Study On The Fabrication Of Micro-optical Fiber And Its Sensing Characteristics By Fusion Tapering Method

In this paper,the multimode/few-mode microfiber based mode interferometers are systematically studied and fabricated by flame-heated drawing technique.And their sensitive characteristics in term of refractive index?RI?are investigated.Furthermore,a micro-cavity strain sensor based on microfiber-assisted?MA?structure is developed.The main contents are as follows:?1?From the principle of evanescent wave,the basic structure and transmission of single-mode microfiber are studied,and the features of microfiber based mode interferometer is analyzed.By beam propagation method,the excitation and coupling of guided modes are simulated in single-mode/multimode microfiber.And the relationship between the parameter setting of fabrication and the tilted angle of waist is obtained.The sensing principles of the microfiber mode interferometer with respects to temperature and RI are also studied theoretically.?2?Through flame-heated drawing technique,multimode and few-mode microfibers with different waist diameters are fabricated,and their RI sensitive characteristics are investigated.The experimental results show that for multimode microfiber its RI sensitivity reaches 3192.67 nm/RIU when the waist diameter is 17.91?m.And for few-mode microfiber the RI sensitivity is increased to 3821.3 nm/RIU with the waist diameter of 16.3?m.Furthermore,an intensity demodulated RI sensor based on the front-tapered multimode fiber is proposed and tested.The results show that,in the range of 1.33-1.37 RIU,our sensor has the intensity sensitivity of-342.82 d B/RIU with high linear response,and achieves high discriminative simultaneous measurement in terms of RI and temperature.?3?The single-mode microfiber with the length of hundred-microns is used as a"bridge",and multiple micro-cavity interferometers with MA structure are prepared.The transmission and reflection spectra of micro-cavity interferometers are analyzed with varied microfiber length,diameter and offset.Moreover,the comprehensive axial-strain tests is performed and the experimental results show that the wavelength strain response is directly related to the microfiber length.When the cavity length is equal to 1284?m,its sensitivity reaches-10 pm/??with high linearity.Further,the lateral strain?curvature?and tangential strain?twisting?are also tested,and the feature of intensity modulation are demonstrated but with the difference of waveband.For the curvature test,the sensitivity reaches-138.3 d B/m^-1 in L band.And in the twisting test,the sensitivity is 23.98 d B/?rad/cm?in C band.