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Optical frequency combs in the mid-infrared are required for molecular gas detection applications but their realization in compact microresonator-based platforms is challenging. Here, Griffith et al. demonstrate on-chip broadband comb generation on a silicon microresonator spanning from 2.1 to 3.5 μm.

Phase-coherent frequency combs in the mid-infrared have important potential applications but their fabrication remains challenging. Here, Kuyken et al. demonstrate an octave-spanning frequency comb in the mid-infrared using a highly nonlinear dispersion-engineered silicon waveguide on a silicon-on-insulator chip.

We demonstrate a photon-counting approach that extends the unique advantages of spectroscopy with interfering frequency combs into regions where nonlinear frequency conversion tends to be very inefficient, providing a step towards precision broadband spectroscopy at short wavelengths and extreme-ultraviolet dual-comb spectroscopy.

Orbital angular momentum takes several forms in structured light beams. Here, the authors demonstrate control of dynamic spatiotemporal beams combining two forms of orbital angular momenta, by coherently adding frequency comb lines.

Frequency combs are useful tools in high precision measurement including atomic transitions and atomic clocks. Here the authors demonstrate direct frequency comb spectroscopy to shorter wavelengths by probing a transition frequency in a trapped Mg+ ion using a single mode of a UV frequency comb.

Silicon core fibre is a highly nonlinear waveguide that combines the benefits of both fibre and planar waveguide systems. Here, the authors demonstrate frequency comb generation using a fully-fibre integrated silicon core fibre as a nonlinear mixer.

Laser frequency combs emit a spectrum of equally spaced peaks that can provide precise frequency references useful for astronomy. Here, the authors demonstrate a frequency comb using electro-optical modulation, which has a line spacing that is resolvable using grating spectrographs unlike the mode-locking approach.

An optical frequency comb demodulated on a photodiode can generate a radio frequency signal with high spectral purity at a frequency corresponding to the comb spacing. Here, Liang et al.demonstrate a frequency-comb-based radio frequency photonic oscillator characterized with low phase noise and high frequency stability.

Scientists propose and experimentally demonstrate a new architecture for dual-comb spectroscopy based on all-fibre tunable frequency comb sources using standard telecommunication fibre optics components, opening the way for practical dual-comb spectroscopy.

The precision of frequency combs makes them the ideal tool for applications in areas such as optical metrology. Here, Ideguchi et al. demonstrate real-time spectroscopy with frequency combs where laser instabilities are electronically compensated, and which is based on commercially available components.

Dual-comb interferometry promises to be a high-precision metrology technique, but is hindered by short coherence times that limit the maximum number of averages. Here, Chen et al. achieve mutual coherence times of almost 2000 s by feed-forward stabilization of the carrier-envelope offsets.

By combining Fourier transform spectroscopy with two frequency-shifted combs and cavity ring-down spectroscopy, scientists demonstrate a powerful new tool for ultrahigh sensitivity spectroscopy. The scheme can measure broadband, high-resolution spectra in tens of microseconds, does not require detector arrays and may allow tuning from terahertz to ultraviolet frequencies.

Dual-comb digital holography based on an interferometer composed of two frequency combs of slightly different repetition frequencies and a lensless camera sensor allows highly frequency-multiplexed holography with high temporal coherence.

HTLV-1 type-C causes more severe disease than type-A, but the underlying reason is unclear. Here the authors show in a macaque model how type-C orf-I affects lung pathogenesis and the immune response to HTLV-1, providing a model to test viral targets for disease prevention.

Frequency comb spectroscopy is a recent field of research that has blossomed in the past five years. This Review discusses developments in the emerging and rapidly advancing field of atomic and molecular broadband spectroscopy with frequency combs.

The authors demonstrate an exciting technique to cancel the common-mode vibration of a photonic resonator upon optical frequency division to microwave frequencies. The resulting 10 GHz microwave achieves 22.6 dB suppression of vibration noise, without incurring any penalty in phase-noise performance.

Photonic-chip-based microcomb solitons driven by Pockels nonlinearity—the quadratic χ⁽²⁾ effect—instead of the Kerr soliton are demonstrated in an aluminium nitride microring resonator with a conversion efficiency of 17%.

Optical frequency combs are vital tools for precision measurements, and extending them further into the mid-infrared 'molecular fingerprint' range will open new avenues for spectroscopy. Using crystalline microresonators, Wang et al. demonstrate Kerr combs at 2.5 μm as a promising route into the mid-infrared.

A microcomb source based on a silicon nitride ring resonator is shown to support petabit-per-second data transmission over a multicore optical fibre.

Researchers demonstrate a coherent dual-comb-based spectrometer capable of measuring continuous-wave optical waveforms at time resolutions of 30 µs and 320 µs over terahertz bandwidths. The device is potentially useful for sensing applications such as multispecies gas detection, coherent laser radar and optical metrology.

Atomic clocks using optical transitions have much better frequency stability compared to microwave counterparts, but are also more complex, which means their use has been mostly lab-based so far. Here, the authors demonstrate successful operation of three different optical atomic clocks on a ship at sea for three weeks.

By controlling the group velocity dispersion of a microresonator through proper shape design, scientists generate a comb whose central frequency can be tuned throughout the transparency window of the microresonator host material.

By leveraging microcavity-integrated photonics and Kerr-induced optical frequency division, an integrated photonic millimetre-wave oscillator with low phase noise is demonstrated, achieving –77 dBc Hz^–1 and –121 dBc Hz^–1, respectively, at 100-Hz and 10-kHz offset frequencies, corresponding to –98 dBc Hz^–1 and –142 dBc Hz^–1 when scaled to a 10-GHz carrier.

An optical-frequency comb-based scheme is demonstrated that transfers a 4.5 × 10⁻¹⁶ fractional frequency stability from a 1,062-nm-wavelength laser to a 1,542-nm-wavelength laser. Transfer is also reported down to 4 × 10⁻¹⁸ at 1 s, which is one order of magnitude below that of previously reported work with comparable systems.

The Casimir effect is based on quantum electrodynamical effects between two electrically neutral objects in close proximity. Here Zou et al. observe the Casimir effect between two silicon components on a single micromechanical chip, allowing for an on-chip exploitation of the Casimir force.

This Review discusses the emerging field of mid-infrared frequency comb generation, including technologies based on novel laser gain media, nonlinear frequency conversion and microresonators, as well as the applications of these combs in precision spectroscopy and direct frequency comb spectroscopy.

The authors present a scalable on-chip parallel intensity modulation and direct detection (IM-DD) data transmission system. This system offers an aggregate line rate of 1.68 Tbit/s over a 20-km-long SMF. For the chromatic dispersion compensation of 40-km-SMFs, the energy consumption is ~0.3 pJ/bit, much less than the commercial 400G-ZR coherent transceivers counterparts.

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.

Chemical language models trained on known metabolites can identify previously unknown metabolites from mass spectrometry-based metabolomics data with high accuracy.

An integrated photonic processor, based on phase-change-material memory arrays and chip-based optical frequency combs, which can operate at speeds of trillions of multiply-accumulate (MAC) operations per second, is demonstrated.

The authors demonstrate a multi-dimensional communication scheme that combines wavelength- and mode- multiplexing on photonic integrated circuits using foundry-compatible photonic inverse design and spectrally flattened microcombs

Using two coherent broadband fibre-laser frequency comb sources, a coherent laser ranging system for absolute distance measurements is demonstrated. Its combination of precision, speed and long range may prove particularly useful for space-based sciences.

A new multiplex technique of coherent anti-Stokes Raman spectro-imaging with two laser frequency combs is shown to record molecular spectra of broad bandwidth on a microsecond scale.

Programmable self-assembly can help construct complex nanostructures. Now a mathematical framework can identify if and how a particular structure can be assembled.

Multipartite entanglement is of both fundamental and practical interest, but is notoriously difficult to witness and characterise. Here, Zarkeshian et al. demonstrate multipartite entanglement in an atomic frequency comb storing a single photon in a Dicke state spread over a macroscopic ensemble.

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.

A nine-year transit-timing campaign has measured the extremely low masses and densities of four large planets orbiting the young star V1298 Tau, which are now predicted to contract and form a typical compact super-Earth and sub-Neptune system.

Extending the therapeutic window for acute viral infections could save lives. Here, the authors show that combination treatment with a human monoclonal antibody and remdesivir initiated at 6 days post infection with Marburg virus provides 80% protection in non-human primates.

Previous studies have identified DNA methylation changes in Alzheimer’s disease. Here the authors perform a meta-analysis of DNA methylation datasets to identify epigenetic correlates of Alzheimer’s disease in the prefrontal cortex.