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Therefore, the study of seawater salinity is significant for the prediction of changes in the ocean environment. However, existing methods for measuring seawater salinity generally have the disadvantages of low sensitivity and low accuracy. In this work, we proposed a seawater salinity sensor based on long period fiber grating (LPFG) in the dispersion turning point (DTP), which has demonstrated the possibility to fabricate LPFG with a shorter grating period by CO2 laser in a thin single mode fiber (SMF) of 80 \u03bcm cladding diameter without etching. For obtaining higher sensitivity that could meet the measurement requirement in practice, the proposed sensor was optimized by combining etching cladding and DTP. After the LPFG working near DTP was fabricated by a CO2 laser, the cladding diameter was reduced to 57.14 \u03bcm for making cladding mode LP1,7 work near DTP by hydrofluoric acid (HF) solutions. The experimental results have demonstrated that a sensitivity of 0.571 nm\/\u2030 can be achieved when the salinity increases from 5.001\u2030 to 39.996\u2030, and the sensor shows good repeatability and stability. Based on its excellent performance, the optimized LPFG is a prospective sensor to monitor seawater salinity in real time. Meanwhile, a low-cost way was provided to make LPFG work near DTP instead of ultraviolet exposure and femtosecond laser writing.<\/jats:p>","DOI":"10.3390\/s23094435","type":"journal-article","created":{"date-parts":[[2023,5,1]],"date-time":"2023-05-01T12:12:11Z","timestamp":1682943131000},"page":"4435","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["A Seawater Salinity Sensor Based on Optimized Long Period Fiber Grating in the Dispersion Turning Point"],"prefix":"10.3390","volume":"23","author":[{"given":"Chao","family":"Du","sequence":"first","affiliation":[{"name":"College of Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shuang","family":"Zhao","sequence":"additional","affiliation":[{"name":"College of Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Qiuyu","family":"Wang","sequence":"additional","affiliation":[{"name":"College of Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bin","family":"Jia","sequence":"additional","affiliation":[{"name":"College of Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mingzhe","family":"Zhao","sequence":"additional","affiliation":[{"name":"College of Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Li","family":"Zhang","sequence":"additional","affiliation":[{"name":"College of Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Liqin","family":"Cui","sequence":"additional","affiliation":[{"name":"College of Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China"},{"name":"College of Physics, Taiyuan University of Technology, Taiyuan 030024, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5802-3297","authenticated-orcid":false,"given":"Shizhe","family":"Chen","sequence":"additional","affiliation":[{"name":"Institute of Oceanographic Instrumentation, Qilu University of Technology (Shandong Academy of Sciences), Qingdao 266001, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7137-5203","authenticated-orcid":false,"given":"Xiao","family":"Deng","sequence":"additional","affiliation":[{"name":"College of Physics, Taiyuan University of Technology, Taiyuan 030024, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,4,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"617","DOI":"10.1038\/s41586-021-04370-w","article-title":"Observed poleward freshwater transport since 1970","volume":"602","author":"Sohail","year":"2022","journal-title":"Nature"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"466","DOI":"10.2112\/SI85-094.1","article-title":"Comparison of internal waves in various ocean fields around the korean peninsula","volume":"85","author":"Kim","year":"2018","journal-title":"J. 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