{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,6]],"date-time":"2026-04-06T13:09:49Z","timestamp":1775480989499,"version":"3.50.1"},"reference-count":22,"publisher":"MDPI AG","issue":"21","license":[{"start":{"date-parts":[[2022,10,29]],"date-time":"2022-10-29T00:00:00Z","timestamp":1667001600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Fiosraigh Scholarship Award 2019, TU Dublin"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>A novel micron-range displacement sensor based on a whispering-gallery mode (WGM) microcapillary resonator filled with a nematic liquid crystal (LC) and a magnetic nanoparticle- coated fiber half-taper is proposed and experimentally demonstrated. In the proposed device, the tip of a fiber half-taper coated with a thin layer of magnetic nanoparticles (MNPs) moves inside the LC-filled microcapillary resonator along its axis. The input end of the fiber half-taper is connected to a pump laser source and due to the thermo-optic effect within the MNPs, the fiber tip acts as point heat source increasing the temperature of the LC material in its vicinity. An increase in the LC temperature leads to a decrease in its effective refractive index, which in turn causes spectral shift of the WGM resonances monitored in the transmission spectrum of the coupling fiber. The spectral shift of the WGMs is proportional to the displacement of the MNP-coated tip with respect to the microcapillary\u2019s light coupling point. The sensor\u2019s operation is simulated considering heat transfer in the microcapillary filled with a LC material having a negative thermo-optic coefficient. The simulations are in a good agreement with the WGMs spectral shift observed experimentally. A sensitivity to displacement of 15.44 pm\/\u00b5m and a response time of 260 ms were demonstrated for the proposed sensor. The device also shows good reversibility and repeatability of response. The proposed micro-displacement sensor has potential applications in micro-manufacturing, precision measurement and medical instruments.<\/jats:p>","DOI":"10.3390\/s22218312","type":"journal-article","created":{"date-parts":[[2022,10,30]],"date-time":"2022-10-30T10:47:57Z","timestamp":1667126877000},"page":"8312","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":11,"title":["A Micron-Range Displacement Sensor Based on Thermo-Optically Tuned Whispering Gallery Modes in a Microcapillary Resonator"],"prefix":"10.3390","volume":"22","author":[{"given":"Zhe","family":"Wang","sequence":"first","affiliation":[{"name":"Photonics Research Centre, School of Electrical and Electronic Engineering, Technological University Dublin, D07 ADY7 Dublin, Ireland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Arun Kumar","family":"Mallik","sequence":"additional","affiliation":[{"name":"Tyndall National Institute, University College Cork, Lee Maltings, Dyke Parade, T12 YN60 Cork, Ireland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1536-9452","authenticated-orcid":false,"given":"Fangfang","family":"Wei","sequence":"additional","affiliation":[{"name":"Photonics Research Centre, School of Electrical and Electronic Engineering, Technological University Dublin, D07 ADY7 Dublin, Ireland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Zhuochen","family":"Wang","sequence":"additional","affiliation":[{"name":"Photonics Research Centre, School of Electrical and Electronic Engineering, Technological University Dublin, D07 ADY7 Dublin, Ireland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Anuradha","family":"Rout","sequence":"additional","affiliation":[{"name":"Photonics Research Centre, School of Electrical and Electronic Engineering, Technological University Dublin, D07 ADY7 Dublin, Ireland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2901-7434","authenticated-orcid":false,"given":"Qiang","family":"Wu","sequence":"additional","affiliation":[{"name":"Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle upon Tyne NE1 8ST, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2906-0643","authenticated-orcid":false,"given":"Yuliya","family":"Semenova","sequence":"additional","affiliation":[{"name":"Photonics Research Centre, School of Electrical and Electronic Engineering, Technological University Dublin, D07 ADY7 Dublin, Ireland"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,10,29]]},"reference":[{"key":"ref_1","first-page":"276","article-title":"Differential Inductive Displacement Sensor with Integrated Electronics and Infrared Communication Capabilities","volume":"Volume 8411","author":"Drumea","year":"2012","journal-title":"Advanced Topics in Optoelectronics, Microelectronics, and Nanotechnologies VI"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"2354","DOI":"10.1109\/LPT.2013.2285160","article-title":"High-Sensitivity Displacement Sensor Based on a Bent Fiber Mach-Zehnder Interferometer","volume":"25","author":"Chen","year":"2013","journal-title":"IEEE Photonics Technol. Lett."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"e2122","DOI":"10.1002\/stc.2122","article-title":"Visual\u2013Inertial Displacement Sensing Using Data Fusion of Vision-Based Displacement with Acceleration","volume":"25","author":"Park","year":"2018","journal-title":"Struct. Control Health Monit."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"3346","DOI":"10.1109\/JSEN.2012.2204321","article-title":"Design Strategies for Eddy-Current Displacement Sensor Systems: Review and Recommendations","volume":"12","author":"Nabavi","year":"2012","journal-title":"IEEE Sens. J."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Giffney, T., Xie, M., Yong, A., Wong, A., Mousset, P., McDaid, A., and Aw, K. (2016). Soft Pneumatic Bending Actuator with Integrated Carbon Nanotube Displacement Sensor. Robotics, 5.","DOI":"10.3390\/robotics5010007"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"482","DOI":"10.1115\/1.2902132","article-title":"Multi-Laser Displacement Sensor Used in Accurate Digitizing Technique","volume":"116","author":"Smith","year":"1994","journal-title":"J. Manuf. Sci. Eng. Trans. ASME"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"14105","DOI":"10.3390\/s131014105","article-title":"Optical Fiber-Based MR-Compatible Sensors for Medical Applications: An Overview","volume":"13","author":"Taffoni","year":"2013","journal-title":"Sensors"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"202","DOI":"10.1364\/OL.37.000202","article-title":"High Precision Micro-Displacement Fiber Sensor through a Suspended-Core Sagnac Interferometer","volume":"37","author":"Bravo","year":"2012","journal-title":"Opt. Lett."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"31984","DOI":"10.1364\/OE.22.031984","article-title":"Optical Fiber Axial Micro-Displacement Sensor Based on Mach-Zehnder Interferometer","volume":"22","author":"Shen","year":"2014","journal-title":"Opt. Express"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"787","DOI":"10.1364\/OL.385222","article-title":"Miniature Fabry\u2013Perot Interferometer Based on a Movable Microsphere Reflector","volume":"45","author":"Tian","year":"2020","journal-title":"Opt. Lett."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"42800","DOI":"10.1364\/OE.445192","article-title":"In-Situ Adjustable Fiber-Optic Piezometer Based on Parallelly Structured External Fabry-Perot Interferometers with Vernier Effect and Its Harmonics","volume":"29","author":"Wang","year":"2021","journal-title":"Opt. Express"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1007\/s00340-017-6866-9","article-title":"An \u201cin-Fiber\u201d Whispering-Gallery-Mode Bi-Sphere Resonator, Sensitive to Nanometric Displacements","volume":"124","author":"Kosma","year":"2018","journal-title":"Appl. Phys. B Lasers Opt."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"195","DOI":"10.1364\/OE.26.000195","article-title":"Whispering Gallery Modes in a Single Silica Microparticle Attached to an Optical Microfiber","volume":"26","author":"Liu","year":"2018","journal-title":"Opt. Express"},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Liao, J., Qavi, A., Adolphson, M., and Yang, L. (2022). High-Q WGM Resonators Encapsulated in PDMS for Highly Sensitive Displacement Detection. J. Light. Technol., 1\u201311.","DOI":"10.1109\/JLT.2022.3182627"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"23569","DOI":"10.1364\/OE.432103","article-title":"Thermo-Optic Tuning of a Nematic Liquid Crystal-Filled Capillary Whispering Gallery Mode Resonator","volume":"29","author":"Wang","year":"2021","journal-title":"Opt. Express"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"80","DOI":"10.1038\/s41377-021-00525-6","article-title":"Quantum-dot microlasers based on whispering gallery mode resonators","volume":"10","author":"Zhukov","year":"2021","journal-title":"Light Sci. Appl."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"425","DOI":"10.1364\/OPTICA.1.000425","article-title":"Optomechanically induced transparency and self-induced oscillations with Bogoliubov mechanical modes","volume":"1","author":"Dong","year":"2014","journal-title":"Optica"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Candeloro, A., Razavian, S., Piccolini, M., Teklu, B., Olivares, S., and Paris, M.G.A. (2021). Quantum Probes for the Characterization of Nonlinear Media. Entropy, 23.","DOI":"10.3390\/e23101353"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"21216","DOI":"10.1364\/OE.24.021216","article-title":"Agarose Coated Spherical Micro Resonator for Humidity Measurements","volume":"24","author":"Mallik","year":"2016","journal-title":"Opt. Express"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"11406","DOI":"10.1021\/acsnano.0c03703","article-title":"Thermoplasmonic Optical Fiber for Localized Neural Stimulation","volume":"14","author":"Kang","year":"2020","journal-title":"ACS Nano"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1153","DOI":"10.1103\/PhysRevA.41.1153","article-title":"Thermal Conductivity, Diffusivity, and Heat-Capacity Studies at the Smectic-A -Nematic Transition in Alkylcyanobiphenyl Liquid Crystals","volume":"41","author":"Zammit","year":"1990","journal-title":"Phys. Rev. A"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"2628","DOI":"10.1364\/AO.50.002628","article-title":"Liquid Crystal Infiltrated Photonic Crystal Fibers for Electric Field Intensity Measurements","volume":"50","author":"Mathews","year":"2011","journal-title":"Appl. Opt."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/22\/21\/8312\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T01:05:48Z","timestamp":1760144748000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/22\/21\/8312"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2022,10,29]]},"references-count":22,"journal-issue":{"issue":"21","published-online":{"date-parts":[[2022,11]]}},"alternative-id":["s22218312"],"URL":"https:\/\/doi.org\/10.3390\/s22218312","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2022,10,29]]}}}