Objective The optical-domain Fourier transform provides a new solution for radio-frequency spectrum analysis. While this transform is limited by the acquisition of a large second-order dispersion, the discrete Fourier transform needs to control only the phase of discrete points, which can theoretically solve the problem of obtaining a large dispersion. Methods This study used a fiber optic ring as a discrete dispersion device and a linear frequency modulation signal as the test signal to study the optical-domain discrete Fourier transform. Each transformation in this fast Fourier transform system takes approximately 2.07ns. By observing the waveform delay of the linear frequency modulation signal before and after transformation using an oscilloscope, the transformation delay of the system (~100ns) can be measured. The feasibility of the on-chip integrated optical microring group scheme was examined to expand the instantaneous bandwidth of the system.