Abstract
Metasurfaces have been enabling the miniaturization and integration of complex optical functionalities within an ultrathin platform by engineering the scattering features of localized modes. However, these efforts have mostly been limited to the manipulation of externally produced coherent light, e.g., from a laser. In parallel, the past two decades have seen the development of structured surfaces that emit partially coherent radiation via thermally populated, spatially extended (nonlocal) modes. However, the control over thermally emitted light is severely limited compared to optical metasurfaces, and even basic functionalities such as unidirectional emission to an arbitrary angle and polarization remain elusive. Here, we derive the necessary conditions to achieve full control over thermally emitted light, pointing to the need for simultaneously tailoring local and nonlocal scattering features across the structure. Based on these findings, we introduce a platform for thermal metasurfaces based on quasibound states in the continuum that satisfies these requirements and completes the program of compactification of optical systems by enabling a full degree of control of partially coherent light emission from structured thin films, including unidirectional emission of circularly polarized light, focusing, and control of spatial and temporal coherence, as well as wave-front control with designer spin and angular orbital momenta.
4 More- Received 31 December 2020
- Revised 11 March 2021
- Accepted 30 April 2021
DOI:https://doi.org/10.1103/PhysRevX.11.021050
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Focus
Customizing Thermal Emission
Published 4 June 2021
Theorists have shown that patterned surfaces can transform the emission from a hot object into a polarized, focused light beam.
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Popular Summary
Thermal radiation consists of light generated by random fluctuations of matter, and, as such, it is ubiquitous in nature and modern technology. When produced from conventional materials, thermal radiation is incoherent, broadband, and uncollimated. By filtering it, bulky optics may shape its spectral content, polarization, and spatial features but only at a significant cost in terms of efficiency and device footprint. Here, we engineer nanostructured thin films that operate as thermal metasurfaces, capable of exquisite command over their own thermal radiation. These devices integrate the effects of bulky filters into a single ultrathin structure without sacrificing efficiency. Based on these findings, we demonstrate the possibility of unidirectional thermal emission of light with chosen spin, efficient focusing, and patterning of emission with wave-front features of choice, including carrying a defined orbital angular momentum.
Our study generally unveils how and why thermal radiation is fundamentally limited in engineered nanostructures, and it introduces a route for passive structures to achieve unprecedented command over thermal radiation based on simultaneously controlling light-matter interactions at subwavelength and superwavelength scales. Correlations at superwavelength scales are necessary to increase the coherence of emitted light; control at the subwavelength length scale is needed to shape the emitted wave front and polarization state; coordination of the response at both scales is required to enable thermal metasurfaces.
Our platform holds the promise to enable custom optical light sources, tunable with intuitive design knobs based on symmetry considerations. Beyond thermal sources and photoluminescence, our design principles can also largely benefit coherent systems by extending the conventional operation of metasurfaces to locally and nonlocally tailor coherent light, which is of great interest for emerging nonlinear and quantum optics applications.