Programmable RF-to-optical frequency synthesis with fully stabilized dual-microcomb

Phase-coherent radio-frequency (RF)-to-optical links provide highly frequency-stable optical signals, critical for ultrafast and high-precision metrology. Optical frequency combs generated from mode-locked lasers can achieve this with exceptional accuracy, but face limitations in size, power consumption, and scalability. Microcombs generated from an integrated photonic chip offer a compact, mass-manufacturable alternative with the advantage of achieving the octave-spanning bandwidth, essential for self-referencing. Yet, this is accompanied by comb line spacing outside the bandwidth of conventional electronics. Here, we utilize two ∼1THz microcombs in a Vernier configuration to stabilize their optical frequencies to a common RF reference, establishing a phase-coherent RF-to-optical link for programmable optical frequency synthesis. Importantly, the divided repetition rates extracted from the Vernier scheme enable electronic control and reconfigurability of the comb grid through electro-optic modulation. We demonstrate reduced comb grids of ∼ 10 GHz, facilitating static laser frequency calibration with kHz-resolution and dynamic-tracking. The fully stabilized, octave-spanning dual-comb system can be widely used in applications requiring stable optical frequency sources and high-precision metrology. *Saleha Fatema & Kaiyi Wu contributed equally to this work.