Experimental Study On F-P Interferometer Formed By Hollow-Core PCF

Recently more and more interests are focused on fiber-optic F-P sensors, for they have several outstanding advantages, including immunity to electromagnetic interference, capability of responding to a wide variety of measurands, high resolution, capability of multiplexing, small size, light weight, and resistance to harsh environments. For the advantages of ILFE's special structure, a novel ILFE sensor based on HCPCF was formed. In this paper, several theoretical and experimental researches have done for it based on the previous achievements, such as optimization of the fabrication of the HCPCF F-P, characteristics of temperature, strain, bending etc., and its preliminary application. So this subject has an important guiding significance for the use of HCPCF F-P, and it's surported by The Key Project of Natural Science Foundation of China (Grant No: 60537040). The main work of the research is as follows:1. The loss of the spacing ends of HCPCF F-P was tested, and the result shows that the higher the visibility, the lower the loss. For that result, The fabrication of the HCPCF F-P sensor is optimized by setting the discharge energy and discharge time of the arc welding machine, as well as adjusting the place of two different fibers. And with this setting, the HCPCF F-P sensor with high visibility and good leveling reflective spectrum was made.2. The normal temperature and high temperature characteristics of the HCPCF F-P interference sensors have been studied, respectively. The HCPCF F-P sensor is analyzed from strain effects induced by the pressure, the thermal expansion effect of material and thermo-optic effects, experimentally and theoretically. The results show that at the room temperature, the variations of the cavity length is mainly caused by the thermal expansion effect. However, variations of the cavity length will be affected not only by the thermal expansion effect, but also by the thermo-optic effect at the high temperature. Compared to IFPI sensors, HCPCF F-P sensor has a lower temperature response as the thermo-optic coefficient of silica is much larger than it's thermal expansion coefficient.3. The strain characteristics of HCPCF F-P interference sensors have been experimentally studied. The results show that, for the 3.75mm length HCPCF F-P, the strain sensitivity is about 5.94nm/με, the linearity is about 0.9997, the maximum cross-influence of temperature to the strain is just about 1.5%, the measuring accuracy is about 0.08% FS, and the measurable range of strain is about 2082με. Therefore, this sensor has the outstanding advantages of high strain sensitivity, good linearity and repeatability, large strain measure range, high temperature resistance and low cross-sensitivity of temperature to strain, etc..4. The bending, distortion and transverse load characteristics of the HCPCF F-P interference sensors have been studied too. And the analysis exhibits that the HCPCF F-P interference sensors is insensitive to bending as the hollow core photonic crystal fiber is the optical band-gap type with small bending loss. Furthermore, the distortion experiment shows that the visibility of the interference fringe remains invariant, while the interferometric phase increases linearly with the augment of distortion due to the effect of axial stress. The theoretical and experimental results regarding the transverse load characteristics of HCPCF FP sensor indicates that since the transverse pressure has changed the micro-structure of photonic crystal fibers, the visibility of the interference fringe reduces, the interferometric phase diminishes and the fringe drifts left.5. The quasi-dynamic strain of the rotating blades has been measured by the HCPCF F-P interference sensor. The results indicate that the strain of blades induced by the air resistance and centrifugal force varies linearly with the rotational speed while the speed changes from 600r/min to 1500 r/min. The strain of the measured point is 24.5μεwhen the speed is 1500r/min. Meanwhile, the results show that the vibration strain remains nearly constant in the previous range of rotation speeds.