This study presents a portable multi-component gas sensing system based on Fiber-Enhanced Raman Spectroscopy (FERS). The system achieves efficient gas collection, precise analysis, and rapid response times by leveraging the unique advantages of hollow-core optical waveguides. The large aperture and high reflectivity of silver-coated capillary (SCC) minimize optical power loss and improve the collection efficiency of Raman signals, ensuring high sensitivity and accuracy in gas detection. And by combining SCC and lens with the gas chamber, the integration of the probe has been improved. Additionally, The system's fiber optic probe structure seamlessly connects the Raman probe to the laser and spectrometer via multimode fiber, streamlining signal transmission, allowing it to function as an independent portable probe. Experimental results demonstrate the system's capability for qualitative and quantitative analysis of multi-component gases, achieving detection limits in the low hundreds of parts per million (ppm) for gases such as CH₄, C₂H₄, and C₂H₂, along with other flammable industrial gases. Notably, the system exhibits a rapid response time of 1.5 seconds. This portable FERS-based gas sensing system offers exceptional performance for real-time gas analysis, making it a valuable tool for industrial and environmental monitoring applications due to its compact design, high sensitivity, versatility, and fast response.
The article presents a unique design for a hollow-core anti-resonant fiber, which utilizes a single-layer semi-circular Anti resonant unit positioned around the central core. The simulation analysis reveals this design can achieve transmission over a wide bandwidth of 500-1300nm, while exhibiting relatively low losses at wavelengths near 700-800nm and 900- 1100nm. The anti-resonant fiber with this structure boasts strong wavelength limitation capability for light transmission, along with high transmission stability in a low-loss mode. Based on the simulation analysis results of the changes in loss characteristics, the hollow core anti-resonant fiber we designed has a mode field diameter of approximately 30 microns, and the wall thickness of the core anti-resonant structure is approximately 0.4 microns. By optimizing the process, such as through preform shaping and wire tension adjustment, a 5km long span with high uniformity was achieved for the hollow core anti-resonant fiber, and corresponding tests were carried out. The test results indicate that the total loss value of the hollow anti-resonant fiber, prepared under optimized process conditions, can be managed at a reduced level, with an attenuation of less than 0.1dB/m at 1064nm. Due to the outstanding pure single mode characteristics of optical fibers, there is no obvious mode coupling between the optical signal and the quartz cladding, neither the inner quartz wall in the transmission channel. In devices utilizing fiber enhanced Raman spectroscopy (FERS), this particular fiber can achieve highly sensitive sensing and precise analysis of Raman spectroscopy. Due to its low attenuation characteristics, the system achieves excellent sensing performance in fiber-enhanced Raman spectroscopy systems, enabling precise detection of a 450ppm CO2 concentration. Based on simulation analysis and testing, this article confirms the benefits of this novel fiber in fiber-enhanced Raman spectroscopy systems, presenting a fresh option for researching fiber Raman gas measurement technology.
High-sensitivity sensing of multi-component gases has important applications in environmental monitoring, industrial process control, and biomedical analysis. Fiber-enhanced gas Raman spectroscopy based on node-less anti-resonant hollow-core fibers (AR-HCFs) has advantages for the detection of multi-component gases. AR-HCFs can significantly improve the collection efficiency of gas signals, but the diffusion rate of gas in AR-HCFs is slow under normal pressure, and the gas exchange in AR-HCFs requires the help of gas pressure control devices. In this work, a reflective fiber-enhanced gas Raman system is designed and only one end of the hollow-core fiber is coupled to the optical path, the other end is placed in free space which facilitates rapid gas exchange. Various gases such as CH4, H2, N2, NH3, etc. are injected into optical fibers for systematic research. It takes 70 s to fill the 0.5m-long AR-HCFs with hydrogen at 1.2 Bar, but only 8 s at 1.6 Bar. Due to the influence of the gas viscosity coefficient, the time required for CH4 to fulfill 1m-long AR-HCFs is about 1.4 times that of H2 under the same environment. It is proved that such an optical fiber-enhanced gas Raman system can realize fast gas filling and exchange, and has good detection ability for multi-component gas, which can be used in fields requiring the quick response of gas sensing.
Metal-coated D-shape optical fiber is serving as a polarizer by using its attenuation difference for two orthogonal fundamental modes. This paper presents a novel corrosion sensor, based on an iron-coated optical fiber polarizer. The sensor is fabricated by sputtering a Fe-C film on a side-polished single mode fiber. The extinction ratio and the optical power loss are varying during the corrosion process when the iron-coated sensor is exposed to a corrosive environment. The proposed sensor provides a new approach for monitoring the early-age corrosion of steel structures by tracing the variation of polarization characteristics.
Steel corrosion in concrete leads to severe destructions of the civil engineering structures. The detecting of the early corrosion is especially essential for steel-based structures. This paper summarized a series research works on optical fibre corrosion sensors, based on Fe(C)-coated Fibre Bragg Grating (FBG) and Fe-coated optical fibre polarizer. Three types of optical fibre sensors are presented. Type 1 and type 2, Fe-C coated FBG sensor and Fe coated etched FBG sensor, are both based on Fe(C)-coated FBG. The volume expansion and the RI variation of the coating lead to the FBG central wavelength shift respectively. By monitoring the wavelength shift, the corrosion status is evaluated and monitored. Type 3, Fe-coated optical fibre polarizer, is fabricated by side-polishing a single mode optical fibre and depositing a Fe-film on the polished side-face. The birefringence characteristics of the sensor will be reduced after being corroded, which is used for the corrosion status indicating. The fabrication processes of the three types of sensors are introduced. By investigating the experimental results of corrosion test in NaCl solution, the performance of the sensors are discussed. The experimental results show that the proposed sensors are proved to be sensible of early corrosion.
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