It’s necessary to upgrade the existing scheme automatic control of the optical signal. The presented design was created to maintain the output power of an atomic frequency standard (AFS) based on rubidium-87 atoms at a given level, correcting changes in its operation introduced by external conditions. An improved circuit for automatic gain control with an additional link in the form of a proportional-integral-derivative (PID) controller and an improved circuit for extracting the ‘error’ signal are presented. A separate contribution of the subtractor and PID controller to the final gain control is considered, and mathematical modeling of microwave devices included in the microwave path is carried out.