Abstract

With blue-green laser emission from frequency-doubled crystals a commercial reality and with healthy prospects for semiconductor diodes and fiber lasers, there is a need for an external modulator operating at visible wavelengths. The success of lithium niobate at 800–850 nm and 1300–1550 nm may not translate to short wavelengths because of photodarkening. An alternative at 800–850 nm, however, has been the Al_0.3Ga_0.7As/GaAs multiple-quantum-well (MQW) modulator. IC the GaAs well width in such a structure, is reduced and confinement is thereby increased, the excitonic absorption used in modulation can be made to occur at shorter wavelengths, however, it reaches a limit of around 650 nm for 20-Å a wells. For even shorter wavelengths it is necessary to increase the aluminum content in the wells, beyond the composition at which the material becomes indirect. Despite the indirect nature of the material, electroabsorption effects have been reported at wavelengths as low as 570 nm (Ref. 2), indicating the potential for use of this material combination in modulation.

© 1995 Optical Society of America