Fabrication Of Microfiber Knot Resonator And Its Application In Refractive Index Sensing

Similar to electronic devices,miniaturization and integration is the growing trend of the optical devices.As an important basic device of micro-nano photonic integrated circuits,Microfiber is an important means to explore all-optical systems.Since the optical field transmitted along the microfiber is low,and the bending loss of the microfiber is also low,the transmission spectrum of the microfiber knot resonator made from microfiber can reach a high quality factor.Moreover,The microfiber knot resonator keeps good resonance characteristics when it is put in water or embedded in low-refractive-index polymeric material.Based on the above advantages,the microfiber knot resonator can be used for sensing the physical parameters in the aqueous solution.This dissertation mainly studied the optical properties of microfiber knot resonator in aqueous solution and its application in refractive index sensing.This dissertation first introduces the research background of microfiber and the cutting-edge microfiber fabrication method,explores the characteristics of microfiber and various optical devices based on microfiber,and reviews the basic theory of microfiber in aqueous solution.Based on the distribution of the fundamental mode energy field transmitted along the microfiber,the theoretical analysis of a single microfiber resonator(MKR)and the series connection of two MKR in aqueous solution is carried out.The twin-cone microfiber was melt-drawn by two different fire heads.When a ceramic fire head is used,the common single-mode fiber is melted by burning hydrogen gas.Since the inner diameter of the ceramic fire head is wide and the generated flame is stable,the intermediate flat zone of the double-cone microfiber can be up to 1.2 cm in length,and the middle is gentle.The area diameter is as small as 200 nm.The other is to use a hydrogen-oxygen mixed metal fire head to melt the common single-mode optical fiber by burning a mixed gas of hydrogen and oxygen.The intermediate flat zone of the double-cone microfiber made of hydrogen and oxygen has a length of 0.9 cm,and the diameter of the intermediate smooth zone is Up to 2 ?m.However,since the flame temperature generated by the hydrogen-oxygen mixed fire head is high,the drawn micro fiber has good flexibility and is not easy to break.Aiming at the problem that the MKR has high loss and the structure of it is not strong by the method of fabricating the MKR by the commonly used truncated double-cone microfiber,a method for directly forming MKR without truncating the biconical microfiber is studied.The MKR produced by this method has low loss and a firm structure.In this paper,a single MKR was placed in an aqueous solution for temperature and refractive index sensing.The experimental results show that MKR has good resonance characteristics in aqueous solution.The output spectrum of the resonantor can also be well matched with the simulation,such as the overall spectral shape,the size of the cavity diameter and the corresponding relationship of the FSR of the output spectrum.And the simplified theoretical calculation of MKR sensitivity is basically consistent with the experiment.Finally,The measurements of the refractive index of the aqueous solution by the series connection of two MKR were performed.