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X-shaped plasmonic antenna on a quantum cascade laser
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View: Figures


Image of FIG. 1.
FIG. 1.

FDTD simulations of the x-antenna. (a) Near-field of the x-antenna, on a linear scale, with the E-field enhancement factor indicated on the right, with the maximum shown at the top . The simulations are normalized to an incoming plane wave of 1 V amplitude, thus automatically giving a measure of the enhancement factor. The horizontal and vertical directions are defined here for the purposes of simplicity. (b) (Black line) A linescan of the near-field across the horizontal of the antenna shown in (a), with the length (in ) along the -axis, and E-field enhancement along the -axis. It is seen, and can be assumed from the geometry, that only a single enhanced spot is expected. (Other line) A linescan along the vertical of the x-antenna. From this it is seen that a different profile would be expected along the two polarizations. It is seen that a high confinement is achieved in both directions, with the strong enhancement in the antenna gap, which is 80 nm across in the calculations.

Image of FIG. 2.
FIG. 2.

A representation of the a-SNOM setup, at the edge of the QCL device. (a) The tip oscillates at . (b) A mirror is placed to the rear of the device, to collect the scattered signal. (c) Two aspheric ZnSe lenses are used to focus the light onto the Mercury-cadmium-telluride detector element (d).

Image of FIG. 3.
FIG. 3.

Experimental results of the x-antenna. (a) Operating characteristics of the QCL used. The L-I shows a 1.15 A threshold at room temperature, with the inset giving the associated spectrum, centered at . (b) SEM image of two x-antennas on the QCL facet. The top edge of the facet is on the left of the image. Multiple antennas were patterned, to account for the unknown mode profile of the laser. (c) AFM topographic image of the x-antenna. (d) Simultaneously obtained a-SNOM optical image of the antenna in (c). A clear bright spot is seen at the center of the structure, as expected from simulation. (e) Three-dimensional image of the optical signal of (d). (f) Horizontal linescan of the antenna, with the confinement factor of about FWHM. (g) Vertical linescan of the antenna, with the confinement factor of about . There is some correspondence with the simulations in this regard, together with the differing profiles across the gap and antenna lengths.

Image of FIG. 4.
FIG. 4.

FDTD simulations of the tip-antenna interaction. (a) The AFM tip is here centered at the gap, and 10 nm above the surface. It is seen that the gold AFM tip pulls the field from the center of the gap. (b) Linescans across the antenna surface. The electric field is seen to be further enhanced by the presence of the AFM tip, but is also responsible for a broadening of the FWHM, especially along the plane of polarization. The black line is the perpendicular polarization. (c) The AFM tip is here away from the center of the antenna, along the plane of polarization. (d) The surface near-field with the AFM tip perpendicular to the antenna length, away from the center.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: X-shaped plasmonic antenna on a quantum cascade laser