We calculate the modal power distribution of a randomly and linearly polarized (LP) multimode beam inside a cylindrical fiber core from knowledge of spatial-intensity profiles of a beam emitted from the fiber. We provide an exact analysis with rigorous proofs that forms the basis for our calculations. The beam from the fiber end is collimated by a spherical lens with a specific focal length. The original LP-mode basis is transformed by the spherical lens and forms another orthogonal basis that describes the free-space beam. By using this basis, we calculate the modal power distribution from the mutual-intensity profile. This is acquired by adopting a well-known mutual-intensity-profile-retrieving technique based on measurements of the intensity patterns several times after two orthogonal cylindrical lenses with varying separation. The feasibility of our decomposition algorithm is demonstrated with simulations.
© 2004 Optical Society of America
Daniel Beom Soo Soh, Johan Nilsson, Seungin Baek, Christophe Codemard, Yoonchan Jeong, and Valery Philippov, "Modal power decomposition of beam intensity profiles into linearly polarized modes of multimode optical fibers," J. Opt. Soc. Am. A 21, 1241-1250 (2004)