Diagnostics and Characterization of Photonic Circuits by Wide-Field Spatiotemporal Imaging

The growing diffusion of integrated photonic technologies requires fast and noninvasive quality control techniques for mass production. We present a general diagnostic technique for subps imaging of photonic circuits combining wide-field optical microscopy and optical gating. The simultaneous access to multiple parameters of a photonic structure enables an unprecedented characterization of its functional design as opposed to typical single-domain techniques such as frequency or time domain reflectometry and near-field microscopy. The noncontact and nonperturbative nature of the technique makes it relevant for both planar and three-dimensional circuits, as well as for silicon, polymeric, or hybrid platforms. We apply our technique to different photonic chip components fabricated by Direct Laser Writing, revealing the spatial and temporal hallmarks of fabrication imperfections causing losses or deviations from the intended device behavior. At the same time, the technique allows in situ probing of the key properties of photonic devices as the local propagation constants of guided modes or the quality factor of resonant elements. Our method is relevant for both the scientific and the industrial communities, as it lends itself to be scaled up to in-line quality control thanks to its nonscanning nature.