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Sketch of sample geometries. The elementary waveguide structure is a wide and thick silicon dioxide stripe on a thick gold thin film on glass. We investigate waveguide bends defined by the bend radius and directional couplers defined by an edge-to-edge distance .
SP waveguide bends. Leakage radiation microscope images of waveguide bends as sketched in Fig. 1 with bend radii of (a) 10, (b) 12, (c) 15, and (d) . The bright saturated spot in (a) is the exciting laser focus launching a SP propagating from right to left on the upper straight part of the waveguide. The panels (b)–(d) share the scale bar shown in (a). (e) The circle symbols show SP propagation lenghts measured from the LRM images; the diamond symbols show the normalized SP transmission through the bends as defined in the text. The solid and dashed lines are mere guides for the eye.
Directional SP waveguide coupler. [(a)–(c)] Leakage radiation microscope images of couplers with edge-to-edge waveguide distances of , 300, and , respectively. SPs are launched in the upper waveguide, propagating from right to left. The panels (a) and (b) share the scale bar shown in (c). (d) PSTM image of the coupler with . (e) Coupling length values measured from crosscuts from the whole series of LRM and PSTM images are marked by the circle symbols. The line is an exponential fit to the data.
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