Physics Tomorrow Letters

Introduction

Waveguide -to-free-space outcoupling has enabled new developments in optical-phased arrays, beamsteering, LiDAR, and quantum information processing [1], [2], [3], [4], with high outcoupling efficiencies and straightforward fabrication making diffractive grating outcouplers ideal for applications requiring small device footprints and precise beam delivery. In trapped-ion systems, integrated beam delivery in surface traps provides a number of benefits over free-space addressing including robustness to external vibrations, tight focusing, and the potential for scalability [4]. Systems for various ion species have been demonstrated [5], [6] as well as high-fidelity entanglement [7], indicating promise for scalable trapped-ion systems with applications from quantum sensing and metrology to large-scale quantum computing [8]. Grating coupler design methodologies are most commonly motivated by efficient coupling to fibers, often for nearinfrared wavelengths [9], [10], [11], [12], [13], [14]. More recently, devices targeting free-space emission have been presented for various applications in atomic systems [15], [16], but current methodologies involve approximations that pose challenges when faced with the stringent demands of these systems, including varied beam waist requirements, operation at multiple wavelengths spanning the UV to IR, and the delivery of nontrivial spatial field profiles. A general approach for grating chirp and apodization was demonstrated in [17], but grating line curvatures for transverse focusing were restricted to back-emitting geometries and determined according to approximations limiting focusing accuracy.