Calculation of a single-mode fiber optic attenuator

Optical attenuators are designed to introduce preset adjustable attenuation into optical fiber systems. They are used for tuning and adjusting equipment, as well as in systems for automatic gain control of optoelectronic converters and for metrological certification of control and measuring equipment for fiber-optic information transmission systems. To create a mathematical model of a fiber-optic attenuator, the principle of operation of which is based on the longitudinal displacement of fiber optic fibers. The Gauss-Laguerre beam method is used to represent the field in the space between optical fibers. To solve the diffraction problem at the end of an optical fiber, the method of mode orthogonality and the method of orthogonality of eigenfunctions are used. The radiation from the end of the fiber optic is represented as a Gaussian beam. The radius of the Gaussian beam increases as it propagates along the axis. At the same time, the greater the distance from the emitting fiber optic is the receiving fiber optic, the smaller the part of the total optical radiation power gets into its core. The rest is distributed in the shell and can be filtered out by the shell mode filter. A method for calculating a tunable fiber-optic attenuator is proposed, the principle of operation of which is based on the longitudinal displacement of fiber optic fibers. Two-layer (optical fiber in a metal tube) and three-layer (optical fiber in an open space) models are considered. The results of calculating attenuation of attenuators depending on the distance between the ends of optical fibers are presented. The initial nonlinear section of the dependence of attenuation on the distance between the fibers is theoretically justified.