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A novel optical device for coupling a light beam to a planar waveguide structure and for decoupling the guided wave after a certain distance of propagation is demonstrated. The beam coupler comprises two superimposed uniform dielectric diffraction gratings with different periodicities and/or different orientations incorporated into a planar surface-wave supporting structure. The bidiffractive coupler has translational invariant coupling efficiency and is ideally suited for optical surface probing using electromagnetic surface mode propagation over short distances only.
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Ch. Fattinger (1993) studied this question.
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