Andrew Forbes works at University of the Witwatersrand.

Posts

Optical orbital angular momentum analogy to the Stern-Gerlach experiment

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Symmetry breaking has been shown to reveal interesting phenomena in physical systems. A notable example is the fundamental work of Otto Stern and Walther Gerlach [Stern and Zerlach, Z. Physik 9, 349 (1922)] nearly 100 years ago demonstrating a spin angular momentum (SAM) deflection that differed from classical theory. Here we use non-separable states of SAM and orbital angular momentum (OAM), known as vector vortex modes, to demonstrate how a classical optics analogy can be used to reveal this nonseparability, reminiscent of the work carried out by Sternand Gerlach. We show that by implementing a polarization insensitive device to measure the OAM, the SAM states can be deflected to spatially resolved positions.

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The Resilience of Hermite- and Laguerre-Gaussian Modes in Turbulence

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Vast geographical distances in Africa are a leading cause for the so-called digital divide due to the high cost of installing fiber. Free-space optical (FSO) communications offer a convenient and higher bandwidth alternative to point-to-point radio microwave links, with the possibility of repurposing existing infrastructure. Unfortunately, the range of high-bandwidth FSO remains limited. While there has been extensive research into an optimal mode set for FSO to achieve maximum data throughput by mode division multiplexing, there has been relatively little work investigating optical modes to improve the resilience of FSO links. Here, we experimentally show that a carefully chosen subset of Hermite-Gaussian modes is more resilient to atmospheric turbulence than similar Laguerre-Gauss beams, with a predicted upper bound increase in propagation distance of 167% at a mode-dependent loss of 50%.

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