Alexandr P. Bogatov

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.

Intrinsic spontaneous emission-induced fluctuations of the output optical beam power and phase in a diode amplifier

Output optical beam intensity and phase fluctuations are analysed in a classical approach to describing the propagation and amplification of spontaneous emission in the active region of a laser diode with a gain saturated by input monochromatic light. We find their spectral densities and dispersion and the correlation coefficient of the two-dimensional probability distribution function of the fluctuations.

Heterostructure with extended optical waveguide for diode lasers

The thickness and composition of diode heterolaser layers are optimized with respect to the ratio of the optical beam width d to the optical confinement factor Γ. The stability of the vertical near field distribution and the most important waveguide parameters to static changes and dynamic variations of the refractive indices of heterostructure layers is tested in the laser operation mode.

Anomalous dispersion, differential gain, and dispersion of the α-factor in InGaAs/AlGaAs/GaAs strained quantum-well semiconductor lasers

A new procedure for the experimental determination of the differential gain and dispersion of the amplitude-phase coupling coefficient in semiconductor injection lasers was proposed and implemented. The α-factor and differential gain for InGaAs/AlGaAs/GaAs single quantum well (QW) semiconductor lasers were determined using this procedure in a wide spectral range (from 957 to 996 nm) at various pumping current densities (from 280 to 850 A/cm2). The factor which characterizes the dispersion of the group velocity and restricts the minimum duration of the lasing pulse at the level of 10−13 s was experimentally determined for InGaAs lasers for the first time.

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.