Research On Fabrication Technology And Sensing Property Of Novel Photonic Crystal Fiber

With the rapidly development of fiber sensing technology,fiber sensors based on traditional fiber can not meet the current variety of sensing needs.Photonic crystal fiber offers a new approach for miniaturized,diverse,simply and low-cost fiber sensors due to its structural flexibility and unique mode transmission characteristics.In this dissertation,the photonic crystal fiber is designed based on the finite element method,and prepared by the stacking-drawing technology that accumulated for many years.The plenty fiber testing equipment and the perfect fiber sensing system are used as platforms to build and measure photonic crystal fiber sensors.First,two methods for theoretical simulation of photonic crystal fibers are introduced:effective refractive index method and finite element method.Then,by using a finite element method,a large-mode single-mode operating Yb³⁺-doped photonic crystal fiber was analyzed and designed.By adjusting the numerical control of the doped rods in the cladding,the high-order modes in the core can be effectively suppressed and filtered.Then several methods for the preparation of photonic crystal fiber have been introduced,and analysis and comparison of its advantages and disadvantages.The dissertation focus on the stacking-drawing method to prepare photonic crystal fiber.The material selection,cleaning,preparation,post-processing and the preform stacking,bundling,forming,as well as the process of drawing the fiber have been analyzed.Three kinds of photonic crystal fibers which have been designed and prepared are introduced in detail:core micro-structured high birefringence photonic crystal fibers,highly nonlinear photonic crystal fibers,and large-mode field Yb-doped air double-cladding photonic crystal fiber.Three kinds of multi-core photonic crystal fibers with different structures were proposed to build MZI and used for fiber sensing.A dual-core fiber was designed and prepared,which was simulated and calculated using the finite element method.Based on this dual-core fiber,a stable MZI was built,and then measure the curvature and high temperature sensing response.The test results show that the curvature sensitivity and high temperature sensitivity are 2.22 nm/m^-1 and 45.21 pm/?,respectively.A co-axial twin-core photonic crystal fiber is designed,and its transmission mode and limiting loss are simulated by finite element method.Then,a high temperature sensor was built based on the co-axial twin-core photonic crystal fiber.Compared to the high temperature sensor based on the twin-core fiber,the sensitivity was improved to 56 pm/?.A two-dimensional lattice photonic crystal fiber was designed.The cladding contains 37 Ge-doped rods.The curvature sensitivity is improved to 4.09 nm/m^-1 compared to the double-core fiber.A polarization-maintaining photonic crystal fiber combines geometric birefringence and stress birefringence was designed.The superposition of geometric birefringence and stress birefringence makes it possible to achieve birefringence as a high number.A Sagnac interferometer was built based on this kind of B-doped polarization-maintaining photonic crystal fiber and its temperature sensitivity was as high as 1.1 nm/?.A technique for writing photonic crystal fiber long-period gratings by using internal stress release taper is proposed.A 930?m-period grating was written on a B-doped polarization-maintaining photonic crystal fiber,the number of periods was 30,and the temperature sensitivity was 15pm/?.Finally,the light-guiding mechanism of anti-resonant photonic crystal fiber is analyzed,also the relationship between the position of the minimum value of the transmission spectrum and the thickness and refractive index of the cladding structure,the relationship between the loss size and the number of cladding cycles.A heterostructured cladding solid core photonic bandgap fiber was designed.A stable MZI was built,and then its temperature response and curvature response are measured.The curvature sensitivity is as high as 24.3nm/m^-1.In the high temperature range,the temperature sensitivity is as high as 90 pm/?.An anti-resonant hollow fiber for high temperature sensor was proposed.Its core diameter is 31.8?m,and the cladding contains four periodically arranged Ge-doped rings and pure quartz rings.This fiber was prepared using an MCVD process and pressure controlled fiber drawing technology,its modes distribution was analyzed and its bandgap spectrum was measured.An all-fiber high temperature sensor was constructed,the resulst show that the sensitivity was 28 pm/?.