Statistical and Dynamical Intensity Fluctuations from a Saturated Source of Amplified Spontaneous Emission.

N. B. Abraham, Steven Rathgeb Smith

S. P. Adams, N. B. Abraham

N. B. Abraham, Steven Rathgeb Smith

N. B. Abraham, John C. Huang, David A. Kranz +1 more

Intensity fluctuation characteristics of amplified-spontaneous emission are found using intensity rate equations and the noise-amplifier approximation for saturation coupling between two and four competing modes. The existence of more than one mode leads to the retention of relatively large fluctuations in each mode even as the amplifier gain is saturated, an operating regime which by contrast has been shown to reduce significantly the fluctuations when only a single beam is present. The noise-amplifier approximation is found to be an adequate approximation of the effects of the spontaneous emission distributed along the length of a laser amplifier. The intensity fluctuations in all cases approach limiting distributions functions as the amplifier becomes heavily saturated. Characteristics of these limiting distributions are found for one, two, and four beams; for combinations of beams copropagating and counterpropagating; in the presence and absence of loss; for differences in gain; and for saturation of the sources due to high intensities.

Biman Das, Shaun Giammichele

In an optical amplifier, when the gain is non-linear due to gain saturation, the intensity fluctuation statistics are significantly altered from the statistics of the negative-exponential intensity probability distribution function (IPDF) for spontaneous emission and unsaturated amplifiers. We have systematically computed bivariate moments, trivariate moments and central moments, tetravariate moments, as well as bivariate and trivariate cumulants of intensity fluctuations for non-linear coupled-mode optical systems starting from a k -variable multivariate IPDF of a system of n ( k < n ) coupled modes. The multivariate IPDF is a negative polynomial that rests on the assumption that the variation of intensity has a maximum-intensity distribution with the constraint that the total intensity is constant. The assumption holds for multimode optical systems including a thin, long, mirrorless, gas laser where under heavy gain saturation the output tends to become constant although the intensity of any mode displays rapid fluctuations about the average intensity. The multivariate IPDF reduces to the negative-exponential IPDF of spontaneous emission when n is infinite, as expected. The new results for the multivariate characteristics of the intensity fluctuations have shown characteristic signatures that depend on the number of interacting modes, n . The results are also useful for testing the multivariate IPDFs and identifying n for heavily saturated coupled-mode optical systems.

Evgenii B. Aleksandrov, V. N. Kulyasov