| We present a technique which allows us to determine the coupling regime and the cavity Q factor, both important measurements used in microresonators, in a single experiment, getting better accuracy than the normal technique where we use the spectral width of the whispering gallery mode (WGM). Using an acousto-optic modulator we modulate a laser with a sinusoidal input intensity, then we use this to excite the WGMs of a microsphere and with a fast response detector, we detect the input and output response. Using an oscilloscope we can collect the input and output signals from the microresonator. Then using a nonlinear approximation we find the best fit of these data to a sinusoidal function. We find a numerical solution to the mathematical model for transient cavity response and using the experimental parameters, we generate the throughput power from the best fit experimental input power. By matching this mathematical model curve to the best fit experimental throughput data, we can determine if the coupling regime is undercoupled, overcoupled or critically coupled, and we can estimate the cavity quality factor (Q). This technique has low uncertainty compared with the technique used to measure the quality factor Q from a WGM's spectral linewidth (Deltanu). |
