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Fano-resonant ultrathin film optical coatings


Optical coatings are integral components of virtually every optical instrument. However, despite being a century-old technology, there are only a handful of optical coating types. Here, we introduce a type of optical coatings that exhibit photonic Fano resonance, or a Fano-resonant optical coating (FROC). We expand the coupled mechanical oscillator description of Fano resonance to thin-film nanocavities. Using FROCs with thicknesses in the order of 300 nm, we experimentally obtained narrowband reflection akin to low-index-contrast dielectric Bragg mirrors and achieved control over the reflection iridescence. We observed that semi-transparent FROCs can transmit and reflect the same colour as a beam splitter filter, a property that cannot be realized through conventional optical coatings. Finally, FROCs can spectrally and spatially separate the thermal and photovoltaic bands of the solar spectrum, presenting a possible solution to the dispatchability problem in photovoltaics, that is, the inability to dispatch solar energy on demand. Our solar thermal device exhibited power generation of up to 50% and low photovoltaic cell temperatures (~30 °C), which could lead to a six-fold increase in the photovoltaic cell lifetime.

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Fig. 1: Fano resonance in thin-film optical coatings.
Fig. 2: Demonstration and properties of Fano-resonant optical coatings.
Fig. 3: FROC as a beam splitter filter.
Fig. 4: FROCs for hybrid thermal-electric solar energy conversion.

Data availability

The raw numerical data for the figures in the manuscript, as well as the code on the thin-film coupled oscillator theory, are available via GitHub at


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We thank M. Mann and J. A. Fenster for their assistance in taking high-quality photos. We thank H. M. Cao for providing assistance in schematics. M.E. acknowledges fruitful discussions with K. Singer. C.G. acknowledges the support of the Army Research Office, the National Science Foundation and AlchLight. G.S. and M.H. acknowledge the support of the National Science Foundation.

Author information




M.E., C.G., G.S. and M.H. discussed and defined the project. C.G., G.S. and M.H. supervised the research. M.E. developed the approach and initiated the project. T.L., S.A.J., C-H.F. and M.E. fabricated the samples. M.E., T.L., J.R., S.A.J. and N.H. performed the experiments. M.H. developed the coupled oscillator theory. M.E. and J.Z. performed FDTD simulations. M.E. wrote the manuscript with input from all the authors. All authors discussed the results.

Corresponding authors

Correspondence to Mohamed ElKabbash or Michael Hinczewski or Giuseppe Strangi or Chunlei Guo.

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Competing interests

A patent application has been filed on the Fano resonance optical coating scheme in this work.

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Peer review information Nature Nanotechnology thanks Koray Aydin and Jiming Bao for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Discussion, Figs. 1–17, Table 1 and equations (1)–(4) and refs. 1–12.

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ElKabbash, M., Letsou, T., Jalil, S.A. et al. Fano-resonant ultrathin film optical coatings. Nat. Nanotechnol. 16, 440–446 (2021).

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