image: Refractive index sensor and measurement system. view more
Credit: OEA
In a new publication from Opto-Electronic Advances; DOI 10.29026/oea.2021.200041 , Xuezhi Zhang, Boyue Yang, Junfeng Jiang, Kun Liu, Xiaojun Fan, Zhaozhu Liu, Min Peng, Guanlong Chen and Tiegen Liu from Tianjin University, Tianjin, China discuss a side-polished SMS based RI sensor employing perfluorinated POF.
Refractive index is an inherent property of material, which can reflect the concentration, purity and other important information about a material under certain conditions. When the external refractive index changes, some parameters (amplitude, wavelength, intensity, etc.) in the optical fiber will change accordingly. The change of refractive index can be calculated by the change of the parameters mentioned above. Refractive index sensors are widely used in chemical analysis, environmental pollution monitoring, medical diagnosis, food detection and other fields.
Polymer optical fiber has been used in optical fiber sensing, Internet of things, lighting systems and other fields. Compared with SiO2 optical fiber, polymer optical fiber has many advantages, such as light weight, high flexibility, strong plasticity and so on. In recent years, polymer materials have developed rapidly, and there is great potential to improve the material characteristics and fabrication processes. Some research groups have already begun to study and apply polymer optical fiber. In the field of optical fiber sensing, polymer optical fiber has the potential to replace SiO2 optical fiber in some areas, which has a high value and potential for wide application.
Professor Tiegen Liu's research group has proposed a method to fabricate a refractive index sensor based on perfluoropolymer fiber and single mode - multimode - single mode (SMS) structure, which can realize real-time monitoring of external refractive index by multimode interference. Firstly, perfluoropolymer fiber is sandwiched between two single-mode fibers to generate a multimode interference structure; secondly, the perfluoropolymer fiber is polished to improve the sensitivity of the sensor; finally, the parameters affecting the sensitivity of the sensor are studied experimentally.
In the experiment, the polymer optical fiber and SiO2 optical fiber can easily and accurately be connected by a ceramic sleeve; the fine-tuning system with precision of micrometer scale is included in the side-polished device, which ensures the accuracy in side-polished process of the perfluoropolymer optical fiber. In addition, the perfluoropolymer fiber has low water absorption, which makes the sensor work stably in water for a long time and has obvious application in the field of liquid detection. The results show that the refractive index sensitivity is -219.504 dB / RIU.
In conclusion, the fabrication process of the refractive index sensor is simple and easy, realizing real-time measurement of the refractive index with high sensitivity. This method will provide a reference for future development of refractive index fiber sensing.
Article reference: Zhang XZ, Yang BY, Jiang JF, Liu K, Fan XJ et al. Side-polished SMS based RI sensor employing macro-bending perfluorinated POF. Opto-Electron Adv 4, 200041 (2021). doi: 10.29026/oea.2021.200041
Keywords: Refractive Index Sensor / Perfluoropolymer Fiber / Optical Sensing / Plastic Optical Fiber
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Professor Tiegen Liu’s research team is affiliated to the Key Laboratory of Optoelectronic Information Technology of the Ministry of Education, Tianjin University, Tianjin, China. With the support of the National 973 Plan, the National Instrument Project amongst others, the team is mainly focused on the theory and application of optical fiber sensing and optoelectronic detection, including optical fiber pressure sensing, optical fiber disturbance sensing, optical fiber acoustic vibration sensing and optical fiber gas sensing, optical fiber strain/temperature sensing, optical fiber polarization technology, optical microfluidic sensing, optical interconnection device, optical interconnection system and optical fiber intelligent sensor networks. The research group has carried out research on optical fiber sensing in mechanical and thermodynamic areas, aimed at demand in the field of "deep space, deep sea and deep Earth". Fiber sensors and sensing systems can also be applied in many important areas, such as aviation, aerospace, water conservation, electric power and construction, etc. The Optical Fiber Sensing Research Institute of Tianjin University and the Optical Fiber Sensing Sub Technical Committee of the National Technical Committee of Optics and Photonics Standardization were established by Professor Tiegen Liu’s group. The joint Optical Fiber Sensing Research Center of Tianjin University-AVIC Kaitian, Tianjin University-Pukou Optical Fiber Sensing Collaborative Innovation Center were established to carry out in-depth cooperation between Tianjin University, industry and government, to support the transformation from technological achievements to new product innovations.
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