Since the 1990s, fiber Bragg grating-based fiber sensing technology has received extensive attention from scientists, and a lot of research has been carried out. Although the large-scale, fast and cheap grating manufacturing technology and its technology have matured at present, the relatively expensive optical demodulation equipment still limits its wide application in a series of important fields such as industry, chemical industry and building structure inspection. In addition, compared with the traditional optical domain demodulation method, the demodulation method that uses optical filters to convert the grating wavelength drift into a change in power has the advantages of being cheap, simple, and fast in response.

Previously, the research group led by Xia Li, an associate professor in the Department of Optical Communications and Optical Networks, used a cross-Gaussian filtering method to realize the fiber demodulation of the optical fiber gratings. 1763). With the deepening of research, it is found that there are still two shortcomings in this method: one is the need to add two additional Gaussian filter features, which increases the complexity of the system; the other is that the power spectral density of the wide-spectrum light source used is small , Making the sensing demodulation distance and range limited.

Therefore, in the recent work, the research team further designed a weak fiber grating sensing array demodulation method based on the incidence of dual-wavelength narrow linewidth lasers (Figure 1). At the input of the demodulation system, two lasers with a certain center wavelength interval are incident. Utilizing the Gaussian spectral characteristics of the weakly reflecting fiber grating and detecting the power difference, a linear Bragg wavelength to power difference conversion can be obtained (Figure 2). And the slope of their linear relationship can be adjusted simply by controlling the wavelength interval of the dual-wavelength laser. This method does not require filter characteristics like the Gaussian matched filtering method, so the entire demodulation system is relatively simple. According to the current narrow linewidth laser, the output power of the light source can easily reach more than 10 dBm. This method can support sensing demodulation distances of up to 50 km and up to one optical fiber without relay amplification. The effect of demodulation of hundreds of weak inverse gratings simultaneously. It can be predicted that this method will have very good application prospects in various fields of Bragg grating quasi-distributed sensor networks.