Research On Broadband Optical Concentration Technology Based On Grating Side-coupling

Though the technology of grating side-coupling is often applied in fields, such as coupling of light of single wavelength or narrow waveband, pump of fiber laser, integration of optical waveguide, its application for broadband coupling of visible spectrum is rarely studied. Sunlight can concentrate and output at the edge of waveguides by integrating sub-wavelength gratings with waveguides, making it a novel solar concentrator. And the method is just mainly researched on this dissertation for solar concentration.In theory analysis, not only the principle of energy coupling by grating is expounded, but also details two kind of the vector diffraction theory, Time-domain Finite-difference method and the rigorous coupled wave method, which are both based on the Maxwell’s equations and as a theoretical foundation for grating structure simulation and optimization.The sub-wavelength grating parameters have deeply affected on the diffraction efficiency of coupled light, thus these have effect on the energy collected by the side of the waveguide. Several kinds of grating structures were selected and made a fast scan simulation by FDTDsolutions to obtain the optimal structure of different surface types, on which the rectangular of phrase gratingwere verified through RCWA method. Consideringtheimpact factorsof thedifferent incidentangles to the solar concentrator,the diffraction coupling efficiency under different incident was also simulated in this dissertation.The coupled light propagates within the waveguide by total reflection. When the light is propagated to the interface between the waveguide and grating,the energy leakagewill be caused by the occurrence of transmission diffraction.FDTD solutions was also be utilized here to calculate energy loss one timeof several coupling wavelengths in the rectangular gratings. And in phase rectangular grating, the coupling wavelength of 420nm was selected to calculate maximum propagation distance,andtherelationship between coupled energy collected bythe side of waveguide and the length of waveguidewas analyzed as well. At last, the improvements of high contrast gratings are proposed due to severe loss of light propagation.