Research On Fano Effect Of Ring Resonator Based On Periodic Micro-and Nano-structures

Micro-ring resonators(MRRs)have already gained extensive attention in virtue of their compact sizes,high-quality factors,wavelength selectivity,and ease of integration.The transmission spectrum of the simplest single-ring and single-bus MRR consists of periodic dips,whose resonance lineshapes are symmetric Lorentzian.However,the ER and harmonic peak slope of the MRR are not high,and the modulation depth of the MRR is low.The Fano lineshape has an asymmetric and sharp slope.The changing trend of the Fano lineshape is sharper and steeper than the Lorentz line,which can significantly reduce the frequency shift required for on/off switching and improve the detection limit of sensing.Presently,Fano lineshapes have been achieved in various MRR-based structures,such as coupled MRRs,embedded MRRs,and MRRs coupled with a Mach-Zehnder interferometer(MZI).However,these structures are complex and have large footprint,which is not conducive to the ultra-dense integration and require high fabrication accuracy.This work proposes a single MRR with two partially reflecting elements incorporated into the bus waveguide which forms the Fabry Perot cavity.Thus,the Fano resonance is realized by the coupling of waves in the two cavities.The transfer matrix model of the compact structure is established with the reflective wave in the MRR included.Then the transfer function of the structure is obtained and the transmission spectrum is analyzed.It is revealed that the Fano,EIT,and EIA lineshapes originate from the mode-coupling between the Fabry-Perot cavity and the MRR.Based on the model,the formation of each resonance lineshape is analyzed.The conditions under which each resonance lineshape can occur are identified and the characteristics of these resonance lineshapes are studied.Based on the theoretical model,three kinds of structures are designed.The first one is a MRR with two circular air holes as a reflective element.The second one is the periodic micro-nano structure cavity MRR(PC-MRR)The third one is Periodic micro-nano structure MRR.They realize the Fano and other lineshapes.Theoretical model is verified well.In this paper the Fano resonance theoretical model of a single MRR is constructed.Three practical structures are designed which have the advantages of simple compact and excellent performance,and can replace the original complex structure It can provides a powerful candidate for the application of the Fano resonance effect,such as biochemical sensing,filtering,optical switching,and so on.