Design And Property Research On A New Structure Realizing Splittingand Direction Emission Of Photonic Crystal Waveguides Output

In photonic crystal (PC) research, PC line defect waveguides and PC self-collimating waveguides based on the forbidden band characteristics and auto-collimation play an important part. PC waveguide is the most essential component foroptic integrated circuit, photo-communication and light sensing technology based on PCdevices. Moreover, it is also the foundation of designing other PC devices. In realapplication, in order to couple PC waveguide devices with other optical devices more oron, it’s necessary to split or collimate the output light of waveguide. So how to realizesplitting or calibration of PC waveguide output light to couple with other optical devices,is an important direction in develop PC waveguide. Aimed at PC line defect waveguidesand PC self collimating waveguides, this thesis combines numerical stimulation andtheoretical analysis to explore the methods for the output photon of collimation andbeam splitting.In order to lay the foundation for surface structure design in this thesis, using planewave expansion method and super cell technology, dispersion relations of surface maskfrom PC to air and from PC to PC was simulated. From the analysis of the stimulationresult, the variation law for characteristics of PC-air uncoupling surface mask with thesize of surface adjusted dielectric cylinder was obtained, and the variation law forcharacteristics of PC-PC coupling surface mask with the distance of surface and the sizeof surface adjusted dielectric cylinder was obtained.By PC output surface masking and adding point defects, a new PC line defectwaveguide output splitting structures was proposed. Combining numerical stimulationand theoretical analysis, the effects of output surface masking and adding point defectswere analyzed. Using the FDTD method, the characteristics of designed splittingstructure output were numerically stimulated, and the variation law for the number ofoutput space beam with the change of point defect position was studied. The resultshows that when the distance between point defect L=2na, there are n beams in outputspace. The interference principle of coherent point sources can explain stimulationresult. In addition, the influence of both the number of adjusted dielectric cylinder onoutput surface and two additional point defects on secondly output surface on intensityof output light and splitting ratio was further studied.We proposed a new method of combining PC branched waveguide channels andextra modificcation. With this new method, we realized the splitting of PC line defectwaveguide emission, then we stimulated this splitting with FDTD method, theinterference principle of coherent point sources can explain stimulation result very well. Through designing double branch waveguide channels in PC, we got the1—N (oddnumber) splitting of output emission. The variation law of N with ratio of distancebetween double branch to input wavelength was studied systematically, and the reasonwhy N is odd number was analyzed. By adding modification in one of the doublebranch waveguide channels, we got the1—M (even number) splitting of outputemission, the effect of adding modification was studied theoretically. In order to showthe efficiency and flexibility of the designed method, we further investigated outputbeam property of three branched waveguide modified by extra dielectric cylinder.With the method of excite surface waves of PC-air and PC-PC together, a newcompound structure made up of surface masked PC was proposed, which makes itpossible for incident with different frequency propagates with T-shape, Y-shape and L-shape. When the beam propagates with T-shape and L-shape, the output light spreadsalong the PC surface. Based on such design method, the PC surface wave waveguidewith smaller area compared to traditional T-shaped and L-shaped waveguide. Thedispersion relations of this new compound structure were studied with plane-waveexpansion method, the frequency range of T-shaped, Y-shaped and L-shapedpropagation in compound structure was got. We stimulated the T-shaped, Y-shaped andL-shaped propagation with the Finite-difference Time-Domain (FDTD), and got thevariation law of output light intensity by analyzing the stimulation result.To avoid the scattering of self-collimated beams of waveguide, we proposed themethod of adding two layers structure to the PC self-collimated waveguide. Throughanalyzing PC self-collimated waveguide same-frequency curve and the principle of self-collimated two-layer dielectric cylinders, we have achieved highly directional beamingof self-collimated beams from PC structures. Numerical stimulation results show thatdivergence angle of output light is6°, efficiency is68%. In addition, the influence ofdistance between two-layer dielectric cylinders on output distribution was furtherstudied.