SPAD-based time-of-flight for dispersion measurement of integrated waveguides.

The precise control of light propagation through dispersion engineering is essential for the development of compact systems such as chip-integrated coherent sources and amplifiers that aim to manipulate the temporal characteristics of light pulses and exploit nonlinear phenomena in long waveguides. Given the complexity of photonic device design, versatile and broadly accessible dispersion characterization techniques are needed. In this work, we present single photon avalanche diode (SPAD)-based time-of-flight (ToF) dispersion measurements of integrated waveguides that are insensitive to both chip-coupling efficiency and alignment. We demonstrate that SPAD-ToF can be used to measure the magnitude and sign of the dispersion parameter in ultra-low-loss silicon nitride (SiN) spiral waveguides.