本論文重點研究了基於光纖干涉儀的入侵檢測系統的設計與應用。我們透過各個防區的環形共振腔來產生干涉所需之雷射光。防區系統共有四個防禦區域，並且四個防區會各別產生不同波長的訊號光。訊號光會被傳回四個對應的光電探測器以進行後續的訊號處理。
我們的系統僅僅使用四芯光纜中的一條單模光纖來檢測區域的入侵。光纜分為四個部分，每個部分用於檢測周邊區域入侵所引起的干擾。在這項研究中，使用單條光纖將四個不同波長的光學干涉儀給串接起來，用於感測四個區域。這些感測區是獨立運行的，透過分析各個光電探測器接收到訊號光，可以確定各個防區是否遭受入侵。四個防區的訊號光使用分波多工技術分別分開，再經由光電探測器檢測。接收到的訊號通過數據採集卡（DAQ）透過電腦來進行數據的採集和處理。並且我們會使用三個演算法來計算出它們各自的閾值進行比較。只有當所有參數都超過它們各自的閾值時才判定入侵。
本次研究所設計的多區域入侵檢測系統的主要優點在於它僅需使用一條單模光纖即可同時用於感測器和光訊號傳輸。與之前所設計的研究相比，我們的系統不僅為多區域入侵檢測提供了一種更簡單且具有成本效益的方法，而且還更加節省能量的損耗。

In this thesis, we focus on the design and application of intrusion detection system based on optical fiber interferometers. Laser light is generated in each of the ring laser cavities located at defended zones. The system under study has four perimeter zones to be defended with Wavelength-Division-Multiplexed signal lights generated at the four zones, respectively. The laser lights produced from the four perimeter zones are sent back to four different photodetectors for further signal processing.
Only one core, i.e., one fiber, of a four-core fiber cable is used as a disturbance sensor in detecting intrusion along a multi-zone perimeter. The fiber cable is divided into four sections, with each section used for detecting intrusion-induced disturbance in a perimeter zone. In this study, four optical interferometers are constructed along the single fiber for four protected zones, respectively. These protected zones are operated independently, and optical signals transmitted back to the receiver site will be analyzed to determine if there is intrusion upon any perimeter zone. These optical signals from the four perimeter zones are divided using the DWDM technique, and then detected by photodetectors, separately. The obtained signals are get into a personal computer through a data acquisition (DAQ) card for signal acquisition and processing. Three parameters would be derived every 1.024 second from each perimeter zone signal, and compare with their respective thresholds. An intrusion is determined only if all of parameters exceed their respective thresholds.
The main advantage of the proposed multi-zone intrusion detection system resides in the usage of only one single-mode fiber simultaneously for disturbance sensing and optical signal transmission. Compared with one of our previous works, the system provides not only a simpler and cost-effective method for multi-zone intrusion detection, but also a power-efficient way to achieve such a goal.

1. B. E. A. Saleh and M. C. Teich, Fundamentals of Photonics, 1st edition, Wiley Interscience, Hoboken, New Jersey, 1991.
2. J. M. Senior, Optical Fiber Communications: Principle and Practice, 3rd edition, Financial Times/Prentice Hall, 2009.
3. D. Gloge,“Optical fiber theory: Opportunities for advancement abound,”Radio Science, vol. 12, no. 4, pp. 479-490, 1997.
4. T. Okoshi,“Resent advances in coherent optical fiber communication systems, ”Journal of Lightwave Technology, vol. 5, no. 1, pp. 44-52, 1987.
5. F. P. Kapron, D. B. Keck, and R. D. Maurer,“Radiation losses in glass optical waveguides,”Appl. Phys. Lett., vol. 17, no. 10, pp. 423–425, Nov. 1970.
6. A. A. Chtcherbakov and P. L. Swart,“Polarization effects in the Sagnac-Michelson distributed disturbance location sensor,”J. Lightw. Technol., vol. 16, no. 8, pp. 1404-1412, Aug. 1998.
7. S. S. Mahmoud, Y. Visagathilagar, and J. Katsifolis,“Real-time distributed fiber optic sensor for security systems: performance event classification and nuisance mitigation,”Photon. Sensors, vol. 2, no. 3, pp. 225-236, 2012.
8. S. C. Huang et al.,“Fiber optic in-line distributed sensor for detection and localization of the pipeline leaks,”Sensors Actuators A (Phys.), vol. 135, no. 2, pp. 570-579, 2007.
9. H. N., Li, D. S. Li, and G. B. Song,“Recent applications of fiber optic sensors to health monitoring in civil engineering,”Steel Construction, vol. 26, no. 11, pp. 1647-1657, 2004.
10. G. Allwood, G. Wild, and S. Hinckley,“Optical fiber sensors in physical intrusion detection systems: A review,”IEEE Sensors J., vol. 16, no. 14, pp. 5497-5509, Jul. 2016.
11. M. K. Barnoski and S. M. Jensen,“Fiber Waveguides: a Novel Technique for Investigating Attenuation Characteristics,”Appl. Opt. vol 15, no 9 pp 2112–2115, 1976.
12. J. C. Juarez, E. W. Maier, K. N. Choi, and H. F. Taylor,“Distributed fiber-optic intrusion sensor system,”J. Lightw. Technol., vol. 23, no. 6, pp. 2081-2087, Jun. 2005.
13. Y. Shan, W Ji, and X Dong,“An enhanced distributed acoustic sensor based on UWFBG and self-heterodyne detection,”J. Lightwave Technol., vol. 37, no. 11, pp. 2700-2705, Jun. 2019.
14. Z. G. Qin, T. Zhu, L. Chen, and X. Y. Bao,“High sensitivity distributed vibration sensor based on polarization-maintaining configurations of phase-OTDR,”IEEE Photon. Technol. Lett., vol. 23, no. 15, pp. 1091-1093, Aug. 2011.
15. J. C. Juarez and Henry F. Taylor,“Distributed fiber-optic intrusion sensor system,”J. Lightw. Technol, vol. 23, no. 6, pp. 2081-2087, 2005.
16. S. Liang, X. Sheng, S. Lou, Y. Feng, and K. Zhang,“Combination of phase-sensitive OTDR and michelson interferometer for nuisance alarm rate reducing and event identification,”IEEE Photon. J., vol. 8, no. 2, Apr. 2016.
17. C. Qinnan, L. Tiegen, and L. Kun,“An elimination method of polarization-induced phase shift and fading in dual mach–zehnder interferometry disturbance sensing system,”J. Lightw. Technol., vol. 31, no. 19, pp. 3135-3141, Oct. 2013.
18. A. D. Kersey, M.J. Marrone, and A. Dandridge,“Optimization and stabilization of visibility in interferometric fiber-optic sensors using input-polarization control,”J. Lightw. Technol., vol. 6, no. 10, pp. 1599-1609, Oct. 1988.
19. W. Yuan, B. Pang, J. Bo, and X. Qian,“Fiber optic line-based sensor employing time delay estimation for disturbance detection and location,”J. Lightw. Technol., vol. 32, no. 5, pp. 1032-1037, Mar. 2014.
20. H. Wang, S. Qizhen, L. Xiaolei,“Improved location algorithm for multiple intrusions in distributed sagnac fiber sensing system,”Opt Express, vol. 22, no. 7, pp. 7587-7597, Apr. 2014.
21. S. Qiuheng and P. Hekuo,“A novel weak-scattering michelson interferometer based on PBS for long-distance disturbance localization,”J. Lightw. Technol., vol. 38, no. 6, pp. 1543-1549, Nov. 2019.
22. Y. Lin, B. Zheng, and L. Wang,“Cascaded fiber-optic interferometers for multi-perimeter-zone intrusion detection with a single fiber used for each defended zone,”IEEE Sensors J., vol. 21, no. 9, pp .10685-10694, May. 2021.
23. T. Okoshi, K. Kikuchi, and A. Nakayama,“Novel method for high resolution measurement of laser output spectrum,”Electronics letters, vol. 16, no. 16, pp .630–631, 1980.
24. S. Huang, T. Zhu, and Z. Cao,“Laser linewidth measurement based on amplitude difference comparison of coherent envelope,”IEEE Photon. Technol. Lett., vol. 28, no. 7, pp. 759-762, Apr. 2016.