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On-chip noninterference angular momentum multiplexing of broadband light

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Science  13 May 2016:
Vol. 352, Issue 6287, pp. 805-809
DOI: 10.1126/science.aaf1112

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A twist on optical multiplexing

Information can be encoded using various properties of light. Optical multiplexing frequency, brightness, and polarization have played crucial roles in information technologies, high-capacity data storage, high-speed communications, and biological sensing. Angular momentum is another degree of freedom that could increase capacity further. Typically, however, the bulk optical elements used to determine the angular momentum of light limit possible on-chip processing. Ren et al. take a nanophotonics approach to measure and sort light co-propagating with different states of angular momentum (see the Perspective by Molina-Terriza). The approach is promising for on-chip multiplex processing of optical signals.

Science, this issue p. 805; see also p. 774

Abstract

Angular momentum division has emerged as a physically orthogonal multiplexing method in high-capacity optical information technologies. However, the typical bulky elements used for information retrieval from the overall diffracted field, based on the interference method, impose a fundamental limit toward realizing on-chip multiplexing. We demonstrate noninterference angular momentum multiplexing by using a mode-sorting nanoring aperture with a chip-scale footprint as small as 4.2 micrometers by 4.2 micrometers, where nanoring slits exhibit a distinctive outcoupling efficiency on tightly confined plasmonic modes. The nonresonant mode-sorting sensitivity and scalability of our approach enable on-chip parallel multiplexing over a bandwidth of 150 nanometers in the visible wavelength range. The results offer the possibility of ultrahigh-capacity and miniaturized nanophotonic devices harnessing angular momentum division.

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