Experimental demonstration of advanced photonic systems leads to boosted performance

Press/Media: STE Highlight

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(a) An incident beam impinging on the metasurface is converted into a different frequency harmonic that can be focused at any desired focal point. (b) Breakdown of Lorentz reciprocity can be shown by probing the time-reversed process. (c) Photograph of the spatio-temporally modulated metasurface. (d) Top view and cross-section of the unit cell.

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Researchers from Los Alamos National Laboratory, in collaboration with Duke University, demonstrated that ultrathin artificial composites, called metasurfaces, help realize unprecedented electromagnetic phenomena.

In general, the fundamental principle of Lorentz reciprocity governs the functionalities of photonic systems, imposing constraints such as re-emission of absorbed solar energy from photovoltaic cells or transmitting antennas listening to their echoes. This unwanted reciprocity can result in decreased performance.

To boost the performance of these photonic systems, the researchers aimed to break the reciprocity.

“Our goal in this paper was to demonstrate the complete violation of Lorentz reciprocity via mode-conversion,” said Abul Azad, Center for Integrated Nanotechnologies (MPA-CINT).

Violating the Lorentz theorem

Elimination of unwanted reciprocity in photonic systems is challenging. To do so requires violating the Lorentz reciprocity theorem, which states that in a linear, time-independent system with symmetric constitutive optical tensors, the ratio between received and transmitted fields are the same for forward and time-reversed propagation directions.

The researchers introduced a spatio-temporally modulated metasurface (STMM)—an artificial composite material that can convert an incident light beam into a different (non-reciprocal) wave harmonic. In the presence of spatio-temporal modulation, the metasurface allows reflection for the forward scattering direction via photon-to-photon conversion. However, for backward scattering, photons completely couple to surface waves via photon-to-surface wave conversion. This introduces an extreme breakdown of Lorentz reciprocity, leading to giant optical isolation, as no propagative modes are radiated in reverse scattering.

Efficiencies can be improved

The researchers focused on making theoretical predictions and confirming those predictions through experiments. Their work sets the foundation for further modification and improvement.

One such future improvement for the STMM is increasing the conversion efficiency. Currently, most of the reflected power resides in the fundamental harmonic. This can be addressed by using non-harmonic asymmetric time-modulation protocols. In principle, these modifications could result in conversion efficiencies greater than 80 percent.

By independently addressing each individual resonator, the STMM can be used for three-dimensional wave-front shaping, including dynamic beam steering, focusing, and generation of optical angular momentum. The STMM will enable compact multifunctional photonic components with built-in isolators for wireless communication and remote sensing.

Funding and mission

This research was supported by a LANL Laboratory Directed Research and Development (LDRD) award. Part of this work was performed at the Center for Integrated Nanotechnologies (CINT), a U.S. Department of Energy, Office of Basic Energy Sciences user facility. The work supports the Laboratory’s Energy Security mission and the Materials for the Future capability pillar.

Reference: Cardin, A. E., Silva, S. R., Vardeny, S. R. et al. “Surface-wave-assisted nonreciprocity in spatio-temporally modulated metasurfaces.” Nat Commun 11, 1469 (2020). https://doi.org/10.1038/s41467-020-15273-1

Technical contact: Abul Azad

PeriodAug 31 2020

Media coverage

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Media coverage

  • TitleExperimental demonstration of advanced photonic systems leads to boosted performance
    Date08/31/20
    PersonsAbul Kalam Azad, Andrew E. Cardin, Sinhara Rishi Malinda Silva, Shai Raul Vardeny, Andrew E. Cardin, Sinhara Rishi Malinda Silva, Shai Raul Vardeny

Media Type

  • STE Highlight

Keywords

  • LA-UR-20-26731

STE Mission

  • Energy Security

STE Pillar

  • Materials for the Future

STE Publication Year

  • 2020