  Digital-to-analog converters (DAC) are indispensable functional units in
signal processing instrumentation and wide-band telecommunication links for
both civil and military applications. Since photonic systems are capable of
high data throughput and low latency, an increasingly found system limitation
stems from the required domain-crossing such as digital-to-analog, and
electronic-to-optical. A photonic DAC implementation, in contrast, enables a
seamless signal conversion with respect to both energy efficiency and short
signal delay, often require bulky discrete optical components and
electric-optic transformation hence introducing inefficiencies. Here, we
introduce a novel coherent parallel photonic DAC concept along with an
experimental demonstration capable of performing this digital-to-analog
conversion without optic-electric-optic domain crossing. This design hence
guarantees a linear intensity weighting among bits operating at high sampling
rates, yet at a reduced footprint and power consumption compared to other
photonic alternatives. Importantly, this photonic DAC could create seamless
interfaces of next-generation data processing hardware for data-centers,
task-specific compute accelerators such as neuromorphic engines, and network
edge processing applications.
