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Vector beam generation via micrometer-scale photonic integrated circuits and plasmonic nano-antenna arrays

Abstract : Optical nano-antennas have been used for many applications in many contexts. The possibilities to control both field enhancement and spatial distribution, to tune the resonant wavelength, and to design the local phase constitute unique assets that explain the popularity of plasmonic nano-antenna. In this work, we propose to use plasmonic nano-antennas integrated in a silicon photonic integrated circuit to generate special light beams. Our approach is based on the near-infrared light that circulates in a single-mode silicon ring resonator and interacts with a plasmonic nano-antenna array in a coherent way, resulting in an out-of-plane light emission with desired state of polarization and pattern. To guarantee the mode purity of the emitted light beam, a small piece of few-mode-fiber (FMF) or other specially designed fibers, which prefer passage of some optical modes, can be used to filter out unwanted mode components. Practically, radiation can be generated from a gold nanorod excited by the evanescent field of the guided wave of a single-mode silicon waveguide. At the working wavelength, once a longitudinal surface plasmon resonance is excited in a gold nanorod, its amplitude and phase can be tailored in a large range by tuning the strength of the evanescent field and the resonance wavelength. By choosing an appropriate pair of separation distance g from the silicon waveguide, nanorod length l, and separation distance d between these two nanorods, one can build a phase distribution across the whole device, simultaneously enhancing light emission in the normal direction and suppressing it at the tilting angles. At 1.55 μm, we simulate the whole device by finite-difference time-domain.The lower row of Fig. 1(c) shows the field pattern after a 5 mm-long step-index FMF, with a mode purity of ~ 99% and a transmission efficiency of ~ 20%. Furthermore, by utilizing the generated HE21 mode beam, one can compose vortex beams having specific orbital angular momentum (OAM). Our device exhibits attractive features of compactness and weak back-reflection for large-scale photonic integration. Last but not least, we experimentally test the fabrication of above devices. Firstly, silicon substrate of a silicon-on-insulator (SOI) wafer could be etched away by using mixture solution of KOH and isopropyl alcohol. Therefore, the input facet of FMF can be glued directly with the silicon oxide layer through this hole. Secondly, single-mode silicon waveguide and gold nanorod arrays can be fabricated and precisely aligned by using a 2-step electron beam lithography method.
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Submitted on : Monday, February 10, 2020 - 2:50:47 PM
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Yi-Zhi Sun, Renaud Bachelot, Sylvain Blaize, Wei Ding. Vector beam generation via micrometer-scale photonic integrated circuits and plasmonic nano-antenna arrays. 2016 Progress in Electromagnetic Research Symposium (PIERS), Aug 2016, Shanghai, China. pp.4930-4931, ⟨10.1109/PIERS.2016.7735796⟩. ⟨hal-02473008⟩



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