Temperature-calibrated fiber-optic refractometer based on acompact FBG-SMS structure

A novel all-fiber temperature-calibrated refractometer based on a compact fiber Bragg grating(FBG) single-multi-single(SMS)structure is proposed and experimentally demonstrated.The sensor head is composed of a FBG combined with a SMS structure,in which the middle multimode fiber(MMF)section is etched by a time-controlled hydrofluoric.The transmission dip of SMS is extremely sensitive to ambient refractive index(RI)variation,whereas the upstream FBG provides the necessary temperature information for RI calibration.All aforementioned functions are performed via a compact FBG-SMS structure not longer than 25 mm.The proposed sensing device provides a linear RI sensitivity over water or waterbased solutions(RI values near 1.33 at optical wavelengths for most biological and many environmental applications),and has temperature-calibration capability.Hence,the said refractometer is a good candidate for sensing in chemical and biological applications.     

面向管线监测的分布式光纤传感土壤传热研究

现存的管道泄漏监测技术空间分辨率有限,且常规的光纤布置方式难以达到所要求的分辨率。基于此,针对油气管线监测布线问题,在一维平铺式线监测的基础上,提出了正弦式表面监测的光纤铺设方式。以高空间分辨率的光频域反射分布式光纤传感技术为辅助手段,验证了正弦式光纤铺设方法的优越性,其能够全面地反映土壤整个面的温度分布,监测范围变广,漏检可能性降低。采用变量法分析了土壤容重、土壤含水率与土壤导热系数之间的关系以及热源温度对土壤传热的影响,验证了光频域反射分布式光纤传感技术能够精确地监测土壤温度场,并利用土壤温度场的变化规律为其他分布式测温技术在埋地光纤布置时提供指导。     

单偏振单模聚合物光子晶体光纤设计

 设计了一种聚甲基丙烯酸甲酯(PMMA)基的单偏振单模(SPSM)微结构聚合物光纤(MPOF)。利用全矢量有限元法和光束传播法相结合分析了这种光纤的偏振特性和约束损耗。通过优化光纤结构参数,发现在0.51 μm～0.62 μm的可见光波长范围,由于基模两个正交偏振模的截止波长不同,这种微结构聚合物光纤只能传输基模中的一个偏振模,从而实现单偏振单模运转。该11圈圆空气孔六角排列光纤结构的传导偏振模在0.57 μm波长处约束损耗仅为1.13 dB/m,这种低损耗的单偏振单模微结构聚合物光纤可有效消除传统保偏光纤固有的偏振串扰和偏振模色散。     

Temperature-independent refractive index measurement based on Fabry-Perot fiber tip sensor modulated by Fresnel reflection

A simple fiber tip sensor for refractive index(RI) measurement based on Fabry-Perot(FP) interference modulated by Fresnel reflection is proposed and demonstrated.The sensor head consists of an etchinginduced micro air gap near the tip of a single-mode fiber.The microgap and the fiber tip function as two reflectors to form a FP cavity.The external RI can be unambiguously measured by monitoring the fringe contrast of the interference pattern from the reflection spectrum.The experimental results show that the proposed sensor achieves temperature-independent RI measurement with good linear response.The proposed sensor achieves a high RI resolution of up to 3.4×10 5 and has advantages of low cost and easy fabrication.