Fiber grating distributed strain sensor and strain monitoring method thereof

[0083] Embodiment 2, the networking system scheme based on wavelength division multiplexing is as follows Figure 4 Shown: where 1 is the light source module, using figure 1 The tunable laser 11 used in the structure is formed by connecting the acousto-optic modulator 12 and the radio frequency modulator 13 to output an optical pulse sequence. 2 is an optical connector. 3 for figure 1 Fiber optic ring in the structure. 411, 412, 413, 414...41r are cascaded fiber grating sequences connected to the ring-down cavity through the circulator 33. figure 1 The fiber grating sensing unit 4 in the structure is the same, and the other fiber gratings are sequentially cascaded and welded behind the 411 fiber grating. Through this structure, distributed strain sensing within the grating area of ​​multiple fiber gratings can be realized. The distributed strain demodulation method in the grating area of ​​each fiber grating is exactly the same as the process in the above-mentioned experimental principle. Net, greatly reducing the cost of sensors. In this structure, two points to note are:

[0084] 1. All cascaded fiber gratings can be selected as LCFBG or FBG, but the reflection spectra of all fiber gratings cannot be overlapped. Fiber gratings with different reflection wavelengths can be selected in turn within the tuning range of the tunable laser 11 at appropriate intervals as the network transmission. Sense element

[0085] 2. The reflectivity of all fiber gratings should be as consistent as possible, so that there is no need to individually adjust the gain compensation of the EDFA in the cavity for each fiber grating sensing unit, so that the measurement speed is fast and automatic real-time measurement is realized. In actual use, all cascaded fiber gratings can be made into fiber gratings with reflectivity> 99%, and this is easy to achieve in the manufacturing process.

[0086] Embodiment 3, a networking system scheme based on wavelength division multiplexing and time division multiplexing, such as Figure 5 Shown: where 1 is the light source module, and Figure 4 The light source used in the structure is the same. 31, 32, ..., 3j is like figure 1 The fiber optic ring formed in the structure. 411, 412, ... 41r; 421, 422, ... 42r; ...; 4j1, 4j2, ..., 4jr are the cascaded fiber grating sequence groups connected to the fiber ring 31, 32 ... 3j respectively, each level The construction method of connected fiber grating sequence is the same as Figure 4 The construction method in the WDM structure is the same. Each fiber ring and the corresponding cascaded fiber grating sequence constitute a measurement channel, 2 is the s-channel light switch, the number of light switches can reach 16 or even 32 channels, and the light switch is used to select one channel at a time. Which one needs to be measured? The strain distribution of a cascaded fiber grating sequence connects the corresponding channel. Similarly, in this structure, the issues that need attention in the construction rules of the cascaded fiber grating sequence of each channel are the same as Figure 4 The shown WDM networking system scheme is the same, but the fiber grating spectra between different channels can overlap. Through the networking of this scheme, the number of fiber grating access can be increased, the sensing range is further expanded, and the cost of the sensor is further reduced.

[0087] Since multiple fiber grating sensing units are needed in the networking, and in each channel, the reflection spectra of all fiber grating sensing units cannot overlap, therefore, the superimposed spectral width of all sensing units will follow the transmission As the number of sensing units increases, the EDFA noise in the ring-down cavity also increases. When the cavity optical noise increases, the quality of the light pulses circulating in the cavity decreases, and it is difficult to obtain a large number of high quality Cavity ring-down pulse sequence. Therefore, in the networking system, noise management is an issue that must be considered.

[0088] Example 4, Image 6 It is one of the performance optimization schemes of the network system structure, in the basic structure of distributed sensing figure 1 And networking structure Figure 4 On the basis of adding a filter denoising function module, it mainly draws the access scheme of the filter denoising function module, and the other parts not shown are consistent with the aforementioned scheme. A filter fiber grating 8 is connected through the second optical circulator 34 in the ring-down cavity. Along the transmission direction of the light pulse in the ring-down cavity, the second optical circulator 34 is connected after the first fiber circulator 33. The filter fiber grating 8 is fixed on the stress tuning or temperature tuning device, and is connected to the tunable laser 11 through the automatic synchronization trigger device 9 to keep the output wavelength of the light source consistent with the central reflection wavelength of the filter fiber grating 8 to reduce the spontaneous radiation noise of the EDFA Filter out. Through this noise management scheme, the distributed sensing effect of each sensor unit FBG in the networking system can be optimized.