Polarization maintaining fiber: Polarization maintaining fiber transmits linearly polarized light, which is widely used in various fields of national economy such as aerospace, aviation, navigation, industrial manufacturing technology and communications. In the interferometric fiber sensor based on optical coherent detection, the use of polarization-maintaining fiber can ensure that the linear polarization direction remains unchanged, improve the coherent signal-to-noise ratio, and achieve high-precision measurement of physical quantities. As a special type of optical fiber, polarization maintaining fiber is mainly used in sensors such as fiber optic gyroscopes, fiber optic hydrophones, and fiber optic communication systems such as DWDM and EDFA. Because fiber optic gyroscopes and fiber optic hydrophones can be used for military inertial navigation and sonar, they are high-tech products, and polarization-maintaining fiber is its core component, so polarization-maintaining fiber was once included in the list of embargoes against China by western developed countries. Now some domestic optical fiber production companies can produce it.
In the drawing process of polarization-maintaining fiber, due to the structural defects generated inside the fiber, the polarization-maintaining performance will be reduced, that is, when linearly polarized light is transmitted along a characteristic axis of the fiber, part of the optical signal will be coupled into another perpendicular to it. The characteristic axis ultimately causes the polarization extinction ratio of the output polarized light signal to decrease. This defect affects the birefringence effect in the fiber. In the polarization maintaining fiber, the stronger the birefringence effect, the shorter the beat length, and the better the polarization state of the transmitted light is maintained .
Even if an ordinary optical fiber is manufactured symmetrically, it will be mechanically stressed and become asymmetric in practical applications, resulting in birefringence. Therefore, the polarization state of light will change irregularly when transmitted in an ordinary optical fiber. The main influencing factors are wavelength, curvature, temperature and so on.
Polarization maintaining fiber can solve the problem of polarization state change, but it cannot eliminate the birefringence phenomenon in the fiber. On the contrary, the design of the fiber geometry can produce a stronger birefringence effect to eliminate the stress on the polarization state of the incident light. Impact.
Therefore, polarization-maintaining fibers are generally used in applications that are more sensitive to polarization, such as interferometers, or lasers, or in the connection between a light source and an external modulator, and so on.
