Micromachining Fabriaction And Application Of Space Division Multiplexing Fiber Optical Device

Space division multiplexing（SDM）fiber is widely used in micromachining fabrication and application of optical fiber device,due to its multiple parallel transmission channel.Various optical fiber micromachining technologies have been proposed for the optical fiber devices fabrication.Among them,femtosecond laser micromachining technology and optical fiber fused tapering micromachining technology have great application prospects in the fabrication and application of optical fiber sensing and communication devices because of their high machining accuracy and strong programming ability.Therefore,the research on SDM fiber optical device based on femtosecond laser and fiber fused tapering micromachining technology has certain scientific research value and potential significant social and economic benefits.In this thesis,micromachining and fabrication of SDM fiber devices are investigated,including fabrication and characterization of reflective intensity modulated（RIM）displacement sensor,parallel Fabry-Perot interferometers（FPI）based on multicore fiber end face micromachining,mode selective converter based on few-mode fiber（FMF）end face micromachining,and photonic lantern based on the fiber bundle axial micromachining.The innovative research outcomes are summarized as follows:（1）In order to solve the disadvantage of dead zone and the limited measurement range arising in the RIM seven-core fiber displacement sensor,a micromachining assisted RIM seven-core fiber displacement sensor is proposed to simultaneously reduce the range of dead zone and increase the measurement range of displacement.Then,selective micro-hole fabrication is performed with the help of the self-developed femtosecond laser fabrication platform,leading to the successful verification of its sensor performance.In comparison with traditional RIM seven-core fiber displacement sensor,the proposed seven-core fiber displacement sensor based on the micromachining can reduce the range of dead zone from150μm to 20μm and increase the measurement range of displacement from 250μm to400μm.（2）To solve the disadvantage of small cavity difference in multicore fiber parallel FPI,parallel FPI arising in the single multicore fiber with various cavity lengths are simultaneously obtained by combining femtosecond laser end face micromachining technology and specialty fiber fusion technology.A discriminative sensing of temperature-strain is demonstrated when temperature and strain of 20～80℃and 0～1000με,respectively.The FPI located at the central core has a cavity length of 26μm,with a temperature sensitivity of 0.74pm/℃and strain sensitivity of 8.3pm/με.Meanwhile,the FPI at the outer core has a cavity length of 61μm,with a temperature sensitivity of 1.37pm/℃and strain sensitivity of 3.7pm/με.Measurement error of temperature and strain are smaller than 2%and 2.5%,respectively.（3）For the ease of realizing mode selective excitation in the mode division multiplexing transmission technology,an FMF mode converter based on the fiber end face micromachining is experimentally demonstrated.A micro-slot structure for LP₀₁ to LP₁₁mode conversion is inscribed into the end face of FMF through the femtosecond laser micromachining.In the C band,the LP₁₁ mode converter has an average insertion loss of2.7d B,and the mode field intensity overlap integral coefficient is more than 65%.The mode field intensity overlap integral coefficient is 87%at 1550nm.（4）To reduce the relatively large insertion loss and promote the low fabrication repeatability of photonic lantern,bridge fiber with a double cladding structure is proposed to reduce the mode field evolution along the taper direction,so that the performance of photonic lantern can be substantially improved.The self-fabricated three-mode photonic lantern based on fiber bundle axial fused tapering micromachining possess a LP₀₁ average insertion loss of 1.1d B and LP₁₁ average insertion loss of 0.9d B,together with a mode group isolation of more than 10dB.