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In QCLs there are no effects such as carrier density dependent index of refraction, therefore no current tuning is observed. The only tuning mechanism is temperature tuning of the index of refraction of the waveguide that changes the apparent optical length of the wavelength selection grating. This of course will result in an observable current tuning: the higher the current gets, the higher becomes the average temperature of the active region of the QCL. But this apparent current tuning is based on temperature tuning only.