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Proceedings Paper

Modal decomposition for measuring the orbital angular momentum density of light
Author(s): Christian Schulze; Daniel Flamm; Angela Dudley; Andrew Forbes; Michael Duparré
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Paper Abstract

We present a novel technique to measure the orbital angular momentum (OAM) density of light. The technique is based on modal decomposition, enabling the complete reconstruction of optical fields, including the reconstruction of the beams Poynting vector and the OAM density distribution. The modal decomposition is performed using a computer-generated hologram (CGH), which allows fast and accurate measurement of the mode spectrum. The CGH encodes the modes of interest, whose powers and relative phase differences are measured from the far-field diffraction pattern of the illuminating optical field with the hologram transmission function. In combination with a classical measurement of Stokes parameters, including a polarizer and a quarter-wave plate in front of the hologram, the polarization state of each mode is measured. As a consequence, any arbitrary vector field can be reconstructed, including amplitude, phase, and polarization. Having all information on the optical field, the Poynting vector and the OAM density can be calculated directly. We applied our method to beams emerging from optical fibers, which allows us to investigate arbitrary coherent superposition of fiber modes with complexly shaped intensity and polarization distributions. The excitation of certain mode mixtures is done by appropriate input coupling and using diffractive phase masks to shape the input beam and hence enhance the excitation efficiency of distinct modes. The accuracy of the achieved results is verified by comparing the reconstructed with the directly measured beam intensity, revealing excellent agreement.

Paper Details

Date Published: 5 March 2013
PDF: 8 pages
Proc. SPIE 8637, Complex Light and Optical Forces VII, 863719 (5 March 2013); doi: 10.1117/12.2004263
Show Author Affiliations
Christian Schulze, Friedrich-Schiller-Univ. Jena (Germany)
Daniel Flamm, Friedrich-Schiller-Univ. Jena (Germany)
Angela Dudley, Council for Scientific and Industrial Research, National Laser Ctr. (South Africa)
Andrew Forbes, Council for Scientific and Industrial Research, National Laser Ctr. (South Africa)
Michael Duparré, Friedrich-Schiller-Univ. Jena (Germany)

Published in SPIE Proceedings Vol. 8637:
Complex Light and Optical Forces VII
Jesper Glückstad; David L. Andrews; Enrique J. Galvez, Editor(s)

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