Micromachine Aligns Optical Fiber

Kevin Robinson

Aligning optical fibers in manufacturing production lines may soon become easier, thanks to an active fiber optic microaligner developed by The Boeing Co. in St. Louis. The prototype device is 4 mm square and 0.5 mm high, small enough to fit inside optical packages, reducing or eliminating the need for costly, obtrusive external alignment systems.
According to Larry Pado, manager of the Defense Advanced Research Projects Agency-sponsored project, packaging optical components consumes 40 to 50 percent of their total cost. Aligning fiber optics to laser diodes in devices such as repeaters and optical switches is labor-intensive if done manually and very costly if done by robots. "We started out working on optical switching where we had to align 32 single-mode fibers," he said. "We wanted a better way to do that." In production, the devices should cost around $5 each.

Microfabrication
The researchers fabricated the aligner using a photolithography process. As the optical fiber lies in a channel, tiny actuators move it in three dimensions until it is correctly aligned. The actuators can move the fiber in excess of 20 µm in each direction, generating more than 10 mN of force in the process. The team has created two styles of aligner, mounted and unmounted. In the mounted unit, a movable base is attached by retainer springs to a fixed base. The unmounted unit is designed to fit into a micromachined hole where there are walls for the actuators to push against. While both devices cost about the same, Pado said that the unmounted unit is slightly easier to manufacture.
Although the researchers have not designed an automated controller for the unit, Pado said that creating one will not be difficult. They already have the device attached to a battery and controlled by manual controls. He explained that automating the controls will be a matter of attaching an intensity meter to the fiber optic and running a feedback loop to control the movements until the coupled intensity is highest. Once this is achieved, the fiber can be soldered in place.
Boeing researchers recently presented the device at SPIE/Photonics West in San Jose, where Pado said it generated substantial interest. "I am sure there are applications for this that we have not even considered," he said. For example, a researcher might use it in electron microscopy to move a sample.
Pado said that reducing the size of the device to less than 1 mm³ should not pose much of a challenge.