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Self-referencing turns pulsed laser systems into self-referenced frequency combs. Such frequency combs allow counting of optical frequencies and have a wide range of applications. The required optical bandwidth to implement self-referencing is typically obtained via nonlinear broadening in optical fibers. Recent advances in the field of Kerr frequency combs have provided a path toward the development of compact frequency comb sources that provide broadband frequency combs, exhibit microwave repetition rates and are compatible with on-chip photonic integration. These devices have the potential to significantly expand the use of frequency combs. Yet to date, self-referencing of such Kerr frequency combs has only been attained by applying conventional, fiber-based broadening techniques. Here we demonstrate external broadening-free self-referencing of a Kerr frequency comb. An optical spectrum spanning two-thirds of an octave is directly synthesized from a continuous wave laser-driven silicon nitride microresonator using temporal dissipative Kerr soliton formation and soliton Cherenkov radiation. Using this coherent bandwidth and two continuous wave transfer lasers in a 2 f– 3 f self-referencing scheme, we are able to detect the offset frequency of the soliton Kerr frequency comb. By stabilizing the repetition rate to a radio frequency reference, the self-referenced frequency comb is used to count and track the continuous wave pump laser’s frequency. This work demonstrates the principal ability of soliton Kerr frequency combs to provide microwave-to-optical clockworks on a chip. Frequency combs: on-chip integration on track A compact, precision tool for counting and tracking laser frequencies may improve atomic clocks and optical data transmission devices. Frequency combs use laser pulses to produce equally spaced spectra that can link radio frequencies to optical domains. Tobias Kippenberg and colleagues from École Polytechnique Fédérale de Lausanne, Switzerland, have found a way to miniaturize frequency combs by coupling a continuous wave laser to an on-chip silicon nitride microresonator. This setup produced solitary waves, or solitons, that generate terahertz frequency combs with a broad spectral range—a critical requirement for frequency metrology. When combined with an amplification system based on non-linear crystals, the team’s approach eliminates the need for bulky, external sources typically used for frequency broadening. The technology is amenable to integration with both photonic elements and silicon microchips.

Femtosecond laser pulses enable the synthesis of light across the electromagnetic spectrum and provide access to ultrafast phenomena in physics, biology, and chemistry. Chip-integration of femtosecond technology could revolutionize applications such as point-of-care diagnostics, bio-medical imaging, portable chemical sensing, or autonomous navigation. However, current chip-integrated pulse sources lack the required peak power, and on-chip amplification of femtosecond pulses has been an unresolved challenge. Here, addressing this challenge, we report  >50-fold amplification of 1 GHz-repetition-rate chirped femtosecond pulses in a CMOS-compatible photonic chip to 800 W peak power with 116 fs pulse duration. This power level is 2–3 orders of magnitude higher compared to those in previously demonstrated on-chip pulse sources and can provide the power needed to address key applications. To achieve this, detrimental nonlinear effects are mitigated through all-normal dispersion, large mode-area and rare-earth-doped gain waveguides. These results offer a pathway to chip-integrated femtosecond technology with peak power levels characteristic of table-top sources. Amplification of laser pulses is key for ultrafast and broadband measurements in physics, biology, and chemistry. Here, the authors show that a femtosecond pulse amplifier, providing 800 Watts of peak power, can be integrated on a photonic chip.

Efficient light-matter interaction lies at the heart of many emerging technologies that seek on-chip integration of solid-state photonic systems. Plasmonic waveguides, which guide the radiation in the form of strongly confined surface plasmon-polariton modes, represent a promising solution to manipulate single photons in coplanar architectures with unprecedented small footprints. Here we demonstrate coupling of the emission from a single quantum emitter to the channel plasmon polaritons supported by a V-groove plasmonic waveguide. Extensive theoretical simulations enable us to determine the position and orientation of the quantum emitter for optimum coupling. Concomitantly with these predictions, we demonstrate experimentally that 42% of a single nitrogen-vacancy centre emission efficiently couples into the supported modes of the V-groove. This work paves the way towards practical realization of efficient and long distance transfer of energy for integrated solid-state quantum systems. The confined surface plasmon-polariton modes in plasmonic waveguides are a promising platform for single-photon manipulation in small, coplanar architectures. Here, Bermúdez Ureña et al . demonstrate efficient coupling of a single quantum emitter to the supported modes of a V-groove plasmonic waveguide.

THz oscillators generated via frequency-multiplication of microwaves are facing difficulty in achieving low phase noise. Photonics-based techniques, in which optical two tones are translated to a THz wave through opto-electronic conversion, are promising if the relative phase noise between the two tones is well suppressed. Here, a THz (≈560 GHz) wave with a low phase noise is provided by a frequency-stabilized, dissipative Kerr microresonator soliton comb. The repetition frequency of the comb is stabilized to a long fiber in a two-wavelength delayed self-heterodyne interferometer, significantly reducing the phase noise of the THz wave. A measurement technique to characterize the phase noise of the THz wave beyond the limit of a frequency-multiplied microwave is also demonstrated, showing the superior phase noise of the THz wave to any other photonic THz oscillators (>300 GHz). Low phase-noise THz wave generation is in high demand for applications such as wireless communications and radars. Here, the authors generate low-noise THz waves via photodetection of the carrier of a Kerr frequency comb, which is repetition-rate stabilized using a two-wavelength delayed self-heterodyne interferometer.

Dissipative solitons can be found in a variety of systems resulting from the double balance between dispersion and nonlinearity, as well as gain and loss. Recently, they have been observed to spontaneously form in Kerr nonlinear microresonators driven by a continuous wave laser, providing a compact source of coherent optical frequency combs. As optical microresonators are commonly multimode, intermode interactions, which give rise to avoided mode crossings, frequently occur and can alter the soliton properties. Recent works have shown that avoided mode crossings cause the soliton to acquire a single-mode dispersive wave, a recoil in the spectrum, or lead to soliton decay. Here, we show that avoided mode crossings can also trigger the formation of breather solitons, solitons that undergo a periodic evolution in their amplitude and duration. This new breather soliton, referred to as an intermode breather soliton, occurs within a laser detuning range where conventionally stationary (i.e., stable) dissipative Kerr solitons are expected. We experimentally demonstrate the phenomenon in two microresonator platforms (crystalline magnesium fluoride and photonic chip-based silicon nitride microresonators) and theoretically describe the dynamics based on a pair of coupled Lugiato-Lefever equations. We show that the breathing is associated with a periodic energy exchange between the soliton and a second optical mode family, a behavior that can be modeled by a response function acting on dissipative solitons described by the Lugiato-Lefever model. The observation of breathing dynamics in the conventionally stable soliton regime is relevant to applications in metrology such as low-noise microwave generation, frequency synthesis, or spectroscopy.

Microcombs—optical frequency combs generated in microresonators—have advanced tremendously in the past decade, and are advantageous for applications in frequency metrology, navigation, spectroscopy, telecommunications, and microwave photonics. Crucially, microcombs promise fully integrated miniaturized optical systems with unprecedented reductions in cost, size, weight, and power. However, the use of bulk free-space and fiber-optic components to process microcombs has restricted form factors to the table-top. Taking microcomb-based optical frequency synthesis around 1550 nm as our target application, here, we address this challenge by proposing an integrated photonics interposer architecture to replace discrete components by collecting, routing, and interfacing octave-wide microcomb-based optical signals between photonic chiplets and heterogeneously integrated devices. Experimentally, we confirm the requisite performance of the individual passive elements of the proposed interposer—octave-wide dichroics, multimode interferometers, and tunable ring filters, and implement the octave-spanning spectral filtering of a microcomb, central to the interposer, using silicon nitride photonics. Moreover, we show that the thick silicon nitride needed for bright dissipative Kerr soliton generation can be integrated with the comparatively thin silicon nitride interposer layer through octave-bandwidth adiabatic evanescent coupling, indicating a path towards future system-level consolidation. Finally, we numerically confirm the feasibility of operating the proposed interposer synthesizer as a fully assembled system. Our interposer architecture addresses the immediate need for on-chip microcomb processing to successfully miniaturize microcomb systems and can be readily adapted to other metrology-grade applications based on optical atomic clocks and high-precision navigation and spectroscopy.Key steps towards photonic interposers for integrated optical synthesizers are shown: filters, mixers, linear processing of an octave-spanning microcomb, integration of microcomb and interposer layers, and a system-level feasibility analysis.

Nitrogen vacancy (NV) centres in diamond are promising elemental blocks for quantum optics 1 , 2 , spin-based quantum information processing 3 , 4 and high-resolution sensing 5 , 6 , 7 , 8 , 9 , 10 , 11 . However, fully exploiting the capabilities of these NV centres requires suitable strategies to accurately manipulate them. Here, we use optical tweezers 12 as a tool to achieve deterministic trapping and three-dimensional spatial manipulation of individual nanodiamonds hosting a single NV spin. Remarkably, we find that the NV axis is nearly fixed inside the trap and can be controlled in situ by adjusting the polarization of the trapping light. By combining this unique spatial and angular control with coherent manipulation of the NV spin and fluorescence lifetime measurements near an integrated photonic system, we demonstrate individual optically trapped NV centres as a novel route for both three-dimensional vectorial magnetometry and sensing of the local density of optical states. A single nitrogen-vacancy centre in a diamond nanocrystal can be trapped by optical tweezers and manipulated in all spatial directions.

High-power tunable lasers are intensely pursued due to their vast application potential such as in telecom, ranging, and molecular sensing. Integrated photonics, however, is usually considered not suitable for high-power applications mainly due to its small size which limits the energy storage capacity and, therefore, the output power. In the late 90s, to improve the beam quality and increase the stored energy, large-mode-area (LMA) fibers were introduced in which the optical mode area is substantially large. Such LMA fibers have transformed the high-power capability of fiber systems ever since. Introducing such an LMA technology at the chip-scale can play an equally disruptive role with high power signal generation from an integrated photonics system. To this end, in this work we demonstrate such a technology, and show a very high-power tunable laser with the help of a silicon photonics based LMA power amplifier. We show output power reaching 1.8 W over a tunability range of 60 nm, spanning from 1.83 µm to 1.89 µm, limited only by the seed laser. Such an integrated LMA device can be used to substantially increase the power of the existing integrated tunable lasers currently limited to a few tens of milliwatts. The power levels demonstrated here reach and surpass that of many benchtop systems which truly makes the silicon photonics based integrated LMA device poised towards mass deployment for high power applications without relying on benchtop systems.

We demonstrate high energy Q-switched pulse generation with the help of a large mode area gain waveguide in a silicon photonics device. Output pulse energy >150 nJ and laser slope efficiency of 40% is shown.

Here, we report on a CMOS-compatible thulium-doped high power continuous wave (CW) optical amplifier, leveraging large mode-area gain waveguides. The amplifier structure combines a silicon nitride waveguide above which a sputtered 1250 nm-thick thulium-doped alumina gain layer is deposited. We demonstrate >220 mW output signal power at center wavelength of 1850 nm inside a 9-cm-long amplifier. Small signal gain of >15 dB is achieved.