IV.24 - Laser diodes?
This section was contributed by Kathy Meehan, meehan@srvr.third-wave.com.
The first semiconductor lasers were fabricated in 1962 independently by three different groups (GE, IBM and ???, none of which currently makes semiconductor lasers). They are utilized in a number of different applications, most notably the compact disc players. The commercially available wavelengths cover a spectral range (with a few holes) from the visible to the mid-infrared, with a blue GaN laser on one horizon and HgCdTe lasers on the other.
A laser can be described as a gain medium in an optical cavity. In the case of a semiconductor laser, the gain medium is a specific layer, usually sandwiched by a p-type and n-type layer - the reason why they are frequency refered to as laser diodes. The gain medium, generally called the active region, is a direct bandgap semiconductor. The population inversion is created by forward biasing the p-n junction, injecting electrons and holes into the gain medium. These electrons and holes recombine to create light, photons. In an indirect semiconductor such as Si,Ge, and GaP, the electrons and holes recombine to create heat, phonons. The photons created have an energy approximately equal to the bandgap of the material used in the active region. In order to have red light, the active region must be composed of material with a bandgap of ~640nm (GaInP). The active region composed of InGaAs will emit light at ~1.65um. The optical cavity can be formed by breaking the semiconductor along crystal planes (a process called cleaving). The reflectivity of these natural mirrors is ~30%, but can be modified by applying dielectric coatings to create high or low reflectivity mirrors.
Visit this laser FAQ for some more practical information on buying and using laser diodes.
References:
- "Laser Diodes are Power-Packed" by D. Botex in the IEEE Spectrum, June 1985. A good reference on a variety of different device structures that have been explored. The InGaAsP structures are still used in the telecommunication lasers. Does not cover quantum well structures.
- Semiconductor Lasers and Heterojunctions by Casey and Panish. A good reference on the materials used and some of the earlier devices. A classic, but out of print. Some of the materials information can also be found in a series of books entitled Properties of ???, Properties of GaAs is an example.
- Semiconductors and Semimetals, edited by Willardson and Beers. A 30+ volume series on research topics that the editors believe will be significant in the long run. They are usually right. Several volumes deal with semiconductor lasers and some materials issues in fabricating them.
- Gaseous Electronics by A. Yariv. A good reference to lasers in general.
Companies: See also The Laser-Focus Buyers Guide or The Photonics Directory, Laurin Publication
High Power Lasers: Laser bars and/or muliple laser diodes coupled to multimode fiber, Optical Powers >5W, multiple mode, "large" spectral output, used as slab waveguide pumps for solid state lasers, welding, laser ablation (medical).
- SDL, 80 Rose Orchard Way, San Jose, CA 95134-1356 (408) 943-9411
- Opto Power, 3321 E. Global Loop, Tuscon, AZ 85706 (520) 746-1234
- Applied Optronics, 111 Corporate Blvd. Bldg. J, South Plainfield, NJ (908) 753-6300
Telecommunication Lasers (1.3um, 1.5um and EDFA pumps):
- AMP-Lytel, 61 Chubb Way, Somerville, NJ (908) 685-2000
- Lasertron - no longer in business
- Laser Diode, 4 Olsen Avenue, Edison, NJ 08820 (908) 549-9001
600-680nm (GaInP)
- SDL, 80 Rose Orchard Way, San Jose, CA 95134-1356 (408) 943-9411
- Toshiba America Electronic Components, 9775 Toledo Way, Irvine, CA 92718 (714) 455-2000
780-980nm (AlGaInAs)
- SDL, 80 Rose Orchard Way, San Jose, CA 95134-1356 (408) 943-9411
- EG&G Optoelectronics, Montgomeryville, PA 215-368-4003
- Applied Optronics, 111 Corporate Blvd. Bldg. J, South Plainfield, NJ (908) 753-6300
1.7-2.0um (strained InGaAs)
- Applied Optronics, 111 Corporate Blvd. Bldg. J, South Plainfield, NJ (908) 753-6300
- SDL, 80 Rose Orchard Way, San Jose, CA 95134-1356 (408) 943-9411
2.7um (GaInAsSb)
- Sensors Unlimited, 3490 US Rte. 1, Bldg. 12, Princeton, NJ 08540 (609) 520-0610
3-4um (lead salts)
- Laser Photonics, 200 Bulfinch, Andover, MA 01810-1140 (508) 683-6480
Vertical Cavity Surface Emitting Lasers (VCSELs)
- Jack J's company in Colorado
Blue/Blue-Green (AlInGaN or II-VI)
Associated Technologies
- Diamond Submounts:
Diamonex, Norton Diamond - Micro-Optics:
Big Sky, Nippon Sheet Glass, Corning - Diode-pumped Solid State Lasers:
Coherent, Spectra-Physics