{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,6]],"date-time":"2025-11-06T01:01:29Z","timestamp":1762390889437,"version":"build-2065373602"},"reference-count":20,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2020,2,15]],"date-time":"2020-02-15T00:00:00Z","timestamp":1581724800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100004663","name":"Ministry of Science and Technology, Taiwan","doi-asserted-by":"publisher","award":["MOST 108-2218-E--011-009"],"award-info":[{"award-number":["MOST 108-2218-E--011-009"]}],"id":[{"id":"10.13039\/501100004663","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We design and compare the splitting ratio wavelength flatness of directional coupler (DC), Mach-Zehnder directional coupler (MZDC), and tandem MZDC. All coupler responses are analyzed, and tandem MZDC performance is the best in the wavelength insensitivity compared with the other two. An MZDC with any coupling ratio could be utilized to match the maximum flatness in a 40-nm wavelength range. To extend a broad flatness range, the tandem MZDC is proposed and still follows the Mach Zehnder structure taking two MZDCs as couplers connected through a decoupled region. Unlike DC, MZDC with the flat wavelength response has a non-linear output phase. Hence, using two wavelength-insensitive MZDCs as the coupling function in a tandem MZDC could demonstrate a more extensive decoupled phase term to maximize the flat wavelength response. The tandem MZDC theoretically demonstrates the splitting ratio with 100-nm flatness in the wavelength range from 1250 nm to 1350 nm. Finally, a point spread function through the tandem MZDC shows a 24-dB signal-to-noise ratio improvement in optical coherence tomography applications.<\/jats:p>","DOI":"10.3390\/s20041054","type":"journal-article","created":{"date-parts":[[2020,2,20]],"date-time":"2020-02-20T03:20:03Z","timestamp":1582168803000},"page":"1054","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Tandem Mach Zehnder Directional Coupler Design and Simulation on Silicon Platform for Optical Coherence Tomography Applications"],"prefix":"10.3390","volume":"20","author":[{"given":"Yi-Ting","family":"Lu","sequence":"first","affiliation":[{"name":"Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Benedictus Yohanes Bagus","family":"Widhianto","sequence":"additional","affiliation":[{"name":"Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Shih-Hsiang","family":"Hsu","sequence":"additional","affiliation":[{"name":"Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8080-2094","authenticated-orcid":false,"given":"Che-Chang","family":"Chang","sequence":"additional","affiliation":[{"name":"Graduate Institute of Translational Medicine, College of Medical Science and Technology, Taipei Medical University, Taipei 11031, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,2,15]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Drexler, W.E., and Fujimoto, J.G. 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