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The light-current characteristic (LCC) of quantum dot (QD) lasers is studied in the presence of internal optical absorption loss, which varies with charge carrier density in the waveguide region. Depending on the parameters of the structure, the LCC is shown to be either one- or two-valued. In one-valued LCC, the output optical power increases with increasing injection current, approaches its maximum, rolls over on further increasing current, and finally goes to zero at the maximum operating current. The output power in the first branch of a two-valued LCC behaves similarly to that in a one-valued LCC with the only difference that it is non-zero at the maximum operating current, beyond which the lasing quenches. Besides, at a certain current (second threshold current) exceeding the threshold current for the first branch (first threshold current), the second branch emerges in the LCC. The output power in this branch increases monotonously with increasing current; at the maximum operating current (which is the same as that for the first branch), the two branches merge together. An analytical criterion is derived, which determines whether the LCC will be one- or two-valued. The following parameters enter into this criterion and hence control the shape of the LCC: cross-section of internal loss, maximum modal gain (which, in turn, is controlled by the QD-size dispersion), cross-section of carrier capture into QDs, thickness of the waveguide region, and spontaneous radiative recombination coefficient in that region. The transformation of the LCC shape (from one- to two-valued), which occurs via the variation of the above parameters, is discussed.
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