Phase-front shaping of extended beams in waveguide arrays

Summary form only given. Coupled waveguide arrays lend themselves very well to photonic engineering through tailoring of the propagation and coupling constants [1]. Especially interesting is the manipulation of collective Floquet Bloch waves (extended beams see Figure 1 top, a and d) that propagate over several waveguides through evanescent coupling and their manipulation for classical and quantum data processing. Phase-front shaping of these waves is crucial for compact imaging and photonic circuitry in the classical and quantum regime up to multiqbit architectures where phase-shifters are instrumental [2]. Segmentation of a waveguide enables a change of its propagation constant [3] and thus segmentation patterns can shape the phase front of a beam. Image reconstruction has indeed been demonstrated using π shifts [4]. We demonstrate here complete phase-front shaping in waveguide arrays by means of more general segmented patterns for a novel imaging approach. We implement three emblematic functions related to three phase profiles in III-V waveguide arrays: beam steering (linear wedge-profile), focusing and defocusing (quadratic lens-like profile) and diffraction (cosine profile). We evaluate the operation of those patterns by measuring maps of the output intensity profile as a function of the position of injection (x
_injection
=0 corresponds to the center of the patterns). The experimental maps clearly exhibit the desired effects (see Figure 1 for steering and focusing). The excellent agreement between the simulation and the experiment validates the concept of extensive phase front shaping via segmentation patterns, the fabrication and our capacity to design and fabricate more complex functions.