Title :
Minimal group refractive index dispersion and gain evolution in ultra-broad-band quantum cascade lasers
Author :
Gmachl, C. ; Soibel, A. ; Colombelli, R. ; Sivco, D.L. ; Capasso, F. ; Cho, A.Y.
Author_Institution :
Lucent Technol. Bell Labs., Murray Hill, NJ, USA
Abstract :
The group refractive index dispersion in ultra-broad-band quantum cascade (QC) lasers has been determined using Fabry-Perot spectra obtained by operating the lasers in continuous wave mode below threshold. In the wavelength range of 5-8 μm, the global change of the group refractive index is as small as +8.2 × 10/sup -3/ μm/sup -1/. Using the method of Hakki and Paoli (1975), the subthreshold gain of the lasers has furthermore been measured as a function of wavelength and current. At the wavelength of best performance, 7.4 μm, a modal gain coefficient of 16 cm/spl middot/kA/sup -1/ at threshold and a waveguide loss of 18 cm/sup -1/ have been estimated. The gain evolution confirms an earlier assumption that cross-absorption restricted laser action to above 6 μm wavelength.
Keywords :
electroluminescence; optical dispersion; optical losses; quantum cascade lasers; refractive index; waveguide lasers; 5 to 8 micron; 7.4 micron; AlInAs layers; Fabry-Perot spectra; Hakki Paoli method; InGaAs layer; InGaAs-AlInAs; InP; InP substrate; continuous wave mode operation; cross-absorption; gain evolution; global group refractive index change; group refractive index dispersion; modal gain coefficient; semiconductor waveguides; subthreshold electroluminescence spectra; subthreshold gain; ultra-broad-band quantum cascade lasers; waveguide loss; Current measurement; Fabry-Perot; Gain measurement; Laser modes; Performance gain; Performance loss; Quantum cascade lasers; Refractive index; Waveguide lasers; Wavelength measurement;
Journal_Title :
Photonics Technology Letters, IEEE
DOI :
10.1109/LPT.2002.804677
