The commonly used method of introducing high birefringence can be achieved by introducing geometrically symmetrical non-uniform stress into the fiber core of the preform, by adding two stress rods of modified glass components on both sides of the core.
Stressed polarization-maintaining optical fiber mainly relies on the difference in the thermal expansion coefficient of the embedded stress rod and the fiber core to generate thermal stress. Under the action of thermal stress, the refractive index of the material changes, resulting in a birefringence effect.
Another solution is to use an elliptical core, the elliptical shape itself produces a certain degree of shape birefringence even in the absence of mechanical stress.
The structure of polarization maintaining fiber:
Elliptical cladding type, bow tie type and panda type are three types of polarization maintaining fibers that are widely used, and they all belong to stress type polarization maintaining fibers.
