Recently, photon-pair sources using optical waveguides are considered promising. Especially, high-Q ring resonators have much attention because they can enhance the nonlinear optical processes. In general, Q factor is calculated by the resonant wavelength and the full width at half maximum that obtained by the transmission spectrum. However, it is difficult to obtain the quality factor while photon-pairs are generated in a ring resonator.
In this paper, we report that we estimated the Q factor of a ring resonator using coincidence measurement.