Observation of Intrinsic Quantum Fluctuations in Semiconductor Lasers

In this paper we report the first experimental observation of the excitation of the spiking resonance in a semiconductor laser by the quantum fluctuations intrinsic to the lasing process. Such excitation and the resulting anomalous peaks in the microwave noise spectrum of the laser intensity were initially predicted by McCumber and later calculated in detail for semiconductor lasers by Haug. In the present observations made with continuously operating GaAs junction lasers, this anomalous peak has been observed at currents I from less than 1% to nearly 100% above threshold I(th). The frequency of the peak varied with current a (I/I(th)-1)(1/2), in agreement with previous analytical results. However, the resonant frequency was observed to be independent of temperature between 80 and 150 degrees K, in apparent contradiction with the recent calculations of Haug.