Abstract

We propose and demonstrate a simple and easy-to-implement projective-measurement protocol to determine the radial index p of a Laguerre–Gaussian (LGpl) mode. Our method entails converting any specified high-order LGp0 mode into a near-Gaussian distribution that matches the fundamental mode of a single-mode fiber (SMF) through the use of two phase screens (unitary transforms) obtained by applying a phase-retrieval algorithm. The unitary transforms preserve the orthogonality of modes before the SMF and guarantee that our protocol can, in principle, be free of crosstalk. We measure the coupling efficiency of the transformed radial modes to the SMF for different pairs of phase screens. Because of the universality of phase-retrieval methods, we believe that our protocol provides an efficient way of fully characterizing the radial spatial profile of an optical field.

© 2018 Optical Society of America

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Supplementary Material (2)

NameDescription
» Data File 1       Data for calculating the fidelity of the generated modes. The mode fidelity was determined by calculating the root-mean-squared-error (RMSE) between the ideal and the azimuthally averaged intensity distributions of the various LGlp modes.
» Data File 2       Data showing the coupling efficiencies of different input LG^0_pin modes to the SMF after the application of the phase-screens corresponding to the LG^0_pscreen mode. Here, pin represents the radial index of the input mode.

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