Design And Performance Analysis Of High Accuracy Dual-parameter Sensing Model Based On Dual-mode Photonic Crystal Microcavity

Sensors based on photonic crystal microcavities have been widely used in sensing fields due to small mode volumn,strong light control ability,easy integration and unlabeled detection.In recent years,multi-parameter sensors with high integration and multi-parameter sensing capability have become the research trend of sensing technology.Dual-parameter sensors based on photonic crystal microcavities have been proposed continuously.On this basis,how to improve the detection accuracy of the dual parameter sensor is a problem that needs to be focused on.Through the analysis of the dual-parameter sensing theory,the accuracy of dual-parameter detection can be effectively improved by increasing the sensitivity difference by using the different electric field distribution.Traditional dual-parameter sensors based on photonic crystal microcavities combine two photonic crystal microcavities with different modes by means of cascading,parallel or side coupling,which undoubtedly increases the complexity of the equipment and also introduces the mutual interference between the microcavities.This paper studies the photonic crystal microcavities that support the coexistence of different optical modes,and proposes two kinds of high-accuracy dual-parameter sensors based on single photonic crystal dual-mode microcavity.The main research results include the following contents:Firstly,based on the dual-parameter sensing theory,this paper analyzes the maximum detection error that may be caused by the wavelength shift error under the condition that all the combinations of the sensitivity and the wavelength shift take positive and negative values are considered,and the ratio of the maximum shift error to the maximum resonant wavelength shift error,the error factor(?),is introduced as an index to evaluate the detection accuracy of the dual-parameter sensor.By analyzing the calculation formula of the error factor,it is found that increasing the sensitivity difference between the two resonant wavelengths is helpful to reduce the error factor and achieve higher accuracy.Therefore,in consideration of the great response difference of optical modes with different electric field distributions to the environment changes,this paper proposes a method to increase the sensitivity difference by using different optical sensing modes,so as to effectively improve the detection accuracy of the dual parameter sensor.Secondly,this paper proposes an ultra-compact high-accuracy dual-parameter sensor based on a one-dimensional stacked photonic crystal nanobeam dual-mode cavity.By linearly modulating the length and width of the stack,the air mode and the dielectric mode are simultaneously existed in a single photonic crystal nanobeam cavity.The effective mode volumes of 0.1(?a/nPVA)3 and 1.8(?d/nSi)3,and the quality factors of Qa=3.7×105 and Qd=6.3×104 are numerical simulation obtained for air mode and dielectric mode,respectively.The surface of the nanobeam cavity is covered with a layer of water-absorbing polyvinyl alcohol(PVA)material,which converts the change of external relative humidity into the change of refractive index.Through the control variable method,the resonant wavelength shift with the change of humidity and temperature was simulated and analyzed respectively,and the humidity sensitivity of-764.3pm/%RH and 58.9pm/K were obtained.Compared with the previously reported optical sensors that can simultaneously detect humidity and temperature,the humidity sensitivity of the sensor is not only 1?4 times higher,but also the temperature sensitivity is very competitive.In the case of simultaneous detection of humidity and temperature,the humidity error factor and temperature error factor are 0.004 and 0.043,respectively,indicating that the 1pm wavelength shift error will only lead to a humidity error of 0.004%RH and a temperature error of 0.043K at most,which is expected to achieve high Accuracy.In addition,the size of the sensor is only 14×0.67×0.67?m3(length×width×height),and the structure is compact and easy to integrate.Thirdly,a high accuracy dual-parameter sensor based on double-layer coupled photonic crystal slab dual-mode microcavity is proposed for simultaneous detection of refractive index and temperature.The sensor consists of two perfect photonic crystal slabs placed parallel to each other at a close distance.Under the condition that the plane wave light source is incident vertically,the transverse-magnetic-like mode and transverse-electric-like mode are excited at the same time.Furthermore,the principle of Fano resonance in photonic crystal slab and the phenomenon of photon tunneling are introduced,the light transmission process of the sensing system is analyzed,the theoretical model is established,and the transmission formula is deduced.By comparison,the theoretical transmission spectrum calculated by the transmission formula and the simulated transmission spectrum show good agreement.The optimized microcavity can achieve high quality factor and high modulation depth simultaneously.Through numerical simulations,the quality factors of transverse-magnetic-like mode and transverse-electric-like mode both reach the order of 105,the refractive index sensitivities are 960 nm/RIU and 210 nm/RIU,respectively,and the temperature sensitivities are-66.5pm/K and 50.75pm/K,respectively.Compared with reported dual-parameter sensors that detect refractive index and temperature simultaneously,the quality factor of the sensor is increased by 1-2 orders of magnitude,and the refractive index sensitivity is also significantly improved.The error factors of refractive index sensing and temperature sensing are calculated as 1.87×1 0-6 and 1.87×10-2,respectively.The relative deviations of refractive index detection and temperature detection are verified by simulation as low as 0.6%and 1.0%,respectively,indicating that the detection results have high accuracy.In summary,this paper puts forward an effective method to improve the detection accuracy of the dual-parameter sensor,and designs two high accuracy dual-parameter sensors based on a one-dimensional stacked photonic crystal nanobeam dual-mode cavity and a two-dimensional double-layer coupled photonic crystal slab dual-mode microcavity,respectively.The sensitivity,quality factor and detection accuracy of the sensor are significantly improved,which provides an innovative idea for the design of the high accuracy dual-parameter sensor.