{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T11:16:11Z","timestamp":1760181371706,"version":"build-2065373602"},"reference-count":24,"publisher":"MDPI AG","issue":"21","license":[{"start":{"date-parts":[[2020,10,26]],"date-time":"2020-10-26T00:00:00Z","timestamp":1603670400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000038","name":"Natural Sciences and Engineering Research Council of Canada","doi-asserted-by":"publisher","award":["RGPIN-2020-06302"],"award-info":[{"award-number":["RGPIN-2020-06302"]}],"id":[{"id":"10.13039\/501100000038","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001804","name":"Canada Research Chairs","doi-asserted-by":"publisher","award":["950231352"],"award-info":[{"award-number":["950231352"]}],"id":[{"id":"10.13039\/501100001804","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Random fiber gratings (RFGs) have shown great potential applications in fiber sensing and random fiber lasers. However, a quantitative relationship between the degree of randomness of the RFG and its spectral response has never been analyzed. In this paper, two RFGs with different degrees of randomness are first characterized experimentally by optical frequency domain reflectometry (OFDR). Experimental results show that the high degree of randomness leads to low backscattering strength of the grating and strong strength fluctuations in the spatial domain. The local spectral response of the grating exhibits multiple peaks and a large peak wavelength variation range when its degree of randomness is high. The linewidth of its fine spectrum structures shows scaling behavior with the grating length. In order to find a quantitative relationship between the degree of randomness and spectrum property of RFG, entropy was introduced to describe the degree of randomness induced by period variation of the sub-grating. Simulation results showed that the average reflectivity of the RFG in dB scale decreased linearly with increased sub-grating entropy, when the measured wavelength range was smaller than the peak wavelength variation range of the sub-grating. The peak reflectivity of the RFG was determined by \u03ba2L\u0394P (where \u03ba is the coupling coefficient, L is the grating length, \u0394P is period variation range of the sub-grating) rather than \u03baL when \u0394P is larger than 8 nm in the spatial domain. The experimental results agree well with the simulation results, which helps to optimize the RFG manufacturing processes for future applications in random fiber lasers and sensors.<\/jats:p>","DOI":"10.3390\/s20216071","type":"journal-article","created":{"date-parts":[[2020,10,26]],"date-time":"2020-10-26T10:38:35Z","timestamp":1603708715000},"page":"6071","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["Random Fiber Grating Characterization Based on OFDR and Transfer Matrix Method"],"prefix":"10.3390","volume":"20","author":[{"given":"Zichao","family":"Zhou","sequence":"first","affiliation":[{"name":"Department of Physics, University of Ottawa, 25 Templeton Street, Ottawa, ON K1N 6N5, Canada"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2325-1198","authenticated-orcid":false,"given":"Chen","family":"Chen","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Ottawa, 25 Templeton Street, Ottawa, ON K1N 6N5, Canada"}]},{"given":"Ping","family":"Lu","sequence":"additional","affiliation":[{"name":"National Research Council Canada, Ottawa, ON K1A 0R6, Canada"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6144-0937","authenticated-orcid":false,"given":"Stephen","family":"Mihailov","sequence":"additional","affiliation":[{"name":"National Research Council Canada, Ottawa, ON K1A 0R6, Canada"}]},{"given":"Liang","family":"Chen","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Ottawa, 25 Templeton Street, Ottawa, ON K1N 6N5, Canada"}]},{"given":"Xiaoyi","family":"Bao","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Ottawa, 25 Templeton Street, Ottawa, ON K1N 6N5, Canada"}]}],"member":"1968","published-online":{"date-parts":[[2020,10,26]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"105001","DOI":"10.1088\/1612-202X\/ab3a28","article-title":"Coherent Raman lasing in a short polarization-maintaining fiber with a random fiber Bragg grating array","volume":"16","author":"Abdullina","year":"2019","journal-title":"Laser Phys. 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