Twin-field (TF) quantum key distribution (QKD) has emerged as a promising method for repeater-free long-distance secure communication, with the longest demonstration covering 1000 km [1]. It is a measurement-device-independent QKD protocol, where the two users send weak coherent states, to a central node for single-photon interference followed by single-photon detection. Due to this, TF-QKD has a square root dependence of the key rate on channel transmission, making it possible to cover longer distances than conventional or commercial devices[2]. In previous implementations, a narrow linewidth laser has been used as the master or reference laser, frequency stabilised by locking the laser to a frequency reference, such as the atomic transition of acetylene or an ultra-low expansion (ULE) cavity using RF-locking [1], to achieve high coherence throughout the entire system. The RF-locking method requires a large and complex infrastructure that is sensitive to misalignment and is relatively expensive, bulky, and fragile [3]. Here, we demonstrate an all-fibre frequency reference as an alternative to ULE cavities for TF-QKD, offering lower complexity and intrinsic alignment, a simplified setup built with telecom compatible components, and a smaller footprint, which makes it easier to deploy in existing fibre telecom infrastructures.

Two-dimensional periodically poled LiNbO₃ and LiTaO₃ lattices afford unique spectral and spatial functionalities, enabling coherent parametric sources and amplifiers for advanced classical and quantum applications [1,2]. Such capabilities can be further enhanced with structured optical excitations, as highlighted in recent theoretical studies on dual-pump optical parametric generation (OPG) [3]. Here we present results confirming such predictions with experiments in hexagonally poled LiTaO₃ (HexLT) coherently excited by a dual-beam pump at P = 532 nm (Fig.1a, wavevectors k_p1 and k_p2), generating signal (k_s) and idler (k_i) outputs around s ∼ 0.76-0.82 μm and i ∼ 1.50-1.77 μm, respectively. Moreover, we model the OPG process in a semiclassical approximation and 2D beam propagation, extending the results of Ref. [3] beyond plane-wave approximations, to account for realistic experimental conditions. Fig. 1b shows a 2D map of the computed spectral (s) and angular (θs) signal emission from a HexLT lattice pumped by two Gaussian beams whose incidence angles realize the special pump-lattice resonance condition whereby the transverse components of k_p1 and k_p2 match those of reciprocal lattice vectors (G₁₀ and G₀₁ in Fig. 1a). The OPG simulations exhibited excellent agreement with the measured far-field distributions (Fig. 1c) and supported further quantitative analyses of the gain enhancement and coherent OPG response expected in the spectral region of Fig. 1d, explored in subsequent experiments with the setup of Fig. 1e. Fig. 1f shows experimental results (blue circles) alongside simulations (red triangles) and experimental fits (dashed lines), providing evidence for the periodic phase-sensitive response and coherent parametric gain enhancement over single-pump OPG, attainable through control of the relative phase of the two pumps in the HexLT [3]. Further experimental mappings of the signal versus total pump power in dual- and single-pump cases yielded excellent quantitative agreement with the results of our numerical model, resulting in a power amplification factor of around 1.1, matching well the measured visibility seen in the phase-sensitive response of Fig. 1f.

Counterpropagating (CP) χ⁽²⁾ interactions have since the inception of nonlinear optics garnered significant interest due to the unique features of their wave-dynamics and spectral response, stemming from their inherent feedback. The extremely short periods required for their quasi-phase matching (QPM) imply significant technology challenges, that are nevertheless being overcome by advances in periodically poled (PP) materials, with most prominent results achieved in bulk PPKTP under pulsed excitations [1]. Very recently, continuous-wave (CW) operation in ultralow-footprint devices has been achieved on the emerging periodically poled thin film LiNbO₃ (PPTFLN) platform, with symmetric second harmonic generation (SHG) in Z-cut waveguides [2]. Here we present the first results on CP frequency conversion in X-cut PPTFLN, the most widely used cut for photonic integrated circuits in LN [3], which has however proven harder to pole with short periods and high uniformity. At difference to the work of [2], we extensively explore the spectral response in sum frequency generation (SFG) experiments, considering nondegenerate and asymmetric regimes, which provide efficient unidirectional emission.

Polarization control is a crucial functionality for photonic integrated circuits (PIC) used for telecommunication, sensing and quantum key distribution, to name just a few applications [1]. Several approaches have been proposed and demonstrated in silicon and thin-film lithium niobate (TFLN) PICs, entailing birefringence control via stress engineering or waveguide form-birefringence, most often mediated by coupling to higher-order guided modes and combined with electro or thermooptic phase-shifting circuitry [2-3]. Here we present a novel device concept relying on fundamental TE-TM mode coupling in integrated Bragg gratings via the longitudinal fields arising in nanophotonic wires. The device principle can be realized in any PIC platform that provides high light confinement. For its proof-of principle we used our TFLN PICs, achieving perfect agreement between theory and experiments.

The development of a reliable technology for domain engineering in thin film lithium niobate is crucial to leveraging its disruptive potential for integrated nonlinear optics. However, thin film formats present outstanding challenges for traditional poling techniques with specific concern to non-polar cuts and short periods. Here, a novel approach is developed for the periodic poling of x-cut ≈500nm-thick lithium niobate on insulator (LNOI), relying on electron beams. High-quality ferroelectric gratings with periods in the 3.5–0.37 µm range are successfully fabricated, and a comprehensive analysis of their properties by piezoresponse force microscopy is presented, providing evidence for poling in highly non-equilibrium regimes, yielding regular domain gratings that remain stable over several years. Moreover, seamless integration with undoped and 5 mol% MgO-doped LNOI photonic nanowires is demonstrated, together with their nonlinear optical functionality in both co- and counter-propagating waveguide experiments. This novel poling technology appears ideally suited for submicrometric domain patterning of the most widely used cut for LNOI photonic integrated circuits and holds promise for unlocking their full potential for the realization of ultralow-footprint all-optical signal processing chips exploiting engineerable nonlinearities for classical and quantum applications.

We show a record optical amplification-free 400 Gbps PAM4/6/8 net bitrate transmission in the O-band over 500-meter SMF with performance below 6.25% OH HD-FEC threshold using 1 Vpp driving voltage on the TFLN MZM.

Squeezed states of light produced by nonlinear interactions in periodically poled crystals are specially engineered quantum states where the uncertainties in the phase or amplitude quadrature can be traded against each other. These low-noise states have applications in quantum communication, sensing, and computing [1]. To fully exploit these applications, precise phase locking of the squeezed light to a local oscillator (LO) phase is essential. For single-pass waveguides the used locking technique has relied on the injection of a frequency-shifted input seed to generate the error signal [1]. Here we assess the advantages and challenges of implementing a technique originally devised for cavity-based squeezed light sources called quantum noise locking (QNL) [2], which features a simplified feedback structure, eliminating the need for an additional frequency shifted field, thereby avoiding seeding and extra optical components. This work experimentally extends QNL to periodically poled LiNbO₃ waveguides for the first time, which allows for phase controlled squeezing, with less than 10 mrad phase noise, over a 50 GHz bandwidth.

We demonstrate a record 170 Gbaud on-off keying C-band silicon photonics ring resonator modulator-based transmitter with performance below the 6.7% overhead HD-FEC threshold after optical back-to-back and transmission over 100 meters of single mode fiber.

Antibodies, disruptive potent therapeutic agents against pharmacological targets, face a barrier in crossing immune systems and cellular membranes. To overcome these, various strategies have been explored including shuttling via liposomes or biocamouflaged nanoparticles. Here, we demonstrate the feasibility of loading antibodies into exosome-mimetic nanovesicles derived from human red-blood-cell membranes, which can act as nanocarriers for intracellular delivery. Goat-antichicken antibodies are loaded into erythrocyte-derived nanovesicles, and their loading yields are characterized and compared with smaller dUTP-cargo molecules. Applying dual-color coincident fluorescence burst analyses, the loading yield of nanocarriers is rigorously profiled at the single-vesicle level, overcoming challenges due to size-heterogeneity and demonstrating a maximum antibody-loading yield of 38-41% at the optimal vesicle radius of 52 nm. The achieved average loading yields, amounting to 14% across the entire nanovesicle population, with more than two antibodies per loaded vesicle, are fully comparable to those obtained for the much smaller dUTP molecules loaded in the nanovesicles after additional exosome-spin-column purification. The results suggest a promising new avenue for therapeutic delivery of antibodies, potentially encompassing also intracellular targets and suitable for large-scale pharmacological applications, which relies on the exosome-mimetic properties, biocompatibility, and low-immunogenicity of bioengineered nanocarriers synthesized from human erythrocyte membranes.

We report on an optical-amplification-free O-band SiP RRM-based IM/DD link with unprecedented data rates achieved below the 6.25%-OH HD-FEC threshold. Transmission of 206 Gbaud OOK and 112 Gbaud PAM4 over 500-m SMF are successfully demonstrated.