An embodiment of the inventive concept includes an optical signal generating circuit, a controlling circuit, a waveform shaping circuit, and an output circuit. The optical signal generating circuit generates a first optical signal including pulses. The controlling circuit generates a control signal indicating a first pulse to be attenuated in magnitude among the pulses. The waveform shaping circuit attenuates a magnitude of the first pulse based on the control signal and the first optical signal, and generates a second optical signal including pulses corresponding to the pulses included in the first optical signal and the first pulse having the attenuated magnitude. The output circuit outputs an electric signal of bands corresponding to differences between frequencies of the pulses included in the second optical signal based on the second optical signal. A band corresponding to the first pulse among the bands of the electric signal is adjusted as the magnitude of the first pulse is attenuated.