Frequency control of self-sustained pulsating laser diodes by uniform impurity doping into multiple-quantum-well structures

The self-sustained pulsating frequency in index guided AlGaAs multiple-quantum-well (MQW) laser diodes is controlled by impurity doping into the active region to reduce the relative intensity noise induced by optical feedback through a short optical path. Uniform n-type impurity doping into an MQW structure more effectively reduces the frequency by decreasing the differential gain than does modulation doping with an n-type impurity. Uniform doping of 1/spl times/10/sup 18/ cm/sup -3/ into each quantum well layer reduces the frequency to less than 0.8 GHz, which corresponds to half or two-thirds that of undoped lasers. The uniformly n-doped self-sustained pulsating lasers provided low noise characteristics with a relative intensity noise below 1/spl times/10/sup 3/ Hz/sup -1/ under an optical feedback of 20% even with a short optical path length of 60 mm.