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Here the authors demonstrate ultraviolet astronomical frequency combs, derived from the near-infrared domain via efficient harmonic generation in nanophotonic waveguides, to provide precision calibration to astronomical spectrographs for exoplanet science and precision cosmology.

An integrated optical parametric amplifier with an ultra-wide bandwidth was implemented using geometrically optimized low-loss nonlinear rib silicon nitride waveguides including the demonstration of broadband all-optical wavelength conversion.

On-chip microcombs could be used to synchronize optoelectronic systems.

By pairing an octave-spanning terahertz microcomb with a terahertz Vernier microcomb, a continuous-wave laser at 871 nm is frequency divided to a radiofrequency clock output at 235 MHz. This laser is designed for frequency doubling to reach the ytterbium ion clock transition at 435.5 nm.

Researchers demonstrated coherent dissipative Kerr solitons with a conversion efficiency exceeding 50% and good line spacing stability. The results may facilitate practical implementation of a scalable integrated photonic architecture for energy-efficient applications.

Understanding noise dynamics in frequency combs is crucial for applications. Here, the authors study the phase noise dynamics and the linewidth of soliton microcombs, revealing that some comb lines can be more quiet than the pump laser itself.

When a laser is tuned across a split energy level, photonic diatomic molecules in two linearly coupled microresonators support the formation of self-enforcing solitary waves, featuring coherent, tunable and reproducible microcombs with up to ten times higher net conversion efficiency than the state of the art.

Dark-pulse combs may be useful for coherent communications since they display high power conversion efficiency. Here, the authors report the first demonstration of coherent wavelength division multiplexing using dark pulse microresonator combs high signal-to-noise while maintaining a low on-chip pump power.

Frequency combs have the potential to be used as multi-wavelength sources in future optical communications through fiber. Here the authors demonstrate joint phase processing of multi-wavelength comb transmission, and show two schemes to improve performance and reduce complexity.

High-speed communication systems that use optical fibres often require hundreds of lasers. An approach that replaces these lasers with a single, ring-shaped optical device offers many technical advantages. See Letter p.274

Platicons microcombs can be generated in photonic molecules from a continuous-wave pump, but their spectrum is typically distorted. The authors observe the formation of a platicon microcomb using a photonic molecule realized with two coupled microcavities, resulting in engineered microcomb spectrum approaching the ideal single microresonator case.

Frequency combs produced by solitons in silicon-based optical microresonators are used to transmit data streams of more than 50 terabits per second in telecommunication wavelength bands.