Re-configurable Mode-sorter for Arbitrary Mode Generation and Detection

Pixelated approaches to wavefront sensing and generation are commonplace, but inefficient and present core challenges for development of effective phase array antenna due to the physical limitation in grating coupler placement and 2D Nyquist sampling limits. A major challenge in the use of pixelated PICs for free-space applications is that arrays of grating couplers commonly have low fill factor due to manufacturing constraints and waveguide cross-coupling, that lead to significant loss of power to grating lobes. We present a new programmable approach for free-space optical mode sorting that combines a re-configurable photonic integrated circuit (PIC) with a passive Optical Mode Selective Interface (OMSI) that eliminates grating lobes and fill factor losses. This approach can reduce the number of required on-chip optical inputs by a factor of more than 4, and sort spatial modes in four different orthogonal mode groups with a mean inter-channel cross-talk for sorting of approximately 22dB without any change to the physical optical system. This approach could alleviate many of the issues related to scaling of PIC technologies, reducing both optical losses and complexity for future systems that incorporate PIC devices.