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Integrated optical frequency combs are powerful tools for optical spectroscopy. Here, authors demonstrate low-power, detectable-rate soliton microcombs from telecom to visible bands, including wavelength-multiplexed operation, using ultra-low-loss silicon nitride waveguides.

A microwave-rate soliton microcomb whose repetition rate can be modulated at 75 MHz. Moreover, the repetition rate can be locked to an external microwave reference by direct injection locking or feedback locking without external modulation.

Germano-silicate used as a building material for integrated photonics circuits substantially reduces optical losses, approaching levels comparable to those in optical fibres.

Using two-point optical frequency division based on a frequency-agile single-mode dispersive wave, a microwave signal source with record-low phase noise using a microcomb is demonstrated, offering over tenfold lower phase noise than state-of-the-art approaches.

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.

Fibre-optic waveguides are used to provide timing delays for different sensing and signal processing applications, but their transfer to on-chip platforms is a challenge. Here low-loss delay lines based on whispering-gallery spiral waveguides up to 27 m long are produced, presenting a scalable alternative.

Microwaves are of interest for applications such as communications, radar and metrology. Here, Li et al. demonstrate an on-chip microresonator device for the generation of microwaves by optical means, instead of the usual electronic devices.

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.

A turnkey regime for soliton microcombs is demonstrated, in which solitons are generated by switching on a co-integrated pump laser, eliminating the need for photonic and electronic control circuitry.

precisely controllable integrated optical gyroscope based on stimulated Brillouin scattering is used to study non-Hermitian physics, revealing a four-fold enhancement of the Sagnac scale factor near exceptional points.

Nanocavity optomechanical systems can exhibit strong dynamical back-action between mechanical motion and the cavity light field. Here, optical control of mechanical motion within two different nanocavity structures is demonstrated. A form of optically controlled mechanical transparency is also demonstrated, which is analogous to electromagnetically induced transparency.

Using silicon nitride waveguides processed by plasma-enhanced chemical vapour deposition, full integration of ultrahigh-Q resonators with other photonic devices is now possible, representing a critical advance for future photonic circuits and systems.

Spontaneous parametric down-conversion was used to generate narrowband photon pairs with a high spectral brightness in a high-Q silicon nitride microresonator.

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.

Bright solitons are produced through the interaction of pulse pairs generated via a continuous-wave fibre laser, which pumps two coupled microresonators featuring normal dispersion. Multicolour pulse pairs over multiple rings can also be generated, of great promise for applications such as all-optical soliton buffers and memories, study of quantum combs and topological photonics.

Dissipative Kerr solitons in microresonators have recently been shown to generate frequency combs via Cherenkov radiation. Here, Yiet al. demonstrate hysteresis behaviour and a single-mode dispersive wave that can improve the stability of microcombs.

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.

On-Chip integration of laser systems led to impressive development in many field of application like LIDAR or AR/VR to cite a few. Here the authors harness Pockels effect in an integrated semiconductor platform achieving fast on-chip configurability of a narrow linewidth laser.

A Sagnac gyroscope based on Brillouin ring lasers on a silicon chip is presented. The stability and sensitivity of this on-chip planar gyroscope allow measurement of the Earth’s rotation, with an amplitude sensitivity as small as 5 deg h⁻¹ for a sinusoidal rotation, an angle random walk of 0.068 deg h^−1/2 and bias instability of 3.6 deg h⁻¹.

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.

Optical absorption and nonlinear index are important performance drivers in devices like microcombs. Here the authors use resonance-enhanced nonlinear spectroscopy to characterize absorption limits and nonlinear index for some integrated photonic materials.

Chip-based architectures for mid-infrared gas sensing could enable many applications. In this direction, the authors demonstrate a microcomb-based dual-comb spectroscopy sensor with GHz resolution in the mid-IR band, with stability completely determined by a single high-Q microresonator.

Here the authors explore the noise spectrum of soliton microcomb when the pump is decoupled from the solitons motion by balancing the Raman shift with the emitted dispersive wave. Based on the analysis of the phase noise and the soliton repetition rate, they identify the uncorrelated thermal fluctuations as underlying mechanism.

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.

Counter-propagating solitons are generated in microresonator systems, producing dual-soliton frequency-comb streams with different repetition rates but high relative coherence useful for spectroscopy and laser ranging systems.

Using only conventional semiconductor processing on a silicon wafer, researchers successfully fabricate an on-chip resonator with a record Q-factor of 875 million — around 20 times higher than previous results. They also demonstrate stimulated Brillouin lasers as an example application to emphasize the size control feature of the fabrication method and the ultrahigh-Q available from these resonators.

In a photonic crystal, the periodicity of the host medium is used to manipulate the properties of light, whereas in a phononic crystal it is mechanical vibrations that are subject to such control. Here, a structure that acts as both a photonic and phononic crystal — an 'optomechanical' crystal — is described; the strong coupling between photons and phonons realized in this structure should find application in a host of sensing and communication technologies.

Solitonic modes that are redshifted due to a Raman-related effect are reported in optical microcavities, and termed Stokes solitons.

This paper demonstrates a high-Q microcavity for surface plasmons that is fabricated by coating the surface of high-Q silica microresonator with a thin layer of noble metal. This structure enables room-temperature operation with a Q-factor of around 1380 in the near infrared for surface plasmon modes. The work also includes a coupling scheme where a tapered optical fibre is in near-contact with the cavity, which provides a convenient way for selectively exciting and probing confined plasmon modes.

In order to study the dynamics of solitons in microresonators, which underlie nonlinear phenomena like Kerr comb generation, both high temporal resolution and long record times are needed. Here, the authors develop a coherent sampling method to directly image the temporal behavior of solitons.

Operating a laser gyroscope near an exceptional point has been shown to enhance its responsivity. However, here the authors demonstrate in theory and experiment that the enhanced responsivity is exactly compensated by increased noise that is inherent to this system near the exceptional point.

Using CMOS-ready ultra-high-Q microresonators, a highly coherent electrically pumped integrated laser with frequency noise of 0.2 Hz² Hz⁻¹, corresponding to a short-term linewidth of 1.2 Hz, is demonstrated. The device configuration is also found to relieve the dispersion requirements for microcomb generation that have limited certain nonlinear platforms.

Chip-based microresonator frequency combs are currently limited to the infrared spectral region. Here, the authors generate combs whose center frequency approaches the visible spectrum enabled by combining geometrical and mode-hybridization dispersion control in silica microresonators.

Achieving high output power and low noise integrated lasers is a major challenge. Here the authors experimentally demonstrate integrated lasers from a Si/SiN heterogeneous platform that shows Hertz-level linewidth, paving the way toward fully integrating low-noise silicon nitride photonics in volume using real devices for lasing.

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.

Three-dimensional integration of distributed-feedback lasers and ultralow-loss silicon nitride waveguides results in ultralow-noise lasers without the need for optical isolators.

 Fully integrated photonics at submicrometre wavelengths is realized by a heterogeneous integration technology.

Despite larger nonlinear coefficients, waveguide losses have prevented using semiconductors instead of dielectric materials for on-chip frequency-comb sources. By significantly reducing waveguide loss, ultra-low-threshold Kerr comb generation is demonstrated in a high-Q AlGaAs-on-insulator microresonator system.

Quantum jitter fundamentally limits the performance of microresonator frequency combs. The timing jitter of the solitons that generate the comb spectra is analysed, reaching the quantum limit and establishing fundamental limits for soliton microcombs.

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.

The fact that photons of light carry momentum and can therefore exert mechanical force is not just an academic curiosity; such forces have already been harnessed for a variety of applications. Here, an extreme optomechanical regime is created using a system of simple photonic structures engineered in such a way that light and mechanical energy are localized in a tiny volume on a silicon chip, so that the mechanical rigidity of the resulting structure is dominated by the optical forces.