I wasn't referring to ToF measurement, I was referring to two diodes measuring the difference in phase of a subcarrier intensity modulated signal. Essentially the subcarrier is a intensity modulation of the light. At XX MHz the optical output power will go from 100% to 0% and then back. If two diodes receive the light at the same distance then difference in phase will be zero (i.e. correlating the two signals will have a 0 lag). If the two diodes are separated by a distance, then one diode will receive a greater optical signal and one will receive a smaller optical signal. Correlating the two received signals (or measuring the phase difference) will directly correspond to the difference in distance between the two diodes - this is because the light travels at a fixed speed and the intensity of the signal directly corresponds to the physical distance. Obviously there isn't a unique solution since the diodes could be spaced at multiples of the wavelength, but for a fixed area this isn't a problem.

This only requires knowledge of the subcarrier modulation frequency, as any diode can be picked as the reference and the others matched to it. This isn't an ideal way of doing distance measurement because noise will greatly effect the estimate, but it's certainly do-able.