Study On The Application And Optimization Of Periodic Structures In Silicon-based Photonic Devices

The emergence of integrated circuits has led to the industrial revolution,but with the reduction of line width,the development bottleneck of integrated circuits is becoming more and more prominent.In order to "continue" Moore's law,the study of integrated optical circuits has been the concern of scientists.At the same time,because of the natural advantages and the compatibility with CMOS technology,silicon-based photonic integration has become a hot spot in the field of photonic integration.Optical periodic structures have special modulation effects on light and have been widely studied and applied,because by changing some parameters of the structures,people can control the propagation of light actively.In this paper,the applications of silicon-based optical periodic structures of different dimensions were studied and optimized.Studying on the one-dimensional periodic structure arrayed waveguide grating(AWG),we presented a design with good performance and carried out a series of optimizations.Researching on the two-dimensional periodic structure photonic crystal(PhC)super lens,we analyzed the imaging principle and optimized image quality.We also in-depth analyzed contributions of different modes to the imaging.(1)In AWG,the length differences between neighboring arrayed waveguides are all the same,which leads to a stable interference field in the image plane.Light of different wavelengths follows a certain dispersion rule and is focused at the image plane.In a specific wavelength focusing position,a specific wavelength can be separated.In this paper,a software was used to simulate the device.With limited computing resource,a set of computing parameters was determined to make sure that simulation time was not too long and the line was not obviously distorted.By changing design parameters,we optimized the intensity distribution of the image field.In the optimized device,simulation insertion loss and crosstalk were 1.56dB and-18dB with low precision meshes respectively.The effective index of a multimode wide waveguide was less sensitive to the waveguide's width change than that of a single-mode narrow waveguide.Hence,multimode wide waveguides used in AWG improved its tolerance against the imperfect fabrication.Short tapers connecting a slab and rectangular waveguides reduced the crosstalk between adjacent waveguides;Short tapers also reduced AWG's size.It was proved the short parabolic taper with a certain length had high transmission.(2)PhCs can realize negative refraction because of special band structures and can be used to make super lenses.We analyzed and verified the relationship between modulation transfer functions of different surface terminations and their image fields.By changing the surface termination,we smoothed the peak,realized wide-angle resonance of PhC surface modes and optimized the image quality.We attained a small FWHM and a close to isotropic circular wavefront under a certain surface termination.Contributions of different PhC modes to imaging were also studied.Beyond the cutoff angle,only the evanescent modes were excited inside the PhC and they had important participation in the imaging.The coupling amplitudes of different PhC modes changed with surface terminations.The lowest order mode's resonance peak was narrow and higher order modes' were wide.In the near field,the image field distribution characteristics of the PhC super lens kept unchanged when the point source was moved in two dimensions.So our methods and conclusions were proved to be right.A silicon-based chip test platform was introduced in this paper.The principles of grating coupling and end-face coupling were also analyzed.AWG was tested by grating coupling,and the results were analyzed in detail.