Views: 430 Author: Site Editor Publish Time: 2022-01-23 Origin: Site
What is Polarization Maintaining Optical Fiber?
Polarization Maintaining Optical Fiber (PMF, Polarization Maintaining Optical Fiber) is a special fiber that overcomes the influence of environmental factors on the polarization state in the fiber during transmission by increasing the inherent birefringence properties of the fiber, and maintains the polarization state of the light wave transmitted in the fiber. In the field of optical fiber communication, the stability and communication capacity of the optical transmission system can be improved, and the error caused by polarization coupling in the optical path can be significantly reduced in the optical fiber sensing system.
Polarization Maintaining Optical Fiber Classification
Polarization maintaining optical fibers generally include geometric olarization maintaining optical fibers and stress polarization maintaining optical fibers. Geometric polarization maintaining optical fibers are mainly elliptical core polarization maintaining fibers, which are used in some special application fields.
The stress-type polarization-maintaining fibers mainly include panda-type, oval-type, butterfly-type and bow-tie polarization-maintaining fibers.
Panda-type polarization-maintaining fiber has natural advantages in the performance of the fiber, whether it is birefringence, geometric characteristics, structural symmetry or longitudinal uniformity of the fiber. At the same time, because the manufacturing process of panda-type polarization-maintaining fiber does not need to be completed in one step , Independently manufacturing each component can effectively control the structure and composition of the optical fiber, which can ensure that each preform can be drawn into a uniform polarization-maintaining optical fiber product with a length of tens of kilometers or even more than 100 kilometers, which is suitable for mass production. Therefore, the panda type is commonly used in China. Polarization maintaining fiber.
What are the parameters of polarization maintaining fiber?
01 Fast and slow axes
Two stress regions with different expansion coefficients from the fiber cladding are made on both sides of the single-mode fiber core. During the drawing process of the fiber preform, the fiber rapidly drops from high temperature to low temperature. During the cooling process, 2 A stress zone shrinks, the amount of which is hindered by the surrounding quartz. The core of the fiber is pulled outward along the direction (x-axis) of the two stress regions, and there is a compressive stress in the direction orthogonal to it (y-axis), which produces stress birefringence in the core, forming 2 main axes that are orthogonal to each other.
The refractive indices in the two principal axis directions are different. In the direction of stress application, the effective refractive index of the fiber core is higher, and the light transmission speed is slower, becoming the slow axis, which is the principal axis of the polarization maintaining fiber. In the other direction, light travels faster, called the fast axis.
02 beat length
The beat length of the polarization-maintaining fiber represents the length of the optical fiber transmitted by the composite polarization state of the transmitted light in the polarization-maintaining fiber jumper to complete a periodical change.
Physically, the beat length reflects the corresponding fiber length Lp when the phase difference between the two linearly polarized modes of the fundamental mode changes from 0 to 2Π.
The shorter the beat length, the more elastic the fiber is to the polarization irregularity effect, and the stronger the fiber's ability to maintain polarization for linearly polarized light.
03 Extinction ratio
Extinction ratio is an index to measure the stability of polarization maintaining fiber performance.
When a beam of linearly polarized light is incident exactly along a certain optical axis of the polarization-maintaining device, the polarization mode will be excited on the orthogonal axis, and the power ratio of the two orthogonal axes is the extinction ratio.
What are the applications of polarization maintaining fiber?
Optical devices prepared from polarization-maintaining fibers are widely used in polarization multiplexing communications, lasers, polarization optical devices, polarization sensing, fiber optic gyroscopes, fiber optic hydrophones, and other fields such as polarization mode compensation.