Research On Goos-h Nchen Shift In A Light Waveguide

It is thought by geometric optics that the reflection point and the incidence point coincide with each other when a light beam impinge onto an interface, only a phase shift is introduced. But this is not the truth, Goos and H(a|¨)nchen made an experiment in 1947 which proves a lateral shift between them, this is so called Goos-H(a|¨)nchen (GH) shift. It is because each plane wave component of the incident beam undergoes a slight different phase change after total internal reflection.At a single dielectric interface, the GH shift is of the order of wavelength. The smallness of the shift for optical wavelengths had impeded its direct observation in a single reflection. In the past two decades, various schemes were proposed to enhance the effect, such as asymmetric double-prism structure, near the Brewster dip on reflection from a weakly absorbing semi-infinite medium, at the angle of defect mode of photonic crystals and so on.In fact, when a light beam impinges on the interface between two dielectric media, the electromagnetic energy of the incoming beam penetrates into the second medium and builds up an evanescent wave which would propagate along the interface for some distance before re-emerging into the former medium. The lateral displacement is then proportional to the penetration depth of the light field; the question resolves itself into how to effectively increase the penetration depth for direct measurement of the GH shift. In this paper, by using the ultrahigh order modes in a symmetrical metal-cladding optical waveguide (SMCW), we obtain tremendous GH shift greater than 1700 wavelengths, and in further investigate we show that the lateral displacement increases with the thickening of the guiding slab at the well excitation of ultrahigh order modes.A new tunable optical filter is fabricated based on the enhanced GH effect in the SMCW structure; we can tune the filter to get the desired centre wavelength through changing the position of the aperture.