Align Fiber Collimators to Create Free Space Between Single Mode Fibers
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 is single mode. Some differences in collimator designs, and their effects on the characteristics of the collimated beams, are also discussed.
Components used in this demonstration include a fiber-coupled laser, triplet fiber optic collimators, kinematic mounts, an adapter between each mount and collimator, a power sensor, a SM1 thread adapter for the power sensor, a fiber adapter cap with SM1 threads, a power meter, fiber optic patch cables (FC/PC single mode, hybrid single mode, and step-index multimode), a fiber connector cleaner, storage reels for fiber patch cables, 2" posts, and 0.5" post holders.
Date of Last Edit: April 1, 2021