 1985, using a new crystal growth technique called metalorganic chemical vapor deposition, succeeded in developing a red laser capable of continuous oscillation at room temperature for the first time in the world.

We then focused our attention on the process technology for manufacturing the device, and developed a transverse mode control structure. This structure narrows down the emitted light to the extremely small spot necessary for a semiconductor laser serving as a light source for optical recording. As a result, a high-quality beam suitable for use as a light source for optical discs was realized in 1986. Furthermore, in a press release in November of the same year, we announced the successful reproduction of highdefinition optical discs using the red semiconductor laser. Needless to say, this was the world’s first optical disc using red laser technology. Toshiba went on to play a leading role in the formulation of standards for DVD incorporating red laser technology, which were announced in December 1995. This was followed by the commercialization of the world’s first DVD in 1996.

Another field of application of this technology was barcode readers. The red helium-neon (He-Ne) gas laser was already being used as a light source for such devices, and there were expectations that a large market for point of sales (POS) systems could be realized if these lasers were replaced by compact, power-saving semiconductor lasers with the same waveband. The power consumption of He-Ne gas lasers ranged from 10 W to several tens of watts, compared with a level of around 0.1 W for semiconductor lasers. The GaAlAs infrared semiconductor laser (wavelength: 780 nm) for CD use was unable to provide the reflectivity contrast specified in the JIS standards for blue barcodes, but the wavelength of the InGaAlP red semiconductor laser (670 nm) was close to that of the He-Ne laser (633 nm) and was able to satisfy the JIS standards. This InGaAlP red semiconductor laser opened up the large POS market, particularly in the U.S., and for a certain period Toshiba held the top share of more than 90% in this market.

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