Abstract

The spectral tunability of quantum well semiconductor lasers is found to approach the range of dye lasers. Gain spectra calculations predict, for a particular pumping condition, a wide spectral range of nearly flat gain from quantum well lasers. This flattening results from contributions to the gain, at high pumping current, from electron-hole transitions in the second (n = 2) quantized state. In addition, the gain spectrum is stretched out to shorter wavelengths. Consequently, properly designed quantum well lasers can have an effective tuning range 2 to 3 times that of conventional semiconductor lasers. This flat gain spectrum enabled us to tune broad area, single quantum well lasers over a spectral width of 90 nm with an external grating. No antireflection coating of the lasers was required. Rather, the condition of broad, flattened gain was achieved by optimizing the length of the lasers to near 200 μm. Power output from the free side of the tuned lasers exceeded 200 mW (pulsed) in a single longitudinal mode over most of the spectrum. The 11% tuning range achieved is the largest published value for a semiconductor laser. This work was supported in part by the National Science Foundation and the Office of Naval Research, and M. Mittelstein acknowledges support from a Newport Research Award.

© 1988 Optical Society of America