Statistics of intensity of backscattered semiconductor laser radiation in single-mode optic fiber

We have studied the statistics of the intensity of backscattered radiation of a semiconductor laser in single-mode optic fiber as a function of the probing laser pulse duration and coherence time. It is shown that, at a given radiation source coherence time, the intensity distribution function varies, depending on the pulse duration, from nearly exponential to nearly Gaussian. The exponential statistics provides a better sensitivity for a coherent reflectometer with direct detection. Using the calculated distribution function, it is possible to qualitatively determine the degree of deterioration of the reflectometer sensitivity with respect to external factors during increasing probing pulse duration or decreasing laser coherence time. These data provide criteria for the optimum choice of a radiation source for the coherent fiber-optic reflectometer.