| Micro-structured fiber optic sensors?MFOSs?refer to the sensors with micron-scale structures fabricated on ordinary optical fibers and the sensors fabricated on the micro and nano fibers using modern advanced technologies,such as micromachining or micromanipulation.MFOSs have diverse structures,and various required optical properties can be obtained by appropriate design.A variety of novel MFOSs have emerged with the deepening of research.The research of their application has become more and more abundant,which has gradually extended to the fields of spectroscopy,non-linear optics,biomedicine and other scientific and technological fields.In this paper,based on microfabrication or micromanipulation methods,two kinds of interferometric MFOSs and one kind of MFOS based on optical tweezers,manufactured through the technology of fusion and taper drawing,are designed and fabricated.These devices are studied from three aspects:theory,experiment and application,which expands the application scope in the field of fiber optic sensing and communication.The main contents of this paper include:A micro-structure fiber optic sensor based on Fabry-Perot?F-P?interference is designed and manufactured,which can simultaneously measure refractive index and temperature.The sensing head was made by splicing a small section of photonic crystal fiber?PCF?with a single mode fiber?SMF?,including an air cavity,a SMF cavity and a PCF cavity.The characteristics of the reflection spectrum are analyzed,and the dip wavelength is obtained by low-pass filtering of the reflection spectrum.Meanwhile,the peak amplitude is obtained by fast Fourier transform?FFT?of the reflection spectrum.The relationship between the deviation of the dip wavelength and the temperature and refractive index?RI?of the medium around the sensor,together with the relationship between the peak amplitude and RI and the temperature,are studied.Then we can get the coefficient matrix to measure the temperature and RI simultaneously.A magnitude sensitivity of 5.30/RIU after FFT and a wavelength sensitivity of 8.46×10-1nm/RIU have been experimentally achieved over the RI range from 1.34 to 1.43.For temperature measurement,a magnitude sensitivity of 6.80×10-4/?and a wavelength sensitivity of2.48×10-3nm/?have been achieved.Easy fabrication,low-cost,better temperature compensation,and two-parameter measurement make it appropriate for practical application.A micro-structure fiber optic Mach-Zehnder?M-Z?hybrid interferometric sensor based on fusion and tapering technology is designed and manufactured,which can be used for RI and temperature measurements at the same time.In addition to the interference caused by different transmission paths of the fundamental modes,it also includes the interference between the cladding modes and the core modes.The optical characteristics of the sensor system are studied by demodulation method based on FFT analysis.The interference spectra caused by different interferences are extracted by band-pass and low-pass filters.Deviations of the dip wavelength with RI and temperature in two interferometric spectra are studied.The coefficient matrix,which can be used to simultaneously measure the temperature and RI,is obtained.The RI sensitivity is 55.22±3.32nm/RIU and 55.84±4.33 nm/RIU,and the temperature sensitivity is 0.045±0.004 nm/°C and 0.143±0.016 nm/°C,respectively.The sensor has the advantages of simple structure,convenient fabrication,compact device size and simultaneous sensing.A novel micro-structured optical fiber tip is designed and manufactured.The hollow cone cavity embedded in the structure can re-focus the light near the tip of the fiber.The electric field distribution at the tip is simulated by finite difference time domain?FDTD?method,and the influence of the geometry of the cavity on the electric field distribution is discussed.The electric field of the cavity is significantly enhanced when the cavity is filled with high refractive index media such as ultraviolet glue.The forces acting on the microspheres in different electric fields are calculated.The specific non-linear relationship between the average velocity of the particles and the applied laser power is obtained.This relationship can be used to measure the microfluid velocity in microfluidics technology.The balance between scattering force and fluid force can be used to study the non-invasive migration of particles.The fabrication of the tip is convenient and controllable.Its special imbedded cavity structure makes it possible to form an adjustable three-dimensional potential well by filled with high refractive index medium. |
PDF Full Text Request