Three-dimensional Si3N4 Microring Resonator For Opyical Filter

Optical filter is an important part of wavelength division multiplexing,which can be used in optical communications and microwave photons to improve the communication capacity of the channel.The filtering principle of optical filters is mainly based on Michelson interference,MZI,Sagnac,microcavity resonators and arrayed waveguide gratings.Among them,the traditional microcavity notch and drop filter are implemented by a simple waveguide coupled to a microring resonator.This device can effectively control the wave shape change by cross coupling.However,the alignment error will affect the output spectrum,and dense filter devices also need more microrings coupling to achieve,which greatly increases the requirements for manufacturing.This paper studies three-dimensional self-coupled filter device based on silicon nitride microcavity,dual-layer cross-coupled tunable resonator system,and double-layer cross-coupled silicon nitride multi-ring resonator system.There are clockwise and counterclockwise modes in the device,which can interference in the output.At the same time,three-dimensional integration provides more tolerance for the device than ordinary planar integration.The self-coupling design reduces the manufacture error to get a stable output effectively.The double-layer cross-coupled microrings filter can achieve more dense filtering,which can improve the active control effectively and design freedom.The main work of the paper is as follows:In the first chapter,the development of optical filters is introduced.Microcavity filters are widely favored because of the compact structure,small size and high sensitivity.The coupling systems of waveguide are known in the packaging field,which are composed of precision instruments and excellent algorithms.In the second chapter,the theoretical design of micro-ring filters is introduced.The electromagnetic simulation of optical devices is mostly based on the Maxwell's equations.The high-precision FDTD simulation calculates accurately but still take a long time.In this paper,after waveguide modes and coupling are simulated by models of Rsoft,the transmission matrix method is used to analyze the transmission spectrum of the device.In the third chapter,a characterization system of an optical filter is introduced.The device packaging is one of the biggest challenges for integrated optical waveguide devices.Based on the coupling of silicon nitride waveguide devices,a self-feedback coupling system is designed by using Thorlab's precision instruments and an advanced optical power meter.Multiple automatic coupling search algorithms are studied.lab VIEW language is used to extract the power indicator in real time,and adjust the position of the three-axis displacement platform to ensure the maximum coupling.The fourth chapter of the thesis focus on the introduction of silicon nitride microcavity filters.A self-coupled structure effectively improved the manufacturing tolerance.The bottom layer racetrack resonator coupled with a top layer S-bend feedback waveguide,which is analyzed by the transfer matrix method and simulated by Matlab for the spectra.The different resonance spectra can be seen by changing the coupled coefficient between the waveguide and resonator.The output spectra can be tuned effectively by the heater.In the fifth chapter,we study the affect more microrings to optical filter.The top-layer S-bend waveguide cross-coupled with the racetrack resonator on a bottom layer,one and two microrings adding to the top layer.The transmission matrix and the iterative method are used to analyzed the output spectra with more microrings,which effectively improve the filtering characteristics of the device.They can be used for dense wavelength division multiplexing system.The three-dimensional integrated devices reduce the size while increasing the manufacturing tolerance.It also effectively improves the active modulation of the device.To address the problem of inevitable manufacturing errors in the manufacturing process,an effect of alignment errors from waveguide thickness and width on the output spectrum is studied in detail.With the increasing of the sub-microring,the coupling coefficient also increases,which effectively improves the freedom of adjustment of the device.Waveguide and microcavity are symmetrically coupling in the article.However,the coupled coefficients often change due to manufacturing errors.For the asymmetric structure of the coupling coefficient,the output spectrum is observed under the change of the coupling coefficient.The output spectrum has good stability,which can be used in optical switches,modulators,optical filters,etc.