High-dimensional spatial mode sorting and optical circuit design using multi-plane light conversion

Multi-plane light converters (MPLCs) are an emerging class of optical devices capable converting a set input spatial modes to new target output modes. This operation represents linear transformation—a much sought after capability in photonics. MPLCs have potential applications both the classical and quantum optics domains, fields ranging from communications computing imaging. They consist series diffractive elements (the “planes”), typically separated by free space. The phase delays imparted each plane determined process inverse-design, most often using adjoint algorithm known as wavefront matching method (WMM), which optimizes correlation between actual MPLC outputs. In this work, we investigate high mode capacity create arbitrary sorters circuits. We focus on designs possessing low numbers planes render these experimentally feasible. To best control scenario, develop inverse-design algorithm, based gradient ascent with specifically tailored objective function, show how, low-plane limit, it converges substantially lower modal cross-talk higher fidelity than those achievable WMM. demonstrate several prototype few-plane high-dimensional sorters, operating up 55 modes, sorting photons their Zernike or orbital angular momentum state, arbitrarily randomized basis. discuss advantages drawbacks proof-of-principle prototypes describe future improvements. Our work points bright for MPLC-based technologies.