PM Fiber Measurements Used to Align Incident Polarization State (Viewer Inspired)| Thorlabs Insights

Polarization-maintaining (PM) fiber can only preserve the polarization state of input light that is both linearly polarized and correctly aligned to one of the two PM fiber's axes. Due to this, setups for coupling light into a PM fiber often include a linear polarizer and some means for rotating the orientation of the input polarization state. This Video Insight demonstrates two methods for aligning linearly polarized input light. The first approach uses a polarimeter, and the second uses a linear polarizer in front of a power sensor. Both approaches require smoothly increasing or decreasing the fiber’s birefringence, which is accomplished in this Video Insight by heating or cooling the fiber.

When coupling light into PM fiber, it is important to first align the system to achieve maximum coupling efficiency, as previously shown for FiberBenches (    • Align FiberPorts on a FiberBench (Vie...   ) and for fiber collimators (    • Align Fiber Collimators to Create Fre...   ). The next step is to use one of the methods demonstrated in this Video Insight to ensure the input light is linearly polarized and oriented parallel with either the slow or the fast axis of the PM fiber. This alignment enables the PM fiber to preserve the input polarization state, since the light travels along only one of the fiber's axes.

Both polarimeter and analyzing polarizer methods measure the PM fiber's optical output. This video shows that better alignment corresponds with the polarimeter data tracing smaller circles around a point on the Poincaré sphere’s equator. These data are shown alongside and compared with measurements of the optical power transmitted through an appropriately oriented linear polarizer. Better alignment corresponds to smaller-amplitude power oscillations. The video also includes a brief discussion of PM fibers and an introduction to relevant features on the Poincaré sphere.

Additional PM Fiber information:
https://www.thorlabs.com/newgrouppage...

00:00 Introduction
01:20 PM Fiber and Light
04:16 Beam Path
04:53 Poincaré Sphere Features
05:55 Add Linear Polarizer to FiberBench
06:40 Align using Polarimeter
09:02 Power Meter Alignment Background
10:52 Optimize Analyzing Polarizer Orientation
12:03 Align using Power Meter
12:52 Comments on the Two Approaches

Components used in this Demonstration Include:
- LP660-SF50 Pigtailed 660 nm Laser Diode: https://www.thorlabs.com/newgrouppage...
- ITC4001 Laser Diode and TEC Controller: https://www.thorlabs.com/newgrouppage...
- LDM9LP Pigtailed Laser Diode Mount: https://www.thorlabs.com/newgrouppage...
- FB-76 FiberBench (One Axis): https://www.thorlabs.com/newgrouppage...
- HCA3-SM1 FiberBench Wall Plate (FiberPort Compatible): https://www.thorlabs.com/newgrouppage...
- PAF-X-2-A FiberPort: https://www.thorlabs.com/thorproduct....
- FBR-LPVIS Rotating Linear Polarizer: https://www.thorlabs.com/newgrouppage...
- WPHSM05-670 Half-Wave Plate Ø0.5”: https://www.thorlabs.com/newgrouppage...
- FBRP Rotation Mount, FiberBench Design: https://www.thorlabs.com/newgrouppage...
- FB-51 FiberBench (One Axis, Used to Hold Components): https://www.thorlabs.com/newgrouppage...
- PTC1/M Temperature-Controlled Breadboard: https://www.thorlabs.com/newgrouppage...
- PAX1000VIS Polarimeter: https://www.thorlabs.com/newgrouppage...
- CLR1 Rotatable Lens Mount, Ø1: https://www.thorlabs.com/newgrouppage...
- F240APC-B Fiber Collimator for FC/APC Connectors : https://www.thorlabs.com/newgrouppage...
- AD12F Threaded Adapter (Collimator to Mount)): https://www.thorlabs.com/newgrouppage...
- LMR1 Lens Mount: https://www.thorlabs.com/newgrouppage...
- WG41010 Optical Window: https://www.thorlabs.com/newgrouppage...
- Linear Polarizer: https://www.thorlabs.com/navigation.c...
- S120C Power Sensor: https://www.thorlabs.com/newgrouppage...
- PM400 Optical Power Meter: https://www.thorlabs.com/newgrouppage...
- Single Mode Fiber Patch Cables: https://www.thorlabs.com/navigation.c...
- PM Fiber Patch Cables: https://www.thorlabs.com/navigation.c...

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