Research And Application Of Microfiber-Assisted Mach-Zehnder Interferometers

Due to micro-nano fiber（MNF）has high surface field and evanescent waves,the sensitivity can be improved very highly.The microfiber-assisted Mach-Zehnder Interferometer（MMZI）can achieve characteristics of comb transmission by multimode interference（MMI）and has some advantages such as high sensitivity,fast response and stabilization for detecting variables.In this paper,three MMZIs apply in areas of fiber filter and fiber sensors basing on researches of relevant theories are proposed.Using different fabrication and fiber materials,good properties of filtering and sensing are achieved.The main research work and conclusions are drawn as follows:1.Tapered-drawing Fiber Bragg grating（FBG）,Comb fiber filter whose 3-d B bandwidth is 1.6842 nm and contrast is 18 d B is fabricated firstly.By analyzing by theory and simulation,the structure of tapered-drawing grating is confirmed MMZI with chirp long period fiber grating（CLPG）-tapered fiber（TF）-CLPG.Detecting refractive index of Na Cl solution,the reciprocal of comb transmission’s bandwidth of MMZI has linear relationship with refractive index.The tunable accuracy of channel near 1550 nm is 0.64318 nm^-1/RIU.2.Using the way combining arc discharging and tapered-drawing,MMZI with separated core and double spindle structure is fabricated firstly.Due to MNF and separated core structure can excite more high mode,the sensitivity of sensor can be improved.By simulating field distribution,the transmission process of light has been determined.The spectrum of MMZI was analyzed and fitted by theory.When the length of central tapered area is 4 mm,the sensitivities of temperature and curvature are 1.2904 nm/oC and 56.1947 nm/m^-1,respectively.Increasing the length of central tapered area,the sensitivity of MMZI can be improving.When the length of central tapered area is 4 mm,the sensitivities of temperature and curvature are 1.7563 nm/oC and 56.1947 nm/m^-1,respectively.The sensitivity of temperature is the highest in reports about inline Mach-Zehnder interferometer.3.Polarization maintaining fiber（PMF）after tapered-drawing is used for acoustic sensor.Due to the stress area at central area of PMF is broken in the process of teapered-drawing,MMZI with structure of PMF-no PMF-PMF is fabricated.Using MMZI to detect curvature,the sensitivity is 1.7542 nm/m^-1.Transonic transducer system combining MMZI with source（BBS）,circulator,FBG and photodetector is detected sinusoidal acoustic wave whose frequencies are 280,300,320,340 and 360 Hz.When frequencies are 280 Hz and 300 Hz,sensitivities are about 1.5 m V/Pa.When frequencies are 320 Hz and 340 Hz,sensitivities are about 7 m V/Pa.When frequency is 360 Hz,sensitivity is about 3 m V/Pa.