Aleksei A. Stratonnikov

Phase and amplitude fluctuations in α-DFB lasers due to spontaneous emission

Fluctuations in the single-frequency operation of an ?-DFB laser due to spontaneous emission are considered theoretically. A semi-classical approach is used, which is based on the scalar wave equation for the field; the complex field distribution inside the cavity and spatial hole burning (SHB) are accounted for. The expressions for the linewidth and the spectral density of the low-frequency power fluctuations are obtained. The dependences of these quantities on the pumping level are calculated using a numerical model of the ?-DFB laser. These dependences show non-trivial behaviour owing to the SHB and the field distribution changing with increasing pumping. The calculations show that the natural linewidth of such a laser may be as low as ?kHz, which is about three orders of magnitude less than typical values for the solitary diode lasers. This is the result of a good spectral and spatial selectivity of the ?-DFB laser cavity.

Brightness and filamentation of a beam from powerful cw quantum-well In{sub 0.2}Ga{sub 0.8}As/GaAs lasers

Near- and far-field patterns are studied for powerful (above 2-W cw output) quantum-well heterojunction InGaAs/AlGaAs/GaAs lasers. The maximum radiation brightness was 1.7107 W cm-2 sr-1. It is shown that the radiation filamentation is already observed 10 — 20% above the lasing threshold. The filamentation period decreases from 50 to 10 μm with increasing pumping current from almost the lasing threshold to an excess of 20% over the threshold. The filamentation results in the tenfold decrease in the radiation brightness of lasers compared to the theoretical value.