Optical fiber sensing technology based on Bragg gratings has received extensive attention and research by scientists since the 1990s. Although large-scale, fast and cheap grating production technology and its technology are mature, more expensive optical demodulation devices still limit its extensive application in a series of important fields such as industrial, chemical and building structure inspection. In addition, compared with the traditional optical domain demodulation method, the optical filter is used to convert the drift of the grating wavelength into the change of the power. The demodulation method has some advantages such as low cost, simplicity and fast response. However, the detection method of the traditional linear edge filter has been limited by the disadvantage of the smaller demodulation wavelength range (1-20 nm), making it difficult to apply it in distributed sensing.
In response to the above questions, the research group led by Associate Professor Xia Li of Wuhan Optoelectronics National Laboratory, School of Optics and Electronic Information, designed a demodulation method based on cross-gaussian filter (Figure 1). In the demodulation side, two Gaussian eigen filters with a certain center misalignment are used to make the power response curves of both ends have the same dislocation Gaussian features. Using power-difference detection, it is just a matter of converting a linear Bragg wavelength to power difference (Figure 2). And, the slope of their linear relationship can be easily adjusted by controlling the size of the misalignment between the filters. Because this method does not rely on the linear area of ​​the filter for linear measurements as traditional methods do, it has the potential to be of great advantage in the wavelength range of a demodulatable Bragg grating. Depending on the current state of the art in which Gaussian filters are made, a wavelength range of several hundreds or even thousands of nanometers of the demodulator can be achieved. In addition, this method has very flexible and adjustable sensitivity and measuring range, so it has good adaptability to different measurement application requirements. It can be predicted that this method has a very good application prospect in the field of Bragg grating sensing.
The research result "Wavelength interrogation fiber Braggingrating sensors on crossed optical microscopes" was published on Optics Letters (Vol. 40, Iss. 8, pp. 1760-1763) on April 15,
This work was supported by the 863 Project "Convergence and Innovation Demonstration Network Based on Telecommunication Network" (Project No. 2011AA01A110) and the Independent Innovation Research Fund of Huazhong University of Science and Technology (2014TS042).
Figure 1: Cross-Gaussian filter demodulation Bragg grating structure diagram
Figure 2: (a): The power of both ends of the grating with Bragg grating wavelength curve. (B): The result of subtracting the power curve at both ends
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