What types of polarization-maintaining fibers are there?

Polarization-Maintaining Fiber (PMF) can be divided into several main types based on its structural design. Each type of polarization-maintaining fiber has its own characteristics and applicable scenarios. The following are common types of polarization-maintaining fibers:

Stress-induced polarization-maintaining fiber:

PANDA polarization-maintaining fiber: This fiber gets its name from its cross-sectional shape that resembles a panda’s face, with two symmetrically distributed stress rods surrounding the core. It produces a birefringence effect by adding stress rods on both sides of the core, thereby maintaining the polarization state of light.

Bow-tie polarization-maintaining fiber: The cladding of this type of fiber is shaped like a bow tie, and non-circular cladding geometry is used to introduce birefringence.

Elliptical core or elliptical cladding type polarization-maintaining fiber:
These fibers achieve birefringence by making the core or cladding elliptical. The major and minor axes of the ellipse provide different refractive index paths, so that the two orthogonal polarization modes have different propagation constants, thereby achieving polarization state maintenance.
Side-hole or Depressed cladding polarization-maintaining fiber:
Side-hole or Depressed cladding polarization-maintaining fiber usually creates grooves next to the core or reduces the refractive index in certain areas to create additional stress points and enhance the birefringence effect.
Polarization-maintaining fiber in photonic crystal fiber (PCF):
Photonic crystal fiber is a fiber with a periodic array of air holes. By adjusting the arrangement of these holes, birefringence can be introduced without changing the shape of the core, thereby achieving the purpose of polarization maintenance.
Double-clad polarization-maintaining fiber:
Double-clad fiber is mainly used in high-power laser transmission applications, where the inner cladding is used to guide the pump light, while the outer cladding provides mechanical protection and support. When it comes to polarization control, polarization-maintaining properties can be added to the double-cladding structure, such as by embedding stress rods in the double cladding.
Other special designs:
With the development of technology, researchers continue to explore new materials and technologies to improve the performance of polarization-maintaining fibers, such as using new glass formulations, nanostructures, etc. to meet specific application requirements.
The type of polarization-maintaining fiber you choose depends on the requirements of the specific application scenario, such as the required wavelength range, insertion loss, extinction ratio, return loss, etc. In addition, for some precision measurement systems, you may also need to consider aspects such as temperature stability and bending sensitivity.

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