Align Fiber Collimators to Create Free Space Between Single Mode Fibers | Thorlabs Insights

Two collimators, inserted into a fiber optic setup, provide free-space access to the beam. The first collimator accepts the highly diverging light from the first fiber and outputs a free-space beam, which propagates with an approximately constant diameter to the second collimator. The second collimator accepts the free-space beam and couples that light into the second fiber. Some collimation packages, including the pair used in this demonstration, are designed for use with optical fibers and mate directly to fiber connectors.

Ideally, 100% of the light emitted by the first fiber would be coupled into the second fiber, but some light will always be lost due to reflections, scattering, absorption, and misalignment. Misalignment, typically the largest source of loss, can be minimized using the alignment and stabilization techniques described in this video.

In this demonstration, the first fiber is single mode. The optical power incident on the second collimator, as well as the power output by the second fiber, are measured. When the second fiber is multimode with a 50 µm diameter core, alignment resulted in 91% of the power incident on the second collimator being measured at the fiber output. This value was 86% when the second fiber was single mode. Some differences in collimator designs, and their effects on the characteristics of the collimated beams, are also discussed.

For more information about the modified thin lens equation we used to model Gaussian beams, see
https://www.thorlabs.com/newgrouppage... .

00:00 - Introduction
00:41 - Characteristics of Collimated Beams
02:32 - Reduce Degrees of Freedom
03:46 - Baseline Power Measurement
04:37 - Coarse Alignment Using a Multimode Fiber
06:38 - Attach Single Mode Fiber to Second Collimator
08:28 - First Alignment Approach: Misalign & Maximize
10:02 - Second Alignment Approach: Misalign & Misalign

Components used in this demonstration include:
- S1FC635 Fiber-Coupled 635 nm Laser: https://www.thorlabs.com/newgrouppage...
- TC12FC-633 Triplet Fiber Optic Collimator: https://www.thorlabs.com/newgrouppage...
- KM100 Kinematic Mount: https://www.thorlabs.com/newgrouppage...
- AD12NT Adapter (Between Collimator and Mount): https://www.thorlabs.com/newgrouppage...
- S130C Power Sensor: https://www.thorlabs.com/newgrouppage...
- SM1A29 Thread Adapter (Gives Power Sensor SM1 Threads): https://www.thorlabs.com/newgrouppage...
- S120-FC Fiber Adapter Cap with SM1 Threads: https://www.thorlabs.com/newgrouppage...
- PM400 Power Meter: https://www.thorlabs.com/newgrouppage...
- P1-630A-FC-1 Single Mode FC/PC Patch Cable: https://www.thorlabs.com/newgrouppage...
- P5-630A-PCAPC-1 Single Mode Hybrid Patch Cable: https://www.thorlabs.com/newgrouppage...
- M42L01 Step Index Multimode Fiber Patch Cable: https://www.thorlabs.com/newgrouppage...
- FCC-7020 Fiber Connector Cleaner: https://www.thorlabs.com/newgrouppage...
- FSR3 Storage Reel for Patch Cables: https://www.thorlabs.com/newgrouppage...
- TR2 2" Post: https://www.thorlabs.com/newgrouppage...
- PH2 0.5" Post Holder: https://www.thorlabs.com/newgrouppage...

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