In this paper, we establish an experimental setup for testing fiber optic ring and Add-Drop resonators. The transmission spectrum is measured in slow and fast sweeping of laser wavelength. It is shown that for high modulation frequency of the laser source, the ringing phenomenon appears and the transmission becomes oscillatory. Then, using a mathematical model for amplitude variation of field inside resonator and fitting experimental results with theoretical ones, we will be able to determine the physical characteristics of the resonator such as Q-factor, coupling coefficient, coupling regime and photon lifetime.