Influence of spatially inhomogeneous gain saturation, caused by a standing wave, on the amplitude — frequency modulation characteristic of semiconductor laser radiation

The framework of linearised laser equations for the field and charge carriers is used to obtain an analytic expression which describes the modulation response function of a semiconductor laser and takes account of spatially inhomogeneous gain saturation caused by a standing wave. Account is also taken of spatial variations of the carrier density along the cavity axis, which appear because of different rates of stimulated recombination near the standing-wave nodes and antinodes, and because of ‘expulsion’ of free carriers from the wave antinodes by electrostriction forces. It is shown that the influence of the standing wave leads to a change in the response function near a resonant frequency f₀ and has a minor effect on the value of this function at frequencies exceeding f₀. Therefore, this influence has practically no effect on the maximum modulation frequency f_m of a semiconductor laser.