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Photocurrent detection of the orbital angular momentum of light

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Science  15 May 2020:
Vol. 368, Issue 6492, pp. 763-767
DOI: 10.1126/science.aba9192

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Optical vortices on demand

Light has several degrees of freedom (wavelength, polarization, pulse length, and so on) that can be used to encode information. A light beam or pulse can also be structured to have the property of orbital angular momentum, becoming a vortex. Because the winding number of the vortex can be arbitrary, the channel capacity can be expanded considerably. Zhang et al. and Ji et al. developed nanophotonic-based methods for generating and electrically detecting light with arbitrary orbital angular momentum, a goal that has remained an outstanding challenge so far (see the Perspective by Ge). The nanophotonic platform provides a route for developing high-capacity optical chips.

Science, this issue p. 760, p. 763; see also p. 707

Abstract

Applications that use the orbital angular momentum (OAM) of light show promise for increasing the bandwidth of optical communication networks. However, direct photocurrent detection of different OAM modes has not yet been demonstrated. Most studies of current responses to electromagnetic fields have focused on optical intensity–related effects, but phase information has been lost. In this study, we designed a photodetector based on tungsten ditelluride (WTe2) with carefully fabricated electrode geometries to facilitate direct characterization of the topological charge of OAM of light. This orbital photogalvanic effect, driven by the helical phase gradient, is distinguished by a current winding around the optical beam axis with a magnitude proportional to its quantized OAM mode number. Our study provides a route to develop on-chip detection of optical OAM modes, which can enable the development of next-generation photonic circuits.

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