Controlling propagation and coupling of waveguide modes using phase-gradient metasurfaces

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Research on two-dimensional designer optical structures, or metasurfaces, has mainly focused on controlling the wavefronts of light propagating in free space. Here, we show that gradient metasurface structures consisting of phased arrays of plasmonic or dielectric nanoantennas can be used to control guided waves via strong optical scattering at subwavelength intervals. Based on this design principle, we experimentally demonstrate waveguide mode converters, polarization rotators and waveguide devices supporting asymmetric optical power transmission. We also demonstrate all-dielectric on-chip polarization rotators based on phased arrays of Mie resonators with negligible insertion losses. Our gradient metasurfaces can enable small-footprint, broadband and low-loss photonic integrated devices.

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Figure 1: Unidirectional phase gradient dΦ/dx introduced by a metasurface causes asymmetric waveguide mode coupling.
Figure 2: Asymmetric optical power transmission in waveguides patterned with gradient metasurfaces.
Figure 3: Experimental demonstration of asymmetric optical power transmission in waveguides patterned with gradient metasurfaces.
Figure 4: Mid-infrared waveguide mode converters and polarization rotator based on plasmonic gradient metasurfaces.
Figure 5: Experimental demonstration of mid-infrared waveguide mode converters.
Figure 6: Telecom waveguide mode converters based on dielectric gradient metasurfaces.


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The work was supported by the Air Force Office of Scientific Research (grant no. FA9550-14-1-0389, through a Multidisciplinary University Research Initiative programme), a Defense Advanced Research Projects Agency Young Faculty Award (grant no. D15AP00111) and the National Science Foundation (grant no. ECCS-1307948). The authors acknowledge funding from the Ministry of Defense, Singapore, and from the Defense Threat Reduction Agency (grant no. HDTRA1-13-1-0001). A.C.O. acknowledges support from the NSF IGERT programme (grant no. DGE-1069240). Research was carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the US Department of Energy, Office of Basic Energy Sciences (contract no. DE-SC0012704). The authors thank M. Lipson, R. Osgood Jr, P.-T. Lin and L. Zhang for discussions.

Author information

Z.L., M.-H.K. and N.Y. conceived and designed the experiments. Z.L., M.K. and C.W. fabricated the devices, with M.L. and A.S.'s assistance. M.K., Z.L., Z.H., C.W., S.S. and A.C.O. performed the measurements and analysed the data, with A.M.A., M.L. and N.Y.'s supervision. Z.L. and M.K. developed theoretical models and conducted numerical simulations, with N.Y.'s supervision. Z.L., M.K. and N.Y. wrote the manuscript, with input from all co-authors. All authors discussed the results and commented on the manuscript.

Correspondence to Nanfang Yu.

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Li, Z., Kim, M., Wang, C. et al. Controlling propagation and coupling of waveguide modes using phase-gradient metasurfaces. Nature Nanotech 12, 675–683 (2017) doi:10.1038/nnano.2017.50

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