Time-varying orbital angular momentum generated by a metasurface
Time-varying orbital angular momentum generation by a digitally encoded metasurface.
Credit: Zhang et al, doi 10.1117/1.AP.5.3.036001
Researchers encode a metasurface to generate time-varying OAM beams, for a higher order twist on structured light.
The orbital angular momentum (OAM) of electromagnetic waves — a kind of “structured light” — is associated with a helical or twisted wavefront. The helical modes are characterized by a topological charge. OAM beams with distinct topological charges are mutually orthogonal, which allows them to carry information and to be multiplexed. OAM multiplexing affords increased channel capacity and spectral efficiency — highly useful in fiber-based and free-space communications. OAM beams also have qualities that are useful for optical trapping, lattices, and more.
Unlocking the potential of OAM has advanced thanks to persistent research efforts globally. As reported in Advanced Photonics, researchers from The Hong Kong University of Science and Technology (HKUST) and City University of Hong Kong (CityU) recently developed time-varying OAM beams using a space-time encoded digital metasurface. They used a field-programmable gate array (FPGA) to control the reflection phase of the atoms at the metasurface in the microwave regime.
By exploiting the flexible programmability of the metasurface, they construct different modes of the time-varying OAM beams having a time-dependent phase profile in each time layer. This allows not only a time-varying topological charge but also a higher-order twist in the envelope wavefront structure of the OAM beam in terms of a nonlinear time-dependence in phase, which functions as an additional degree of freedom to allow greater capacities for application.
For their experimental demonstration, the team developed a two-probe mapping method to dynamically map the time-varying OAM field including amplitude and phase patterns at various instants of time. In addition, they performed spectrum analysis targeting OAM mode decomposition on measured field patterns, which demonstrated the high mode purity of the generated time-varying OAM and the designed higher-order twist in the envelope wavefront structure.
Their innovative approach, combining the metasurface’s space-time digital encoding and the two-probe field mapping technique, results in a versatile platform for generating and observing time-varying OAM — as well as other spatiotemporal excitations.
The proposed time-varying OAM beams have application potential for dynamic particle trapping, time-division multiplexing, information encryption, and beyond.
Read the Gold Open Access article by J. Zhang et al., “Generation of time-varying orbital angular momentum beams with space-time-coding digital metasurface,” Adv. Photon. 5(3), 036001 (2023), doi 10.1117/1.AP.5.3.036001.
Journal: Advanced Photonics
DOI: 10.1117/1.AP.5.3.036001
Article Title: Generation of time-varying orbital angular momentum beams with space-time-coding digital metasurface
Article Publication Date: 17-Apr-2023
Media Contact
Daneet Steffens
SPIE–International Society for Optics and Photonics
daneets@spie.org
Office: 360-685-5478
All latest news from the category: Physics and Astronomy
This area deals with the fundamental laws and building blocks of nature and how they interact, the properties and the behavior of matter, and research into space and time and their structures.
innovations-report provides in-depth reports and articles on subjects such as astrophysics, laser technologies, nuclear, quantum, particle and solid-state physics, nanotechnologies, planetary research and findings (Mars, Venus) and developments related to the Hubble Telescope.
Newest articles
Pinpointing hydrogen isotopes in titanium hydride nanofilms
Although it is the smallest and lightest atom, hydrogen can have a big impact by infiltrating other materials and affecting their properties, such as superconductivity and metal-insulator-transitions. Now, researchers from…
A new way of entangling light and sound
For a wide variety of emerging quantum technologies, such as secure quantum communications and quantum computing, quantum entanglement is a prerequisite. Scientists at the Max-Planck-Institute for the Science of Light…
Telescope for NASA’s Roman Mission complete, delivered to Goddard
NASA’s Nancy Grace Roman Space Telescope is one giant step closer to unlocking the mysteries of the universe. The mission has now received its final major delivery: the Optical Telescope…