Sensing And All-optical Modulation Characteristics Research Based On Microfiber Coil Resonator

Micro/nanofiber has been widely used in numerous scientific research fields,such as optical communication,lasing,sensing,defense,medicine,nonlinear optics,etc.Micro/nanofiber has a range of advantages,e.g.strong evanescent field,easy fabrication,simple structure,compact,great flexibility,anti-electromagnetic interference,etc.,which allow it to meet the different demands in many application fields.Micro/nanofiber resonator is a kind of optical fiber device with a high optical quality factor based on its strong evanescent field.The transmitted light can form effective optical coupling and resonance with the resonator.Micro/nanofiber resonators have been used in lots of application fields such as filter,sensing,and modulation etc.Micro/nanofiber resonator consists of three types:loop,knot,and coil.Among them,micro/nanofiber coil resonator(MCR),as the only three-dimensional(3D)structure,has a couple of advantages,for instance,long coupling length and high coupling efficiency,which allow it using as an ideal carrier for realizing a variety of optical sensors and modulators.MCR can combine with other functional materials because of the strong evanescent field and the long coupling region.This feature can effectively expand the applications of MCR in sensing and modulation fields.Although MCR has many advantages,few research outcomes have been reported so far,and the exploration of its working mechanism and applications is not in-depth enough.Therefore,it is of practical significance and value to research MCR.In this work,we have conducted in-depth investigation on the optical transmission characteristics and applications of MCR.The MCR was designed and fabricated to conduct comprehensive and detailed research on its temperature sensing characteristics based on the theoretical model of MCR.The salinity sensor and the ultra-high resolution Pb²⁺ions sensor was realized based on the MCR microfluidic cavity.Finally,the combination possibility of MCR and two-dimensional material was explored.The all-optical modulators based on MCR and two-dimensional material(black phosphorus and MXene)were realized.First,the temperature sensing characteristics of MCR were studied comprehensively.A temperature sensor was realized by the MCR fabricated by silica microfiber.Optimizing the manufacture parameters of the MCR,including the diameter of the MCR support rod,the distance between adjacent microfiber coils,the number of turns,and the microfiber diameter,the maximum temperature response of 0.237 nm/^oC was obtained.To explore more sensing applications for MCR,a microfluidic cavity based on the MCR structure was obtained by dissolving the support rod,and the salinity sensing of the liquid environment was realized.The salinity sensitivity in the liquid environment of the MCR microfluidic cavity reached 15.59 nm/%,and the minimum resolvable salinity change was about 1.3×10^-3%.On this basis,the detection of Pb²⁺ions in water was achieved by depositing black phosphorous(BP)nanosheets inside the MCR microfluidic cavity.The Pb²⁺ions sensor had a detection limit of 0.03 ppb for Pb²⁺ions and had the advantages of fast response time and high stability.Finally,all-optical modulation was realized based on the MCR and MCR microfluidic cavity.An all-optical modulator was achieved using MCR incorporating BP nanosheets.The modulation rates to resonance wavelength and extinction ratio were 0.033 nm/mW and 0.180d Bm/mW,respectively.Another all-optical modulator was achieved by depositing MXene on the inner wall of the MCR microfluidic cavity.The modulation rates to resonance wavelength,extinction ratio,and phase were 50 pm/mW,0.554 d Bm/mW,and 0.262?/mW,respectively.The modulation of the output pulse was also realized by adding a mechanical chopper in the modulation device.The rise time and fall time are 0.179 and 0.145 ms,respectively.In this work,a series of optical devices based on the MCR structure were designed theoretically and achieved experimentally due to its unique optical properties.Based on the temperature sensing characteristics of MCR,a temperature sensor with a high sensitivity was realized,and the relationship between fabrication parameters and temperature sensitivity was characterized by adjusting the fabrication parameters of MCR;a salinity sensor and Pb²⁺ions detection in the water were investigated based on the innovative MCR microfluidic cavity structure;all-optical modulators were achieved using MCR incorporating with two-dimensional materials:black phosphorus and MXene.All the research outcomes will greatly promote the applications of MCR in the fields of fiber sensors,all-optical modulation etc.These results also pave the way for further development of interdisciplinary research between fiber optics and functional materials.