Research On Micro-Nano Optical Force Sensing For Interventional Diagnosis

In recent years,with the rapid development of science and technology,people have been paying more attention on health.Pressure in the human body is one of the important vital characteristics and its measurement is widely used in interventional diagnostics as an important factor for determining the patient’s condition.Consequently,the performance requirement for pressure sensors in the field of interventional medicine is even higher.Currently,the traditional piezoelectric sensors have obvious problems such as electromagnetic interference,zero calibration requirement for disconnection-reconnection,limited torque,and a high probability of large drift.Since optical sensors not only can compensate for these problems,but also have advantages such as small size,lightness and flexibility,high sensitivity,high accuracy,good stability,small drift,and reasonable biocompatibility,it becomes one of the hottest researching spots.Currently,the commonly used optical force sensors are utilizing optical fibers as the sensing medium.However,decreasing size and cost is still an urgent requirement for these sensors due to the increasing attention on people’s health and the proposal of global precision medical care.Surface lattice resonance has features such as small size(micro-nano size),suppressed radiation loss,a large volume of enhanced field,narrow linewidth,and high-quality factor.Therefore,this thesis proposes a highly sensitive micro and nano mechanical sensor based on intensity demodulation of the strong coupling between surface lattice resonance and Fabry-Pérot cavity.It provides a basis for the realization of compact sensors and low-cost sensing systems,which contributes to the foundation for the study of micro and nano optical force sensors.The main content and outcomes are summarized below.Firstly,the surface lattice resonance using an asymmetric metal-dielectric-metal nanopillar array structure in an asymmetric environment is proposed to achieve a quality factor of 77 with an improvement of 24% compared to the symmetric period(quality factor62),and the geometrical parameters are simulated and optimized.The results show that the asymmetric period is not always higher than the symmetric period in terms of quality factor,which notably leaves certain pitfalls for the processing design of sensors based on surface lattice resonance with high quality factor.Secondly,the quality factor of the lattice resonance is further improved to 86 by near-field coupling.Consequently,a force sensing mechanism based on surface lattice resonance is proposed with a 1 nm change in spacing distance and a corresponding 42 nm shift in resonance wavelength.Its geometrical parameters are simulated and optimized as well.It is demonstrated that the structure range of the sensor is limited(at the nanoscale),which paves the way of the later micro-nano-mechanical sensor based on surface lattice resonance with a strong coupling system of Fabry-Pérot cavity.Thirdly,the strong coupling system between the SLRs mode and the photonic Fabry-Pérot cavity mode is proposed.The SLRs mode can be strongly coupled to each order of the photonic Fabry-Pérot cavity mode(i.e.odd and even orders),reaching a cleavage energy of 153 me V in the visible band,which is about 9.5% of the resonance energy in the visible band.The geometrical parameters are optimized by simulation,then,the sensor is fabricated.Although,the experiment results are not satisfying,it lays the foundation for the strong coupling-based micro-nano-mechanical sensor.Last but not least,the strong coupling-based micro-nano-mechanical sensor is proposed,which is a strongly coupled sensing system with surface lattice resonance and Fabry-Pérot cavities in a homogeneous environment.The achieved splitting energy reaches225 me V,which is 36% of the resonance energy.For the bonded cleavage mode at low energies,the electric field can be enhanced by a factor of 1673,which is 2.5 times of that in SLRs.When 2D gold nanorod periodic arrays are placed at a distance ratio of 1:3 from the two gold cavities,the results show that surface lattice resonances can be strongly coupled to both Fabry-Pérot cavity resonances of odd and even orders.Compared to the surface lattice resonance,the electric field is enhanced by a factor of 3 with a corresponding enhancement factor of 1935,and the enhancement of the electric field extends to most space of the Fabry-Pérot cavity.This allows the sensor to be demodulated with intensity and the obtained sensitivity is 9.132 nm/kPa.