Broadband graphene polarizer

Journal name:
Nature Photonics
Volume:
5,
Pages:
411–415
Year published:
DOI:
doi:10.1038/nphoton.2011.102
Received
Accepted
Published online

Abstract

Conventional polarizers can be classified into three main modes of operation: sheet polarizer using anisotropic absorption media, prism polarizer by refraction and Brewster-angle polarizer by reflection1. These polarizing components are not easily integrated with photonic circuits. The in-line fibre polarizer, which relies on polarization-selective coupling between the evanescent field and birefringent crystal2 or metal3, 4, 5, 6, 7, is a promising alternative because of its compatibility with most fibre-optic systems. Here, we demonstrate the operation of a broadband fibre polarizer based on graphene, an ultrathin two-dimensional carbon material. The out-coupled light in the telecommunication band shows a strong s-polarization effect with an extinction ratio of 27 dB. Unlike polarizers made from thin metal film, a graphene polarizer can support transverse-electric-mode surface wave propagation due to its linear dispersion of Dirac electrons.

At a glance

Figures

  1. Fibre-to-graphene coupler and optical polarization.
    Figure 1: Fibre-to-graphene coupler and optical polarization.

    a, Schematic model of fibre-to-graphene coupler based on a side-polished optical fibre. LG, propagation distance (length of covered graphene film). Polarization angle θ is defined as the angle between the polarization direction of the analyser (in xy plane) and the graphene plane (yz plane). b, Optical image of laterally polished optical fibre. Red arrows indicate joints (separated by ~15 mm) between the side-polished and unpolished sections. c, Optical image showing a planar section of optical fibre covered by few-layer (~4–5 layers) graphene film, which gives a darker contrast compared to the naked region. d, Optical image showing radiative green light from the fibre-to-graphene coupler with excitation at 532 nm (~1 mW). e,f, Polarized optical image of the radiative light along the s (e) and p (f) polarizations (taken under the same illumination light intensity). The radiative line along the axis of the fibre core in e indicates a strong interaction between the graphene and the excitation light.

  2. Broadband polarizing effect of graphene.
    Figure 2: Broadband polarizing effect of graphene.

    a, Polar image measured at 488 and 532 nm (LG = 2.1 mm). The curves are cos2 fits. The green line indicates the projection of the graphene film in the xy plane (Fig. 1a). CCD, charge-coupled device. b, Polar image measured at 980 nm (LG = 3 mm) and 1,550 nm (LG = 2.1 mm). c, Polarization measurements conducted in the wavelength range 820–955 nm (LG = 3 mm) and in the telecommunication C-band from 1,530 to 1,630 nm (LG = 2.1 mm). The output maximum (green area) and minimum (yellow area) were recorded at polarization angles θ = 0° and 90°, respectively. d, Polarization extinction ratio as a function of LG measured at 1,550 nm. The saturation and reduction of the extinction ratio at larger LG are attributed to the limitation of our measurement system because both polarization modes are greatly weakened and the TM polarization mode is attenuated beyond the detection minimum of the power meter (−50 dBm). The error bars represent standard deviation of the measurements.

  3. Numerical model.
    Figure 3: Numerical model.

    a,b, Perspective view (a) and cross-section (b) of the side-polished optical fibre. c, Two-dimensional theoretical model showing the graphene/silica fibre and cladding/core interfaces in the plane of incidence (σ, surface conductivity of graphene; refractive index, n1 = 1.0, n2 = 1.468, n3 = 1.463). In the model, we assume z to be the direction of propagation, x is perpendicular to the graphene plane and y is invariant.

  4. Numerical calculation of electromagnetic modes in graphene.
    Figure 4: Numerical calculation of electromagnetic modes in graphene.

    a, Real part of the effective index neff of the possible modes in a monolayer graphene–fibre hybrid waveguide. b, Imaginary part of neff for each mode. c, Attenuation of TM and TE polarizations of each mode. d, Propagation length of the TM and TE polarizations of each mode. e, Simulated broadband polarization effect in the visible–NIR range for monolayer graphene with different values of LG. Solid dots, simulation results; open circles, experimental results. f, Simulated polarization extinction ratio (solid lines) as a function of LG for a varying number of layers at 1,550 nm. Circles: experimental results for monolayer graphene.

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Author information

Affiliations

  1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543

    • Qiaoliang Bao,
    • Candy Haley Yi Xuan Lim,
    • Yu Wang &
    • Kian Ping Loh
  2. School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798

    • Han Zhang &
    • Ding Yuan Tang
  3. Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 3 Research Link, Singapore 117602

    • Bing Wang
  4. Department of Physics, Southeast University, Nanjing, China 211189

    • Zhenhua Ni
  5. Service OPERA-photonique, Université libre de Bruxelles (U.L.B.), 50 Avenue F. D. Roosevelt, CP 194/5, B-1050 Bruxelles, Belgium

    • Han Zhang

Contributions

K.P.L. supervised the project. K.P.L. and Q.B. planned the project. Q.B. and H.Z. conceived the original concept and performed most of the experiments. B.W. and Q.B. contributed to the numerical calculations. Z.N. contributed to measurements in the visible range. H.Z. and D.Y.T. contributed to the experiments in the NIR range. C.H.Y.X.L. and Y.W. contributed to graphene synthesis. K.P.L. and Q.B. analysed the data and co-wrote the paper. All authors discussed the results and commented on the manuscript.

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The authors declare no competing financial interests.

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