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Opt."],"published-print":{"date-parts":[[2026,10,1]]},"abstract":"<jats:p>Precise alignment of single-mode fiber (SMF) collimators is a fundamental challenge in free-space optical (FSO) experiments due to tight spatial and angular coupling tolerances. This application note presents a practical and reproducible three-phase methodology for manual SMF collimator alignment, integrating visual targeting, intermediate multimode fiber coarse capture, and SMF fine alignment. Demonstrated across a 100\u00a0m indoor FSO range at 0\u00a0dBm transmit power, the approach achieves \u221215.72dBm coupled optical power in under 5\u00a0min. This methodology enables rapid link establishment for proof-of-concept FSO demonstrations, allowing quick verification of efficient coupling prior to investment of time and resources in developing a dedicated pointing, acquisition, and tracking (PAT) system.<\/jats:p>","DOI":"10.1364\/ao.613986","type":"journal-article","created":{"date-parts":[[2026,9,4]],"date-time":"2026-09-04T15:00:05Z","timestamp":1788534005000},"page":"9621","update-policy":"https:\/\/doi.org\/10.1364\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["On manual alignment of single-mode fiber collimators for free-space optical links"],"prefix":"10.1364","volume":"65","author":[{"ORCID":"https:\/\/orcid.org\/0009-0004-2834-6588","authenticated-orcid":true,"given":"Shivam","family":"Bhutiani","sequence":"first","affiliation":[{"name":"Indian Institute of Technology (IIT)\u2014Bombay"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5988-9420","authenticated-orcid":true,"given":"Shalabh","family":"Gupta","sequence":"additional","affiliation":[{"name":"Indian Institute of Technology (IIT)\u2014Bombay"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"285","published-online":{"date-parts":[[2026,9,21]]},"reference":[{"key":"ao-65-28-9621-R1","doi-asserted-by":"publisher","first-page":"703","DOI":"10.1002\/j.1538-7305.1977.tb00534.x","type":"journal-article","volume":"56","author":"Marcuse","year":"1977","journal-title":"Bell Syst. 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All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.","name":"copyright","label":"Copyright"}]}}