A team of scientists from FSUE VNIIA im. NL Dukhova “State Corporation” Rosatom “, MSTU im. N.E.Bauman and ITSP RAS succeeded in creating plasmonic waveguides based on thin gold films with a record propagation length of 250 μm. New waveguides with unique properties will find application in integrated optical circuits, high-sensitivity waveguide sensors, as well as optical interconnects for high-performance computing systems of a new generation.
Integral waveguide optics (waveguides are microscopic wires, but not for electric current, but for light) is a rapidly developing area of modern physics and technology. It opens up new possibilities for transmitting and controlling signals on microcircuits, manufacturing ultrasensitive chemical and biological sensors, optical gyroscopes, accelerometers, spectrometers and other sensors. The use of integrated optics technologies makes it possible to create miniature and low-cost devices with low power consumption, which, for example, can be built into various modern portable gadgets.
One of the promising types of optical waveguides are plasmonic waveguides with transverse dimensions less than the operating wavelength of light. It is not just light that propagates along such waveguides, but the so-called plasmons – coupled oscillations of the light field and conduction electrons (electron plasma) in a metal. It is plasmonic waveguides that have properties that make them, in some cases, more preferable for use than traditional dielectric or semiconductor waveguides, for example, made of silicon. The point is that plasmon waveguides often allow direct connection of electronic and optical components of nanodevices without additional converters.
The plasmon wave has a high localization of the field near the metal surface, for example, in narrow (less than 500 nm wide) gaps between metal structures or on various metal objects on a nanometer scale. Such a localized field makes it possible to enhance the interaction of the plasmon with the substance surrounding the metal. This property is widely used to enhance the sensitivity of chemical and biological sensors, as well as to increase the efficiency and speed of switches (modulators) of optical signals transmitted through waveguides on a chip. In addition, due to the high reflectivity of the metal, it is possible to create miniature and highly efficient components for controlling plasmons in waveguides: their excitation, redirection and focusing, as with ordinary light using lenses and mirrors. Such elements are plasmonic diffraction gratings, plasmonic mirrors and plasmonic antennas. Another advantage of plasmonic waveguides is that the metal films on the basis of which they are made can be used as built-in electrodes to control the properties of plasmonic devices.
Optical plasmonic waveguide Al2O3 / Au / Al2O3. (a) Model of an optical plasmon waveguide. SEM images of an optical plasmon waveguide: (b) an input element in the form of a grating, (c) an output element in the form of a grating, (d) an enlarged image of a grating.
In the joint REC “Functional micro- / nanosystems” of FSUE “VNIIA im. NL Dukhova “State Corporation” Rosatom “and MSTU im. N.E.Bauman developed a technology for creating plasmon waveguides based on thin gold films, demonstrating unsurpassed characteristics – a record free path of a surface plasmon of 250 μm at optical wavelengths. At the same time, the results obtained are fully consistent with the predicted results of numerical simulations carried out by a team of theoreticians under the leadership of Alexander Merzlikin, Deputy Director for Science, ITPE RAS. An experimental study of the created plasmonic devices was carried out by the Dukhov VNIIA in the laboratory of Alexander Baryshev. The demonstrated signal propagation length is the record for a similar type of plasmon waveguide based on gold published in the literature.
“The achieved record length of signal propagation is the result of model optimization of the plasmon waveguide design and the high level of technology developed in Baumanke. Due to the high degree of homogeneity of thin gold films, attenuation and scattering of plasmons in them is minimized. When crossing such waveguides, the signal does not flow from one to another, and this property allows increasing the packing density and thus makes plasmonic waveguides the optimal solution for interconnections in semiconductor chips. Together we have developed fundamentally new devices that will make assemblies of processors on a chip, plasmon lasers and sensors even more efficient, ”said Alexander Merzlikin.
To create plasmonic waveguides with record characteristics, ultrathin (10–12 nm – less than a hundred atomic layers) continuous gold films without defects were used. The second component of success is our own know-how of waveguide fabrication, including a complex multistage process of plasma-chemical etching, optimized for each stage of the formation of a three-layer thin-film structure Al2O3 / Au / Al2O3.
“Etching a stack of gold with aluminum oxide is an extremely complex process that almost always leads to the complete degradation of the optical properties of ultrathin gold films. Our guys managed to develop a non-trivial etching technology, which not only ensures the formation of high-quality nanostructures, but also makes it possible to achieve optical and plasmon properties higher than the level of the world’s best samples. I hope that the technological know-how of MSTU and VNIIA will become a driver for the development of this promising field of nanophotonics, ”said Ilya Rodionov, Director of the Functional Micro- / Nanosystems REC.
“The developed technological know-how is already used in the creation of ultrasensitive optical gas sensors (for more details, see the publication Optical Properties of Tungsten Trioxide, Palladium, and Platinum Thin Films for Functional Nanostructures Engineering in Optics Materials Express), and the demonstrated waveguide designs due to their miniature , supersensitivity and convenience of excitation / detection of plasmon waves have competitive advantages for the development of laboratory elements on a chip, ”said Alexander Baryshev.
Использованы материалы статьи:«Quarter-Millimeter Propagating Plasmons in Thin-Gold-Film-Based Waveguides for Visible Spectral Range»; Vladimir V. Kornienko; Alina А. Dobronosova; Anton I. Ignatov; Michail Andronik; Ilya A. RodionovAlexey N. Shaimanov, Nikita S. Smirnov, Georgy M. Yankovskii, Alexander V. Baryshev, Alexander M. Merzlikin; журнал IEEE Xplore, Journal of Lightwave Technology, июль 2021 г.
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