INTENSITY FLUCTUATIONS OF AMPLIFIED SPONTANEOUS EMISSION IN BIDIRECTIONAL LASER-AMPLIFIERS

Intensity fluctuations of amplified spontaneous emission (ASE) in a bidirectional laser amplifier are analysed using a noise amplifier rate equation model. In contrast to the unidirectional case, in which saturation leads to laserlike intensity statistics, we have found that the saturation, as the mechanism for coupling between the counter-propagating beams, in general leads to a non-zero asymptotic value for the intensity fluctuations. For a symmetric amplifier the normalized variance of the output intensity fluctuations declines with increasing amplifier length from the initial value of unity to a limiting value of approximately 0·277. In contrast, when the noise sources of the two counter-propagating beams have unequal mean intensities, the normalized variance of the stronger beam declines more rapidly with length to less than 0·277 while for the weaker beam it reaches a limiting value greater than 0·277. We also find that there are features of the mode competition which are closely related to those observed in a two-mode ring laser. © 1979 Taylor & Francis Group, LLC.