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Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection

Nature Photonics volume 1, pages 176–179 (2007)Cite this article

Abstract

In 1880, by studying light passing through Earth's atmosphere, Lord Rayleigh mathematically demonstrated that graded-refractive-index layers have broadband antireflection characteristics1. Graded-index coatings with different index profiles have been investigated for broadband antireflection properties, particularly with air as the ambient medium2,3,4. However, because of the unavailability of optical materials with very low refractive indices that closely match the refractive index of air, such broadband antireflection coatings have not been realizable. Here we report the fabrication of TiO2 and SiO2 graded-index films deposited by oblique-angle deposition, and, for the first time, we demonstrate their potential for antireflection coatings by virtually eliminating Fresnel reflection from an AlN–air interface over a broad range of wavelengths. This is achieved by controlling the refractive index of the TiO2 and SiO2 nanorod layers, down to a minimum value of n = 1.05 in the case of the latter, the lowest value so far reported.

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Figure 1: Low-n material.
Figure 2: Different index profiles for graded-index coating.
Figure 3: TiO2–SiO2 graded-index coating.
Figure 4: Reflectivity of graded-index coating.

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Acknowledgements

The authors gratefully acknowledge support from Sandia National Laboratories (USA), Crystal IS Corporation (USA), Samsung Advanced Institute of Technology (Korea), the Army Research Office (USA), the New York State Office of Science, Technology and Academic Research (USA), the National Science Foundation (USA) and the Department of Energy (USA).

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Authors and Affiliations

  1. Future Chips Constellation, Rensselaer Polytechnic Institute, 110 8th Street, Troy, 12180, New York, USA

    J.-Q. Xi, Martin F. Schubert, Jong Kyu Kim, E. Fred Schubert, Minfeng Chen & Shawn-Yu Lin

  2. Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, 12180, New York, USA

    J.-Q. Xi, E. Fred Schubert & Shawn-Yu Lin

  3. Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, 12180, New York, USA

    Martin F. Schubert, Jong Kyu Kim & E. Fred Schubert

  4. Graduate Institute of Electro-Optical Engineering, National Taiwan University, Taipei, Taiwan, R.O.C.

    Minfeng Chen

  5. Crystal IS, Inc, Green Island, 12183, New York, USA

    W. Liu & J. A. Smart

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  1. J.-Q. Xi
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Correspondence to E. Fred Schubert.

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Xi, JQ., Schubert, M., Kim, J. et al. Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection. Nature Photon 1, 176–179 (2007). https://doi.org/10.1038/nphoton.2007.26

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