Optical Band Stop Filters Based On A Multimode Photonic Crystal Nanobeam Waveguide

The development of silicon photonics is just a few decades, but is prosperous in today's information society. No matter in the optical chips, optical inter-connects, optical computing or the optical sensing, the smaller and fine, high performance and power saving optoelectronic devices or the silicon integration is always the focus of Chinese and foreign scholars.It`s due to the cyclical changes of the refractive index in the space of the photonic crystals, there will be photonic band gap similar as the semiconductor, namely PBG: the frequency of light or electromagnetic wave falls within the band gap range can not propagate in the photonic crystals. In addition, the coupling between the defect modes in photonic crystal will form mini stop band. The mini stop band can transfer light energy from the fundamental mode to the backwards high order modes, resulting in a bandgap in the frequency domain. The mode coupling is the basic mechanism of many functional optical nano devices, and it will be a good platform with the photonic crystals, which can produce many promissing and valuable applications.Based on the above background, an optical band stop filter using mini stop band in one dimensional photonic crystal nanobeam is designed. The optical band stop filter is extremely sensitive with high 3 dB bandwidth and low reflection light in an ultra compact structure in less than 40 ?m in length. Also the structure parameters of the device can be adjusted and achieve a large range change of 3 dB bandwidth of 27 nm to 90 nm and center wavelength of 1.41 ?m to 1.71 ?m which can be very functional in practical application. In addition, the filter curves obtained by simulations is extremely steep, with smooth edges and the center wavelength loss is over 40 dB showing excellent filtering performance. The filter can achieve the same performance with a significantly small size compared with the long period grating.In this thesis, we introduce the theory of the photonic crystals at first, including the expansion of the plane wave method and finite difference time domain following with the model structure and working method of the device. Than we use the three-dimensional finite difference time domain algorithm simulates the transmission spectrums of the device and compare the filtering effects when the major structural parameters change. Also the Gaussian apodization and extra taper holes' methods are used for further optimization, which greatly suppresses the oscillations of the both band edges and reduces the reflection light. At last, we try to make the device. And the test results are presented and analyzed.The optical band stop filter can be a reference for the development and application of the photonic crystal and mini stop band. It also can contribute to the future development of silicon integrated optoelectronic devices.