In order to realize refractive index ( RI) measurement with low cost and high precision , a multimode fiber liquid refractive index sensor based on U-shaped microstructure was fabricated by femtosecond laser micromachining.The relationship of the variation of the optical power of the sensor , the depth of the U-shaped groove and the refractive index of the liquid in the U-shaped groove were studied.The influence of the different ablation lengths on the sensitivity was also discussed.The sensing mechanism was analyzed based on the influence of the radiation theory and the model.The results show that the sensor has a good linear response in the range of 1.3331 ~1.3731 ( refractive index ), and can reach 5700μW/RIU ( refractive index unit ) sensitivity.While in the case of 10dB loss, a good sensitivity can be obtained at 20μm ablation length.The sensor has advantages of simple structure , easy preparation , high sensitivity and low cost.It has wide application prospect in chemistry , biology , medicine and environmental monitoring.%为了实现低成本、高精度的折射率测量,采用飞秒激光微加工技术,制备出基于U形微结构的多模光纤液体折射率传感器.研究了传感器的通光功率变化值与U形槽深度以及U形槽内液体折射率的关系,同时探究了在相同光损耗情况下不同烧蚀长度对灵敏度的影响,并使用射线理论和模式理论对传感机理进行了分析.结果表明,该传感器在折射率1.3331~1.3731范围内具有良好的线性响应,且可以做到5700μW/RIU的灵敏度;同时在10dB损耗情况下20μm烧蚀长度具有较好的灵敏度.该传感器具有结构简单、容易制备、灵敏度高和低成本等优点,在化学、生物、医学、环境监测等方面有广泛的应用前景.
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