Fiber Bragg Gratings are made by laterally exposing the core of a single-mode fiber to a periodic pattern of intense laser light. The exposure produces a permanent increase in the refractive index of the fiber’s core, creating a fixed index modulation according to the exposure pattern. This fixed index modulation is called a grating.
At each periodic refraction change a small amount of light is reflected. All the reflected light signals combine coherently to one large reflection at a particular wavelength when the grating period is approximately half the input light’s wavelength. This is referred to as the Bragg condition, and the wavelength at which this reflection occurs is called the Bragg wavelength. Light signals at wavelengths other than the Bragg wavelength, which are not phase matched, are essentially transparent. This principle is shown in Figure 1.
Therefore, light propagates through the grating with negligible attenuation or signal variation. Only those wavelengths that satisfy the Bragg condition are affected and strongly back-reflected. The ability to accurately preset and maintain the grating wavelength is a fundamental feature and advantage of fiber Bragg gratings.
The central wavelength of the reflected component satisfies the Bragg relation: λBragg = 2nΛ, with n the index of refraction and Λ the period of the index of refraction variation of the FBG. Due to the temperature and strain dependence of the parameters n and Λ, the wavelength of the reflected component will also change as function of temperature and/or strain, see Figure 2. This dependency is well known what allows determining the temperature or strain from the reflected FBG wavelength.
關于聚華科技
杭州聚華光電科技有限公司是一家基于物聯網光纖傳感器技術從事土木工程結構健康監測與預警管理的高新技術企業，聚華是專業的光纖光柵傳感器產品提供商和土木工程結構健康監測一站式解決方案優質合作伙伴。公司專注于橋梁、隧道、邊坡、基坑、地鐵、礦山、電力等土木工程領域的結構健康監測相關產品的研發、生產、推廣與應用，以提供野外光纖傳感器自動化監測產品、工程結構安全監測一站式解決方案見長。主要以光纖光柵傳感器技術、分布式光纖測溫技術、工程安全自動化云計算軟件、工程化專業領域數據分析為技術核心。www.hzjzgcls.com
At each periodic refraction change a small amount of light is reflected. All the reflected light signals combine coherently to one large reflection at a particular wavelength when the grating period is approximately half the input light’s wavelength. This is referred to as the Bragg condition, and the wavelength at which this reflection occurs is called the Bragg wavelength. Light signals at wavelengths other than the Bragg wavelength, which are not phase matched, are essentially transparent. This principle is shown in Figure 1.
Figure 1: Working principle of FBG
Therefore, light propagates through the grating with negligible attenuation or signal variation. Only those wavelengths that satisfy the Bragg condition are affected and strongly back-reflected. The ability to accurately preset and maintain the grating wavelength is a fundamental feature and advantage of fiber Bragg gratings.
The central wavelength of the reflected component satisfies the Bragg relation: λBragg = 2nΛ, with n the index of refraction and Λ the period of the index of refraction variation of the FBG. Due to the temperature and strain dependence of the parameters n and Λ, the wavelength of the reflected component will also change as function of temperature and/or strain, see Figure 2. This dependency is well known what allows determining the temperature or strain from the reflected FBG wavelength.
Figure 2: FBG response as function of strain
關于聚華科技
杭州聚華光電科技有限公司是一家基于物聯網光纖傳感器技術從事土木工程結構健康監測與預警管理的高新技術企業，聚華是專業的光纖光柵傳感器產品提供商和土木工程結構健康監測一站式解決方案優質合作伙伴。公司專注于橋梁、隧道、邊坡、基坑、地鐵、礦山、電力等土木工程領域的結構健康監測相關產品的研發、生產、推廣與應用，以提供野外光纖傳感器自動化監測產品、工程結構安全監測一站式解決方案見長。主要以光纖光柵傳感器技術、分布式光纖測溫技術、工程安全自動化云計算軟件、工程化專業領域數據分析為技術核心。www.hzjzgcls.com