Research And Application Of Finite Element-Artificial Transmitting Boundary Method On The Optics

In this dissertation, Finite Element Method is combined with the ArtificialTransmitting Boundary that often deals with boundary problems in seismology, whichis called Finite Element-Artificial Transmitting Boundary Method. Since the artificialboundary is fictitious, the wave would travel through it without any reflection, thusthis method can effectively eliminate the effect of reflective wave on the calculations,and accurately calculate the distribution of the light field and sound field consequently.Here, this method is used in calculation on optical waveguide, acousto-optic tunablefilters and wave scattering. From the results of calculation, it can be found that thismethod proves highly effective in these aspects.The first is its application on Y-branch optical waveguide. Optical waveguide isthe core of the integrated optics. Most devices in integrated optics, such as opticalmodulator, switches, power dividers, couplers, wavelength division multiplexers,filters, beam analyzers and lenticules, are all based on the optical waveguides.Therefore, the optical waveguides are the center of integrated optics. Y-branch opticalwaveguide is also one of important optical devices, so design and calculation on itbecomes significant. Here, we use the presented method to design and calculate it, andget the power transmittance 52.8%. The result is in agreement with others, and showsthe practicability of this method.The second is its application on calculation on side-lobe suppression ofacousto-optic tunable filters (AOTF). AOTF are very attractive in communication andnetwork as they offer a broad tuning range, a fast tuning speed, and a simultaneousfiltering capability. However, the magnitude of side-lobe affects indirectly the qualityof its performance;hence the side-lobe suppression becomes very indispensable.According to the side-lobes change as the width of sound waveguide changes, twokinds of structure are designed, one is Cosine function as weighting function;one isGauss function as weighting function. And the optical filter responses of the TE-TMmode conversions of AOTF with different weighting functions are calculated. Resultsshow that the AOTF with Gaussian weighting functions are better than AOTF withCosine weighting function.The final is its application on wave scattering problems. The distributions ofscattering field from different scatterers are presented, which indicate this method isuseful in calculation on scattering problems.