Why PM Fiber Requires Linearly Polarized Light Aligned to an Axis | Thorlabs Insights Topic Focus

Polarization-maintaining (PM) fiber is a type of single mode fiber designed to maintain linearly polarized light, under the condition the input light is linearly polarized AND the linear polarization is aligned to either the fast or slow polarization axis of the fiber.

Single mode fiber naturally guides two perpendicular polarization states, which in theory should remain perfectly in phase. In real-world single mode fibers, manufacturing imperfections and stress-related perturbations create unpredictable amounts of birefringence and phase shift. In addition, it is relatively easy for light to be exchanged between polarization states. Due to this, standard single mode fibers will not maintain the light’s input polarization state.

Structures embedded in PM Fibers create stress on the core that increases the birefringence and suppresses the transfer of light between orthogonal polarization states. Because of this, PM fibers are effective at maintaining polarization, but only when the input light is linearly polarized and aligned with one of the fiber’s two polarization axes.

0:06 Polarization in SM Fiber
0:46 A Look Inside PM Fiber
1:15 Why Input Linear Polarization

To watch a video demonstrating an approach used to align input linearly polarized light to a PM fiber’s axis, click:    • PM Fiber Measurements Used to Align Incide...  

For more photonics how-to videos, visit: https://www.thorlabs.com/newgrouppage...