The invention relates to a method of determining the autocorrelation function g(τ) of an optical signal. The inventive method comprises the following steps consisting in: determining the instants (ti) at which the photons appear; for a pre-determined set of pulses (w), calculating function s(w) = Si e-jwti, wherein e-jwti = coswti + sinwti, the summation being performed on all of the pulses received; determining the square S(w) of the modulus of function s(w); and calculating the Fourier transform g(τ) of the power spectrum S(w) for a pre-determined set of temporal variation values.