Photonics Research, Volume. 12, Issue 12, 2863(2024)

Manifestation of super chiral exceptional points in a plasmonic metasurface

Haojie Li, Guoxia Yang, Anwen Jiang, Min Ni, Qianwen Jia, Fengzhao Cao, Jiayi Zhang, Bokun Lyu, Dahe Liu, and Jinwei Shi*
Author Affiliations
  • Applied Optics Beijing Area Major Laboratory and Key Laboratory of Multiscale Spin Physics, Ministry of Education, School of Physics and Astronomy, Beijing Normal University, Beijing 100875, China
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    Figures & Tables(8)
    Design and characteristics of PT-symmetric metasurface. (a) Schematic of PT-symmetric metasurface composed of orthogonal oriented sliver nanorods with local gain. Typical parameters: Px=Py=800 nm, l1=260 nm, s1=50 nm, l2=281 nm, s2=90 nm, and h1=h2=50 nm. (b) Illustration of a system with two coupled resonators where radiation loss and dissipative loss are distinguished. (c),(d) Riemann surfaces of the complex eigenvalues of the matrix S^ versus the (g,δ) parameters, showing (c) real and (d) imaginary parts of the eigenvalues. (e) Evolution of EP (blue curve) and ZP (red curve), with the super chiral EP (SCEP) denoted by a red solid star and the topological phase transition point (TP) by a hollow star. The white and green areas represent the PT-symmetric phase and the PT-symmetry broken phase, respectively.
    PT-symmetric phase transition and SCEP. (a)–(f) Chiral-component transmission spectra and total chiral transmission spectra of the system (a), (d) in PT-symmetric phase, (b), (e) at SCEP, and (c), (f) in PT-symmetry broken phase. The Rabi splitting, resulting from strong coupling of orthogonally oriented nanorods, is clearly observed in PT-symmetric phase. At SCEP, the circular components Trr, Tll, and Tlr almost decrease to zero at 1398 nm in (e). (g) Results of electric field amplitude and phase difference for x-polarization incident light. (h) Near-ideal CCD [(Trl−Tlr)/(Trl+Tlr)] and CD with values of 0.995 and 0.98 are realized at SCEP, respectively. (i) The phase flip of Tlr is observed near SCEP with w1=186 nm.
    Unidirectional invisibility and polarization converter. (a) Schematic of unidirectional invisibility at SCEP, where only one chiral component can transmit through the metasurface. (b) Total transmission spectra for circularly polarized incident light, (c) transmission spectra for RCP and LCP components, and (d) amplitude and phase difference of transmitted electric fields for backward incidence (−z direction) at SCEP. (e) Schematic of a polarization converter at the topological phase transition point (TP). (f) Transmission spectra for RCP and LCP components for forward incidence at TP. Amplitude and phase difference of transmitted electric fields for (g) RCP incidence and (h) LCP incidence. Δφ=φ(Ex)−φ(Ey).
    Generation of arbitrary polarization states on the Poincaré surface under an LP beam incident on metasurfaces. (a) Polarization states of the transmitted light for different values of g are plotted on the Poincaré sphere at 1398 nm. Si (i=1, 2, 3) denote the three Stokes parameters. (b)–(k) Electric field amplitude and phase difference of the transmitted light with varying separation between the nanorods. Polarization states across the entire Poincaré surface can be obtained by rotating the unit cell of metasurfaces.
    Left-handed SCEP with fixed gap w1=264 nm. (a) Chiral-total transmission spectra and (b) chiral-component transmission spectra of the system at left-handed SCEP. (c) Results of electric field amplitude and phase difference for x-polarization incident light.
    Transmission spectra of metasurfaces without gain–loss difference. (a)–(c) Chiral-total transmission spectra and (b)–(d) chiral-component transmission spectra of the system with different gap w1.
    Numerical calculation results of LP incidence with varying g. tl and tr represent the transmission of LCP and RCP components with an LP beam through the metasurface, respectively. When w1<225 nm, the blue and red curves represent tr and tl, respectively; when w1>225 nm, the blue and red curves represent tl and tr, respectively. This is determined by the geometric symmetry of the structure. The special points on the Poincaré sphere are also marked here. (Blue, green, yellow, and red stars represent TP, right-handed SCEP, left-handed SCEP, and LP, respectively.)
    The transmission polarization can be extended from the Poincaré sphere meridian to the entire surface by rotating the metasurface unit cell. (a) Transmission polarization states are plotted on the Poincaré surface at 1398 nm (take the transmission polarization axes along 30° and 120° as examples). Si (i=1, 2, 3) denote the three Stokes parameters. (b)–(g) Electric field amplitude and phase difference with different unit cell rotation angles at w1=225 nm [(b), (c) LP], w1=210 nm [(d), (e) right-handed elliptically polarized], and w1=240 nm [(f), (g) left-handed elliptically polarized], respectively, where Δφ=φ(Ex)−φ(Ey).
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    Haojie Li, Guoxia Yang, Anwen Jiang, Min Ni, Qianwen Jia, Fengzhao Cao, Jiayi Zhang, Bokun Lyu, Dahe Liu, Jinwei Shi, "Manifestation of super chiral exceptional points in a plasmonic metasurface," Photonics Res. 12, 2863 (2024)

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    Paper Information

    Category: Surface Optics and Plasmonics

    Received: Jul. 26, 2024

    Accepted: Oct. 3, 2024

    Published Online: Nov. 27, 2024

    The Author Email: Jinwei Shi (shijinwei@bnu.edu.cn)

    DOI:10.1364/PRJ.537395

    CSTR:32188.14.PRJ.537395

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