How does the Model 9091 fiber aligner work?
This single-mode fiber aligner operates differently than others on the market because it incorporates the "kinematic" principle in its design. Thus, it has exactly only one constraint and five actuators for each independent degree of freedom. Adjust the aligner's X and Y positions using two side-mounted screws. An extra pair of X-Y adjustments provides fine resolution by turning the coarse-adjustment screws via a cam, maintaining the kinematic design. 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 axis. Turning two adjacent screws provides pure tilt. To simplify tilt and Z motion in the positioner, we added a knob to the center screw. The center screw 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 still with an Allen key while turning the knob causes the two remaining screws to turn and tilt the fiber end.
How do I optimize the coupling efficiency when using the Model 9091 fiber aligner?
Efficient coupling into single-mode fibers requires five degrees of adjustability with sub- micron resolution and, if you don't want to keep realigning your system, good long-term stability. Built using kinematic principles, our Model 9091 and Model 9016 fiber positioners have exactly five degrees of freedom and one constraint. In order to couple light efficiently into an optical fiber, it is important not only to adjust the position of the fiber with precision and stability but also to focus most of the light onto the fiber's core. This requires that the diameter of the focused beam matches the diameter of the fiber's modal-field, which is often just a little larger than the actual fiber-core diameter.
To match these diameters, you will want to use a lens with an approximate focal length of f, where f=[d x D x π]/ [4 x l] and d is the modal field diameter of the fiber (also the beam diameter at the focus), D is the 1/e2 diameter of the collimated beam, and l is the wavelength. When focusing into a fiber, be sure that the numerical aperture (NA) of the focused beam is smaller than the NA of the fiber to maximize coupling efficiency. If you are collimating a beam from a fiber, you also need to make sure the NA of the lens is larger than that of your fiber or diode so that you are capturing all the available light. This analysis will give you a good estimate, but you may find that you need to try a few lenses to get optimum focusing.
Is there any data on the long-term stability of the Model 9091 fiber aligner?
We tested our Model 9091 single-mode fiber positioner over a 34-hour period and saw less than 1 µm of drift. We used a 4-micron core fiber at 633 nm. The lens was optimized to match the beam input mode diameter to the fiber modal diameter.