Microcavity Interferometer Based On Multimode Fiber And Microfiber Assisted

To date,the reported microfiber-assisted open-cavity Mach-Zehnder interferometer is based on the single-mode-fiber-microfiber-single-mode-fiber(SMF)structure.The periodic uniformity and extinction ratio(ER)of fringes are limited by the core diameter of<10?m.To improve the preparation efficiency,based on the principle of modal interference,the multi-mode fiber and micro-fiber assisted micro-cavity interferometer(MMA-MI)was proposed and prepared in this thesis by meas of flame brush and arc discharge technology.And the research mainly focuses on the characteristics and sensitivity-enhancement of strain response.The MMA-MI structure has the uniform period of fringes and high extinction ratio,and the axial size can be flexibly adjusted in the range of micron to millimeter,with higher sensitivity and better flexibility.Therefore,it has great potential in the fields of biochemical sensing,high-precision engineering monitoring,and fiber-optic laboratory applications.The main contents are as follows:(1)The interference principle of MMA-MI is studied and the sensing characteristics in terms of temperature,refractive index and strain are theoritically analyzed.The energy distributions of light field with variable structure parameters are characterized by simulation.And the results show that the ER value of MMA-MI can be32.34 d B under the optimized parameters.The effect of cavity length perturbation on the energy of cladding modes is verified,and the selective relationship between the intensity of fringe and cavity length is quantified,which provides the foundation for the realization of MMA-MI strain sensor based on intensity demodulation.(2)The MMA-MIs based on varied core diameter of multimode fiber are fabricated experimentally,and the performance comparisons of output interference fringes are conducted with the varied length and diameter of microfiber.Then,the characteristics of temperature and refractive index(RI)are tested and the experimental results show that the temperature/RI response is independent on the varied cavity length.The temperature sensitivity is about 80 pm/°C,and the average RI sensitivity is up to 17000 nm/RIU.(3)The selective relationship between cavity length(L_c)and strain of MMA-MI is verified experimentally.For a short cavity length(L_c<600?m),the strain response is mainly intensity-changed,and the maximum sensitivity reaches 0.074 d B/??.When L_c>1000?m,the strain response becomes the typical wavelength shift,and the sensitivity is inversely proportional to cavity length.Furthermore,to improve sensitivity,the MMA-MI is modified through sandwitching a piece of tapered-microfiber fabricated by arc discharge technique.The experimental results show that,by reducing the waist diameter of microfiber,the strain response can be effectively improved and the maximum sensitivity reaches-34.72 pm/??.Moreover,the Vernier effect is realized by means of cascading a hollow-core fiber based Fabry-Perot cavity with adaptive length.And the results show that the sensitivity can be further enhanced about 19.27 times.