Waveguide-Plasmon Polaritons Enhance Transverse Magneto-Optical Kerr Effect

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Waveguide-Plasmon Polaritons Enhance Transverse Magneto-Optical Kerr Effect

Lars E. Kreilkamp, Vladimir I. Belotelov, Jessie Yao Chin, Stefanie Neutzner, Daniel Dregely, Thomas Wehlus, Ilya A. Akimov, Manfred Bayer, Bernd Stritzker, and Harald Giessen

Phys. Rev. X 3, 041019 – Published 25 November 2013

Abstract

Magneto-optical effects in ferrimagnetic or ferromagnetic materials are usually too weak for potential applications. The transverse magneto-optical Kerr effect (TMOKE) in ferromagnetic films is typically on the order of 0.1%. Here, we demonstrate experimentally the enhancement of TMOKE due to the interaction of particle plasmons in gold nanowires with a photonic waveguide consisting of magneto-optical material, where hybrid waveguide-plasmon polaritons are excited. We achieve a large TMOKE that modulates the transmitted light intensity by 1.5%, accompanied by high transparency of the system. Our concept may lead to novel devices of miniaturized photonic circuits and switches, which are controllable by an external magnetic field.

Received 13 March 2013

DOI:https://doi.org/10.1103/PhysRevX.3.041019

This article is available under the terms of the Creative Commons Attribution 3.0 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

Authors & Affiliations

Lars E. Kreilkamp¹, Vladimir I. Belotelov^2,3, Jessie Yao Chin^4,*, Stefanie Neutzner⁴, Daniel Dregely⁴, Thomas Wehlus⁵, Ilya A. Akimov¹, Manfred Bayer¹, Bernd Stritzker⁵, and Harald Giessen⁴

¹Experimentelle Physik 2, Technische Universität Dortmund, D-44221 Dortmund, Germany
²Lomonosov Moscow State University, Faculty of Physics, 119991 Moscow, Russia
³Russian Quantum Centre, 143025 Skolkovo, Moscow Region, Russia
⁴4th Physics Institute and Research Center SCOPE, University of Stuttgart, 70550 Stuttgart, Germany
⁵Institute of Physics, University of Augsburg, 86135 Augsburg, Germany

^*j.chin@physik.uni-stuttgart.de

Popular Summary

Magneto-optical effects describe a collection of intriguing physical phenomena where light-matter interaction can be influenced by a static magnetic field. These effects have found a wide range of applications, for example, in optical isolation and various data-storage technologies. The device design for these applications is usually clumsy and inflexible, as the existing magneto-optical materials impose certain limitations. One approach to overcoming the limitations is to combine magneto-optics with plasmonics, which employs nanostructured metals to achieve strong optical effects and functions that can be engineered on demand. In this paper, we demonstrate how the transverse magneto-optical Kerr effect (TMOKE) of only 150-nm-thick films can be boosted by a sophisticated magneto-plasmonic structure built with metal nanowires.

The TMOKE determines the change in the intensity of light that is transmitted or reflected from a magnetized material when an external static magnetic field switches directions. It exists in ferromagnetic metals such as cobalt and nickel, but the change of the light intensity in those materials is too weak for potential applications. Another problem is that those materials are opaque and therefore cannot be used in transmission geometry. Our hybrid magneto-plasmonic structure not only leads to optical transparency by allowing half of the light to go through, but it also generates large intensity modulations of the transmitted light by magnetic field. The key to these improvements lies in the light-matter interaction in our structure: The magneto-optical thin film in the structure forms a resonant waveguide for photons, and collective oscillations of electrons, or “plasmons,” are excited in the metal wires. Resonant interaction between the photons and the plasmons leads to more transmission and higher sensitivity to the flipping of the applied magnetic field.

Our design offers high flexibility for tailoring the TMOKE by tuning the geometry of the plasmonic structure. The proof-of-concept demonstration may lead to new magnetic sensors and novel miniaturized optical light modulation and switching devices controllable by an external dc magnetic field.

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Vol. 3, Iss. 4 — October - December 2013

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Figure 1
(a) Schematic of the plasmonic system employed to enhance the transverse magneto-optical Kerr effect. The bismuth iron garnet film (blue) is deposited on glass substrate (grey), and the gold nanowires are structured on top. An external magnetic field $B$ is applied in plane. Obliquely incident light (incident angle $θ$ ) is polarized perpendicular to the nanowires (TM polarization). Inside the bismuth iron garnet film, the red lines close to the nanowires illustrate the near-field enhancement due to the plasmonic resonance, and the yellow lines illustrate light bouncing up and down inside the waveguide due to the waveguide mode in a simplified geometrical optics analogy. $N$ is the surface normal of the substrate. The inset shows a scanning electron micrograph of a sample. (b) Measured spectrum of transmittance at a zero $B$ field (red line) and the measured spectrum of the TMOKE signal $δ$ at $\pm 160 mT$ (blue line), with a 9° incident angle for the sample with a 500-nm period.Reuse & Permissions
Figure 2
(a) Measured spectra of the TMOKE signal $δ$ at different static magnetic fields of 1.6 mT, 6.4 mT, 16 mT, 48 mT, and 160 mT, respectively. (b) Measured maximum TMOKE signal $δ_{\max }$ increasing with the external magnetic field. The incident angle is 9°. (c) Measured $δ$ at different incident angles at a magnetic field of 160 mT. From the bottom to the top, the incident angles are $- 9 °$ , $- 7 °$ , $- 5 °$ , $- 3 °$ , $- 1 °$ , 0°, $+ 1 °$ , $+ 3 °$ , $+ 5 °$ , $+ 7 °$ , $+ 9 °$ , and $+ 11 °$ , respectively. The spectra in (a) and (c) are shifted vertically for better visibility.Reuse & Permissions
Figure 3
(a) Measured and (b) simulated transmittance for the structures of a 450-nm period (red lines), a 475-nm period (blue lines), and a 500-nm period (green line). (c) Measured and (d) simulated TMOKE for the structures of a 450-nm period (red lines), a 475-nm period (blue lines), and a 500-nm period (green lines). Illumination is TM polarized with a 9° incident angle. An external magnetic field of 160 mT is applied.Reuse & Permissions
Figure 4
(a) Simulated dispersion diagram of absorbance $A$ for the sample with a 500-nm period for TM polarization. The blue lines indicate the $ω - k$ relations at 5°, 9°, and 11° incident angles, respectively. The high absorbance (bright area, denoted by LP) at around $ω = 2.2 \times 10^{15} s^{- 1}$ is due to the localized plasmon resonance. The dispersive feature in the diagram denoted by WG is due to the waveguide mode. (b) Simulated distribution of the oscillating magnetic field of light $H_{x}$ (amplitude of the $x$ component) along the gold nanowires for the structure of a 500-nm period at a 9° incident angle and a 860-nm wavelength ( $ω = 2.2 \times 10^{15} s^{- 1}$ ). The magnetic field is normalized to the amplitude of the incident light magnetic field. The waveguide and the gold nanowire are outlined by grey lines. (c) Simulated $ω - k$ diagram of the TMOKE signal $δ$ for the structure of a 500-nm period. The external magnetic field is 160 mT, and illumination is TM polarized.Reuse & Permissions

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