Selection of distributed fiber optic sensors

1.Does OFDR equipment use ordinary optical fibers as sensors?

Yes, all types of single-mode fiber can be used directly.

2.How much do these optical fibers cost?

Various single-mode optical fibers range in price from a few cents per meter to tens, hundreds or even thousands of dollars per meter. The selection mainly depends on the test scenario and needs. For example, if you want to measure strain, you can choose bare fiber and tightly sheathed fiber; if you want to measure temperature, you can choose PI fiber within 350℃, aluminum-coated fiber within 400℃, and gold-plated fiber within 700℃.

3.To measure strain, please recommend an optical fiber sensor for me.

To measure strain, we most commonly use polyimide optical fiber (PI fiber for short) and weak reflection fiber grating array in the laboratory. If the test environment is complex, to ensure the survival of the optical fiber, a tight-sheath optical fiber can be selected.

4.What is PI fiber?

Usually optical fiber has a three-layer structure, from the inside to the outside, they are the core, the cladding and the coating. The coating layer has different materials. For example, the coating layer of ordinary single-mode optical fiber is made of acrylic resin, and the coating layer of PI optical fiber is made of polyimide (PI). Both types of single-mode optical fibers can be demodulated using OFDR equipment, but PI optical fiber sensing has better measurement results and is used more often.

5.What are the specific differences between these two types of optical fiber strain tests?

Compared with acrylic-coated optical fiber, PI optical fiber coating material is harder, has a larger elastic modulus, and has better strain transmission effect. In addition, PI optical fiber can also be used for high temperature measurement within 350°C, and the temperature measurement linearity is also very good.

5. You just talked about a fiber Bragg grating sensor. What is it specifically?

Usually the full name is weak reflection fiber grating array, which is a densely distributed weak reflection fiber grating on an optical fiber, and its reflectivity is usually less than 0.1%. Common weak gate arrays include: one gate of 1cm, the length of the gate area is 9mm, and the distance between two adjacent FBGs is 1mm. The preparation process of the weak grating array is the drawing tower online grating technology, which does not need to peel off the coating layer, and the mechanical strength of the optical fiber is high. In addition, weak grid arrays of the same wavelength can be demodulated using OFDR equipment to achieve highly stable, high-resolution, distributed strain temperature measurement.

6.What is fiber Bragg grating sensor specifically?

Usually the full name is weak reflection fiber grating array, which is a densely distributed weak reflection fiber grating on an optical fiber, and its reflectivity is usually less than 0.1%. Common weak gate arrays include: one gate of 1cm, the length of the gate area is 9mm, and the distance between two adjacent FBGs is 1mm. The preparation process of the weak grating array is the drawing tower online grating technology, which does not need to peel off the coating layer, and the mechanical strength of the optical fiber is high. In addition, weak grid arrays of the same wavelength can be demodulated using OFDR equipment to achieve highly stable, high-resolution, distributed strain temperature measurement.

7.Is there any difference between weak grid array and ordinary fiber optic sensing testing?

Generally speaking, the weak grating array has higher Rayleigh scattering signal than ordinary single-mode fiber, so it has good test stability and strong anti-interference ability. It is more suitable for quasi-dynamic measurement, environment with slight vibration or fiber shaking, and can further improve the test Stability and anti-interference ability.

8.What is the test effect of tight-sheath optical fiber, and how to select it?

OFDR equipment sensing indirectly reflects the strain of the structure by measuring the strain of the optical fiber laid on the structure. In order to achieve structural strain measurement, the optical fiber sensor needs to be embedded inside the structure or pasted on the surface of the structure. From the analysis of the strain transmission path, the strain transmission effect of bare fiber is more ideal than that of tight-sheathed optical fiber. The smaller the diameter of tight-sheathed optical fiber, the smaller the strain transmission loss and the better the strain measurement effect. Conventional types of tight-sheathed optical fibers include: 0.9mm diameter, 2mm diameter, and armored optical cables with larger diameters. It is usually recommended to give priority to tight-sheathed optical fibers with small diameters as sensors.