Wavelength sensing based on the Goos-H?nchen effect in the symmetrical metal-cladding waveguide structure

摘要

The Goos-H?nchen (GH) effect, which is enhanced by the resonance of guided modes in the symmetrical metal-cladding waveguide (SMCW) structure, is used to detect slight variations of the light wavelength. The SMCW is a special optical waveguide structure, typically consisting of a guiding layer and two metal-cladding layers. Compared with traditional dielectric waveguide, the SMCW possesses a broader range of effective refractive index (RI), i.e. from zero to the RI of the guiding layer, which enables directly coupling of light energy from free space into the waveguide. Theoretical analysis indicates that the GH effect is closely related to the intrinsic damping and the radiative damping of the waveguide structure. Proper parameters are selected to match the two dampings, and great enhancement of the GH shift is obtained consequently. Ultrahigh-order modes excited in the SMCW with a sub-millimeter scale of the guiding layer exhibit a strong dispersion effect of the light wavelength, which manifests itself as wavelength-dependent lateral shift of the reflected beam. Position sensitive detector is used to monitor the lateral beam shift which changes rapidly with respect to the light wavelength. Since the detecting signal is proportional to the displacement of the light beam, the measurement can effectively avoid being affected by the fluctuation of the light intensity. A wavelength resolution of 0.2 pm near the wavelength of 859 nm is demonstrated in the experiment.