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Net optical gain in a plasmonic waveguide embedded in a fluorescent polymer


Plasmonics—the study of the interaction between electromagnetic waves and electron plasmas on metal surfaces and in metallic nanostructures—has received much attention in recent years, with potential new applications ranging from subwavelength photonic circuits to photothermal cancer therapy1,2,3,4,5. In many cases, however, the substantial attenuation of the electromagnetic wave due to absorption (ohmic loss) in the metal is of serious concern. Introduction of optical gain into the dielectric material adjacent to the metal surface has been identified as a means of compensating for the absorption loss6, but the experimental realization of lossless propagation or optical gain in plasmonic waveguides has proven elusive. Here, we demonstrate direct proof of plasmonic propagation with net positive gain over macroscopic distances. The gain is provided by an optically pumped layer of fluorescent conjugated polymer adjacent to the metal surface in a dielectric–metal–dielectric plasmonic waveguide.

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Figure 1: Schematic of LRSPP waveguides containing a fluorescent polymer blend to provide optical gain and illustration of the gain measurement configuration.
Figure 2: Measurement and optimization of the propagation loss in 4-nm-thick gold LRSPP waveguides.
Figure 3: Transfer of excited-state energy from the fluorescent polymer to the LRSPP plasmonic waveguide.
Figure 4: Measurement of amplified spontaneous emission and optical net gain in LRSPP plasmonic waveguides.


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This work was supported by the Icelandic Research Fund, grant no. 00700221021. The authors thank I. Bald and O. Ingolfsson (University of Iceland) for technical support, A. L. Sobiech for illustrations, and S. I. Bozhevolnyi (University of Southern Denmark), M. B. Christiansen and A. Kristensen (Technical University of Denmark), and J. Kremer (University of Cologne) for fruitful discussions.

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M.C.G. and K.L. conceived, designed and performed the experiments and analysed the data. K.M. contributed materials and N.D. performed simulations. All authors jointly wrote the paper.

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Correspondence to Malte C. Gather.

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The authors declare no competing financial interests.

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Gather, M., Meerholz, K., Danz, N. et al. Net optical gain in a plasmonic waveguide embedded in a fluorescent polymer. Nature Photon 4, 457–461 (2010).

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