{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,6]],"date-time":"2025-12-06T17:11:07Z","timestamp":1765041067758,"version":"build-2065373602"},"reference-count":29,"publisher":"MDPI AG","issue":"21","license":[{"start":{"date-parts":[[2020,10,22]],"date-time":"2020-10-22T00:00:00Z","timestamp":1603324800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Major Projects of Technical Innovation of Hubei","award":["No. 2018AAA040 and No. 2019AAA053"],"award-info":[{"award-number":["No. 2018AAA040 and No. 2019AAA053"]}]},{"name":"Science Fund 239 for Creative Research Groups of the Nature Science Foundation of Hubei","award":["No. 2018CFA004"],"award-info":[{"award-number":["No. 2018CFA004"]}]},{"name":"National Key RD Program of China","award":["2018YFB2100902"],"award-info":[{"award-number":["2018YFB2100902"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We characterized a cascaded long-period gratings (LPGs)-based sensor that was operating at the phase-matching turning point (PMTP). The cascaded LPGs constructed an in-fiber Mach\u2013Zehnder interferometer (MZI), which exhibited a series of high-quality-factor (Q) narrow-bandwidth resonance peaks. As the LPG operated at the PMTP, the proposed sensor showed an ultrahigh refractive index (RI) and temperature sensitivity, and high measurement precision. In this study, we took an in-depth look at the effects of grating separation on Q-factor and sensitivity. The results showed that the sensitivity to the surrounding refractive index (SRI) reached 4741.5 nm\/RIU at 1.4255 and 2138 nm\/RIU, over the range of 1.335\u20131.373. In addition, the temperature sensitivity was around 4.84 nm\/\u00b0C. With a 0.02 nm wavelength resolution, the RI and temperature sensing limits were 9.3 \u00d7 10\u22126 RIU and 5.5 \u00d7 10\u22123 \u00b0C.<\/jats:p>","DOI":"10.3390\/s20215978","type":"journal-article","created":{"date-parts":[[2020,10,22]],"date-time":"2020-10-22T20:51:00Z","timestamp":1603399860000},"page":"5978","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Sensitivity Characterization of Cascaded Long-Period Gratings Operating near the Phase-Matching Turning Point"],"prefix":"10.3390","volume":"20","author":[{"given":"Wei","family":"Zhou","sequence":"first","affiliation":[{"name":"Institute of Microscale Optoelectronics (IMO), Shenzhen University, Shenzhen 518060, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1862-3268","authenticated-orcid":false,"given":"Yanli","family":"Ran","sequence":"additional","affiliation":[{"name":"Institute of Microscale Optoelectronics (IMO), Shenzhen University, Shenzhen 518060, China"}]},{"given":"Zhijun","family":"Yan","sequence":"additional","affiliation":[{"name":"School of Optical and Electronic Information, National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan 430074, China"}]},{"given":"Qizhen","family":"Sun","sequence":"additional","affiliation":[{"name":"School of Optical and Electronic Information, National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan 430074, China"}]},{"given":"Chen","family":"Liu","sequence":"additional","affiliation":[{"name":"School of Optical and Electronic Information, National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan 430074, China"}]},{"given":"Deming","family":"Liu","sequence":"additional","affiliation":[{"name":"School of Optical and Electronic Information, National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan 430074, China"}]}],"member":"1968","published-online":{"date-parts":[[2020,10,22]]},"reference":[{"key":"ref_1","first-page":"212","article-title":"Ovel optical biosensing technologies for detection of mycotoxins","volume":"109","author":"Naboka","year":"2019","journal-title":"Opt. 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