{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,13]],"date-time":"2025-12-13T07:21:05Z","timestamp":1765610465017,"version":"build-2065373602"},"reference-count":63,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2024,5,23]],"date-time":"2024-05-23T00:00:00Z","timestamp":1716422400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"scope of Bauman Moscow State Technical University state task","award":["FSFN-2024-0060","22-79-00225"],"award-info":[{"award-number":["FSFN-2024-0060","22-79-00225"]}]},{"name":"framework of a Russian Science Foundation","award":["FSFN-2024-0060","22-79-00225"],"award-info":[{"award-number":["FSFN-2024-0060","22-79-00225"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>In the paper, a new method of phase measurement error suppression in a phase-sensitive optical time domain reflectometer is proposed and experimentally proved. The main causes of phase measurement errors are identified and considered, such as the influence of the recording interferometer instabilities and laser wavelength instability, which can cause inaccuracies in phase unwrapping. The use of a Mach\u2013Zender interferometer made by 3 \u00d7 3 fiber couplers is proposed and tested to provide insensitivity to the recording interferometer and laser source instabilities. It is shown that using all three available photodetectors of the interferometer, instead of just one pair, achieves significantly better accuracy in the phase unwrapping. A novel compensation scheme for accurate phase measurements in a phase-sensitive optical time domain reflectometer is proposed, and a comparison of the measurement signals with or without such compensation is shown and discussed. The proposed method, using three photodetectors, allows for very good compensation of the phase measurement errors arising from common-mode noise from the interferometer and laser source, providing a significant improvement in signal detection. In addition, the method allows the tracking of slow temperature changes in the monitored fiber\/object, which is not obtainable when using a simple low-pass filter for phase unwrapping error reduction, as is customary in several systems of this kind.<\/jats:p>","DOI":"10.3390\/s24113338","type":"journal-article","created":{"date-parts":[[2024,5,23]],"date-time":"2024-05-23T09:04:25Z","timestamp":1716455065000},"page":"3338","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Instability Compensation of Recording Interferometer in Phase-Sensitive OTDR"],"prefix":"10.3390","volume":"24","author":[{"given":"Konstantin V.","family":"Stepanov","sequence":"first","affiliation":[{"name":"Laser and Optoelectronic Systems Department, Radio Electronics and Laser Technology Faculty, Bauman Moscow State Technical University, 2-nd Baumanskaya 5-1, 105005 Moscow, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6772-1572","authenticated-orcid":false,"given":"Andrey A.","family":"Zhirnov","sequence":"additional","affiliation":[{"name":"Laser and Optoelectronic Systems Department, Radio Electronics and Laser Technology Faculty, Bauman Moscow State Technical University, 2-nd Baumanskaya 5-1, 105005 Moscow, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1534-5688","authenticated-orcid":false,"given":"Tatyana V.","family":"Gritsenko","sequence":"additional","affiliation":[{"name":"Laser and Optoelectronic Systems Department, Radio Electronics and Laser Technology Faculty, Bauman Moscow State Technical University, 2-nd Baumanskaya 5-1, 105005 Moscow, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Roman I.","family":"Khan","sequence":"additional","affiliation":[{"name":"Laser and Optoelectronic Systems Department, Radio Electronics and Laser Technology Faculty, Bauman Moscow State Technical University, 2-nd Baumanskaya 5-1, 105005 Moscow, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kirill I.","family":"Koshelev","sequence":"additional","affiliation":[{"name":"Laser and Optoelectronic Systems Department, Radio Electronics and Laser Technology Faculty, Bauman Moscow State Technical University, 2-nd Baumanskaya 5-1, 105005 Moscow, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1910-7575","authenticated-orcid":false,"given":"Cesare","family":"Svelto","sequence":"additional","affiliation":[{"name":"Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alexey B.","family":"Pnev","sequence":"additional","affiliation":[{"name":"Laser and Optoelectronic Systems Department, Radio Electronics and Laser Technology Faculty, Bauman Moscow State Technical University, 2-nd Baumanskaya 5-1, 105005 Moscow, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2024,5,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"291","DOI":"10.1006\/ofte.1996.0036","article-title":"A review of recent developments in fiber optic sensor technology","volume":"2","author":"Kersey","year":"1996","journal-title":"Opt. Fiber Technol."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"4015","DOI":"10.1063\/1.1145411","article-title":"An overview of fiber-optic sensors","volume":"66","author":"Udd","year":"1995","journal-title":"Rev. Sci. Instrum."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"40","DOI":"10.1016\/S0924-4247(99)00368-4","article-title":"Fiber optic sensor technology: An overview","volume":"82","author":"Grattan","year":"2000","journal-title":"Sens. Actuators A Phys."},{"key":"ref_4","unstructured":"Francis, T.S., and Yin, S. (2002). Fiber Optic Sensors, Marcel Dekker Inc."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1064","DOI":"10.1109\/JLT.0082.921915","article-title":"Fiber-optic sensing: A historical perspective","volume":"26","author":"Culshaw","year":"2008","journal-title":"J. Lightw. Technol."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"12667","DOI":"10.1109\/JSEN.2020.3010572","article-title":"Enhanced Backscattering Optical Fiber Distributed Sensors: Tutorial and Review","volume":"21","author":"Tosi","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"18471","DOI":"10.1109\/JSEN.2022.3197730","article-title":"Improving OFDR distributed fiber sensing by fibers with enhanced rayleigh backscattering and image processing","volume":"22","author":"Wang","year":"2022","journal-title":"IEEE Sens. J."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"S156","DOI":"10.3103\/S1062873822700599","article-title":"Application of Optical Frequency Domain Reflectometry for the Study of Polarization Maintaining Fibers","volume":"86","author":"Ovchinnikov","year":"2022","journal-title":"Bull. Russ. Acad. Sci. Phys."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Belokrylov, M.E., Kambur, D.A., Konstantinov, Y.A., Claude, D., and Barkov, F.L. (2024). An Optical Frequency Domain Reflectometer\u2019s (OFDR) Performance Improvement via Empirical Mode Decomposition (EMD) and Frequency Filtration for Smart Sensing. Sensors, 24.","DOI":"10.3390\/s24041253"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"854","DOI":"10.1109\/JQE.1983.1071932","article-title":"Theory of backward Rayleigh scattering in polarization-maintaining single-mode fibers and its application to polarization optical time domain reflectometry","volume":"19","author":"Nakazawa","year":"1983","journal-title":"IEEE J. Quantum Electron."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1175","DOI":"10.1364\/JOSA.73.001175","article-title":"Rayleigh Backscattering Theory for Single-Mode Optical Fibers","volume":"73","author":"Nakazawa","year":"1983","journal-title":"J. Opt. Soc. Am."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"2326","DOI":"10.1109\/JQE.1981.1070695","article-title":"Measurement and analysis on polarization properties of backward Rayleigh scattering for single-mode optical fibers","volume":"17","author":"Nakazawa","year":"1981","journal-title":"IEEE J. Quantum Electron."},{"key":"ref_13","unstructured":"Taylor, H.F., and Lee, C.E. (1993). Apparatus and Method for Fiber Optic Intrusion Sensing. (5194847 A), U.S. Patent."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Park, J., Lee, W., and Taylor, H.F. (1998, January 16). Fiber optic intrusion sensor with the configuration of an optical time-domain reflectometer using coherent interference of Rayleigh backscattering. Proceedings of the SPIE 3555, Optical and Fiber Optic Sensor Systems, Beijing, China.","DOI":"10.1117\/12.318220"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"134","DOI":"10.1117\/12.484911","article-title":"Distributed fiber optic pressure\/seismic sensor for low-cost monitoring of long perimeters","volume":"5090","author":"Choi","year":"2003","journal-title":"Proc. SPIE"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"2081","DOI":"10.1109\/JLT.2005.849924","article-title":"Distributed fiber-optic intrusion sensor system","volume":"23","author":"Juarez","year":"2005","journal-title":"J. Light. Technol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1968","DOI":"10.1364\/AO.46.001968","article-title":"Field test of a distributed fiber-optic intrusion sensor system for long perimeters","volume":"46","author":"Juarez","year":"2007","journal-title":"Appl. Opt."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Barrias, A., Casas, J.R., and Villalba, S. (2016). A Review of Distributed Optical Fiber Sensors for Civil Engineering Applications. Sensors, 16.","DOI":"10.3390\/s16050748"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Wang, Z., Lu, B., Ye, Q., and Cai, H. (2020). Recent Progress in Distributed Fiber Acoustic Sensing with \u03a6-OTDR. Sensors, 20.","DOI":"10.3390\/s20226594"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Gorshkov, B.G., Y\u00fcksel, K., Fotiadi, A.A., Wuilpart, M., Korobko, D.A., Zhirnov, A.A., Stepanov, K.V., Turov, A.T., Konstantinov, Y.A., and Lobach, I.A. (2022). Scientific Applications of Distributed Acoustic Sensing: State-of-the-Art Review and Perspective. Sensors, 22.","DOI":"10.3390\/s22031033"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1407","DOI":"10.1109\/JLT.2021.3135653","article-title":"A Review of Distributed Fiber\u2013Optic Sensing in the Oil and Gas Industry","volume":"40","author":"Ashry","year":"2022","journal-title":"J. Light. Technol."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Sun, Y., Li, H., Fan, C., Yan, B., Chen, J., Yan, Z., and Sun, Q. (2022). Review of a Specialty Fiber for Distributed Acoustic Sensing Technology. Photonics, 9.","DOI":"10.3390\/photonics9050277"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Stepanov, K.V., Zhirnov, A.A., Koshelev, K.I., Chernutsky, A.O., Khan, R.I., and Pnev, A.B. (2021). Sensitivity Improvement of Phi-OTDR by Fiber Cable Coils. Sensors, 21.","DOI":"10.3390\/s21217077"},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Stepanov, K.V., Zhirnov, A.A., Chernutsky, A.O., Koshelev, K.I., Pnev, A.B., Lopunov, A.I., and Butov, O.V. (2020). The Sensitivity Improvement Characterization of Distributed Strain Sensors Due to Weak Fiber Bragg Gratings. Sensors, 20.","DOI":"10.3390\/s20226431"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"94910E","DOI":"10.1117\/12.2178282","article-title":"Analysis of the acoustic response in water and sand of different fiber optic sensing cables","volume":"Volume 9491","author":"Hofmann","year":"2015","journal-title":"Sensors for Extreme Harsh Environments II"},{"key":"ref_26","unstructured":"Goldner, E.L., Andersen, J.K., and Cherbettchian, A.H. (2015). Fiber Optic Acoustic Sensor Arrays and Systems, and Methods of Fabricating the Same. (No. 9217801), U.S. Patent."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"526","DOI":"10.1364\/OL.44.000526","article-title":"Spectral shadowing suppression technique in phase-OTDR sensing based on weak fiber Bragg grating array","volume":"44","author":"Jason","year":"2019","journal-title":"Opt. Lett."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"677","DOI":"10.1109\/LPT.2018.2811411","article-title":"Interrogation of ultra-weak FBG array using double-pulse and heterodyne detection","volume":"30","author":"Liu","year":"2018","journal-title":"IEEE Photonics Technol. Lett."},{"key":"ref_29","first-page":"104640X","article-title":"Long distance \u03a6-OTDR system based on Raman and EDFA synthetic amplification. In AOPC 2017: Fiber Optic Sensing and Optical Communications","volume":"10464","author":"Tian","year":"2017","journal-title":"Int. Soc. Opt. Photonics"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"5866","DOI":"10.1364\/OL.39.005866","article-title":"Ultra-long phase-sensitive OTDR with hybrid distributed amplification","volume":"39","author":"Wang","year":"2014","journal-title":"Opt. Lett."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"9157D5","DOI":"10.1117\/12.2071255","article-title":"175 km Phase-sensitive OTDR with Hybrid Distributed Amplification","volume":"9157","author":"Wang","year":"2014","journal-title":"Proc. SPIE"},{"key":"ref_32","unstructured":"Pnev, A.B., Stepanov, K.V., Zhirnov, A.A., Nesterov, E.T., Chernutsky, A.O., Laptev, A.S., Shelestov, D.A., Koshelev, K.I., and Karasik, V.E. (2019). Multichannel Fiber-Optic Device for Recording Vibration Effects with One Receiving Registration Module. (2695058), RU Patent."},{"key":"ref_33","unstructured":"Nesterov, E.T., Pnev, A.B., Kireev, A.V., Stepanov, K.V., Zhirnov, A.A., Karasik, V.E., and Shelestov, D.A. (2018). Fiber-Optical Distribution Vibroacoustic Sensor Based on Phase-Sensitive Reflectometer and Method of Improving Its Characteristics of Sensitivity. (2650853), RU Patent."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"65","DOI":"10.1080\/10739149.2020.1780253","article-title":"Vibration monitoring for the West-East Gas Pipeline Project of China by phase optical time domain reflectometry (phase-OTDR)","volume":"49","author":"Li","year":"2021","journal-title":"Instrum. Sci. Technol."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"872","DOI":"10.4028\/www.scientific.net\/AMM.385-386.872","article-title":"Overview of fiber optic pipeline monitoring sensors","volume":"246","author":"Li","year":"2013","journal-title":"Appl. Mech. Mater."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"2925","DOI":"10.1364\/OE.28.002925","article-title":"Fiber distributed acoustic sensing using convolutional long short-term memory network: A field test on high-speed railway intrusion detection","volume":"28","author":"Li","year":"2020","journal-title":"Opt. Express"},{"key":"ref_37","unstructured":"Vidovic, I. (2020). Railway Infrastructure Condition Monitoring and Asset Management\u2014The Case of Fibre Optic Sensing. [Ph.D. Dissertation, Verlag Der Technischen Universit\u00e4t Graz]."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"693","DOI":"10.1111\/1365-2478.12141","article-title":"Vertical seismic optical profiling on wireline logging cable","volume":"62","author":"Hartog","year":"2014","journal-title":"Geophys. Prospect."},{"key":"ref_39","first-page":"987","article-title":"Compressional- and shear-wave studies of distributed acoustic sensing acquired vertical seismic profile data","volume":"36","author":"Wu","year":"2017","journal-title":"J. Geophys."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"1328","DOI":"10.1038\/s41598-018-36675-8","article-title":"Distributed Acoustic Sensing Using Dark Fiber for Near-Surface Characterization and Broadband Seismic Event Detection","volume":"9","author":"Dou","year":"2019","journal-title":"Sci. Rep."},{"key":"ref_41","doi-asserted-by":"crossref","unstructured":"Zhirnov, A.A., Chesnokov, G.Y., Stepanov, K.V., Gritsenko, T.V., Khan, R.I., Koshelev, K.I., Chernutsky, A.O., Svelto, C., Pnev, A.B., and Valba, O.V. (2023). Fiber-Optic Telecommunication Network Wells Monitoring by Phase-Sensitive Optical Time-Domain Reflectometer with Disturbance Recognition. Sensors, 23.","DOI":"10.3390\/s23104978"},{"key":"ref_42","doi-asserted-by":"crossref","unstructured":"Makarenko, A.V. (2016, January 13\u201316). Deep Learning Algorithms for Signal Recognition in long Perimeter Monitoring Distributed Fiber Optic Sensors. Proceedings of the 2016 IEEE 26th International Workshop on Machine Learning for Signal Processing (MLSP), Vietri sul Mare, Italy.","DOI":"10.1109\/MLSP.2016.7738863"},{"key":"ref_43","first-page":"102080","article-title":"Deep learning based multi-threat classification for phase-OTDR fiber optic distributed acoustic sensing applications. SPIE Commer","volume":"10208","author":"Aktas","year":"2017","journal-title":"Sci. Sens. Imaging"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"143473","DOI":"10.1109\/ACCESS.2021.3121767","article-title":"A Recognition Method for Multi-Radial-Distance Event of \u03a6-OTDR System Based on CNN","volume":"9","author":"Shi","year":"2021","journal-title":"IEEE Access"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"016103","DOI":"10.1117\/1.OE.57.1.016103","article-title":"Pattern recognition based on time-frequency analysis and convolutional neural networks for vibrational events in \u03c6-OTDR","volume":"57","author":"Xu","year":"2018","journal-title":"Opt. Eng."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"2975","DOI":"10.1364\/AO.444811","article-title":"Machine learning methods for identification and classification of events in \u03d5-OTDR systems: A review","volume":"61","author":"Kandamali","year":"2022","journal-title":"Appl. Opt."},{"key":"ref_47","doi-asserted-by":"crossref","unstructured":"Al-Ashwal, N.H., Al Soufy, K.A.M., Hamza, M.E., and Swillam, M.A. (2023). Deep Learning for Optical Sensor Applications: A Review. Sensors, 23.","DOI":"10.20944\/preprints202306.0860.v1"},{"key":"ref_48","doi-asserted-by":"crossref","unstructured":"Parker, T., Shatalin, S., Farhadiroushan, M., and Miller, D. (2013, January 17\u201320). Distributed Acoustic Sensing: Recent Field Data and Performance Validation. Proceedings of the 4th EAGE Passive Seismic Workshop, Amsterdam, The Netherlands.","DOI":"10.3997\/2214-4609.20131303"},{"key":"ref_49","unstructured":"Shatalin, S., Parker, T., and Farhadiroushan, M. (2021). Distributed Acoustic Sensing in Geophysics, Wiley."},{"key":"ref_50","first-page":"808","article-title":"Surface seismics with DAS: An emerging alternative to modern point-sensor acquisition","volume":"39","author":"Bakulin","year":"2020","journal-title":"J. Geophys."},{"key":"ref_51","doi-asserted-by":"crossref","unstructured":"Tabata, S., Maruyama, M., Watanabe, Y., and Ishikawa, M. (2019). Pixelwise Phase Unwrapping Based on Ordered Periods Phase Shift. Sensors, 19.","DOI":"10.3390\/s19020377"},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"2470","DOI":"10.1364\/AO.21.002470","article-title":"Analysis of the phase unwrapping algorithm","volume":"21","author":"Itoh","year":"1982","journal-title":"Appl. Opt."},{"key":"ref_53","unstructured":"Listvin, A.V., and Listvin, V.N. (2005). Optical Fiber Reflectometry, LESARart. (In Russian)."},{"key":"ref_54","doi-asserted-by":"crossref","unstructured":"Kocal, E.B., Y\u00fcksel, K., and Wuilpart, M. (2020, January 8). Combined Effect of Multi-Reflection and Spectral Shadowing Crosstalk in Phase-OTDR System Using Fiber Bragg Grating Array. Proceedings of the Optical Fiber Sensors Conference 2020, Alexandria, VA, USA.","DOI":"10.1364\/OFS.2020.T3.40"},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"2892","DOI":"10.1002\/mop.30178","article-title":"Improved \u03a6-OTDR system with narrow pulses for quantitative strain measurement based on ultra-weak fiber bragg grating array","volume":"58","author":"Zhang","year":"2016","journal-title":"Microwave Opt. Technol. Lett."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"054103","DOI":"10.1117\/1.OE.55.5.054103","article-title":"Enhanced \u03a6-OTDR system for quantitative strain measurement based on ultra-weak fiber Bragg grating array","volume":"55","author":"Zhang","year":"2016","journal-title":"Opt. Eng."},{"key":"ref_57","first-page":"6802412","article-title":"A high performance distributed optical fiber sensor based on \u03a6-OTDR for dynamic strain measurement","volume":"9","author":"Zhang","year":"2017","journal-title":"IEEE Photon. J."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"87","DOI":"10.3103\/S8756699023010053","article-title":"Effects of laser phase noise on the operation of coherent reflectometers when using fibers with arrays of artificial reflectors","volume":"59","author":"Fomiryakov","year":"2023","journal-title":"Optoelectron. Instrum. Data Process."},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"19990","DOI":"10.1364\/OE.460302","article-title":"Laser source frequency drift compensation in \u03a6-OTDR systems using multiple probe frequencies","volume":"30","author":"Zabihi","year":"2022","journal-title":"Opt. Express"},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"689","DOI":"10.1364\/AO.21.000689","article-title":"Optical techniques to solve the signal fading problem in fiber interferometers","volume":"21","author":"Sheem","year":"1982","journal-title":"Appl. Opt."},{"key":"ref_61","doi-asserted-by":"crossref","first-page":"3865","DOI":"10.1063\/1.329853","article-title":"Optical fiber interferometers with [3 \u00d7 3] directional couplers: Analysis","volume":"52","author":"Sheem","year":"1981","journal-title":"J. Appl. Phys."},{"key":"ref_62","doi-asserted-by":"crossref","first-page":"616","DOI":"10.1063\/1.93626","article-title":"Passive stabilization scheme for fiber interferometers using (3 \u00d7 3) fiber directional couplers","volume":"41","author":"Koo","year":"1982","journal-title":"Appl. Phys. Lett."},{"key":"ref_63","doi-asserted-by":"crossref","first-page":"143","DOI":"10.1117\/12.935808","article-title":"Passively Stabilized Fiber Interferometers Using (3\u00d73) Fiber Directional Couplers","volume":"412","author":"Koo","year":"1983","journal-title":"Fiber Opt. Laser Sens. I"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/24\/11\/3338\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T14:47:18Z","timestamp":1760107638000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/24\/11\/3338"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2024,5,23]]},"references-count":63,"journal-issue":{"issue":"11","published-online":{"date-parts":[[2024,6]]}},"alternative-id":["s24113338"],"URL":"https:\/\/doi.org\/10.3390\/s24113338","relation":{},"ISSN":["1424-8220"],"issn-type":[{"type":"electronic","value":"1424-8220"}],"subject":[],"published":{"date-parts":[[2024,5,23]]}}}