Orbital Angular Momentum States Of Light Research Articles

Identification of Diffracted Vortex Beams at Different Propagation Distances Using Deep Learning

The Orbital angular momentum (OAM) of light is regarded as a valuable resource in quantum technology, especially in quantum communication and quantum sensing and ranging. However, the OAM state of light is susceptible to undesirable experimental conditions such as propagation distance and phase distortions, which hinders the potential for the realistic implementation of relevant technologies. In this article, we exploit an enhanced deep learning neural network to identify different OAM modes of light at multiple propagation distances with phase distortions. Specifically, our trained deep learning neural network can efficiently identify the vortex beam’s topological charge and propagation distance with 97% accuracy. Our technique has important implications for OAM based communication and sensing protocols.

Orbital Angular Momentum Modes (De)multiplexer without Mode Conversion based on Strongly Guiding Coupled Ring-core Fibers

The mode-matching&#x002F;finite-element (MM&#x002F;FE) method based on complex power matching is applied for the design of strongly guiding coupled ring-core fibers (RCFs) to modulate orbital angular momentum (OAM) beams. The evolutions of polarization and OAM states of light in the coupler are investigated. Due to the effects of linear birefringence and spin-orbit interaction (SOI), the OAM beam with opposite polarization and topological charge (TC) is observed at a certain distance to the end of the coupler after the coupling region in the form of complex supermodes. The impacts of separation distance and wavelength on the maximum coupling efficiency and inter-modal crosstalk are investigated to achieve the optimum trade-off between the crosstalk and the coupling length. Two types of OAM couplers with separated OAM modes of TC <inline-formula><tex-math notation="LaTeX">$l = \pm1$</tex-math></inline-formula> are proposed, both of which can achieve high coupling efficiency (<inline-formula><tex-math notation="LaTeX">$\gt 99\%$</tex-math></inline-formula>) and low crosstalk (<inline-formula><tex-math notation="LaTeX">$\rm{\lt - 21\,dB}$</tex-math></inline-formula>) at 1550 nm wavelength without mode conversion. The proposed design approach has great potential in the (de)multiplexing of OAMs since it leads to a novel mechanism for sorting OAM modes in waveguides without destroying the integrity of OAM modes.

Broadband detection of multiple spin and orbital angular momenta via dielectric metasurface.

Light beams carrying spin angular momentum (SAM) and orbital angular momentum (OAM) have created novel opportunities in the areas of optical communications, imaging, micromanipulation and quantum optics. However, complex optical setups are required to simultaneously manipulate, measure and analyze these states, which significantly limits system integration. Here, we introduce a novel detection approach for measuring multiple SAM and OAM modes simultaneously through a planar nanophotonic demultiplexer based on an all-dielectric metasurface. Coaxial light beams carrying multiple SAM and OAM states of light upon transmission through the demultiplexer are spatially separated into a range of vortex beams with different topological charge, each propagating along a specific wavevector. The broadband response, material dispersion and momentum conservation further enable the demultiplexer to achieve wavelength demultiplexing. We envision the ultracompact multifunctional architecture to enable simultaneous manipulation and measurement of polarization and spin encoded photon states with applications in integrated quantum optics and optical communications.

High-purity orbital angular momentum states from a visible metasurface laser

Orbital angular momentum (OAM) from lasers holds promise for compact, at-source solutions for applications ranging from imaging to communications. However, conjugate symmetry between circular spin and opposite helicity OAM states (±l) from conventional spin–orbit approaches has meant that complete control of light’s angular momentum from lasers has remained elusive. Here, we report a metasurface-enhanced laser that overcomes this limitation. We demonstrate new high-purity OAM states with quantum numbers reaching l = 100 and non-symmetric vector vortex beams that lase simultaneously on independent OAM states as much as Δl = 90 apart, an extreme violation of previous symmetric spin–orbit lasing devices. Our laser conveniently outputs in the visible, producing new OAM states of light as well as all previously reported OAM modes from lasers, offering a compact and power-scalable source that harnesses intracavity structured matter for the creation of arbitrary chiral states of structured light. A metasurface laser generates orbital angular momentum states with quantum numbers reaching l = 100. Simultaneous output vortex beams, with Δl as great as 90, are demonstrated in the visible regime.

High-dimensional structured light coding/decoding for free-space optical communications free of obstructions.

Bessel beams carrying orbital angular momentum (OAM) with helical phase fronts exp(ilφ)(l=0;±1;±2;…), where φ is the azimuthal angle and l corresponds to the topological number, are orthogonal with each other. This feature of Bessel beams provides a new dimension to code/decode data information on the OAM state of light, and the theoretical infinity of topological number enables possible high-dimensional structured light coding/decoding for free-space optical communications. Moreover, Bessel beams are nondiffracting beams having the ability to recover by themselves in the face of obstructions, which is important for free-space optical communications relying on line-of-sight operation. By utilizing the OAM and nondiffracting characteristics of Bessel beams, we experimentally demonstrate 12 m distance obstruction-free optical m-ary coding/decoding using visible Bessel beams in a free-space optical communication system. We also study the bit error rate (BER) performance of hexadecimal and 32-ary coding/decoding based on Bessel beams with different topological numbers. After receiving 500 symbols at the receiver side, a zero BER of hexadecimal coding/decoding is observed when the obstruction is placed along the propagation path of light.