  To manipulate cold atoms in spatially constrained quantum engineering
platforms, we developed a lensless optical system with a $\sim$1 $\mu$m
resolution and a transverse size of only 225 $\mu$m. We use a multimode optical
fiber with a high numerical aperture, which directly guides light inside the
ultra-high-vacuum system. Spatial light modulators allow us to generate control
beams at the in-vacuum fiber end by digital optical phase conjugation. As a
demonstration, we use this system to optically transport cold atoms towards the
in-vacuum fiber end, to load them in optical microtraps and to re-cool them in
optical molasses. This work opens new perspectives for setups combining cold
atoms with other optical, electronic or opto-mechanical systems with limited
optical access.
