Basic principles of fibre Bragg grating (FBG) based sensor utilize in different applications for temperature, humidity, refractive index, and strain. Most optical fibre sensor devices today construct utilize fibre Bragg grating technology. In this study we have inscribed two long period fibre Bragg grating (LPFBG) experimentally, and used these two LPFBG as sensors for measure sucrose concentration. i.e. for refractive index sensing. It’s fabricated by using a short segment of no core fibre (NCF) and the carbon- dioxide (CO₂) laser. A point-by-point technique was employed using varying laser power levels (1.6 W and 3 W) to enhance the interaction between light in a coreless fiber (NCF) and its surrounding medium. This method proved to be highly effective for fabricating long-period fiber Bragg gratings (LPFBGs), offering a simple, fast, and cost-efficient approach. The resulting gratings exhibited Bragg wavelengths of 1539.585 nm at 1.6 W and 1553.373 nm at 3 W. Correspondingly, the grating periods (Λ) were measured to be 118.00 µm and 161.197 µm. These results demonstrate that increasing the laser power leads to an increase in both the grating period and the Bragg wavelength. The sucrose concentration various from 0 to 50%, the wavelength shifts into redshift (towards longer wavelength) when using this concentrations, best result obtained at 40%. The relation between the transmission wavelength and sucrose concentration for two NCF-LPFBG sensor (p = 1.6 W, 3 W) exhibited polynomial behaviour (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12596_2025_2775_Article_IEq1.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="85" /> </InlineMediaObject> <EquationSource Format="TEX">${R}^{2}=0.967)$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi>R</mi> </mrow> <mn>2</mn> </msup> <mrow> <mo>=</mo> <mn>0.967</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, and (<InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12596_2025_2775_Article_IEq2.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="85" /> </InlineMediaObject> <EquationSource Format="TEX">${R}^{2}=0.999)$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi>R</mi> </mrow> <mn>2</mn> </msup> <mrow> <mo>=</mo> <mn>0.999</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> respectively with sensitivities of (0.272 nm/%), and (0.348 nm/%) respectively were obtained. Based on the results, the second NCF-LPFBG sensor fabricated with a 3 W laser power demonstrated superior performance. It exhibited a larger wavelength shift of 16.05 nm compared to 14.83 nm for the first sensor (1.6 W), indicating higher sensitivity. The novelty of this research lies in the variation of the CO2 laser power for each sensor within the NCF type, as well as the successful application of the point-by-point technique directly in the NCF structure..

Fabrication long period fiber Bragg grating based on no-core fiber for sucrose concentration sensing

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发表日期：

2025年5月24日

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Nidaa L. Mahgoob,
Anwaar A. Al-Dergazly

摘要

Basic principles of fibre Bragg grating (FBG) based sensor utilize in different applications for temperature, humidity, refractive index, and strain. Most optical fibre sensor devices today construct utilize fibre Bragg grating technology. In this study we have inscribed two long period fibre Bragg grating (LPFBG) experimentally, and used these two LPFBG as sensors for measure sucrose concentration. i.e. for refractive index sensing. It’s fabricated by using a short segment of no core fibre (NCF) and the carbon- dioxide (CO₂) laser. A point-by-point technique was employed using varying laser power levels (1.6 W and 3 W) to enhance the interaction between light in a coreless fiber (NCF) and its surrounding medium. This method proved to be highly effective for fabricating long-period fiber Bragg gratings (LPFBGs), offering a simple, fast, and cost-efficient approach. The resulting gratings exhibited Bragg wavelengths of 1539.585 nm at 1.6 W and 1553.373 nm at 3 W. Correspondingly, the grating periods (Λ) were measured to be 118.00 µm and 161.197 µm. These results demonstrate that increasing the laser power leads to an increase in both the grating period and the Bragg wavelength. The sucrose concentration various from 0 to 50%, the wavelength shifts into redshift (towards longer wavelength) when using this concentrations, best result obtained at 40%. The relation between the transmission wavelength and sucrose concentration for two NCF-LPFBG sensor (p = 1.6 W, 3 W) exhibited polynomial behaviour ( ${R}^{2}=0.967)$ $R^{2} = 0.967)$ , and ( ${R}^{2}=0.999)$ $R^{2} = 0.999)$ respectively with sensitivities of (0.272 nm/%), and (0.348 nm/%) respectively were obtained. Based on the results, the second NCF-LPFBG sensor fabricated with a 3 W laser power demonstrated superior performance. It exhibited a larger wavelength shift of 16.05 nm compared to 14.83 nm for the first sensor (1.6 W), indicating higher sensitivity. The novelty of this research lies in the variation of the CO₂ laser power for each sensor within the NCF type, as well as the successful application of the point-by-point technique directly in the NCF structure.