| Photonic crystals are broadly applied in the areas of optical communication because of their unique light control characteristics,low loss,small volume and easy integration.For photonic crystal sensors,the common structures mainly include one-dimensional photonic crystal nanobeam structure and two-dimensional photonic crystal slab structure.Facing the increasingly complex sensing environment,based on refractive index and temperature sensing,many sensing methods such as solution,gas concentration,humidity,pressure and so on are proposed.At the same time,sensors based on photonic crystal cavity coupled system are attractive for researchers.On the one hand,multi-parameter sensing can be realized by using the resonant modes of multiple microcavities,on the other hand,high-performance sensing can be realized by using the coupling effect between optical modes.As a common interference effect,electromagnetic induced transparency-like(EIT-like)effect has a unique transmission spectrum,which has been widely studied in physical fields such as metasurface and has been used in the design of high-performance sensors.In addition,because the transmission spectrum of EIT effect based on mode interference and Autler-Towns splitting(ATS)effect based on non-mode interference are very similar,the distinction of the two mechanisms has also been concerned by researchers.At present,there is a few researches on EIT-like effect based on photonic crystal,and there is also a lack of research on the design of high-performance sensors based on it.Therefore,this paper will design a photonic crystal high-performance sensor structure based on EIT-like effect combined with one-dimensional photonic crystal nanobeam cavity and analyze its sensing performance.The research contents of this paper mainly include:Firstly,a single-parameter sensor with single-mode photonic crystal nanobeam cavity coupled structure based on EIT-like effect is designed to realize the sensing of methane concentration.Firstly,based on the temporal coupled-mode theory,the model of double microcavity cascaded sidecoupling structure is established,and the expression of transmission spectrum is obtained.Then,combined with the theoretical model,the sensor structure is designed,which is composed of two air-mode photonic crystal nanobeam microcavities with circular holes,which are cascaded on the same side and coupled to the waveguide.In order to improve the sensitivity of the sensor to methane gas,the circular hole is filled with methane sensitive material.The sensitive material will interact with methane to make its refractive index change linearly if the concentration of methane in the environment changes.In order to obtain the transmission spectrum with obvious transparent window,the adjustment between the resonant wavelengths of microcavities is realized based on the thermooptical effect of material.Besides,the interference conditions between modes are changed by adjusting the center spacing between microcavities and the spacing between microcavity and waveguide.In this process,the average weight of EIT theoretical model and ATS theoretical model in the transmission spectrum is calculated by Akaike’s information criterion(AIC),which is used as an evaluation index to optimize the sensor structure.Finally,the electric field distribution of the transparent window is analyzed and the offset of the transparent window of the sensor in different methane concentration environment is detected based on the simulation results of the simulation software.The sensitivity of the sensor is-0.494 nm/%.Secondly,a dual-parameter sensor with dual-mode photonic crystal nanobeam cavity coupled structure based on EIT-like effect is designed to realize the sensing of refractive index and temperature.The sensor structure adopts the structure that two photonic nanobeam cavities are cascaded on the same side and coupled to the bus waveguide.The two microcavities are dielectric-mode photonic crystal nanobeam cavity based on stacks and air-mode photonic crystal nanobeam microcavity based on circular holes.In order to make the sensor more sensitive to temperature,temperature sensitive material SU-8 with larger thermo-optic coefficient is coated outside the photonic crystal cavity with stacks.The coupling structure with obvious transparent window is obtained by adjusting the center spacing between microcavities and the spacing between the microcavity and the waveguide.The refractive index sensitivity of airmode resonance in the sensor is 215 nm/RIU and the temperature sensitivity is 19 pm/K;The refractive index sensitivity of dielectric-mode resonance is 0 nm/RIU and the temperature sensitivity is-83 pm/K.Through analysis,the sensor not only realize dual-parameter sensing of refractive index and temperature based on sensing matrix,but also has strong ability to resist external interference such as reading errors.In conclusion,this paper focuses on the photonic crystal highperformance sensing mode based on EIT-like effect.On the one hand,a single-parameter sensor with single-mode photonic crystal nanobeam cavity coupled structure based on EIT-like effect is designed,which can realize the sensing of methane concentration.On the other hand,a dualparameter sensor with dual-mode photonic crystal nanobeam cavity coupled structure based on EIT-like effect is designed,which can realize the dual-parameter sensing of refractive index and temperature in liquid environment.In the process designing the sensor,the measurement of mode interference degree in photonic crystal nanobeam microcavity coupling structure is realized through AIC calculation,which provides an idea for the design and analysis of photonic crystal microcavity coupling structure sensor. |
