As a new type of passive device, fiber grating (FBG) has successfully opened up a new path for optical communication and optical sensing, and since the application of fiber grating technology, this technology has been rapidly developed in the field of optical fiber sensing technology and high-speed optical fiber communication. However, in the field of optical sensing, the polarization effect has the advantages of fast response speed and high efficiency, and the polarization sensitivity characteristics of optical fibers can be used for sensing, and the ultrafast polarization response characteristics of the device can be used for all-optical signal processing, which makes the research on polarization correlation characteristics very meaningful.
Polarization-dependent losses are measured when FBG is pressurized
The schematic diagram of the test loading device is shown in Figure 1, the test is carried out with an optical vector analyzer (OCI-V), the measurement mode is reflective measurement, and the polarization dependent loss (PDL) of FBG reflection can be obtained in one scan, and the center wavelength of the tested FBG is 15480-1548.At 3nm, the pressure loading device is to place the FBG flat between the two steel plates, place an optical fiber of the same diameter in the parallel position of the FBG to ensure that the FBG is balanced under pressure, and place weights of different weights on the upper steel plate for loading, which are 1kg, 2kg, 4kg, 6kg and 10kg respectively.
Figure 1Schematic diagram of the test loading device.
Figure 2PDL test charts of A-0KN, B-10KN, C-20KN, D-40KN, E-60KN, and F-100KN.
Figure 2 is the test chart under different pressures, from which it can be seen that the PDL of the optical band near the center wavelength tends to zero when there is no pressure, and two peaks appear at both ends near the center wavelength after the pressure is applied (the position of the circle in the figure), as the pressure gradually increases, the peak value of the wave becomes larger and larger, and the peak value of the wave appears when the pressure reaches 60kN, and with the increase of pressure, the two peaks gradually approach, and the flat area where the middle PDL tends to zero gradually shrinks. When the pressure reaches 100 kN, the crest is distorted, the crest height is reduced, and the middle PDL flat area disappears.
In summary, it is found that the pressure will have a great impact on the PDL near the center wavelength of FBG, and with the increase of pressure, the peak value of the PDL at both ends of the center wavelength gradually increases, and the smaller area of PDL gradually decreases until it disappears, and the PDL in the band near the center wavelength will be distorted when the pressure is too large. The polarization-dependent loss of FBG can be quickly measured through OCI-V, and the performance of FBG can be judged by its polarization-related characteristics, which provides a judgment standard for whether it can accurately carry out communication transmission and optical sensing.
Optical vector analysis system OCI-V
OCI-V is an optical vector analysis system that quickly detects related parameters such as optical loss, dispersion, and polarization.