Abstract: Apparatus and method for high-speed analog-to-digital conversion employs photonic circuits with variable light-absorption. A coherent light source is clocked to produce a stream of coherent light pulses onto which is modulated an analog signal to be converted to digital form. An optical splitter divides the stream of pulses into a number of streams that is proportional to the resolution sought. A passive photonic quantizer absorbs, to a predetermined degree, the light energy of the incident pulse streams. The output of a fully absorbed pulse does not trigger a comparator. Pulse streams of sufficient intensity pass through the light absorbers, and their output does trigger the comparator. The output state of the comparators may be read into a digital memory to form a digital word that represents the analog signal during any discrete clock interval. Most of the elements of the apparatus can be fabricated on a substrate of photonic semiconducting material.