The Theory And Simulation Study Of Single Micro-ring Resonator Filter With Doubled Free Spectral Range

With the rapid development of communication services and Internet business, opticalfiber communication system with high transfer rate, long transmission distance and largechannel capacity has become a development trend of modern communications. Opticaldevices are the core of the fiber-optic communications systems. As a kind of opticaldevices, optical micro-ring resonator doesn’t need cavity surface to provide feedback andhas great advantages which can integrate all kinds of optical devices onto one substrateand therefore can significantly reduce the cost of optical fiber communication system. Thebasic application of the optical resonator is filters. The performance improvement is thefoundation of the other applications, and large free spectral range can decrease crosstalkbetween channels, so this paper mainly focus on how to expand the free spectral range ofthe micro-ring resonator filters. The main work of this article is:On the basis of optical waveguide theory, the basic methods of micro-ring resonator,coupled mode theory, transfer matrix method and finite difference time domain methodare researched. The output spectrum of two-bus one-ring resonator is analyzed by thesimulation software of OptiFDTD, which verifies the frequency selection and filteringeffect of micro-ring resonator filter.The operation principle and performance indicators of the micro-ring resonator areanalyzed. The mathematical model is derived using transfer matrix method for a singlemicro-ring resonator filter, as well as the series of dual micro-ring filter. The effects of thecoupling coefficient, micro-ring radius, refractive index of waveguide and loss on theoutput spectrum are discussed, laying the foundation for further study of doubled freespectral range of micro-ring resonator filter.Two kinds of micro-ring resonator filter structure with doubled free spectral range areproposed. The first structure is a U-shaped waveguide coupled single micro-ring structure.The effects of the distance between the coupling point of the U-shaped waveguide, thecoupling coefficient, the waveguide refractive index, and loss on their output spectrum arediscussed. The second structure is a dual-port input single micro-ring structure, which adds the Add port input and the phase shifter in the two-bus one-ring resonator structure.The impacts of the phase shift of the phase shifter, the coupling coefficient, the loss on theoutput spectrum are discussed. According to the discussion of the results, the twostructures both can achieve doubled free spectral range by adjusting the distance betweenthe two coupling points of the U-shaped waveguide and the phase shift. Meanwhile thefilters can obtained a good filtering effect by selecting an appropriate coupling coefficient.These numerical studies provide a strong theoretical basis for the expansion of micro-ringresonator free spectral range.