| The optical micro-cavity is an optical resonator with a size on the order of microns or submicron.It can confine the light to a small region due to the effects of reflection,total reflection,scattering or diffraction on a discontinuous refractive index interface.It has a wider range applications in modulation area and sensing capabilities and a free spectral range than conventional media micro-cavities.Optical micro-cavity is widely used in optoelectronic.It provides great research value and application prospects in the fields of optical communication,sensing,laser and signal processing.Recently,Optical fiber-based optical micro-cavity has become the research hotspot as the rapidly developing of the optical fiber technology.Various fiber micro-cavity has sprung up,i.e.fiber Fabry-Perot?F-P?micro-cavity,fiber Mach-Zehnder?M-Z?micro-cavity,fiber bubble micro-cavity,photonic crystal fiber defect cavity,etc.These devices has been reported to be used in refractive index?RI?measurement,temperature measurement,pressure measurement,stress measurement,magnetic measurement,load measurement,etc.The advance and development of the Femtosecond?Fs?laser has enrich the method of fabricating fiber micro-cavity devices.In this work,research has been focus on gradually transplanting the micro-cavity from the fiber end face to the core of the fiber.Optical fiber end micro-cavity,fiber F-P micro-cavity and fiber M-Z micro-cavity have been fabricated by use of Fs-Laser Wet Etching Technology and a whispering gallery mode micro-cavity have been fabricated using femtosecond laser two-photon polymerization technology.The sensing characteristics of fiber micro-cavity devices in terms of refractive index,temperature,gas pressure and bovine serum protein were studied.The main contents and research results of this paper are as follows:?1?The mechanism of the interaction of femtosecond lasers with substances,the working principle of wet etching technology and the development and application of femtosecond laser wet etching technology have been studied.In addition,two-photon polymerization technology combined with femtosecond lasers have been applied in the micro-and nano-devices fabrication.?2?According to the fabrication requirement of optical micro-cavity,we have designed and built a set of Fs-laser micromachining system,which includes Fs-laser,spectroscope,half wave plate,gran prism,reflector,microscope system and high precision3d electric displacement platform.The holding tool for the optical fiber during the wet etching technology have been designed and fabricated.In addition,another system used for femtosecond laser two-photon polymerization microfabrication have been constructed by utilizing the seed light?reputation rate:80MHz?of the Fs laser according to the characteristics of two-photon polymerization-high repetition frequency.?3?A concentric annular structure,an optical fiber end surface spiral structure and an optical fiber end surface array lens structure have been fabricated on the cross-section of the optical fiber by use of a femtosecond laser wet etching technique.Experiments have been made to investigate the influence of different parameters and different diffraction patterns of different structures have been found by observing the mode fields of these devices.?4?An in-cell fiber F-P micro-cavity sensor was fabricated by use of a femtosecond laser wet etching technique and it was successfully applied to tension,gas pressure,refractive index sensing.?5?An embedded M-Z micro-cavity sensor was fabricated by using femtosecond laser wet etching technique and successfully applied to the determination of bovine serum protein concentration.Firstly,the refractive index change of silica was induced by femtosecond laser,and the contour of the M-Z micro-cavity was produced at the interface between the fiber and the cladding;then the air micro-cavity was formed by the etchant along the region whose refractive index has been modulated.In order to ensure the sensitivity of the sample,it is necessary to perform a refractive index test on the sample before testing the concentration of bovine serum protein.Finally,the RI sensitivity obtained is-10055 nm/RIU and the detection limit is 3.5×10-5 RIU.The RI sensing of the sample can be realized the by distinguishing the concentration of the BSA,since there is a slight RI differences between the BSA of different concentration.The sensitivity of the BSA measured in the experiment was-38.9 nm/?mg/mL?,and the detection limit was2.57×10-4 mg/m L.?6?It has been found that a WGM resonance cannot be excited in a ring-shaped WGM resonator fabricated by using femtosecond laser wet etching technique.The reason for this is that the bubbles generated in the chemical reaction of the etchant and silica in the wet etching process that adheres to the cavity walls will prevent the chemical reaction,thereby an uneven surface is formed.So the complete WGM resonance due to the large scattering loss of light.Therefore,femtosecond laser two-photon polymerization technology has become the first choice to fabricate thee ring-shaped WGM resonators on the surface of micro-fibers,and it reduces the roughness of the annular cavity effectively and improves the quality of the annular cavity.The ring-shaped WGM resonators with different diameters was fabricated successfully and applied to temperature sensing with a sensitivity of 1.97 nm/°C and a Q factor of 1.9×103. |
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