A high-speed D/A converter using optics

The authors have proposed and demonstrated in preliminary manner the advantages of using optical techniques in D/A converters, to provide high accuracy conversion at potentially enormous speeds. The principle of the optical D/A converter proposed is shown schematically. An intensity-stabilized optical source, feeds a parallel array of N nominally identical modulators, whose transmissions are each switched between zero and unity according to the clocked input parallel digital word comprising voltages V_n (n=1 to N). The intensities emerging from the modulators pass through a fixed array of neutral density filters arranged in a binary sequence (i.e. having transmissions varying as 2^1-n), prior to being focussed or imaged on to the output detector, by the lens. The net current flowing in the detector circuit is accurately proportional to the total incident optical intensity and therefore provides the required analog output waveform