Assisted Focus Adjustment for Free Space Optics System Coupling Single-Mode Optical Fibers

This paper presents a method for adjusting a free space optics (FSO) system that links two single-mode optical fibers using collimators with a symmetrical configuration. It operates as if the two optical fibers were seamlessly connected without the need for any photoelectric devices. Collimator focusing, as well as axis alignment, is critical for low-loss transmission. A simultaneous optimization requires a task of six degrees of freedom (DOFs) in total. The assisted focus adjustment proposed here is performed for an FSO system to match a specified link span using an optomechatronic system in advance of its installation. Thus, the six-DOF task is mitigated, leaving an axis alignment task only. Then, the tuned FSO system can be combined with an existent misalignment compensation mechanism for beam acquisition/tracking at the installation site if necessary.