Spatial-diversity detection of optical vortices for OAM signal modulation

Area of Science:

• Optical physics
• Information optics
• Wavefront sensing

Background:

• Orbital angular momentum (OAM) multiplexing is a promising technique for increasing data transmission capacity.
• Accurate identification of OAM states is crucial for reliable OAM-based communication systems.
• Existing methods for OAM state detection can be sensitive to environmental disturbances like beam wandering.

Purpose of the Study:

• To propose and validate a novel method for identifying orbital angular momentum (OAM) states in vortex superpositions.
• To develop a robust OAM detection technique that mitigates the effects of beam wandering.
• To demonstrate the efficacy of the proposed method in a practical experimental setup.

Main Methods:

• Utilizing a Shack-Hartmann (SH) sensor as a spatial-diversity detector to analyze vortex superpositions.
• Defining and calculating local OAM at each pixel of the SH sensor image.
• Constructing an OAM spectrum from local OAM measurements.
• Employing a low-complexity algorithm to determine topological charges from the OAM spectrum.

Main Results:

• Successfully identified OAM states within vortex superpositions using the proposed SH sensor-based method.
• The developed algorithm demonstrated robustness against beam wandering, a common challenge in optical transmissions.
• The technique was validated through successful testing on experimental data from a 200 m transmission link.

Conclusions:

• The proposed Shack-Hartmann sensor-based method provides an effective and robust approach for identifying OAM states.
• The technique's resilience to beam wandering makes it suitable for practical OAM communication systems.
• This method advances the field of OAM detection and has potential applications in high-capacity optical communications.