| Today's optical applications require high-performance semiconductor lasers. Semiconductor lasers started as the simple Fabry-Perot homojunction lasers in early 1960s, but now, extremely sophisticated semiconductor lasers are being used daily for a variety of applications such as communications, storage, and remote sensing. Such applications require a high degree of control over the spectral characteristics of semiconductor lasers.;One of the most important developments for control over the wavelength and linewidth of semiconductor lasers is the use of periodic structures. These small, periodic structures, with dimensions in the order of wavelength of light, result in significant change in the spectral characteristics of semiconductor lasers by inducing periodic variations in index/gain of the material. Needless to say, these small structures are extremely difficult to fabricate. However, intense research and development efforts have been invested in these structures with great success. The result is tunable single-wavelength output from semiconductor lasers at predetermined wavelengths.;The next technical challenge is to increase the number of lasing modes with as much control over the wavelength and linewidth as in today's single-wavelength semiconductor lasers. By utilizing multiple sections of periodic structures, dual-wavelength InGaAs-GaAs ridge waveguide semiconductor lasers have been fabricated. Not only do these dual-wavelength lasers operate at predetermined wavelengths, but the wavelength separations between the two lasing modes can be tuned electronically. |
