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Published March 19, 2012 | Published
Journal Article Open

Light trapping beyond the 4n^2 limit in thin waveguides


We describe a method for determining the maximum absorption enhancement in thin film waveguides based on optical dispersion relations. For thin film structures that support one, well-confined guided mode, we find that the absorption enhancement can surpass the traditional limit of 4n^2 when the propagation constant is large and/or the modal group velocity is small compared to the bulk value. We use this relationship as a guide to predicting structures that can exceed the 4n^2 light trapping limit, such as plasmonic and slot waveguides. Finally, we calculate the overall absorption for both single and multimode waveguides, and show examples of absorption enhancements in excess of 4n^2 for both cases.

Additional Information

© 2012 American Institute of Physics. Received 6 January 2012; accepted 29 February 2012; published online 23 March 2012. The authors acknowledge helpful discussions with E. Schiff, P. Saeta, M. Leite, S. Burgos, E. Feigenbaum, E. Kosten, J. Fakonas, D. O' Carroll, J. Grandidier, V. E. Ferry, and K. Aydin. This work was supported by the Energy Frontier Research Center program of the Office of Science of the Department of Energy under Grant DESC0001293 (J.N.M.) and by Department of Energy under Grant DOE DE-FG02-07ER46405 (D.M.C.).

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August 19, 2023
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