【作者】 李敏；

【导师】 曲士良；

【作者基本信息】 哈尔滨工业大学 ， 物理学， 2016， 博士

【摘要】 双光子聚合技术制备的结构具有高分辨、高精度和生物兼容性等特点,在微机械、微光学和生物医疗等领域已被广泛应用。近年来,有人利用双光子聚合技术在光纤端面制备聚合物微结构对光纤的输出光场进行调制,有效地避免了集成器件中复杂的光电转换系统,在集成器件中有着重要的应用价值。光纤传感器因具有体积小、重量轻和抗电磁干扰等特点在器件的集成化发展中也发挥着重要的作用。然而,传统的光纤传感器受光纤材料本身固有特性的限制,如热膨胀系数低、杨氏模量大,在用于对温度、应变和声波等参数传感时,其灵敏度很难得到进一步提高。本文中,作者提出将飞秒激光双光子聚合技术制备的微结构与光纤结合获得一种新型光纤传感结构,理论和实验研究其传感特性,实现了高灵敏的温度、折射率和声波传感。具体工作如下:利用双光子聚合技术制备透射式马赫增德尔(Mach-Zehnder,简称MZ)光纤温度传感结构,实现高灵敏的温度传感。利用飞秒激光双光子聚合技术在光纤微腔中制备出一条长300μm的聚合物波导,在光纤内形成MZ干涉。通过精确控制聚合物波导在光纤微腔中的尺寸和位置,获得了高质量的MZ透射干涉谱。其温度传感特性的理论和实验研究结果表明,由于聚合物波导材料的热膨胀系数高达52 ppm/°C,提出的透射式MZ光纤传感结构的温度灵敏度达到了-205 pm/°C。利用双光子聚合技术制备反射式液腔法布里珀罗干涉(Fabry–Pérot,简称FP)光纤传感结构,实现了超高灵敏度的温度传感。利用飞秒激光双光子聚合技术在光纤端面的中心位置制备一个超小体积的长方体密封液体腔,光纤内的光经过光纤端面和聚合物固体壁的两个界面反射,形成了三光束FP干涉。与固态聚合物的热膨胀系数52 ppm/°C相比,液态聚合物的热膨胀系数高达4.5×105 ppm/°C。因此,通过将液态聚合物密封在FP微腔内,使该结构的温度灵敏度达到了877 pm/°C。与同样尺寸的全固态聚合物光纤温度传感结构相比,其灵敏度提高了3倍。利用双光子聚合技术在光纤端面制备超紧凑的开腔FP光纤传感结构,实现了高灵敏的液体折射率传感。利用双光子聚合技术在光纤末端面制备出凯旋门聚合物结构,该结构与光纤端面结合形成一个三光束FP开腔。由于待测液体可以填充到开腔内直接影响FP干涉相位差,其液体折射率传感灵敏度达到1539nm/RIU。在实际测量时,液体折射率大小会受到环境温度的影响,我们采用传感矩阵的方法,利用该结构干涉谱中两个干涉峰不同的折射率与温度传感灵敏度,实现了液体折射率和环境温度的同时测量,提高了液体折射率测量准确度。利用双光子聚合技术制备悬空薄膜FP光纤声波传感结构,通过精确控制干涉长度实现了高灵敏的声波传感。FP光纤声波传感结构的理论分析结果表明,其声压灵敏度与激光的工作波长有关,精确控制FP干涉长度可以使其声压灵敏度最高点刚好固定在激光工作波长1550 nm处。利用双光子聚合技术设计并制备腔长和膜厚分别为16μm和1.5μm的悬空薄膜FP光纤声波传感结构,其反射干涉谱的斜率最大处刚好位于1550 nm。当声波频率为1 k Hz时,悬空薄膜FP光纤声波传感结构的声波灵敏度达到1 V/Pa,线性度达到94.814%。更多还原

【Abstract】 Microstructures fabricated by two-photon polymerization(TPP)technique are widely applied in micro mechanical,micro optical,and biological and medical fields owing to their advantages of high resolution,high precision and biological compatibility.In recent years,the microstructures on the optical fiber end-faces fabricated by using TPP technique have been reported to modulate the output light field.These structures are widely applied in integrated devices as the complex photoelectric conversion system is effectively avoided.Optical fiber sensors also have important applications in the integrated micro-device owing to their small sizes,light weights and anti-electromagnetic interference.However,their sensitivities in temperature,strain and acoustic detection are difficult to be further improved due to the low thermal expansion coefficient and high young’s modulus of fiber material.In this paper,we proposed novel fiber sensing structures by integrating the microstructure on the fiber end using TPP technique.Their sensing properties were investigated theoretically and experimentally.The research work has been summarized in details as follows.A transmission Mach-Zehnder(MZ)fiber temperature sensing structure with high sensitivity was fabricated by using TPP technique.A polymer waveguide with length of 300 μm was fabricated inside the fiber micro-cavity by using femtosecond laser TPP technique,which forms a MZ interferometer.The high quality transmission spectrum was obtained by precisely controlling the length of polymer microstructure and its position inside the micro-cavity.Both the theory and experiment investigating result show that,as the polymer waveguide is with higher coefficient of thermal expansion,the temperature sensitivity of proposed MZ fiber sensing structure reaches-205 pm/°C.A reflection liquid cavity Fabry–Pérot(FP)fiber sensing structure with high temperature sensitivity was fabricated by using TPP technique.An ultracompact rectangular liquid polymer cavity was fabricated on the end face of the single-mode fiber by using TPP technique.The light was reflected at the end face of optical fiber and two interfaces of solid polymer wall,which forms three waves FP interference.Compared with the thermal expansion coefficient of solid polymer(52 ppm/°C),the one of liquid polymer reaches 4.5×105 ppm/°C.Therefore,through sealing the liquid polymer inside the FP cavity,the temperature sensitivity of the proposed sensing structure reaches up to 877 pm/°C.Compared with the same size of all solid state polymer fiber temperature sensing structure,its sensitivity is increased by 3 times.An ultracompact open cavity FP with high refractive index(RI)sensitivity was fabricated by using TPP techniqu.A triumphal arch polymer microstructure was fabricated on the end face of fiber by using TPP technique,which combined with the fiber forms a three waves FP open cavity.As the measured liquid can be filled into the FP open cavity,the optical difference was changed directly.The RI sensitivity of proposed sensing structure can reach up to 1539 nm/RIU.In practice,the RI of liquid is affected by the ambient temperature,using the sensitivity matrix method,the liquid RI and temperature can be simultaneously determined by measuring the temperature RI sensitivities of two peaks,the measurement accuracy of liquid RI was improved.An ultracompact suspended thin film FP fiber sensing structure with high acoustic sensitivity was fabricated using TPP technique.The theory of FP fiber acoustic sensing structure shows that the acoustic sensitivity is related to the laser work wavelength.By precise controlling the interference length of FP,the largest sensitivity of FP just was fixed at the laser wavelength of 1550 nm.A suspended thin film FP fiber acoustic sensing structure with cavity length of 16 μm and film thickness of 1.5 μm was fabricated by using TPP technique,it’s the largest slope of reflection spectrum was just at 1550 nm.When the frequency is 1 k Hz,the acoustic sensitivity of suspended thin film FP reaches up to 1 V/Pa,and the linearity reaches up to 94.814%.更多还原