An all-optical analog-to-digital converter capable of sampling at 50GS/s is described. The ADC works in the frequency domain. The RF signal is sampled by electro-optically steerable gratings and quantized by a set of detectors with scalable apertures. An all-optical analog-to-digital converter capable of sampling at 50 GS / s is described. The ADC works in the frequency domain. The RF signal is sampled by electro-optically steerable gratings and quantized by a set of detectors with scalable apertures.