Transformation of paraxial beams in arbitrary multimode parabolic-index fiber tapers by using a quantum-theoretical...

The transformation of Gauss-Laguerre beams with a spherical wave front in a parabolic-index taper as well as the mode-coupling coefficients between the beams and the modes of the fiber behind the taper was analytically investigated in paraxial approximation by using a quantum-theoretical formalism. The taper model that is used here has an infinitely extended parabolic-index profile with an arbitrary longitudinal variation. For such taper elements we have demonstrated some matching and mode-filtering properties, which may be useful for different applications.