Optimal Coherence Length Control in Interferometric Fiber Optic Hydrophones via PRBS Modulation: Theory and Experiment
Interferometric fiber optic hydrophones (IFOHs) are highly sensitive for underwater acoustic detection but face challenges owing to the trade-off between laser monochromaticity and coherence length. In this study, we propose a pseudo-random binary sequence (PRBS) phase modulation method for laser co...
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2025-07-01
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| author | Wujie Wang Qihao Hu Lina Ma Fan Shang Hongze Leng Junqiang Song |
| author_facet | Wujie Wang Qihao Hu Lina Ma Fan Shang Hongze Leng Junqiang Song |
| author_sort | Wujie Wang |
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| description | Interferometric fiber optic hydrophones (IFOHs) are highly sensitive for underwater acoustic detection but face challenges owing to the trade-off between laser monochromaticity and coherence length. In this study, we propose a pseudo-random binary sequence (PRBS) phase modulation method for laser coherence length control, establishing the first theoretical model that quantitatively links PRBS parameter to coherence length, elucidating the mechanism underlying its suppression of parasitic interference noise. Furthermore, our research findings demonstrate that while reducing the laser coherence length effectively mitigates parasitic interference noise in IFOHs, this reduction also leads to elevated background noise caused by diminished interference visibility. Consequently, the modulation of coherence length requires a balanced optimization approach that not only suppresses parasitic noise but also minimizes visibility-introduced background noise, thereby determining the system-specific optimal coherence length. Through theoretical modeling and experimental validation, we determined that for IFOH systems with a 500 ns delay, the optimal coherence lengths for link fibers of 3.3 km and 10 km are 0.93 m and 0.78 m, respectively. At the optimal coherence length, the background noise level in the 3.3 km system reaches −84.5 dB (re: rad/√Hz @1 kHz), representing an additional noise suppression of 4.5 dB beyond the original suppression. This study provides a comprehensive theoretical and experimental solution to the long-standing contradiction between high laser monochromaticity, stability and appropriate coherence length, establishing a coherence modulation noise suppression framework for hydrophones, gyroscopes, distributed acoustic sensing (DAS), and other fields. |
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| institution | Kabale University |
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| language | English |
| publishDate | 2025-07-01 |
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| spelling | doaj-art-a2e5b70cd1b446b9b127dd8ea1c602c52025-08-20T03:36:23ZengMDPI AGSensors1424-82202025-07-012515471110.3390/s25154711Optimal Coherence Length Control in Interferometric Fiber Optic Hydrophones via PRBS Modulation: Theory and ExperimentWujie Wang0Qihao Hu1Lina Ma2Fan Shang3Hongze Leng4Junqiang Song5College of Meteorology and Oceanology, National University of Defense Technology, Changsha 410073, ChinaCollege of Meteorology and Oceanology, National University of Defense Technology, Changsha 410073, ChinaCollege of Meteorology and Oceanology, National University of Defense Technology, Changsha 410073, ChinaCollege of Meteorology and Oceanology, National University of Defense Technology, Changsha 410073, ChinaCollege of Meteorology and Oceanology, National University of Defense Technology, Changsha 410073, ChinaCollege of Meteorology and Oceanology, National University of Defense Technology, Changsha 410073, ChinaInterferometric fiber optic hydrophones (IFOHs) are highly sensitive for underwater acoustic detection but face challenges owing to the trade-off between laser monochromaticity and coherence length. In this study, we propose a pseudo-random binary sequence (PRBS) phase modulation method for laser coherence length control, establishing the first theoretical model that quantitatively links PRBS parameter to coherence length, elucidating the mechanism underlying its suppression of parasitic interference noise. Furthermore, our research findings demonstrate that while reducing the laser coherence length effectively mitigates parasitic interference noise in IFOHs, this reduction also leads to elevated background noise caused by diminished interference visibility. Consequently, the modulation of coherence length requires a balanced optimization approach that not only suppresses parasitic noise but also minimizes visibility-introduced background noise, thereby determining the system-specific optimal coherence length. Through theoretical modeling and experimental validation, we determined that for IFOH systems with a 500 ns delay, the optimal coherence lengths for link fibers of 3.3 km and 10 km are 0.93 m and 0.78 m, respectively. At the optimal coherence length, the background noise level in the 3.3 km system reaches −84.5 dB (re: rad/√Hz @1 kHz), representing an additional noise suppression of 4.5 dB beyond the original suppression. This study provides a comprehensive theoretical and experimental solution to the long-standing contradiction between high laser monochromaticity, stability and appropriate coherence length, establishing a coherence modulation noise suppression framework for hydrophones, gyroscopes, distributed acoustic sensing (DAS), and other fields.https://www.mdpi.com/1424-8220/25/15/4711interferometric fiber optic hydrophonecoherence lengthparasitic interference noisepseudo-random binary sequence |
| spellingShingle | Wujie Wang Qihao Hu Lina Ma Fan Shang Hongze Leng Junqiang Song Optimal Coherence Length Control in Interferometric Fiber Optic Hydrophones via PRBS Modulation: Theory and Experiment Sensors interferometric fiber optic hydrophone coherence length parasitic interference noise pseudo-random binary sequence |
| title | Optimal Coherence Length Control in Interferometric Fiber Optic Hydrophones via PRBS Modulation: Theory and Experiment |
| title_full | Optimal Coherence Length Control in Interferometric Fiber Optic Hydrophones via PRBS Modulation: Theory and Experiment |
| title_fullStr | Optimal Coherence Length Control in Interferometric Fiber Optic Hydrophones via PRBS Modulation: Theory and Experiment |
| title_full_unstemmed | Optimal Coherence Length Control in Interferometric Fiber Optic Hydrophones via PRBS Modulation: Theory and Experiment |
| title_short | Optimal Coherence Length Control in Interferometric Fiber Optic Hydrophones via PRBS Modulation: Theory and Experiment |
| title_sort | optimal coherence length control in interferometric fiber optic hydrophones via prbs modulation theory and experiment |
| topic | interferometric fiber optic hydrophone coherence length parasitic interference noise pseudo-random binary sequence |
| url | https://www.mdpi.com/1424-8220/25/15/4711 |
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