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Measurement of the radial mode spectrum of photons through a phase-retrieval method



Omar S. Magana Loaiza


We propose and demonstrate a simple and easy-to-implement projective-measurement protocol to determine the radial index š¯‘¯ of a LaguerreĀ–Gaussian (LGš¯‘™š¯‘¯) mode. Our method entails converting any specified high-order LG0š¯‘¯ 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.
Optics Letters


Paraxial wave optics, spatial light modulators, phase retrieval and optical fibers
Created December 14, 2018, Updated July 8, 2019