Research On The Goos-h(?)nchen Effect And The Liquid Measurement In The Symmetrical Metal-cladding Waveguide

The symmetrical metal-cladding waveguide (SMCW), which consists of a metal couplinglayer, a guiding layer and a metal substrate, is one kind of planar waveguides. The real part ofthe dielectric constant of the metal coupling layer is negative in the visible and near-infraredregions, thus the incident light can be conveniently coupled into the guiding layer by thefree-space coupling technology. There is no need of prism or grating, and the effectiverefractive index (RI) can cover the range from zero to the RI of the guiding layer. Since thethickness of guiding layer is extended to a millimeter scale, the SMCW can accommodatetens of thousands of guided modes. Among them, the so-called ultrahigh-order modes, whosefull width at half maximum (FWHM) is extremely small, is polarization-independent andhighly sensitive response to the variation of optical parameters (RI and thickness, etc.) in theguiding layer. Therefore, it is easy to explore and develop the optical sensors based on theaforementioned properties of SMCW. Besides, in the SMCW, the Goos-H nchen (GH) shiftof the reflected light can be largely enhanced to a millimeter scale on condition that theintrinsic damping and the radiative damping are matching well to each other. The enhancedGH shift also high sensitively responds to the variation of the optical parameters in theguiding layer. Based on the enhanced GH shift and its sensitivity characteristic, theapplication research on four differential fields are systematically described in this dissertation.1. A13space-division electro-optical switch, in which the PMN-PT transparent ceramicacts as the guiding layer of SMCW, is realized based on the electrically tuned GH shift. The research and development of optical switch is helpful to alleviate the increasing need ofoptical signal exchange and control in the optical network. Compared to other electro-opticalmaterials, such as LiNO3crystal, the PMN-PT transparent ceramic exhibits many merits,including large electro-optical coefficient, no electric hysteresis effect,polarization-independent and quick response speed. Because of the electro-optical andconverse-piezoelectric effect, the RI and thickness of the PMN-PT transparent ceramic can bealtered by the external electric field, thus the GH shift of the SMCW is accordingly changed.A three-pinhole array is put in the reflected light path and the reflected light can be tuned topass through every selected pinhole of them under three different external electrical fields.Both the crosstalk and switching time of the electro-optical switch are small.2. A highly-sensitive temperature sensor, in which the BK7glass acts as the guiding layerof SMCW, is proposed based on the enhanced GH shift. Temperature is one of the most basicphysical parameters. The mechanical, electrical and optical parameters of many materials aretemperature-dependent, and these temperature-dependent rules can be employed to trigger theemergence of new temperature sensors. The optical temperature sensor attracts considerableconsideration because it is immune to the external electromagnetic interference. Owing to thethermo-optical and thermal expansion effect, the temperature fluctuation can lead to thevariation of the RI and thickness of BK7glass, which give rise to changes in the GH shift ofreflected light. Experimental results show that there is a linear relationship between thevariation of GH shift and the temperature fluctuation, and a0.2oC temperature fluctuation cancause a GH shift of76m. The smallest variation of GH shift that can be detected with ourposition sensitive detector is2m, therefore, we deduce that the minimum detectabletemperature variation in our temperature sensor is about510-3oC.3. A1D self-assembly and optically tuned periodic-like column distribution of ferrofluid isrealized in a ferrofluid-filled SMCW. The intensity and the GH shift of the reflected light canbe all-optically tuned. The micro-nano structures with artificial periods attract considerable consideration owing to many attractive properties, such as the photonic band gap. However,once the ordered structure has been fabricated, its structure parameters cannot be tuned by theexternal stimuli. In our structure, the electromagnetic energy coupled from the incident light isendlessly reflected between the two metal layers, and an energy distribution somewhat similarto the phenomena of standing wave in a Fabry-Perot cavity is formed in the guiding layer. Theelectromagnetic energy in the guiding layer is nearly enhanced to70times when compared tothat of the incident light. A significant gradient in the light intensity field will induce agradient force to attract the particles into the region of highest intensity. Therefore, thegenerated periodic energy pattern in the guiding layer can push the magnetic nanoparticles tothe high power density areas via the optical trapping effect, and the magnetic nanoparticleswill aggregate together to form a optically tuned periodic-like microstructure of ferrofluids. Inthe experiment, the intensity and the GH shift of the probe light can be optically tuned by thepower of the pump light. Besides the optical trapping effect, the Soret effect, which can causethe magnetic nanoparticles to escape from the “hotter” regions to the “cooler” ones, is anotherorigin of the rearrangement of the magnetic nanoparticles. There is a critical pump lightpower. When increasing the pump beam power, if it is lower than the critical one, moremagnetic nanoparticles will be concentrated into the high power density areas from the lowpower density areas due to the optical trapping effect; once the control beam power is largerthan the critical one, the Soret effect will become dominant and lead to a negative feedback,i.e., the magnetic nanoparticles will escape from the high power density areas to the lowerpower density areas.4. By injecting the chiral liquid into the guiding layer of SMCW, a new determinationmethod of its enantiomeric excess is theoretically proposed and experimentally demonstrated.From the microcosmic view, the constituent molecules of many materials are mirrorasymmetrical, i.e., left handedness and right handedness. All most the organic compounds,which take part in several important process of physiology, are chiral molecules but have only one kind of enantiomers. Therefore, the two kinds of enantiomers of many drug moleculeshave different pesticide effects. The physical properties of two kinds of enantiomericmolecules are the same expect that there is a slight refractive index (RI) difference (~10-6)between the left (-) and right (+) circularly polarized light. In our experiment, the polarizationof the incident light is exchanged between the left and right circular polarizations by operatinga polarization modulation system, the intensity of the reflected light beam from the SMCWare detected by a photodiodes, and then the enantiomeric excess of the chiral liquid can bedetermined by the circular differences in the reflected intensity. Owing to the highly sensitiveresponse of the ultrahigh-order mode to the variation of the optical parameters in the guidinglayer and their polarization-independent property, our method can determine the enantiomericexcess with a high sensitivity. Taking limonene and carvone chiral liquids as proofs, thedeterminations of enantiomeric excess down to2.1%and1.2%are achieved.