An apparatus and method are disclosed to digitize an input electrical signal. A sequence of nonuniformly spaced optical pulses impinges an optical modulator, where the pulses are modulated by the electrical input signal, the optical pulses being detected by one or more photoreceivers, the photoreceiver outputs being electrically sampled in analog-to-digital converters and then processed in a digital signal processor (DSP) in order to measure the electrical input signal. The series of nonuniform pulses are formed by interleaving L uniformly spaced pulse streams each of repetition period T and where fmax, the maximum allowable spectral frequency of the input electrical signal, is greater than 4·L·f/2, where f=1/T.