  We introduce a design for a tip-tilt sensor with integrated single-mode fiber
coupling for use with the front-end prototype of the iLocater spectrograph at
the Large Binocular Telescope to detect vibrations that occur within the
optical train. This sensor is made up of a micro-lens array printed on top of a
fiber bundle consisting of a central single-mode fiber and six surrounding
multi-mode fibers. The design in based on a previous prototype that utilized a
multi-core fiber with seven single-mode fibers. With this updated design, we
are able to achieve a better sensing throughput. We report on the modeled
performance: if the beam is perfectly aligned, 69% light is coupled into the
central single-mode fiber feeding the scientific instrument. When the beam is
not aligned, some of the light will be coupled into the outer sensing fibers,
providing the position of the beam for tip-tilt correction. For this design we
show that there is a linear response in the sensing fibers when the beam is
subject to tip-tilt movement. Furthermore we introduce an adaptive optics
testbed, which we call the Koenigstuhl Observatory Opto-mechatronics Laboratory
(KOOL), this testbed currently simulates vibrations at the Large Binocular
Telescope, and in collaboration we have extended it to allow single-mode fiber
coupling tests.
