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A synthesizer that combines a fixed low-noise photonic oscillator and a direct digital synthesizer—and is based on components that can all be integrated on chip—can create microwave signals that are tunable with low noise.

Continuum generation in optical fibres has enabled many applications, like optical frequency combs. Here, Ohet al. demonstrate controlled dispersive-wave generation in on-chip silica waveguides, which could have a similar impact on integrated devices.

Optical reference cavities are important in precision time keeping and low-noise microwave generation. Here as a step towards their miniaturization, the authors demonstrate a chip-based reference cavity that uses a spiral geometry to improve stability by introducing thermal and mechanical immunity.

Direct f–2f self-referencing of a microresonator-based optical frequency comb is demonstrated at a repetition rate of 16.4 GHz. The carrier envelope offset frequency and repetition rate are stabilized to a hydrogen maser-based atomic clock.

Broadband Fabry–Pérot etalons are used as calibration sources in radial velocity exoplanet detection. This Article explores their performance limits and models the physical mechanism behind their complex measured chromatic drift.

A combination of two Nobel ideas circumvents the trade-off between power and accuracy in ultraviolet spectroscopy.

We leverage advances in integrated photonics to generate low-noise microwaves with an optical frequency division architecture that can be low power and chip integrated.

By combining engineered dispersion and chirped quasi-phase matching in multisegment nanophotonic thin-film lithium niobate waveguides, the generation of gap-free frequency comb spanning from 330 to 2,400 nm can be realized with only 90 pJ of pulse energy at 1,550 nm.

Self-injection locking of an on-chip laser to a milimetre-scale vacuum-gap Fabry–Pérot cavity is demonstrated, with a phase noise of –97 dBc Hz^–1 at a 10-kHz offset frequency and a fractional frequency stability of 5 × 10⁻¹³ at 10 ms, enabling next-generation high-performance integrated systems.

A soliton microcomb as an astronomical spectrograph calibrator is presented. It can ultimately have a footprint of a few cubic centimetres, and reduced weight and power consumption, attractive for precision radial velocity measurement.

Design and fabrication techniques that allow analogous dispersion control in chip-integrated optical microresonators are presented, allowing higher-order, wide-bandwidth dispersion control over an octave of spectrum.

A broadband frequency 'comb' provides, in a single laser beam, about a million optical modes with very narrow linewidths and precisely known absolute frequency positions. A technique has been developed that enables the resolution of the modes of a frequency comb and the simultaneous detection of them in a parallel manner.

Femtosecond laser pulses can generate self-organized nonlinear gratings in nanophotonic waveguides, providing both quasi-phase-matching and group-velocity matching for second-harmonic generation, and enabling simultaneous χ² and χ³ nonlinear processes for laser-frequency-comb stabilization.

Ultralow-noise erbium:fibre comb technology allows the generation of a comb spanning six octaves, from the ultraviolet (350 nm) to the mid-infrared (22,500 nm), with a resolving power of 10¹⁰ across 0.86 PHz of bandwidth.

The nonlinear dynamic interaction between optical comb frequencies and microresonator modes are not yet fully understood. Here, the authors demonstrate a method to characterize microcomb states and observe discrete phase steps that have not been observed in conventional frequency combs.

The observation of soliton crystals in monolithic Kerr microresonators is reported. The physics of such resonators is explored in a regime of dense soliton occupation, offering a way to increase the efficiency of Kerr combs.

Researchers demonstrate a microwave generator based on a high-Q optical resonator and a frequency comb functioning as an optical-to-microwave divider. They generate 10 GHz electrical signals with a fractional frequency instability of ≤8 × 10⁻¹⁶ at 1 s.

Shot noise originates from the discrete nature of optical field detection. By exploiting correlations in the shot-noise spectrum of optical pulse trains, scientists improve shot-noise-limited optical pulse timing measurements by several orders of magnitude. A photodetected pulse train timing noise floor at an unprecedented 25 zs Hz^−1/2 is reported.

An optical-frequency synthesizer based on stabilized frequency combs has been developed utilizing chip-scale devices as key components, in a move towards using integrated photonics technology for ultrafast science and metrology.

By employing difference-frequency generation, a mid-infrared dual-comb spectrometer covering the 2.6 to 5.2 µm range is demonstrated with comb-tooth resolution, sub-MHz frequency precision and accuracy, and a spectral signal-to-noise ratio as high as 6,500.

A network of optical atomic clocks based on three different atomic species is reported and their frequency ratios are measured with uncertainties at or below 8 × 10⁻¹⁸.