The Research On Optical Passive Filter Based On Silicon Microresonators

Microwave signal processing plays a very important role in modern communications and military.Traditional microwave signal processing technology is limited by electrical sampling rate and high frequency performance,which cannot meet the increasing demand of processing speed.Compared with traditional microwave signal processing,microwave photonic signal processing technology based on optical device has the advantages of large processing bandwidth,strong anti-electromagnetic interference and high flexibility.One of the key issues in microwave photonic signal processing is to design an optical filter that meets the requirements.Based on mature semiconductor manufacturing technology,siliconbased photonics has attracted much attention.It inherits the advantage of low cost,high stability and large-scale expansion of silicon-based integrated circuit manufacturing industry,and has wide application value.In siliconbased integrated devices,silicon-based micro-resonators not only small size,flexible structure,but also has a high quality factor,and wavelength selectivity and other characteristics.So it is very promising technology solutions of the microwave photon optical filter.For the filter design,the quality factor and the rectangular factor is the most critical of the two indicators,where the quality factor determines of the filter bandwidth,and the rectangular coefficient describes the filter spectral steepness,the more ideal filter,the smaller the rectangular coefficient.Therefore,this paper focuses on how to integrate silicon-based micro-resonators to improve the quality factor and filter rectangles.Innovation points and contributions can be summarized as follows:1)We experimentally show that using ridged waveguide could improve quality factor of silicon-based microring resonator.Firstly,we introduce the ridged waveguide for reducing the transmission loss of silicon waveguide and the process is explored and experimentally demonstrated.We carefully select the thickness of the wafer and the etch depth,and measure waveguide losses by using spiral waveguides.Two kinds of micro-ring resonators are fabricated by this process.It is verified that this kind of waveguide could improve the quality factor of the resonator compared with the deep silicon etching.2)We propose two schemes to improve the rectification coefficient of the filter based on silicon-based microring resonators,including cascading(coupled resonator optical waveguide)CROW structure,which not only makes the filter spectrum steeper,but also can maintain the flat-top filter,meantime we can add the heater to achieve a variable bandwidth.We have fabricated a single-stage cascade micro-loop cascade structure and preliminary verify the feasibility of the scheme.Another scheme is based on the Mach-Zehnder interference with microdisk-Sagnac loop mirrors,we can obtain a special electromagnetic transmission spectrum by introducing the coupling between different optical paths in the device.With the two resonant peak staggering the state,we can get high-rectangular,flat-top passband filter spectrum.We simulated and fabricated silicon-based devices and verified the proposed scheme.3)We also propose a bandpass filter by introducing cascaded Sagnac reflectors and fabricate multiple resonators made up of Sagnac mirrors to obtain high-order filter spectra,which improves the sharpness of the filter spectrum.This filter has advantages which is compact and reconfigurable,and it could be applied to some high-quality factor filters or optical buffers.