The invention relates to a method of determining a time-of-flight of an optical signal between a starting point and a reflection point of an optical path, comprising: supplying to the path at least one optical probing signal; detecting an electrical return signal according to an optical return signal returning from the path in response to a corresponding one of the probing signals using direct detection; deriving at least one receive code sequence by sampling and slicing the return signal using a sampling rate corresponding to a bit rate of a sequence of pulses of the probing signal; determining a correlation function by correlating the transmit code sequence and the at least one receive code sequence; and identifying a main peak of the correlation function that corresponds to the reflection point and a time position of the peak, and determining the time-of-flight as the time position of the peak.