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It is an important challenge to reduce the power consumption and size of lasers, but progress has been impeded by quantum noise overwhelming the coherent radiation at reduced power levels. Thus, despite considerable progress in microscale and nanoscale lasers, such as photonic crystal lasers, metallic lasers and plasmonic lasers, the coherence length remains very limited. Here we show that a bound state in the continuum based on Fano interference can effectively quench quantum fluctuations. Although fragile in nature, this unusual state redistributes photons such that the effect of spontaneous emission is suppressed. Based on this concept, we experimentally demonstrate a microscopic laser with a linewidth that is more than 20 times smaller than existing microscopic lasers and show that further reduction by several orders of magnitude is feasible. These findings pave the way for numerous applications of microscopic lasers and point to new opportunities beyond photonics.Quantum noise is suppressed by a bound state in the continuum (BIC) approach, enabling a microlaser with narrow linewidth compared to other small lasers.

Fano interference and nonlinearity are exploited to achieve self-pulsing of a laser at gigahertz frequencies. The semiconductor lasers in use today rely on various types of cavity, making use of Fresnel reflection at a cleaved facet 1 , total internal reflection between two different media 2 , Bragg reflection from a periodic stack of layers 3 , 4 , 5 , 6 , 7 , 8 , mode coupling in a high contrast grating 9 , 10 or random scattering in a disordered medium 11 . Here, we demonstrate an ultrasmall laser with a mirror, which is based on Fano interference between a continuum of waveguide modes and the discrete resonance of a nanocavity. The rich physics of Fano resonances 12 has recently been explored in a number of different photonic and plasmonic systems 13 , 14 . The Fano resonance leads to unique laser characteristics. In particular, because the Fano mirror is very narrowband compared to conventional laser mirrors, the laser is single mode and can be modulated via the mirror. We show, experimentally and theoretically, that nonlinearities in the mirror may even promote the generation of a self-sustained train of pulses at gigahertz frequencies, an effect that has previously been observed only in macroscopic lasers 15 , 16 , 17 , 18 . Such a source is of interest for a number of applications within integrated photonics.

Single indistinguishable photons at telecom C-band wavelengths are essential for quantum networks and the future quantum internet. However, high-throughput technology for single-photon generation at 1550 nm remained a missing building block to overcome present limitations in quantum communication and information technologies. Here, we demonstrate the high-throughput fabrication of quantum-photonic integrated devices operating at C-band wavelengths based on epitaxial semiconductor quantum dots. Our technique enables the deterministic integration of single pre-selected quantum emitters into microcavities based on circular Bragg gratings. Respective devices feature the triggered generation of single photons with ultra-high purity and record-high photon indistinguishability. Further improvements in yield and coherence properties will pave the way for implementing single-photon non-linear devices and advanced quantum networks at telecom wavelengths. An efficient way of realising a large number of telecom single-photon emitters for quantum communication is still missing. Here, the authors use a wide-field imaging technique for fast localization of single InAs/InP quantum dots, which are then integrated into circular Bragg grating cavities featuring high single-photon purity and indistinguishability.

Today’s optical communication systems are fast approaching their capacity limits in the conventional telecom bands. Opening up new wavelength bands is becoming an appealing solution to the capacity crunch. However, this ordinarily requires the development of optical transceivers for any new wavelength band, which is time-consuming and expensive. Here, we present an on-chip continuous spectral translation method that leverages existing commercial transceivers to unlock the vast and currently unused potential new wavelength bands. The spectral translators are continuous-wave laser pumped aluminum gallium arsenide on insulator (AlGaAsOI) nanowaveguides that provide a continuous conversion bandwidth over an octave. We demonstrate coherent transmission in the 2-μm band using well-developed conventional C-band transmitters and coherent receivers, as an example of the potential of the spectral translators that could also unlock communications at other wavelength bands. We demonstrate 318.25-Gbit s −1 Nyquist wavelength-division multiplexed coherent transmission over a 1.15-km hollow-core fibre using this approach. Our demonstration paves the way for transmitting, detecting, and processing signals at wavelength bands beyond the capability of today’s devices. Continuous spectral translation could allow expansion of the bandwidth available for communication without having to develop transceivers for the new bands. Here, the authors demonstrate this using AlGaAsOI nanowaveguides as spectral translators between the mature telecom C band and the 2-μm wavelength band.

Passive photonic crystals have been shown to exhibit a multitude of interesting phenomena, including slow-light propagation in line-defect waveguides. It was suggested that by incorporating an active material in the waveguide, slow light could be used to enhance the effective gain of the material, which would have interesting application prospects, for example enabling ultra-compact optical amplifiers for integration in photonic chips. Here we experimentally investigate the gain of a photonic crystal membrane structure with embedded quantum wells. We find that by solely changing the photonic crystal structural parameters, the maximum value of the gain coefficient can be increased compared with a ridge waveguide structure and at the same time the spectral position of the peak gain be controlled. The experimental results are in qualitative agreement with theory and show that gain values similar to those realized in state-of-the-art semiconductor optical amplifiers should be attainable in compact photonic integrated amplifiers. Slow-light propagation provides the means to enhance and control light–matter interactions and it has been predicted to increase the gain coefficient of active waveguides. Here, Ek et al. experimentally demonstrate that the gain of a material can be enhanced using slow-light effects in photonic crystals.

Stimulated Raman scattering is an attractive way to extend the operation spectral range of optical sources. However, the spectral extension range of a tunable Raman laser is limited by the Raman frequency shift and pump tuning bandwidth. This makes it challenging to realize chip-scale, widely tunable Raman lasers, as on-chip lasers only provide limited pump power and tuning bandwidth. Here, we tackle this by dispersion engineering of a thin-film lithium niobate microring resonator, where its high-quality factor ( ~ 2.5 million) ensures a sub-milli-watt (0.8 mW) threshold for Raman lasing while its strong normal dispersion with suppressed avoided mode crossing restrains the competing Kerr comb generation process. Combining the multi-wavelength Raman gain response of lithium niobate and cascaded Raman lasing, we demonstrate a widely tunable Raman laser covering 1592–1955 nm, showing a 335-nm spectral extension range from a 94-nm-tuning-bandwidth pump laser. Our demonstration paves the way to realize chip-scale, widely-tunable Raman lasers. Extending the spectral range of on-chip tunable Raman laser is challenging due to the limited Raman frequency shifts and pump tuning bandwidth. The authors combine the dispersion engineering of thin film lithium niobate with cascaded Raman lasing to realize a widely tunable laser with 335-nm spectral extension and sub-milliwatt threshold.

Graphene-based photodetectors, taking advantage of the high carrier mobility and broadband absorption in graphene, have recently seen rapid development. However, their performance with respect to responsivity and bandwidth is still limited by the weak light-graphene interaction and large resistance-capacitance product. Here, we demonstrate a waveguide-coupled integrated graphene plasmonic photodetector on a silicon-on-insulator platform. Benefiting from plasmon-enhanced graphene-light interaction and subwavelength confinement of the optical energy, a small-footprint graphene-plasmonic photodetector is achieved working at the telecommunication window, with a large a bandwidth beyond 110 GHz and a high intrinsic responsivity of 360 mA/W. Attributed to the unique electronic band structure of graphene and its ultra-broadband absorption, operational wavelength range extending beyond mid-infrared, and possibly further, can be anticipated. Our results show that the combination of graphene with plasmonic devices has great potential to realize ultra-compact, high-speed optoelectronic devices for graphene-based optical interconnects.

This work shows how to control the surface density and size of InAs/InP quantum dots over a wide range by tailoring the conditions of Stranski-Krastanov growth. We demonstrate that in the near-critical growth regime, the density of quantum dots can be tuned between 10 7 and 10 10   cm - 2 . Furthermore, employing both experimental and modeling approaches, we show that the size (and therefore the emission wavelength) of InAs nanoislands on InP can be controlled independently from their surface density. Finally, we demonstrate that our growth method gives low-density ensembles with well-isolated QD-originated emission lines in the telecom C-band.

In its 60 years of existence, the field of nonlinear optics has gained momentum especially over the past two decades thanks to major breakthroughs in material science and technology. In this article, we present a new set of data tables listing nonlinear-optical properties for different material categories as reported in the literature since 2000. The papers included in the data tables are representative experimental works on bulk materials, solvents, 0D–1D–2D materials, metamaterials, fiber waveguiding materials, on-chip waveguiding materials, hybrid waveguiding systems, and materials suitable for nonlinear optics at THz frequencies. In addition to the data tables, we also provide best practices for performing and reporting nonlinear-optical experiments. These best practices underpin the selection process that was used for including papers in the tables. While the tables indeed show strong advancements in the field over the past two decades, we encourage the nonlinear-optics community to implement the identified best practices in future works. This will allow a more adequate comparison, interpretation and use of the published parameters, and as such further stimulate the overall progress in nonlinear-optical science and applications.