High-efficiency measurement of all orbital angular momentum modes in a light beam

  title={High-efficiency measurement of all orbital angular momentum modes in a light beam},
  author={Haad Yaqub Rathore and Mumtaz Sheikh and Usman A. Javid and Hamza Ahmed and Syed Azer Reza},
  journal={Journal of The Optical Society of America B-optical Physics},
We present an experimental demonstration of a Laguerre–Gauss (LG) spectrum measurement technique using variable focus lenses that is able to measure the strengths of the constituent modes in an unknown incoming light beam with the highest possible efficiency. The experiment modifies the classical projective, phase flattening technique by including a variable-sized pinhole and a two-electronic-lens variable imaging system that is tuned for each mode to give the highest possible detection… 

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A method is demonstrated which uses a series of unitary optical transformations to enable the measurement of light's OAM with an experimental separation efficiency of >92%, which makes it particularly attractive for enhancing the information capacity of multi-level quantum cryptography systems.

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