Visible Photonic Integrated Circuit Diagnosis via Optical Coherence Tomography

Visible photonic integrated circuits (PICs) find applications ranging from AR/VR to quantum control, yet lack a high-resolution, nondestructive diagnostic comparable to optical frequency-domain reflectometry, which has matured for infrared silicon photonics. We adapt spectral-domain optical coherence tomography (SD-OCT) to measure guided-mode back-reflections for visible PICs. A broadband visible source is injected; back-reflections interfere with a local oscillator and are read out on a spectrometer. We validate the method by resolving multiple round-trip echoes in a waveguide-coupled ring resonator via a single port, then apply it to circuits with integrated diamond quantum micro-chiplets (QMCs), clearly resolving input/output facets and PIC–QMC transition zones. The system achieves shot-noise-limited sensitivity, 50 dB dynamic range, 16 um axial resolution, and 2 mm (6 dB) imaging depth. SD-OCT thus provides a practical, high-resolution diagnostic for visible PICs, enabling rapid characterization—such as propagation loss, backscattering, and dispersion of PICs—and supporting higher design and packaging yield.