| A lot of interests have been focused on optical fiber sensing technology in the past three decades because of their advantages such as immunity to electromagnetic interference, intrinsic safety, and capability for remote control, etc. As an important member of functional fiber sensors, Fabry-Perot sensors are better than conventional fiber sensors in the aspects of resolution, accuracy, sensitivity and dynamitic range. Therefore, Fabry-Perot sensors developed rapidly and have great prospect in many fields. After summarizing the principle, multiplexing and actuality of fiber Fabry-Perot sensors in details, we found that the fabrication of FP cavity and demodulating algorithm for multiplexed signals are still remaining as thorny problems either in the process of being widely used or being successfully commercialized.Based on the previous work finished, we proposed novel techniques to fabricate fiber FP sensors and efficient demodulating algorithms, which lay a solid foundation for fiber FP's large-scale applications.The main work completed is listed as following.1. A novel fiber FP cavity fabrication method based on femtosecond laser micromachining technique is proposed for the first time to our knowledge. Femtosecond laser micromachining technique could fabricate micrometer size FP cavities on a single mode fiber under the control of a computer. Compared with traditional fabrication methods, this technique is capable of manufacturing fiber F-P cavities in batch with good reproducibility without need of expensive masks. By cooperating with"The State Key Laboratory of Transient Optics and Photonics"(Xi'an Institute of Optics and Precision Mechanics of CAS), we successfully created a micro extrinsic Fabry-Perot interferomete(rMEFPI)on a corning single mode fiber using a Ti:sapphier femtosecond laser.2. The strain and temperature characteristic tests of the MEFPI were carried out in the thesis. Fist of all, the author derived the relationship between the MEFPI structure and its interference properties in theory. In order to improve the property, we adopted acid etching method in our experiment, which shows an effective way to change the end face reflectivity. Secondly, the strain experimental results indicate that the change in wavelength has good linear relationship with strain, in the range of 0 ~350με, the strain sensitivity is 0. 006nm /με.Thirdly, we found the MEFPI haa a negative temperature coefficient which differs from traditional fiber F-P sensors. Finally, we provide reasonable explanations to this phenomenon qualitatively.3. Since the multiplexing of MEFPI is difficult because it has only a few fringes due to its short cavity length, therefore, we mainly focus on the multiplexing of F-P sensor with a cavity length usually more than 200um in this thesis. Aiming to enhance the number of multiplexed F-P sensors, a modern spectral estimation method is introduced for the first time for processing of multiplexing signals. We designed and established a system for pressure test based on Pisarenko harmonic reconstruction algorithm, and then proposed a novel frequency estimation method - Eigenvalue decomposition (EVD) and Singular value decomposition (SVD) of autocorrelation matrix. Based on the EVD&SVD algorithm, we carried out an experiment and achieved an accuracy of better than±12μεwhen the adjacent cavity length difference is only about 20u m. In addition, the signal processing speed is significantly increased as the number of data sequence could be reduced to 400 which have great application potential in sensing networks with large scale multiplexing capability. |
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