We report on the experimental observation of abruptly autofocusing waves. This interesting family of wave packets has been realized by using a radially symmetric Airy intensity distribution. As demonstrated in our experiments, these waves can exhibit unusual features, such as the ability to autofocus by following a parabolic trajectory toward their focus.

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This approach permits much finer adjustments of the beam direction and position when compared to other beam steering techniques of the same mechanical precision. This results in a much increased precision, accuracy and mechanical stability. A precision of better than 5 µrad and 5 µm is demonstrated, resulting in a resolution in coupling efficiency of 0.1%. Together with the added flexibility of an additional beam steering element, this allows a great simplification of the design of the fiber coupler, which normally is the most complex and sensitive element on an optical fiber breadboard. We demonstrate a fiber to fiber coupling efficiency of more than 89.8%, with a stability of 0.2% in a stable temperature environment and 2% fluctuations over a temperature range from 10°C to 40°C over a measurement time of 2 G. Drougakis et al.14 hours. Furthermore, we do not observe any non-reversible change in the coupling efficiency after performing a series of tests over large temperature variations. This technique finds direct application in proposed missions for quantum experiments in space [1, 2, 3], e.g. where laser beams are used to cool and manipulate atomic clouds. IntroductionActive optics play a rapidly increasing role in space instrumentation, for example in satellite systems that have started to use LIDAR [4,5,6,7], optical communication [8], and laser ranging [9,10].Space-based quantum technologies and atom clocks rely on an intricate manipulation of a number of ultra-stable laser sources leading to highly complex optical signal conditioning setups, which can be problematic for space missions. In some cases, this can be handled by in-fiber devices, more often, however, the requirements exceed what can be achieved in single mode waveguide devices and optical benches handling fiber to free-space to fiber coupling are required. Examples include cases where precise frequency shifting (acoustooptic modulators) or very high extinction ratios are needed, such as proposals for cold atom experiments in space [11,12]. Many components require single mode fiber to fiber coupling resulting in very stringent requirements in alignment and stability of the optical breadboard and its components. To meet these requirements, the PHARAO cold atom clock designed for space application [13] needed to incorporate active stabilization of many optical components like the mirrors used to inject light into fibers. For the LISA Pathfinder and LISA candidate systems [14,15] the optical components were attached to the breadboard using hydroxyl bonding to achieve high stability standards, albeit at the cost of extreme requirements on the manufacturing process. Another approach used in MAIUS1 mission using a combination of different types adhesives and complex moving parts to steer the beam with high precision [16,17].In this paper, we report on a novel optical beam steering technique (OBST) for fiber to free-space to fiber coupling breadboards. We achieve robust, ultrastable and yet extremely fine beam steering using simple optical elements, lik...