Figure 3

SEM image of sample and scheme of experimental setup. (a) An SEM image of the gold nanoaperture array with slit gratings on both sides; the right part image is with higher magnification to show the detail; each gold nanoaperture is ∼200 nm long and ∼50 nm wide, and the lattice constant s between two slits along the x and the y direction is 570 nm; the nanoaperture array covers an area of 17 µm×100 µm. The symmetrically located slits as out-couplers have a pitch of 400 nm with duty cycle of 50% and a length of 100 µm. Each outcoupler is 25 µm away from the edge of the dipole array. (b) Far-field imaging detection with microscopy set-up. The light acquires a circular polarization after passing through a linear polarizer is along the vertical (+y), and a quarter-wave plate with axis along ±45°. The beam is then focused onto the array of nanoapertures by an objective. The surface plasmons, scattered by the output grating coupler, are collected by another objective, and imaged onto a CCD camera. CCD, charge coupled device; SEM, scanning electron microscopy.