Abstract: A system and method for measuring the temporal delay an optical signal experiences along a path is provided it uses single photon sensitive detectors and multiple optical pulse rates. The multiple optical pulse rates are chosen to allow each to be isolated in post-processing even if only a single detector is employed. The detectors can be time-gated at a repetition rate synchronized but different from the optical pulse rates, including the use of a pulsed-pump up-conversion detector. The pulse rate choice allows improved performance, including an extension of the unambiguous temporal delay range. The ability to isolate the pulse rates can also be used for measuring multiple path delays simultaneously or for spectrally resolving path characteristics without requiring the use of spectral filtering. The post-processing function can be segmented to include an initial signal quality estimation step so further processing can be aborted if it is unlikely to succeed.