High precision optical fiber alignment using tube laser bending

Abstract

In this paper, we present a method to align optical fibers within 0.2 μm of the optimal position, using tube laser bending and in situ measuring of the coupling efficiency. For near-UV wavelengths, passive alignment of the fibers with respect to the waveguides on photonic integrated circuit chips does not suffice. In prior research, it was shown that permanent position adjustments to an optical fiber by tube laser bending meets the accuracy requirements for this application. This iterative alignment can be done after any assembly steps. A method was developed previously that selects the optimal laser power and laser spot position on the tube, to minimize the number of iterations required to reach the target position. In this paper, that method is extended to the case where the absolute position of the fiber tip cannot be measured. By exploiting the thermal expansion motion at a relatively low laser power, the fiber tip can be moved without permanent deformation (only elastic strain) of the tube. An algorithm has been developed to search for the optimal fiber position, by actively measuring and maximizing the coupling efficiency. This search is performed before each bending step. Experiments have shown that it is possible to align the fiber with an accuracy of 0.2 μm using this approach.

Making Light Work of Metal Bending: Laser Forming in Rapid Prototyping

“…One application of laser micro-adjustment is the precise alignment of optical fibers to ensure optimal coupling with a photonic integrated circuit (PIC) [141]. While glass has been successfully laser formed [81,82], laser forming the optical fiber would only produce bends into the fiber, rather than aligning it.…”

“…While glass has been successfully laser formed [81,82], laser forming the optical fiber would only produce bends into the fiber, rather than aligning it. To align the optical fiber, the researchers sheathed the fiber into a thin metal tube and the tube was then laser formed [141,142]. The optical fiber is flexible, so the bend in the metal tube will cause a deflection in the fiber tip.…”

“…The optical fiber is flexible, so the bend in the metal tube will cause a deflection in the fiber tip. In effect, the metal tube is being used as an alignment actuator with sub-micron precision, owing to the controllability of laser forming [141,142].…”