We experimentally demonstrate the direct time-domain characterization of photonic-crystal nanolasers at telecom wavelengths using a nonlinear optical gating technique based on four-wave mixing. This approach enables the temporal characterization of the ultrafast emission dynamics under short-pulse excitation with a picosecond time resolution. When a weak continuous-wave component is added to the pulsed pump, the emission becomes less sensitive to spontaneous-emission noise, resulting in a significantly reduced buildup time. The difference between purely pulsed and hybrid excitation regimes points to the influence of pulse-to-pulse timing fluctuations. To elucidate this effect, we perform Langevin-based simulations that reproduce the experimentally observed broadening and confirm that time jitter, originating from spontaneous emission noise near threshold, dominates the temporal dispersion. These results establish four-wave mixing gating as a powerful method to probe nanolaser dynamics with picosecond precision.

Hybrid photonic circuits, harnessing the complementary strengths of multiple materials, represent a key resource to enable compact, scalable platforms for quantum technologies. In particular, the availability of bright sources of tunable biphoton states is eagerly awaited to meet the variety of applications currently under development. In this work we demonstrate a heterogeneously integrated device working at room temperature that merges biphoton generation and on-chip quantum state engineering, combining an AlGaAs photon-pair source with a CMOScompatible silicon-on-insulator (SOI) circuit. Photon pairs are generated in the C telecom band via spontaneous parametric down-conversion and transferred to the SOI chip through a multimodal evanescent coupling scheme. This design achieves a pair generation rate above 106 s-1mW-1 and a coincidence-to-accidental ratio up to 600. Crucially, the coupling design induces strong and predictable transformations of the biphoton joint spectral amplitude, enabling complex quantum state engineering entirely on-chip in a compact device compliant with electrical pumping. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Non-Hermitian photonics provides a framework to engineer the gain and loss of optical modes in open systems, enabling control of their spectral and dynamical properties. In particular, the ability to dynamically tune modal losses offers a route to implement functionalities traditionally relying on cavity Q-factor modulation, such as Q-switching, within nanophotonic platforms. Here, we demonstrate the generation of short optical pulses in a pair of phase-coupled photonic crystal nanolasers exploiting non-Hermitian coupling. Two waveguide-coupled nanocavities are operated below their individual lasing thresholds and subjected to asymmetric optical pumping, such that a transient carrier-induced detuning modifies the interference conditions between them. This dynamically controls the gain and loss of the collective modes, and, upon crossing a resonance condition, leads to the rapid release of stored carrier energy as an optical pulse. A rate-equation model captures the interplay between carrier dynamics and modal coupling and reproduces the observed behavior. Experiments performed on an indium phosphide platform show pulse generation from cavities that do not lase efficiently on their own in continuous-wave operation, with temporal characteristics governed by carrier dynamics. These results indicate that non-Hermitian coupling can be used to control the effective cavity losses in time, providing a route to pulse generation in integrated photonic systems.

Interfacing cold atoms with nanoscopic dielectric devices offers exciting opportunities for quantum technologies. We focus on enhancing light-matter coupling via slow-mode nanophotonic crystals while addressing challenges in design, nanofabrication, and precise atom delivery near surfaces.

This roadmap consolidates recent advances while exploring emerging applications, reflecting the remarkable diversity of hardware platforms, neuromorphic concepts, and implementation philosophies reported in the field. It emphasizes the critical role of cross-disciplinary collaboration in this rapidly evolving field.

We demonstrate a nonlinear AlGaAs photonic chip generating biphotons with high-dimensional spatial correlations. Photon pairs are generated by parametric down conversion in a waveguide array and simultaneously spread through quantum walks along the various waveguides, allowing to generate various types of high-dimensional entangled states of light. We further implement the Su-Schriefer-Heeger model and demonstrate the topological protection of the SPDC process against disorder. These results highlight nonlinear waveguide arrays as a promising platform for exploring the interplay between nonlinearity, disorder and topology in quantum photonic circuits.

Photonic crystal (PhC) cavities based on III-V materials emerge as key components in integrated photonic circuits thanks to their capability of confining light within small modal volumes and owning high quality factors up to 109 [1]. In particular, InGaP PhC cavities are used to enable applications in the generation of classical and quantum states of light through nonlinear interactions [2], [3]. Such applications require careful design of the PhC cavity to support equally spaced frequency modes. Techniques relying on the nearly-harmonic shaping of the effective photonic potential [1], [4] are used to design PhC cavities with equally space modes and Hermite-Gauss spatial distribution. Integrating these III-V nonlinear sources on silicon waveguides proves necessary to further envisage their usage in complex photonic circuitry. Experimental realizations of multimodal InGaP PhC cavities coupled to an underneath silicon waveguide have been previously reported [3], [5]. However, a study of the coupling between the PhC cavity higher-order modes and the Si waveguide is still missing.

Hybrid photonic devices, harnessing the advantages of multiple materials while mitigating their respective weaknesses, represent a promising solution to the effective on -chip integration of generation and manipulation of non-classical states of light encoding quantum information. We demonstrate a hybrid III-V/Silicon quantum photonic device combining the strong second-order nonlinearity and compliance with electrical pumping of the III-V semiconductor platform with the high maturity and CMOS compatibility of the silicon photonic platform. Our device embeds the spontaneous parametric down -conversion (SPDC) of photon pairs into an Al-GaAs source and their subsequent routing to a silicon -on -insulator circuitry. This enables the on -chip generation of broadband telecom photon pairs by type 0 and type 2 SPDC from the hybrid device, at room temperature and with strong rejection of the pump beam. Two -photon interference with 92% visibility proves the high energy -time entanglement quality characterizing the produced quantum state, thereby enabling a wide range of quantum information applications..

Novel platforms interfacing trapped cold atoms and guided light in nanoscale waveguides are a promising route to achieve a regime of strong coupling between light and atoms in single pass, with applications to quantum non-linear optics and quantum simulation. A strong challenge for the experimental development of this emerging waveguide-QED field of research is to combine facilitated optical access for atom transport, atom trapping via guided modes and robustness to inherent nanofabrication imperfections. In this endeavor, here we propose to interface Rubidium atoms with a photonic-crystal waveguide based on a large-index GaInP slab. With a specifically tailored half-W1 design, we show that a large chiral coupling to the waveguide can be obtained and guided modes can be used to form two-color dipole traps for atoms at 116~nm from the edge of the structure. This optimized device should greatly improve the level of experimental control and facilitate the atom integration.

Exceptional points (EPs) attract lots of attention due to the richness of the phenomenology associated to their presence in the complex eigenspectrum of coupled non-Hermitian systems. Here we provide both a coupled mode theory analysis and an experimental investigation of two nanolasers interacting through a channel-mediated coupling. We demonstrate the transition from Parity-Time (PT) symmetric to PT-broken regime using a thermo-optic control over the laser frequency detuning

We demonstrate supercontinuum generation from 800 to 2000 nm on the highly nonlinear gallium phosphide GaP-on-insulator platform. The supercontinuum is generated in a dispersion engineered waveguide with a length of 13 mm. Femtosecond pulses at the telecom wavelength are broadened in the process. The long length and low loss allow the waveguide to be pumped at the picojoule level.

Tailoring the losses of optical systems within the frame of non-Hermitian physics has appeared very fruitful in the past few years. In particular, the description of exceptional points (EPs) with coupled resonators has become widespread. The on-chip realization of these functionalities is crucial for integrated nanophotonics but requires fine control techniques of the nanodevice properties. Here, we demonstrate pump-controlled directional emission of two coupled nanolasers that distantly interact via an integrated waveguide. This coupling scheme unusually enables both frequency and loss couplings between two cavities, which can be advantageously exploited to reach EPs by either detuning the cavities or controlling the gain of nanolasers. The system can be readily reconfigured from bidirectional to unidirectional emission by adjusting the pump power.

Harnessing high-dimensional entangled states of light presents a frontier for advancing quantum information technologies, from fundamental tests of quantum mechanics to enhanced computation and communication protocols. In this context, the spatial degree of freedom stands out as particularly suited for on-chip integration. But while traditional demonstrations produce and manipulate path-entangled states sequentially with discrete optical elements, continuously coupled nonlinear waveguide systems offer a promising alternative where photons can be generated and interfere along the entire propagation length, unveiling novel capabilities within a reduced footprint. Here we exploit this concept to implement a compact and reconfigurable source of path-entangled photon pairs based on parametric down-conversion in semiconductor nonlinear waveguide arrays. We use a double-pump configuration to engineer the output quantum state and implement various types of spatial correlations, exploiting a quantum interference effect between the biphoton state generated in each pumped waveguide. This demonstration, at room temperature and telecom wavelength, illustrates the potential of continuously coupled systems as a promising alternative to discrete multicomponent quantum circuits for leveraging the high-dimensional spatial degree of freedom of photons.

The increased demands of Deep Learning (DL) stress electronic computing hardware, prompting researchers in new computing paradigms. Neuromorphic photonic, emerged as a candidate, offering high throughput and energy efficiency, by harnessing light’s advantages. Here, we propose and experimentally demonstrate a Microdisk laser as a programmable all-optical activation function (AF) unit for photonic neural networks (PNNs). The device with a footprint of only 44.2 μm2 produced three non-linear AFs at 2Gbaud i.e., Inverse-ELU, Sigmoid and Clipped-GeLU at input power envelopes as low as 11.5 μW, exhibiting energy efficiency of 1.89 pJ/Symbol.

Mainstream Machine learning (ML) leverages on a simplified model of the neuron, the Perceptron, which is efficiently implemented in software running on digital computers. Still, biological neurons process information by exchanging time-depending signals, e.g. spikes. Understanding how to harness "neurons" closer in behaviour to their biological model, is fascinating but challenging. One of the challenges is related to scaling up the number of interconnected neurons. Photonics is regarded as a promising approach [1]. Particularly, the large bandwidth available in optical communication channels suggests applications in specialized computing tasks, where latency is critical. Aiming at an all-optical implementation, computing-related functions such as reconfigurable matrix multiplication [2] and nonlinear activation functions [3] are available in Silicon photonics. Semiconductor lasers have shown a neuron-like response such as excitability [4], i.e. the emission of a well-defined pulse as the excitation goes above a threshold, while microring-based "neurons", exploiting the thermo-optical nonlinearity, have been demonstrated in a silicon photonic circuit [5]. Here we consider a photonic crystal based semiconductor laser, heterogeneously integrated on top of a Silicon on Insulator (SOI) waveguide. The nanolaser is composed by two sections for the gain and saturable absorber: a metal screen ensure selective pumping of the gain section with a CW laser beam. By a suitable choice of the parameters (Q-factor, gain vs absorption ratio and pumping rate), the laser operates in different regimes: excitable, pulsing with variable rate (i.e. implements the Leak Integrate and Fire model of the neuron), bistable and CW. Excitability is shown in the figure: panels (c) to (e) relate to the response to a pulsed excitation as a function of its energy (here estimated before the input coupler to the silicon chip) when the pump is set just below the threshold of self-pulsing. Panel (f) shows the spiking probability, estimated as the fraction of traces where spikes are emitted (the event is detected when signal goes above -40 arb.u.). The spiking probability follows the expected trend with the excitation, already observed in VCSELs [6] and agrees very well with our stochastic implementation of the Yamada model of self-pulsing lasers. This result paves the way to electrically pumped, interconnected spiking nanolasers, operating with manageable (0.1 mA) current levels and sub-nanosecond time scales. References [1] B. J. Shastri et al., "Photonics for artificial intelligence and neuromorphic computing," Nat. Photon. 15, 102 (2021). [2] Y. Shen et al., "Deep learning with coherent nanophotonic circuits," Nat. Photon. 11, 441 (2017). [3] A. Jha et al., "Reconfigurable all-optical nonlinear activation functions for neuromorphic photonics," Opt. Lett. 45, 4819 (2020). [4] H.J. W¨unsche et al., "Excitability of a semiconductor laser by a two-mode homoclinic bifurcation" , Phys. Rev. Lett. 88, 023901 (2001). [5] T. Van Vaerenbergh et al., "Cascadable excitability in microrings," Opt. Express 20, 20292 (2012). [6] F. Selmi et al., "Relative Refractory Period in an Excitable Semiconductor Laser," Phys. Rev. Lett. 112 183902 (2014).

Gallium Phosphide has unique material properties suitable for telecom and mid-infrared applications. Using micro-transfer printing, we demonstrate a low-loss Gallium Phosphide-on-insulator integrated platform with an arbitrarily large coupon area enabling the generation of on-chip supercontinuum generation.

Recent studies on non-Hermitian optical systems having exceptional points (EPs) have revealed a host of unique characteristics associated with these singularities, including unidirectional invisibility, chiral mode switching and laser self-termination, to mention just a few examples. The vast majority of these works focused either on passive systems or active structures where the EPs were accessed below the lasing threshold, i.e. when the system description is inherently linear. In this work, we experimentally demonstrate that EP singularities in coupled semiconductor nanolasers can be accessed and tracked above the lasing threshold, where they become branch points of a nonlinear dynamical system. Contrary to the common belief that unavoidable cavity detuning will impede the formation of an EP, here we demonstrate that this same detuning is necessary for compensating the carrier-induced frequency shift, hence restoring the nonlinear EP in the lasing regime. Furthermore, unlike linear non-Hermitian systems, we find that the spectral location of EPs above laser threshold varies as a function of total pump power and can therefore be continuously tracked. Our work is a first step towards the realization of lasing EPs in more complex laser geometries, and enabling the enhancement of photonic local density of states through non-Hermitian symmetries combined with nonlinear interactions in coupled laser arrays.

MHz-rate generation of time-energy entangled photon pairs is demonstrated on Silicon and InGaP bichromatic Photonic Crystal cavities with µ W-level pump power. High visibility up to 94% is measured with 1 second integration.

Hybrid photonic devices represent a promising solution to the effective on-chip integration of all the components required for the generation, manipulation and detection of non-classical states of light encoding quantum information. We present an AlGaAs source of highly entangled photon pairs envisioned for the hybridization with silicon-on-insulator integrated platforms, in order to take benefit from the strong second order nonlinearity and the compliance with electrical pumping of the III-V platform and the maturity and CMOS compatibility of silicon photonic circuitry, enabling a wide variety of quantum information applications.