Reconfigurable free-space mode generation and detection enabled by an active photonic integrated circuit coupled to a passive mode-selective interface.

Optical mode-sorting and generation are used for a wide range of quantum, sensing and communication applications. High-speed switching between mode sets would allow photonics systems to react to changes in propagation channel in real time. Photonic-Integrated-Circuits (PICs) with phased arrays can rapidly reconfigure their function at MHz depending on installed modulators. As a reconfigurable photonic system, PIC can reconfigure significantly fast than spatial light modulators that are limited to less than 1 kHz. However, phased-arrays are bound by two-dimensional Nyquist-sampling limit and spacing between array elements leads to grating lobe formation, where many additional array elements are needed to mitigate these effects. We leverage a passive Multiple-Plane-Light-Converters (MPLC) as an Optical Mode-Selective Interface (OMSI), coupling a basis set of free-space Hermite Gaussian (HG) modes directly into an active optical mesh implemented on a PIC. The active mesh can generate or sort any free-space mode-set that can be created by a linear superposition of 15 HG modes. Without changing the physical system, we demonstrate the generation and sorting of four orthogonal mode groups, each with 15 modes, achieving a mean intermodal crosstalk for sorting of -22 dB. This approach can allow for rapidly reconfigurable mode-sorters that could be used for quantum or classical communications or sensing applications.