Tapered fiber optic refractive index sensor using speckle pattern imaging

• Published in: Optical fiber technology Vol. 79; p. 103366
• Main Authors: Arı, Fikret, Şerbetçi, Hüsamettin, Navruz, İsa
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-09-2023
• Subjects: Optical fiber sensor; Refractive index; Speckle pattern; Taper geometry effect; Tapered optical fiber; Taper geometry effect; Speckle pattern; Tapered optical fiber; Optical fiber sensor; Refractive index
• ISSN: 1068-5200; 1095-9912
• DOI: 10.1016/j.yofte.2023.103366

•Tapered fiber optic sensor based on speckle pattern imaging is proposed for refractive index sensing.•Effect of TOF sensor geometry on refractive index sensitivity is investigated numerically and demonstrated experimentally.•The fabricated TOF sensor has a waist diameter of 10 μm and a waist length of 3.5 cm.•The sensor is sensitive to refractive index changes of the order of 10-4.•It has been demonstrated that refractive index sensing can be performed by using speckle pattern images instead of OSA in TOF sensors.
In this study, a low-cost and compact refractive index (RI) sensor based on speckle pattern imaging has been proposed and demonstrated numerically and experimentally. We have proven that speckle pattern images recorded with a CCD camera placed at the end of the tapered optical fiber (TOF) are highly sensitive to the RI of the medium to be measured. The effects of the waist diameter and length of the tapered region, which is the sensing part of the fiber, on sensitivity were investigated using the beam propagation method (BPM). It has been seen that the numerical results have compatible with the experimental results. Tapered fiber sensor was fabricated by electric arc discharge technique using step index multimode fiber (SI-MMF) with core and cladding diameters of 105 and 125 μm. The sensor sensitivity increases as the waist diameter decreases and the waist length increases. The sensor, which waist diameter is reduced to 10 μm, is sensitive to RI changes of the order of 10-4. It has been clearly seen that the proposed sensor based on speckle pattern imaging is highly sensitive to RI change.