Generation of radio signals in a system composed of a laser and an optical delay line

An analysis is made of self-modulation oscillations which appear in a fiber-optic communication line forming a closed ring and excited by a semiconductor laser diode. An equivalent circuit of a real laser diode, allowing for its inertia, and representation of a fiber waveguide by an optical delay line are used to obtain expressions for the self-modulation amplitude and frequency, and for the dependence of the modulation frequency on the fiber waveguide parameters and on the operating conditions in the laser diode. Experimental results are shown to support the theoretical conclusions.