Spatial filter investigation of the distribution of power between transverse modes in a fiber waveguide

An experiment was carried out in which a method suggested earlier by the present authors was used to investigate the transverse mode composition of multimode coherent light beams. A study was made of multimode beams in a graded-index waveguide excited by a Gaussian beam. The experimental dependences of the coefficients describing the excitation of four modes on the Gaussian beam radius were in agreement with the theory.