An Integrated-Photonics Optical-Frequency Synthesizer
Daryl T. Spencer, Tara E. Drake, Travis Briles, Jordan R. Stone, Laura C. Sinclair, Connor D. Fredrick, Qing Li, Daron A. Westly, Bojan R. Ilic, Aaron Bluestone, Nicolas Volet, Tin Komljenovic, Seung Hoon Lee, Dong Yoon Oh, Myoung-Gyun Suh, Ki Youl Yang, Martin H. Pfeiffer, Tobias J. Kippenberg, Erik Norberg, Kerry Vahala, Kartik A. Srinivasan, Nathan R. Newbury, Luke Theogarajan, John E. Bowers, Scott A. Diddams, Scott B. Papp
Integrated-photonics microchips now enable a range of advanced functionalities for high- coherence applications like data transmission, for highly optimized physical sensors, and for harnessing quantum states, but with size, extensibility, and portability much beyond tabletop experiments. Through high-volume semiconductor processing built around advanced materials there exists an opportunity to develop devices with enhanced performance to impact applications cutting across disciplines of basic science and technology. Here we show how to synthesize the absolute frequency of a lightwave signal, using integrated photonics to implement lasers, system interconnects, and nonlinear frequency-comb generation. The laser frequency output of our synthesizer is programmed deterministically by a microwave clock across 4 THz near 1550 nm with 1 Hz resolution and traceability to the SI second. This is accomplished with a heterogeneously integrated III/V-Si tunable laser, which is guided by dual dissipative-Kerr- soliton frequency combs fabricated on silicon chips. Through out-of-loop measurements of the phase-coherent, microwave-to-optical link, we verify the fractional-frequency imprecision of the integrated-photonics synthesizer to be 7.0×10^-13^ for a 1 second acquisition and unambiguously constrain any synthesis error at 3.0×10^-15^ on the 195 THz output carrier. Precision optical synthesis, which builds on the ubiquitous capability in the microwave domain, is enabling for measurement of quantum systems and clock metrology, laser range finding, microwave photonics, and coherent data transmission. Our results demonstrate a first path to optical synthesis with integrated photonics, leveraging the low-cost, low-power and compact integrated features of this platform that will be critical for the widespread use and expansion of these many capabilities.