Research On Coupled Microring Resonators With Controllable Q Factor And Its Application

The light in microring resonator transmits in the form of traveling waves.It has simple structure,high Q factor,and potential for high-density integration on a wafer.Recently,optical devices based on microring resonators have been widely studied and applied,such as filters,memories,and optical logic processing.The microring resonator supports multiple resonance modes.The detuning and coupling strength between two resonators has influences on the Q factor and light field of the device.As the coupled microrings work in EIT state and slow light can be obtained for time delay and optical buffering.This paper aims to establish a tunable system and focuses on the interaction between the resonance modes in coupled microrings.It enables the Q factor adjusted,time delay changed continuously between fast and slow light,and optical pulse stored dynamically.This paper proposes a tunable Q factor structure composed of two directly coupled microring resonators,one of which is also coupled to dual waveguides and under control.Based on the coupling and interference of the resonance modes,the mechanism of the Lorentz,Fano and EIT spectrum is analyzed.By shifting the resonance wavelength of the bus-coupled microring,the resonance mode and transmission spectrum of the device changes periodically.When the resonance wavelengths of the two microrings are far apart,transmission spectrum presents Lorentz spectrum.As the resonance wavelengths are close,it presents Fano spectrum.When they are equal,it shows EIT spectrum.Then the coupled microrings structure is realized on silicon on insulator,and the coupling of the two resonance modes is changed by thermo-optical tuning the bus-coupled microring.During the tuning process,the Q factor of the system,the Q factor of the floating microring and optical intensity are adjusted.Shifting the resonance wavelength of the buscoupled microring,it is observed from transmission spectrum that the Q factor of device is adjusted from 56 500 to 16 400.The Q factor of the floating microring is adjustable from49 200 to 12 000.As the coupling distance of the two microrings increases,the Q factor of all resonance modes gradually increases,and the extinction ratio of Lorentz resonance gradually decreases.Meanwhile optical intensity transmits from double peaks to single peak in the EIT state.Based on the controllable Q mechanism,we explore its application in optical buffering.When the device works in the low Q state,it behaves as slow light.And when it works in the high Q state,it behaves as fast light.We built the platforms to test and analyze the time delay in the two states.The time delay of the device varies from 14 ps to-15.0 ps.Tunable fast-to-slow/slow-to-fast light follows the delay bandwidth product.The larger the coupling distance,the smaller the bandwidth and the bigger the time delay.Moreover,pulse capture and release are also achieved using this structure with dynamically tuning of the bus-coupled ring.When the device works in the EIT state,optical pulse can be coupled to the device.And it is stored in the floating microring in the Lorentz resonance state.The maximum storage time can exceed 100 ps.In summary,this paper establishes a controllable Q factor structure,of which the resonance mode and transmission spectrum can be controllable via adjusting the resonance wavelength of the bus-coupled microring.Meanwhile,it can achieve adjustable time delay and store optical pulses in the floating microring.The proposed tunable Q factor system is simple,flexible,and realizable in various integrated photonic platforms,allowing for potential applications in on-chip optical communications and quantum information processing.