An analog-to-digital converter can produce a digital signal representative of an analog input electrical signal. A continuous-wave laser can lock to a multifrequency optical signal and produce a continuous-wave optical signal. An optical amplitude modulator can modulate the continuous-wave optical signal using the analog input electrical signal to produce a first modulated optical signal. An optical splitter can split the first modulated optical signal into a plurality of modulated optical signals. A plurality of detectors can convert the modulated optical signals into respective modulated electrical signals. A plurality of comparators and a decoder arranged in a flash converter topology can receive the modulated electrical signals and output the digital signal using a timing reference derived from the multifrequency optical signal. Using a relatively high-precision multifrequency optical signal, such as produced by a photonic oscillator, can produce a relatively high-precision device.