Research ArticleAPPLIED PHYSICS

High–bit rate ultra-compact light routing with mode-selective on-chip nanoantennas

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Science Advances  19 Jul 2017:
Vol. 3, no. 7, e1700007
DOI: 10.1126/sciadv.1700007

Figures

  • Fig. 1 Scheme of a waveguide-integrated plasmonic nanoantenna for mode-selective polarization (de)multiplexing.

    The device couples light of orthogonal polarizations into different directions and modes of the underlying silicon waveguide.

  • Fig. 2

    (A) Numerical design of the nanoantenna coupling x-polarized light into the TM mode of the waveguide to the right (TM antenna). The electric field distribution (color-coded arrows) in a cutting plane on the right-hand side of the nanoantenna (blue dashed line) shows that the light is coupled to the TM mode. (B) Corresponding design of the TE antenna coupling light to the left-hand side into the TE mode. (C and D) Spectrally resolved directivities of the TM antenna coupling to the right and the TM antenna coupling to the left, respectively.

  • Fig. 3

    (A) Design of the combined TE-TM nanoantenna coupling x-polarized light to the right (blue dashed line) into the TM mode and y-polarized light to the left (red dashed line) into the TE mode of the waveguide. (B) Corresponding electric field plots. (C) Right-to-left (left-to-right) ratio for directional coupling x-polarized (y-polarized) incident light with a maximum at around 1550-nm wavelength.

  • Fig. 4

    (A) Scanning electron microscope (SEM) images of a setup configuration for measuring the coupling ratios of the three nanoantennas shown in (B) (TM antenna), (C) (TE antenna), and (D) (TE-TM antenna). The nanoantennas are placed in the center (red square) between two gold gratings that are used as output ports (yellow squares) to detect the radiation coupled to the right-hand side and to the left-hand side of the waveguide. (B to D) SEM images (top row) of the fabricated antennas and the intensity plots at the left and right output ports detected on the infrared (IR) camera (second row) for x and y polarization of the incident light at 1550-nm wavelength.

  • Fig. 5

    (A) Detected light intensity at the left end of the (cleaved) waveguide with the TE antenna in the center for different polarization angles of the incident light (also indicated as green arrows for the main polarization directions). The light intensity in the TE mode and the TM mode of the waveguide is separated by a polarizing beam splitter in the detection part of the setup and plotted in red and blue, respectively. For vertical polarization at 90° (corresponding to y polarization), the intensity in the TE mode is at its maximum. (B) Detected light intensity at the right end of the (cleaved) waveguide, with the TM antenna on top. Here, we find an intensity maximum for horizontal polarization (0/180°, x polarization) in the TM mode. (C and D) Corresponding plots measured at both the left (C) and the right (D) waveguide end for the combined TE-TM antenna, confirming the coupling of y-polarized (x-polarized) light to the TE mode (TM mode) to the left (right).

  • Fig. 6

    (A) Measured eye diagram for the TM antenna at 10-GHz modulation frequency. The blue-shaded area is used for the statistical evaluation of the signal and the calculation of the BER. (B) Probability density function for the detection of a logical one and zero and the Gaussian fitting used to determine the decision threshold x0 and to calculate the BER. (C) Evaluated BER of the transmission link with the nanoantenna (red dots) and without antenna (black squares) for a series of received powers at the detector. As seen, the two data series are almost identical; therefore, the measured BER is not influenced by the antenna.