Photonic Digital-to-Analog Converters: Architectures, Benchmarking, and Integration Pathways

Photonic digital-to-analog converters (PDACs) are emerging as mixed-signal interfaces for systems in which analog waveform synthesis is tightly coupled to optical carriers, wavelength parallelism, ultrawide bandwidth, or low-loss photonic distribution. Recent demonstrations in silicon photonics, thin-film lithium niobate, indium phosphide, plasmonics, and heterogeneous platforms indicate rapid progress, but the field remains difficult to benchmark because reported results often mix nominal bit count, effective number of bits (ENOB), symbol rate, aggregate data rate, analog bandwidth, projected speed, and device-level energy. This Review synthesizes the PDAC literature into three physically distinct architecture families: parallel PDACs, where weighted contributions are distributed across spatial optical branches; serial PDACs, where weights are encoded in time, wavelength, or noise-shaped pulse sequences; and segmented or hybrid PDACs, where weighting is embedded inside the modulator, emitter, or transmitter structure. The central contribution is a photonic-integrated-circuit (PIC)-centric benchmarking framework that links each architecture to its summation domain, dominant impairments, platform suitability, and converter-level metrics required for fair comparison, including signal-to-noise and distortion ratio (SINAD), spurious-free dynamic range (SFDR), ENOB, integral nonlinearity (INL), differential nonlinearity (DNL), bandwidth, update rate, timing uncertainty, weighting error, and power-accounting boundary. A quantitative audit computes Walden metrics or parity-power barriers only where the reported boundaries permit them and derives explicit 4-, 6-, and 8-bit requirements for extinction ratio, residual weighting error, timing jitter, and segmented-modulator phase accuracy. Among the reports audited here, no PDAC yet exceeds the strongest high-frequency EDAC reference simultaneously in measured ENOB, update rate, output frequency, and complete-power FoM. The analysis positions PDACs as specialized photonic-electronic conversion engines for applications where optical-domain synthesis provides a measurable system advantage rather than as universal replacements for electronic DACs. The most promising regimes include ultrawideband transmitters, microwave photonics, RF-overphotonic links, satellite payloads, arbitrary waveform generation, coherent optical interfaces, and mixed-signal photonic systems.