Fused Fiber Coupler Demux as an Edge Filter for Optical Sensing: A Low-Cost Solution

• Published in: IEEE sensors journal 2025-01, Vol.25 (1), p.523-530
• Main Authors: Mahadevachar, Naveenkumar, Esamudra Sharanappa, Shivaleela, Satya Chidambara Swamy Vaddadi, Venkata
• Format: Article
• Language: English
• Subjects: Configurations; Cost effectiveness; FBG strain sensor; fiber Bragg gratings (FBGs); Fiber gratings; fiber-optic sensors (FOSs); fused fiber optic demux as edge filter; intensity-based interrogator; Interrogation; Optical fiber couplers; Optical fiber filters; Optical fiber sensors; Power measurement; Sensitivity; Strain; Strain measurement; Temperature measurement; Wavelength measurement
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2024.3493139

In this article, we explore an intensity-based interrogation technique using fused fiber demux as an edge filter, for the first time, which is a simple/elegant scheme, offering advantages such as portability and cost-effectiveness without compromising sensitivity. Strain on the FBG causes the grating pitch to vary and hence the reflected Bragg wavelength to shift: 1) peak wavelength/peak power and 2) the integrated power (intensity) variation, of the reflected spectrum are measured after passing through the edge filter. In the first/second configuration, −ve/+ve slope edge filters, respectively, are used, coinciding with strain FBG Bragg wavelength. Furthermore, we propose a third configuration, the edge filter differential slope method, simultaneously using −ve and +ve edge filters, to achieve higher sensitivity than the first and second configurations. The wavelength sensitivity of this interrogator is 1.2 pm/ \pmb {\mu \epsilon } , and the power sensitivity is 13.75 dB/nm, comparable with other configurations. The slope of the edge filter (wavelength range) limits the "range" of measurement. Our proposed methods can also be used in FBG-based temperature sensing applications.