We demonstrate that integrating a high-index doped silica glass waveguide into a large-normal-dispersion fiber ring cavity allows cooperative management of dispersion and nonlinear effects. The tightly confined and birefringent photonic waveguide locally releases the polarization, enabling the generation of vector dissipative solitons. Femtosecond dissipative solitons are obtained with intracavity compression ratios of up to 10.1 and a minimum pulse width of 254 fs. Compared with the fiber-only cavity, integrating the photonic waveguide increases the mode-locking RF signal-to-noise ratio by >10 dB and yields a 67.5% reduction in the integrated relative intensity noise (from 0.0873% to 0.0284%) together with a 58.1% decrease in timing jitter (from 1.567 ps to 0.657 ps). The hybrid cavity further strengthens long-term stability, with the 1-hour RMS power fluctuation decreasing from 0.1000% to 0.0381%, with 61.9% improvement. This work extends the capabilities of integrated photonics in mode-locked lasers and advances the development of low-noise ultrafast fiber lasers.

The intricate process of hormone secretion reveals critical health indicators, including metabolism, stress, and emotional well-being. Cortisol monitoring, in particular, is a valuable diagnostic tool for physical and psychological health. This study introduces a salivary cortisol biosensor by applying a novel type of hollow AgAu nanoislands (HAgAu NIs) materials with enhanced plasmonic effect. The synthesized hollow metallic nanoislands, characterized by their distinctive empty inner cavities, exhibit significantly enhanced localized surface plasmon resonance (LSPR) effect that exceeds conventional solid nanoislands. This enhancement arises from the additional interactions of the plasmon acting on the empty cavity and solid shell, resulting in a greater electric field under light illumination. The enhanced plasmonic effect was analysed through both computational and experimental methods, Finite-Difference Time-Domain (FDTD) simulation reveals an increased electric field in hollow nanoparticles, and experimental results showed improved sensitivity in LSPR-based sensing. The resulting stronger plasmonic effect enhances the biosensing capabilities, showing nearly double the sensitivity compared to conventional nanoislands. Notably, antibodies functionalized HAgAu NIs demonstrated excellent sensitivity for detecting cortisol with a 12.68pg/ml limit of detection. The salivary cortisol detection, ranging from 0.5ng/ml to 25ng/ml, showed linearity with R2 = 0.978, highlighting the practicality and reliability of the developed sensor for clinical applications. In comparison to traditional immunosensors, the demonstrated LSPR-based biosensor offers time-saving and cost-effective functionalities through real-time monitoring and exceptional sensitivity.

We demonstrate the visible supercontinuum generation with emissions of trichromatic lights (red, green and blue) in the slotted highly doped silica glass waveguides which offer extra symmetry-breaking induced $\chi^{(2)}$ beyond the intrinsic $\chi^{(3)}$ nonlinearities. © 2025 The Author(s)

SU(1,1) interferometers use two active parametric amplifiers to replace passive beam splitters of traditional interferometers for wave splitting and superposition. These interferometers involve quantum entangled signal and idler fields and possess a number of advantages over traditional interferometers. Here, we investigate a variant of the SU(1,1) interferometer by using only one parametric amplifier but with either one or both of the signal and idler fields fed back to the same parametric amplifier. Such a geometry is used to accommodate an on-chip micro-ring optical parametric oscillator made of high-index silica glass. An interference fringe is observed, and quantum noise reduction of 4-dB due to destructive quantum interference is measured in the output off the chip. Such an integrated device has potential applications in on-chip precision phase sensing.

Microcombs are optical frequency combs in microresonators [1], [2]. Laser cavity-soliton (LCS) states can be achieved in a system comprising a nonlinear Kerr microresonator nested in a fibre laser [3], resulting in a self-emergent, robust [4], and efficient [5] microcomb. Generally, the platform generally produces a broader variety of states depending on the specific parameter settings of the system. The two critical experimental parameters that need to be adjusted to achieve solitary oscillation via self-emergence [4] are the gain, which controls the state energy, and the length of the main cavity, which governs the group velocity mismatch between the two cavities. When searching for solitary oscillations, these parameters must be spanned over large ranges. While detailed information can be obtained through accurate but time-consuming methods like laser scanning spectroscopy and interferometry, real-time approaches are preferable when handling large datasets. In this work, we introduce a rapid method to distinguish typical lasing states, including soliton states, based on simple experimental properties. Specifically, our approach utilises radiofrequency (RF) data and spectral analysis to map states within nonlinear optical systems in real time, with minimal computational effort when handling large datasets.

Soliton microcombs offer unprecedented laser sources for high-precision ranging due to their merits of high repetition rate, excellent coherence, and compact size. However, high repetition rate limits the nonambiguity range (NAR) of ranging. Previous dual-comb-based methods can extend the NAR, but asynchronous measurement error (AME) is commonly introduced, which greatly limits the ranging accuracy. Here, we propose a cross dual-microcomb absolute ranging scheme based on dispersion-interferometry method. The AME introduced during dynamic measurement is completely eliminated by one-shot spectral sampling, while the NAR is extended from 3 millimeters to 339 meters by Vernier effect when the repetition-rate jitter is 2 hertz. In addition, the excellent system performance has been verified at different distances and the Allan deviation down to 5.63 nanometers after averaging 56 seconds. Our scheme boasts the potential of straightforward chip architecture and minimal detector requirements and provides an advanced method for future high-precision long-distance ranging and miniaturized lidar systems.

Light detection and ranging (Lidar) is indispensable in a variety of fields, encompassing basic science, manufacturing, production, and daily life. Here, from a different perspective, A phenomenon is observed occurring between the optical frequency comb (OFC) and obstacles within the optical frequency domain, which is referred to “breathing spectra,” inspired by the dynamic shape alterations with varying lengths, reminiscent of the oscillatory patterns seen during breathing. Precision length metrology is achieved by retracing the peak positions of dual‐microcomb breathing spectra (DBS) with different repetition rates back to the stable comb optical modes, enabling the attainment of nanoscale accuracy across long distance in a single‐shot measurement while consuming fewer computational resources. Minimum Allan deviations of 1.08 nm at a distance of 0.5 m, and 21.8 nm at a distance of 217 m are experimentally demonstrated. The DBS methodology eliminates the need for auxiliary ranging and other complex steps while being CMOS‐compatible and offering the potential for single‐chip integration, will thus emerge as a competitive and novel alternative in the realm of length metrology applications.

Lasers emitting visible light based on high harmonic generation (HHG) have significantly enhanced measurement capabilities, enabling new applications across precision metrology, attosecond science, and ultrafast time-resolved spectroscopy. This paper discusses the theoretical framework of HHG with a focus on nonlinear effects, examining in depth second-harmonic generation (SHG) and third-harmonic generation (THG) mechanisms, as well as a thermal nonlinear model for pump stability analysis. The current state of HHG within integrated optical circuits is reviewed, with a particular emphasis on its implementation in high-index doped silica glass micro-ring resonators (HDSG MRRs). We conclude by addressing future directions for optimizing these systems to expand their applicability in advanced photonic technologies, highlighting their potential for innovation in both applied and fundamental sciences.

Microcombs require ultralow-noise repetition rates to enable next-generation applications in metrology, high-speed communications, microwave photonics, and sensing, where spectral purity is a central performance metric. Best-performing sources operate actively locked at "quiet points" in parameter space, fixed by device and material properties. Creating broad, low-noise operating regions with relaxed constraints-especially in simplified free-running architectures that avoid electronics-heavy control-remains an open challenge. Here, we demonstrate a symmetry-protected topological Möbius soliton molecule that enables intrinsically low phase noise in a fully free-running microcomb, operating without any external referencing or control. Using a microresonator-filtered laser, we implement a Möbius geometry via interleaved microcavity modes. Upon the formation of a topological Möbius soliton molecule, the free-running laser exhibits over 15 dB of phase-noise suppression across 10 Hz-10 kHz at a 100 GHz repetition rate, yielding -63 dBc/Hz phase noise at 1 kHz and an Allan deviation of 4x10^-10 at 10 s average time-without any external control. We show that the Möbius structure brings dynamic robustness to the comb, and we demonstrate a symmetry-protected topological regime that enables long-term drift-invariant operation. Our results establish a route to intrinsically noise-quenched microcombs operating in a fully free-running configuration, governed by internal physical principles and suitable for field-deployable, low-noise photonic systems.

AbstractMicrowave transversal filters, which are implemented based on the transversal filter structure in digital signal processing, offer a high reconfigurability for achieving a variety of signal processing functions without changing hardware. When implemented using microwave photonic (MWP) technologies, also known as MWP transversal filters, they provide competitive advantages over their electrical counterparts, such as large operation bandwidth, strong immunity to electromagnetic interference, and low loss when processing signals at high frequencies. Recent advances in high‐performance optical microcombs provide compact and powerful multi‐wavelength sources for MWP transversal filters that require a larger number of wavelength channels to achieve high performance, allowing for the demonstration of a diverse range of filter functions with improved performance and new features. Here, a comprehensive performance analysis for microcomb‐based MWP spectral filters based on the transversal filter approach is presented. First, the theoretical limitations are investigated in the filter spectral response induced by finite tap numbers. Next, the distortions are analyzed in the filter spectral response resulting from experimental error sources. Finally, the influence of input signal's bandwidth on the filtering errors is assessed. These results provide a valuable guide for the design and optimization of microcomb‐based MWP transversal filters for a variety of applications.

A laser cavity-soliton (LCS) state can form in a system where a nonlinear Kerr microresonator is embedded in a fibre laser cavity, to produce an optical frequency comb in a microresonator, [1]–[3], resulting in a self-emergent, stable, and efficient microcomb [4], [5]. In general, the system can generate various states depending on specific parameter settings, with two critical parameters for achieving self-emerging solitary oscillations: gain, which controls the soliton's energy, and main cavity length, which governs the group velocity mismatch between the two nested cavities. Hysteresis is a phenomenon in which a system exhibits memory-like behaviour, allowing it to remain in one of two stable states under identical external conditions. This property is associated with bistability. A fundamental aspect of microresonator fibre laser systems is that the emergence of LCS states is intrinsically linked to slow, energy-dependent nonlinearities within the laser cavity [4]. While bistability due to fast Kerr nonlinearity has been extensively studied in soliton formation, it is less understood how the slow energy-dependent nonlinear processes affect it. Investigating this connection is crucial for optimizing the stability and tunability of microcomb states. To demonstrate hysteresis in LCS, we conducted experiments using a dedicated optical setup (Fig. 1a). By sweeping the pump power in opposite directions, we observed the formation of distinct states with different powers (Fig. 1b). Our focus was on the transition between single-soliton and two-soliton states, where we identified a bistable region exhibiting consistent hysteresis (Fig. 1b).

Microcombs, optical frequency combs generated with integrated high Q-factor optical resonators, have emerged as a transformative tool in optics, offering compact chip-scale frequency comb sources that enable advances in metrology, spectroscopy and communications. Limiting factors include efficiency, robustness against environmental noise and long-term stability. A key requirement for many applications is the locking of two major degrees of freedom of the comb, the carrier offset and repetition rate frequencies, on which the positions of the comb teeth depend.

This study presents the use of micro-ring resonator (MRR) devices to extract and enhance nonlinear signals. MRRs “trap” incoming light and, therefore, have been shown to achieve extremely high local intensities of light. Thus, they can be used to facilitate highly nonlinear optical signals that are usually weak in intensity and require high excitation power. By embedding materials that host nonlinear optical processes inside the MRR, we expect to observe an enhancement in the strength of the nonlinear optical signals. This concept is demonstrated here by extracting the Raman signature of graphene that is placed inside a MRR device. A highly doped silica MRR featuring an optical bus waveguide coupled to a ring tuned to near-infrared wavelengths is used. Raman signal with an excitation wavelength of 522 nm via third-harmonic generation inside the MRR is observed. The higher-order Raman signal of the embedded graphene is also observed at the 1597.6 nm excitation wavelength. This work demonstrates the feasibility of the MRR as a nonlinear signal enhancer using high-Q MRR device setups.

Quartz optical fibers are brittle, difficult to repair, and lack reconfigurability, limiting their adaptability in underwater communication. To overcome these impediments, here we show reconfigurable all-liquid optical fibers (RAOFs) produced by structured liquid, tuned by the interfacial assembly and jamming of nanoparticle surfactants at the water-oil interface (interfacial tension <10 mN m-1, refractive index contrast of 0.083). These RAOFs combine the structural stability of the interfacial assemblies with the inherent flexibility of liquids. They support real-time communication on an Ethernet platform (up to 1 Gbps), providing a practical alternative to conventional optical fibers for optical interconnects. Their liquid nature enables broken fibers to be repaired rapidly by a coalescence process. Their softness affords on-demand reconfigurability that enables in-situ fabrication of reconfigurable optical fibers and dynamic manipulation of signal transmission. RAOFs provide a versatile, self-healing, and resilient solution for optical communication systems in dynamic environments.

Recent years have witnessed remarkable progress in enhancing the supercontinuum (SC) generation in highly nonlinear photonic integrated waveguides. In this study, we conduct a comprehensive investigation into supercontinuum (SC) generation in high-index doped silica glass integrated waveguides. We explore a variety of femtosecond pumping wavelengths and input polarization states, demonstrating octave-spanning SC bandwidth from visible to mid-infrared wavelengths.

Frequency-entangled photon pairs play a vital role in various quantum technologies, including quantum computing, quantum communication, and quantum sensing. Broadening the bandwidth of frequency-entangled photon pairs enhances the performance of these technologies. Here, we report the experimental demonstration of the generation of ultra-broadband frequency-correlated photon pairs using a high-index contrast doped glass microring resonator fabricated on a silicon chip. The generated photon pairs exhibit frequency correlation between 106 mode pairs and 212 frequency combs in total, ranging from 1394.0 to 1745.9 nm with the bandwidth of 351.9 nm and covering the telecom E-, S-, C-, L-, and U-bands. The bandwidth of the photon pairs is more than three times larger than the record so far achieved with an on-chip microring resonator. This result will be useful for secure quantum communications and high-resolution quantum optical coherence tomography.

We self-injection lock two DFB lasers to a microring resonator, to enhance frequency-spacing stability, and use these to carry channels with <1 GHz guard-band.

We present a comprehensive investigation of Raman scattering (RS) and supercontinuum (SC) generation in high-index doped silica glass integrated optical waveguides under diverse femtosecond pumping wavelengths and input polarization states. We first report the observation based on a confocal Raman microscope of new Raman peaks different from fused silica at 48 THz and 75 THz, respectively. We then demonstrate broadband supercontinuum generation from 700 nm to 2500 nm when pumping into the anomalous dispersion regime at 1200 nm, 1300 nm, and 1550 nm, respectively. Conversely, narrower SC spectra were generated when pumping in the normal dispersion regime at 1000 nm of self-phase modulation and optical wave breakup. A good agreement is found with numerical simulations of a nonlinear Schrodinger equation including the new Raman response. We also study the impact of the TE/TM polarization modes of the integrated waveguide on SC generation.

We experimentally implement microcomb-based microwave photonic transversal signal processors and test their accuracy for differentiation, integration, and Hilbert transform. A global picture quantifying the impact of different error sources on the overall performance is provided.