These devices are ways of separating wavelengths in a controlled fashion using custom-designed nanophotonic structures. See also the discussion of superprism devices, inverse design in nanophotonics, and complex plasmonic structures.
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M. Gerken and D. A. B. Miller, “Limits to the performance of dispersive thin-film stacks,” Appl. Opt. 44, 3349‑3357 (2005)
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T. Tanemura, K. C. Balram, D.-S. Ly-Gagnon, P. Wahl, J. S. White, M. L. Brongersma, and D. A. B. Miller, “Multiple-Wavelength Focusing of Surface Plasmons with a Nonperiodic Nanoslit Coupler,” Nano Lett. 11, 2693–2698 (2011)