An optical signal analyzing apparatus enables real-time and single-shot analysis simultaneously in both time and frequency domains with spectro-temporal analysis. The apparatus includes a fiber tap coupler for receiving an input optical signal from continuous wave (CW) to ultra-short pulses (femtosecond-picosecond). An optical splitter directs part of the signal to a frequency channel and part to a time channel A photodiode in the time channel directly monitors the intensity evolution and converts it to an electrical signal. In the frequency channel, two sub-channels are provided: one for CW/quasi-CW and one for short-pulse components. A signal processor analyses the time- and frequency-domain data from the time channel and frequency channel and displays the temporal and spectral evolutions simultaneously, so that the two different pieces of information of a non-repeated dynamic event can be correlated in different domains.