Explore the vast range of titles available.

Driven by narrow-linewidth bench-top lasers, coherent optical systems spanning optical communications, metrology and sensing provide unrivalled performance. To transfer these capabilities from the laboratory to the real world, a key missing ingredient is a mass-produced integrated laser with superior coherence. Here, we bridge conventional semiconductor lasers and coherent optical systems using CMOS-foundry-fabricated microresonators with a high Q factor of over 260 million and finesse over 42,000. A five-orders-of-magnitude noise reduction in the pump laser is demonstrated, enabling a frequency noise of 0.2 Hz2 Hz−1 to be achieved in an electrically pumped integrated laser, with a corresponding short-term linewidth of 1.2 Hz. Moreover, the same configuration is shown to relieve the dispersion requirements for microcomb generation that have handicapped certain nonlinear platforms. The simultaneous realization of this high Q factor, highly coherent lasers and frequency combs using foundry-based technologies paves the way for volume manufacturing of a wide range of coherent optical systems.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.

Photonic integrated circuits are widely used in applications such as telecommunications and data-centre interconnects 1 – 5 . However, in optical systems such as microwave synthesizers 6 , optical gyroscopes 7 and atomic clocks 8 , photonic integrated circuits are still considered inferior solutions despite their advantages in size, weight, power consumption and cost. Such high-precision and highly coherent applications favour ultralow-noise laser sources to be integrated with other photonic components in a compact and robustly aligned format—that is, on a single chip—for photonic integrated circuits to replace bulk optics and fibres. There are two major issues preventing the realization of such envisioned photonic integrated circuits: the high phase noise of semiconductor lasers and the difficulty of integrating optical isolators directly on-chip. Here we challenge this convention by leveraging three-dimensional integration that results in ultralow-noise lasers with isolator-free operation for silicon photonics. Through multiple monolithic and heterogeneous processing sequences, direct on-chip integration of III–V gain medium and ultralow-loss silicon nitride waveguides with optical loss around 0.5 decibels per metre are demonstrated. Consequently, the demonstrated photonic integrated circuit enters a regime that gives rise to ultralow-noise lasers and microwave synthesizers without the need for optical isolators, owing to the ultrahigh-quality-factor cavity. Such photonic integrated circuits also offer superior scalability for complex functionalities and volume production, as well as improved stability and reliability over time. The three-dimensional integration on ultralow-loss photonic integrated circuits thus marks a critical step towards complex systems and networks on silicon. Three-dimensional integration of distributed-feedback lasers and ultralow-loss silicon nitride waveguides results in ultralow-noise lasers without the need for optical isolators.

Numerous modern technologies are reliant on the low-phase noise and exquisite timing stability of microwave signals. Substantial progress has been made in the field of microwave photonics, whereby low-noise microwave signals are generated by the down-conversion of ultrastable optical references using a frequency comb 1 – 3 . Such systems, however, are constructed with bulk or fibre optics and are difficult to further reduce in size and power consumption. In this work we address this challenge by leveraging advances in integrated photonics to demonstrate low-noise microwave generation via two-point optical frequency division 4 , 5 . Narrow-linewidth self-injection-locked integrated lasers 6 , 7 are stabilized to a miniature Fabry–Pérot cavity 8 , and the frequency gap between the lasers is divided with an efficient dark soliton frequency comb 9 . The stabilized output of the microcomb is photodetected to produce a microwave signal at 20 GHz with phase noise of −96 dBc Hz −1 at 100 Hz offset frequency that decreases to −135 dBc Hz −1 at 10 kHz offset—values that are unprecedented for an integrated photonic system. All photonic components can be heterogeneously integrated on a single chip, providing a significant advance for the application of photonics to high-precision navigation, communication and timing systems. 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.

Recent advances in nonlinear optics have revolutionized integrated photonics, providing on-chip solutions to a wide range of new applications. Currently, state of the art integrated nonlinear photonic devices are mainly based on dielectric material platforms, such as Si 3 N 4 and SiO 2 . While semiconductor materials feature much higher nonlinear coefficients and convenience in active integration, they have suffered from high waveguide losses that prevent the realization of efficient nonlinear processes on-chip. Here, we challenge this status quo and demonstrate a low loss AlGaAs-on-insulator platform with anomalous dispersion and quality ( Q ) factors beyond 1.5 × 10 6 . Such a high quality factor, combined with high nonlinear coefficient and small mode volume, enabled us to demonstrate a Kerr frequency comb threshold of only ∼36 µW in a resonator with a 1 THz free spectral range, ∼100 times lower compared to that in previous semiconductor platforms. Moreover, combs with broad spans (>250 nm) have been generated with a pump power of ∼300 µW, which is lower than the threshold power of state-of the-art dielectric micro combs. A soliton-step transition has also been observed for the first time in an AlGaAs resonator. 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.

Silicon nitride (SiN) waveguides with ultra-low optical loss enable integrated photonic applications including low noise, narrow linewidth lasers, chip-scale nonlinear photonics, and microwave photonics. Lasers are key components to SiN photonic integrated circuits (PICs), but are difficult to fully integrate with low-index SiN waveguides due to their large mismatch with the high-index III-V gain materials. The recent demonstration of multilayer heterogeneous integration provides a practical solution and enabled the first-generation of lasers fully integrated with SiN waveguides. However, a laser with high device yield and high output power at telecommunication wavelengths, where photonics applications are clustered, is still missing, hindered by large mode transition loss, non-optimized cavity design, and a complicated fabrication process. Here, we report high-performance lasers on SiN with tens of milliwatts output power through the SiN waveguide and sub-kHz fundamental linewidth, addressing all the aforementioned issues. We also show Hertz-level fundamental linewidth lasers are achievable with the developed integration techniques. These lasers, together with high- Q SiN resonators, mark a milestone towards a fully integrated low-noise silicon nitride photonics platform. This laser should find potential applications in LIDAR, microwave photonics and coherent optical communications. 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.

Coherent optics has profoundly impacted diverse applications ranging from communications, LiDAR to quantum computations. However, developing coherent systems in integrated photonics comes at great expense in hardware integration and energy efficiency. Here we demonstrate a high-coherence parallelization strategy for advanced integrated coherent systems at minimal cost. By using a self-injection locked microcomb to injection lock distributed feedback lasers, we achieve a record high on-chip gain of 60 dB with no degradation in coherence. This strategy enables highly coherent channels with linewidths down to 10 Hz and power over 20 dBm. The overall electrical-to-optical efficiency reaches 19%, comparable to that of advanced semiconductor lasers. This method supports a silicon photonic communication link with an unprecedented data rate beyond 60 Tbit/s and reduces phase-related DSP consumption by 99.99999% compared to traditional III-V laser pump schemes. This work paves the way for realizing scalable, high-performance coherent integrated photonic systems, potentially benefiting numerous applications. Researchers demonstrate the high-coherence parallelization in integrated photonics. Their high-coherence, high-power, multiwavelength light source drives a silicon photonic link with a 60 Tbit/s data rate and significantly reduces digital signal processing consumption.

Integrated soliton microcombs benefit a wide range of conventional comb applications through their compactness and scalability. And applications such as optical clocks and biosensing have driven interest in their operation at wavelengths approaching the visible band. However, increasing normal dispersion and optical loss at shorter wavelengths make short pulse operation at low pumping power challenging, especially for detectable-rate microcombs. Here, low-pump-power, detectable-rate soliton microcombs are demonstrated from telecom to visible bands using ultra-low-loss silicon nitride waveguides. Wavelength-multiplexed operation spanning 2/3 octave is also demonstrated in a single device. The results fill a gap needed for realization of integrated self-referenced visible microcombs. 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 Correction to this paper has been published: https://doi.org/10.1038/s41467-021-22031-4

Soliton microcombs are helping to advance the miniaturization of a range of comb systems. These combs mode lock through the formation of short temporal pulses in anomalous dispersion resonators. Here, a new microcomb is demonstrated that mode locks through the formation of pulse pairs in coupled normal dispersion resonators. Unlike conventional microcombs, pulses in this system cannot exist alone, and instead phase lock in pairs wherein pulses in each pair feature different optical spectra. The pairwise mode-locking modality extends to multiple pulse pairs and beyond two rings, and it greatly constrains mode-locking states. Two- (bipartite) and three-ring (tripartite) states containing many pulse pairs are demonstrated, including crystal states. Pulse pairs can also form at recurring spectral windows. We obtained the results using an ultra-low-loss Si3N4 platform that has not previously produced bright solitons on account of its inherent normal dispersion. The ability to generate multicolour pulse pairs over multiple rings is an important new feature for microcombs. It can extend the concept of all-optical soliton buffers and memories to multiple storage rings that multiplex pulses with respect to soliton colour and that are spatially addressable. The results also suggest a new platform for the study of topological photonics and quantum combs.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.

Within the context of globalization, the development of renewable energy is critical for attaining sustainable development, and the digital economy is also a critical driver for achieving it. This article incorporates globalization, renewable energy development, and the digital economy into its research framework, investigates the relationship between globalization and renewable energy development, and explores the moderating effect of the digital economy, using panel data from countries along the Belt and Road (B&R) from 2001 to 2018. It is found that globalization facilitates the development of renewable energy. The 1% increase in globalization results in a 1.06% increase in renewable energy development; the level of globalization has a significant effect on renewable energy development in high-income countries, upper-middle-income countries, and low-income countries, but not in lower-middle-income countries; the digital economy has a moderating effect on the impact of globalization on renewable energy development in countries along the B&R. Simultaneously, the effect of globalization on renewable energy development in B&R countries is influenced by the digital economy’s single threshold effect, and the effect of globalization on renewable energy development is more pronounced when the level of digital economy development is less than the threshold of 0.061. The conclusions of this article have significant implications for the B&R countries’ sustainable development in the contexts of globalization and the digital economy.