A high speed optical sampler is proposed that is driven by cw microwaves. The sampler is composed of waveguide interferometers of the type originally proposed by Martin. A voltage applied to one (or both) arms of the interferometer modulates the interference of the optical radiation at the output. Such an interferometer can be driven at high frequencies if synchronism is maintained between the optical radiation and the applied voltage pattern. Spatially periodic exciting structures can serve this purpose. Deviations from synchronism can be compensated (within limits) by adjustment of the peak amplitude of the microwave voltage. A cascade of four interferometers on LiMb03, driven at 10 GHz, at multiples of (appr.) 3V (3, 6, 12, 24) have a predicted sampling-function width of 2 ps at 20 GHz repetition rate. Experiments on single section and double-section interferometers will be reported.