Evaluation of requirements for phase-shift cavity ring-down spectroscopy biosensing using integrated microring resonators

Add-drop microring resonators (ADMRs) are promising devices for biosensing applications. Here we investigate the conditions required for successful use of the phase-shift cavity ring down spectroscopy (PS-CRDS) detection method for these devices. Parameters investigated include the radius, quality factor, and necessary PS-CRDS modulation rate. We also derive a relationship between quality factor and modulation rate for maximum sensitivity. We conclude that a Q factor of ~10
⁵
would be sufficient to permit a laser modulation frequency of less than 1 GHz, which would make this method practical for point-of-care applications.