The Mechanical Effect Of Novel Flexible Optical Microcavity Biosensor And Its Structural Design And Performance Optimization

In recent years,with the development of flexible optoelectronics,it has shown a great potentiality in the fields of biomedicine,life sciences and military science.Photonic devices has been gradually integrated on flexible substrates rather than rigid substrates,which enables in vitro or in vivo biosensing detection of non-planar integration with the human body.Due to ultrahigh quality factor and low mode volume coming from the confined light interacting with the sensing object multiple times in the resonator which supports the whispering gallery mode?WGM?,flexible photonic device based on WGM resonator can achieve high sensitivity biosensing.However,when the integrated flexible photonic device occurs deformation with small bending radius,large shear deformation takes place in the adhesive layer to minimize elastic deformation energy in the substrate layer and cladding layer due to the elastic modulus mismatch between layers,which induces the undesirable resonance wavelength shift and seriously reduces the accuracy of the detection results.Therefore,it is necessary to study a new method to eliminate the stress on the resonator and effectively control the strain-optical coupling behavior to obtain the biosensing information accurately and realize the actual biosensing application based on the flexible photonic device.The paper firstly simulates the through-stack strain distribution in the flexible photonic device when the uniform force is applied underneath the substrate layer.It's found that conventional multilayer beam bending theory becomes invalid and there are multiple neutral planes distributed in the flexible photonic device structure.According to this result,multi-neutral-axis theory is proposed to describe the through-stack strain distribution in the flexible photonic device.Then two methods are proposed to solve the mismatch between the penetration depth of evanescent wave and the distance from the neutral plane to the detection surface.One is to build a novel sandwitch structure from the perspective of greatly reducing the strain distribution near the optical structural layer.A micro-rigid body is embedded at some proper position inside the cladding layer of the conventional three-layer flim structure.Although the distance from the neutral plane to the detection surface cannot be further shortened,the strain distribution near the detection surface can be greatly reduced to only 10^-3??according to the 2D FEM and 3D FDTD simulation results,leading to a trivial resonance wavelength shift of 10^-4-10^-3 pm which can be totally ignored.Another is to present a single-opening microring resonator?SOMRR?for achieving the simultaneous measurement of refractive index?RI?and pressure from the perspective of completely eliminating the influence of the strain-optical coupling effect.The notch angle lifts the degeneracy of clockwise and counter-clockwise WGMs to excite the mode splitting,forming symmetric and asymmetric standing wave modes?SWMs?in the SOMRR.Through the three-dimensional FDTD simulations of the two SWMs under different external environments and loads,we obtained a RI sensitivity of 77.07 nm/RIU,a high pressure sensitivity of 5.01 pm/kPa for symmetric SWM and a RI sensitivity of 69.54 nm/RIU,a high pressure sensitivity of 5.72 pm/kPa for asymmetric SWM.By solving the inverse matrix of the sensitivity matrix,the resonance wavelength shift respectively caused by the change of RI and pressure can be distinguished.For the biosensing application based on the flexible photonic device,the effect of strain-optical coupling can be eliminated.The paper opens up a new idea to realize ultra-flexible,high-sensitivity and biocoMPatible optical biosensors,and has an important theoretical guiding significance.