Analog-to-digital (AID) converters with sampling rate in the gigabits/sec are desirable in many advanced communication systems including RADAR, microwave and cable links1, and for designing zero intermediate frequency receivers, as well as in the implementation ofhigh-speed test and measurement equipment. Today's electronic AID converters have limiting speeds in the megahertz range, whereas most advanced communication systems operate in the gigahertz range. Optical devices and systems can operate at much higher speeds, and therefore there is great interest to design and implement all-optical A/D converters. Several optical AID converter schemes, intended to circumvent the electronic bottleneck have been proposed2 . Unfortunately, such schemes require complex circuitry for the sampler and/or the quantizer, and often require high-power. As a result these schemes are unsuitable for large-scale system that require low-power consumption, or for systems with many transmit/receive units such as in RADAR or satellite communication systems. We present the design and demonstration of an all-optical A/D converter whose attractive features include 1) direct optical sampling of the input RF signal, 2) optical quantization scheme, 3) utilization of optical signal multiplexing to provide parallel procession of quantized signals at electronic speed, and 4) low-power consumption.