1. In order to provide for the transfer of a large amount of information and to reduce the number of intermediate amplifying devices, it is necessary to increase the power introduced into an optical fiber (1). In the case when the fiber contains a defective seg� ment, the unavoidable absorption and heating of the material result in instability due to absorption rise with temperature (2, 3). When the radiationpower density exceeds its critical value, an opticalbreakdown wave arises that runs along the light guide toward the laser beam (1, 4). Depending on the laserbeam intensity, the wave can be maintained by either the thermalcon� duction mechanism (an analog is the combustion wave (1)) or the hydrodynamic motion (the analog is the detonation wave (3, 4)), the light guide being destroyed in these cases. The present paper is devoted to analysis of the former case and the search for parameters admitting the propagation of this wave. If laser radiation of about 1�W power propagates through a light guide with the opticfiber diameter on the order of 10 micron, then, under certain condi� tions, in the fibercore domain, a white or blue glow arises that moves opposite to the laser beam (1). When the laser acts continuously, the speed of this optical discharge attains about 1 m s -1 . In the pulsed regime (at high power values), the behavior of the discharge is similar to the detonation wave and occurs at a speed on the order of 2 km s -1 , which is commensurable with the velocity (6 km s -1 ) of the longitudinal sound in quartz. Below, we analyze the case when the optical� discharge propagation is similar to that of a slow com� bustion wave (5). The rigorous setting of the problem implies the combined solution of the Maxwell equations and the heatconduction equation (6). We should also know the thermophysical and electrical parameters (e.g., the complex susceptibility) of the opticalfiber material within a wide temperature range from room tempera� ture to ~10 4 K. We restrict our analysis to the simpli�