Complete experimental evaluation of the carrier dependence of the refractive index from the frequency modulation spectra of single mode injection lasers

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Abstract
A new method of evaluating the dependence on carrier density of the propagation constant of the excited mode of a semiconductor laser biased above threshold is applied to a single mode confined double heterostructure-large optical cavity laser operated at 8-mW dc. The method combines the measurements of the Fabry–Perot spectrum of the modulated laser, the relative modulation amplitudes of the coherent and short-wavelength spontaneous powers and the phase difference between the two, and the dependence on dc current of the two emissions. The evaluation is independent of the model of the lasing state, the reduction of the raw data requiring only subthreshold relations between current, voltage, carrier density, and spectrum. The change of the index of refraction of the waveguide mode with the concentration of electron-hole pairs in the recombination region is +1.8×10−22 cm3. Striking inconsistencies among various published accounts indicate a need for critical examination of all such studies.