Technical Note:
Getting the Most from Your Single-Mode-Fiber Aligner

Coupling light into an optical fiber can be one of the most demanding applications for optomechanical hardware. Using poorly constrained or unstable positioners often leads to time-consuming alignment processes, drift, and reduced coupling efficiencies.

Efficient coupling into single-mode (SM) fibers requires five degrees of adjustability with sub-micron resolution and, so you don’t need to keep realigning your system, good long-term stability. We tested our Model 9091 single-mode-fiber positioner over a 34-hour period and saw less than 1 µm of drift, which means that once you align it, it will stay aligned.

Built using kinematic principles, our Model 9091 and Model 9016 multi-mode fiber aligners have exactly five degrees of freedom and one constraint. This unique design eliminates the need for sliding and rolling elements that add instability and hysteresis. For less demanding or multimode fiber applications, our Model 9095 fiber launcher gives you five degrees of freedom at a bargain price.

In order to efficiently couple light into an optical fiber, it is also important to focus most of the light onto the fiber’s core. This requires that the focused beam diameter matches the modal-field diameter of the fiber, which is often just a little larger than the actual fiber-core diameter.

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Stability data: The coupling efficiency of a HeNe laser into a single-mode fiber using our Model 9091 five-axis fiber aligner remains within 10% over 34 hours. Long-term drift is less than 1 µm.

Product Tutorial

Using Your Model 9091 Fiber Aligner

With this aligner, the X and Y positions are actuated by side-mounted screws. An extra pair of X–Y adjustments provides fine resolution by turning the coarse-adjustment screws via a cam.

The fiber end is mounted at the fourth corner of a square formed with three adjustment screws. Turning all three screws the same amount results in pure translation in the Z direction. Turning two adjacent screws provides pure tilt.

To simplify tilt and Z motion in this fiber positioner, we added a knob to the center screw (see figure). This knob is attached to a planetary gear that couples the motion of the three screws. Turning the knob turns all three screws simultaneously, giving you Z translation. Keeping one of the two outer screws stationary (with an Allen-key) while turning the knob causes the two remaining screws to turn and tilt the fiber end.

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Keeping one of the two outer screws stationary with an Allen-key while turning the knob causes the remaining screws to turn, tilting the fiber end.