Theoretical Analysis of Microcavity Simultons Reinforced by χ

High-Q microcavities with quadratic and cubic nonlinearities add lots of versatility in controlling microcombs. Here, we study microcavity simulton and soliton dynamics reinforced by both χ^{(2)} and χ^{(3)} nonlinearities in a continuously pumped microcavity. Theoretical analysis based on the Lagrangian approach reveals the soliton peak power and gain-loss balance are impacted by the flat part of the intracavity pump, while the dark-pulse part of the pump leads to a nearly constant soliton group velocity change. We also derived a soliton conversion efficiency upper limit that is fully determined by the coupling condition and the quantum-limited soliton timing jitter in the χ^{(2,3)} system. Numerical simulations confirm the analytical results. Our theory is particularly useful for investigating AlN microcombs and sheds light on the interplay between χ^{(2)} and χ^{(3)} nonlinearities within microcavity simultons.

Self-starting spatiotemporal mode-locking using Mamyshev regenerators.

Bridging multi-mode fibers and Mamyshev regenerators holds promise for pulse energy scaling in fiber lasers. However, initialization of a multi-mode Mamyshev oscillator remains a practical challenge. Here we report self-starting spatiotemporal mode-locking (STML) in a multi-mode Mamyshev oscillator without active assistance. The first initialized mode-locking is unstable, but stable STML can be attained by increasing the filter separation. Simulations verify the capability of reaching self-starting STML using Mamyshev regenerators and unveil the effect of filter separation on the self-starting ability.

Fundamental linewidth of an AlN microcavity Raman laser.

Raman lasing can be a promising way to generate highly coherent chip-based lasers, especially in high-quality (high-Q) crystalline microcavities. Here, we measure the fundamental linewidth of a stimulated Raman laser in an aluminum nitride (AlN)-on-sapphire microcavity with a record Q-factor up to 3.7 million. An inverse relationship between fundamental linewidth and emission power is observed. A limit of the fundamental linewidth, independent of Q-factor, due to Raman-pump-induced Kerr parametric oscillation is derived.

Pure quartic solitons in dispersion-engineered aluminum nitride micro-cavities.

Pure quartic soliton (PQS) is a new class of solitons demonstrated in recent years and provides innovations in nonlinear optics and its applications. Generating PQSs in micro-cavities offers a novel way to achieve coherent microcombs, presenting a promising application potential. Here we numerically investigate the PQS generation in a dispersion-engineered aluminum nitride (AlN) micro-cavity. To support PQS, a well-designed shallow-trench waveguide structure is adopted, which is feasible to be fabricated. The structure exhibits a dominant fourth-order dispersion reaching up to -5.35×10-3 ps4/km. PQSs can be generated in this AlN micro-cavity in the presence of all-order-dispersion and stimulated Raman scattering. Spectral recoil and soliton self-frequency shift are observed in the PQS spectrum. Furthermore, we find that due to the narrow Raman gain spectrum of crystalline AlN, the PQS evolves directly to chaos rather than turning into a breather. The threshold pump power with which the PQS turns into chaos is also theoretically calculated, which squares with the simulation results.

Raman pure quartic solitons in Kerr microresonators.

Pure quartic solitons (PQSs) are a unique class of solitons advantageous for developing promising applications due to their broad and flat-top spectrum, as well as the distinctive energy scaling law. Here we investigate the characteristics and dynamics of the PQS in the presence of the Raman effect based on Kerr microresonators. Stimulated Raman scattering leads to reduced pulse peak power, self-frequency shifts, and distortion of the symmetry pulse shape of the PQS. Besides, dynamical evolution of the Raman PQS, especially the breathing state, is investigated. We discover the appearance of an intermediate stable state between the existence region of breathers and chaos in the parameter space, which has not been discovered yet in other soliton regimes. A stability analysis is performed to investigate the spatial dynamics in the context of the Raman PQS.

Vector quartic solitons in birefringent fibers.

We theoretically investigated the vector properties of quartic solitons in a pure fourth-order-dispersion birefringent fiber and a quartic-dispersion-dominant mode-locked fiber laser. We found that, compared with scalar pure quartic solitons, a vector quartic soliton (VQS) in the birefringent fiber still preserves the Gaussian shape, except for the distinctions of reduced peak power, central frequency offset, slight frequency chirp, and mitigated oscillatory tails. We also demonstrated that pulse shaping in the mode-locked laser cavity could explicitly facilitate the formation of Kelly sidebands and distortion of oscillatory tails. Furthermore, dynamical evolutions of quartic group-velocity-locked and polarization-rotating vector solitons were obtained to enrich the nonlinear community of VQSs. We believe that our elaborate findings will bring insights into both the fundamental understanding and potential applications of VQSs.

Self-frequency shift of AlN-on-sapphire Kerr solitons.

We study the self-frequency shift of continuously pumped Kerr solitons in AlN-on-sapphire microcavities with Raman gain bandwidths narrower than the cavity free-spectral range. Solitons are generated in ∼230GHz microcavities via high-order mode dispersion engineering. The dependence of the self-frequency shift on soliton pulse width is measured and differs from amorphous material microcavities. Our measurement and simulation reveal the impact of frequency detuning between the cavity resonances and Raman gain peaks, as well as the importance of all three Raman gain peaks. The interplay between the Raman effect and dispersive wave recoil and a potential quiet point are also observed.

Spatiotemporal Mode-Locking in Lasers with Large Modal Dispersion.

Dissipative nonlinear wave dynamics have been investigated extensively in mode-locked lasers with single transverse mode, whereas there are few studies related to three-dimensional nonlinear dynamics within lasers. Recently, spatiotemporal mode locking (STML) was proposed in lasers with small modal (i.e., transverse-mode) dispersion, which has been considered to be critical for achieving STML in those cavities because the small dispersion can be easily balanced. Here, we demonstrate that STML can also be achieved in multimode lasers with much larger modal dispersion, where we find that the intracavity saturable absorber plays an important role for counteracting the large modal dispersion. Furthermore, we observe a new STML phenomenon of passive nonlinear autoselection of single-mode mode locking, resulting from the interaction between spatiotemporal saturable absorption and spatial gain competition. Our work significantly broadens the design possibilities for useful STML lasers thus making them much more accessible for applications, and extends the explorable parameter space of the novel dissipative spatiotemporal nonlinear dynamics that can be achieved in these lasers.

Buildup dynamics of asynchronous vector solitons in a polarization-multiplexed dual-comb fiber laser.

Polarization-multiplexed dual-comb fiber lasers enable significant applications in dual-comb spectroscopy and optical sensing. However, the complexity of the underlying formation dynamics of dual-comb solitons has not been unveiled so far. Here, we capture the real-time spectral evolutions of both vector solitons from the initial fluctuations, with the help of the time-stretch dispersive Fourier transform technique. Both vector solitons experience the relaxation oscillation, quasi-mode-locking, beating dynamics, and mode locking, accompanying central wavelength shifts in opposite directions, which might be induced by the gain saturation during their buildup processes. Moreover, polarization-dependent gain in the gain fiber leads to the different buildup time of both vector solitons. Our findings open new perspectives for dual-comb buildup dynamics and might impact laser design for applications.

Nonlinear multimode interference-based dual-color mode-locked fiber laser.

We present a dual-color-soliton fiber laser at two different wavebands by nonlinear multimode interference. A saturable absorber (SA) with single-mode-multimode (MMF)-single-mode fiber structure is placed in the common branch shared by two sub-cavities. Saturable absorption effects can be simultaneously satisfied at 1.5 and 2 µm at a proper length of the MMF. Dual-color solitons can still remain, even by slightly tuning the length of the MMF. The periodical characteristic of this SA provides a flexible choice of MMF length, making it simple for simultaneous mode locking (SML) at two separate wavebands in practice. Our approach not only paves the way for SML at two or more wavebands by the MMF but also could lead to significant applications in pump-probe spectroscopy.

Carbon nanotube-synchronized dual-color fiber laser for coherent anti-Stokes Raman scattering microscopy.

In this Letter, we present a passively synchronized dual-color fiber laser at 1.03 and 1.53 µm for coherent anti-Stokes Raman scattering (CARS) microscopy. This fiber laser consists of both Yb- and Er-doped laser cavities, combined by an ∼1.2m common branch with a single-walled carbon-nanotube-based saturable absorber. Stable passively synchronized mode-locked state is obtained within a total cavity length mismatch of 50 µm. We demonstrate the capability of the synchronized dual-color fiber laser for CARS spectroscopy in both low- and high-wavenumber regions, with a resolution of 6.6cm-1. Furthermore, a CARS image in the field of view 150×60µm2 of polystyrene at the Raman shift of 3041cm-1 has also been achieved. The results show the feasibility of our passively synchronized dual-color fiber laser to be employed as a stable and low-cost ultrafast laser source for CARS.

Multiple-soliton in spatiotemporal mode-locked multimode fiber lasers.

Experimental observations of spatiotemporal mode-locked multiple-soliton, including harmonic mode locking and multiple pulses, in multimode fiber (MMF) lasers are reported. Numerical simulations are conducted to investigate the nonlinear dynamics of multi-pulsing. The influences of cavity parameters on the spatiotemporal outputs are analyzed by simulations, which agree with the experimental observations qualitatively. This work would contribute to understanding the complex spatiotemporal nonlinear dynamics in MMF lasers.

Stretchable and upconversion-luminescent polymeric optical sensor for wearable multifunctional sensing.

Stretchable sensors with multiple sensory functions are in high demand for healthcare monitoring and artificial intelligence. Despite recent advances in wearable electronic sensors, it remains a significant challenge to achieve simultaneous sensing of both thermal and mechanical stimuli with a single sensor while integrating high stretchability. Herein, a stretchable and multifunctional optical sensor (SMOS) with simultaneous readout of temperature and strain is developed for wearable physiological monitoring of the human body. The SMOS primarily consists of a stretchable optical sensing fiber made from polymer nanocomposites containing lanthanide-based upconversion nanoparticles (UCNPs). Temperature measurements are achieved by ratiometric intensity measurements of the dual-emission UCNPs upon near-infrared excitation. By virtue of the ratiometric detection, the temperature readout of the SMOS is independent of strain deformations, enabling stable and continuous measurements of skin temperature during body motions. Furthermore, deformation of the SMOS by stretching leads to detectable and reversible changes in its light transmission, allowing tensile strains to be simultaneously measured. As a proof of concept, we demonstrate the capabilities of the SMOS in real time and simultaneous detection of both skin temperature and motion activities of the human body.

Free-running dual-comb fiber laser mode-locked by nonlinear multimode interference.

We present a simple and low-cost approach to generate dual combs from a single fiber-ring cavity based on nonlinear multimode interference. A single-mode fiber-graded-index multimode-single-mode fiber structure serves as an all-fiber saturable absorber for mode-locking. A pair of frequency combs with different comb spacing are generated by dual-wavelength and polarization-multiplexed mechanisms. Stable and simplified dual-comb spectroscopy is achieved using the proposed free-running fiber laser, with no need for complex phase-locking configurations. As a principle of concept, we demonstrate the dual-comb fiber laser for spectral determination of fiber Bragg grating (FBG)-based strain sensors, providing a low-cost alternative for interrogation of FBG-based sensing networks.

Soft and Stretchable Polymeric Optical Waveguide-Based Sensors for Wearable and Biomedical Applications.

The past decades have witnessed the rapid development in soft, stretchable, and biocompatible devices for applications in biomedical monitoring, personal healthcare, and human-machine interfaces. In particular, the design of soft devices in optics has attracted tremendous interests attributed to their distinct advantages such as inherent electrical safety, high stability in long-term operation, potential to be miniaturized, and free of electromagnetic interferences. As the alternatives to conventional rigid optical waveguides, considerable efforts have been made to develop light-guiding devices by using various transparent and elastic polymers, which offer desired physiomechanical properties and enable wearable/implantable applications in optical sensing, diagnostics, and therapy. Here, we review recent progress in soft and stretchable optical waveguides and sensors, including advanced structural design, fabrication strategies, and functionalities. Furthermore, the potential applications of those optical devices for various wearable and biomedical applications are discussed. It is expected that the newly emerged soft and stretchable optical technologies will provide a safe and reliable alternative to next-generation, smart wearables and healthcare devices.

Quantum Dots-Doped Tapered Hydrogel Waveguide for Ratiometric Sensing of Metal Ions.

Advances in fluorescent nanomaterials and photonics have led to a new generation of photonic devices for applications in biosensing, diagnostics, and therapy. However, for clinical utility, biocompatibility and limited light guiding in tissues pose significant challenges. Here, we report a new type of soft, biocompatible, and tapered optical waveguide with capability of delivering light in deep tissues and demonstrate it as a ratiometric probe for rapid point-of-care detection of metal ions. The waveguide was made from quantum dots (QDs)-incorporated biocompatible hydrogels and coated with a thin sensing film to ensure fast exchanges with the surrounding analytes. The tapered design of the waveguide allows more light extraction for efficient excitation of the coating film. To achieve ratiometric measurements, two types of QDs with well-resolved emission bands are synthesized and immobilized in the waveguide and the coating film, respectively. We show that the ratiometric readout of the waveguide sensor is free of environmental disturbances and exhibits negligible drifts when applied in various environments such as being immersed in water or embedded in tissues. The waveguide device provides a new photonic-sensing platform that may allow being engineered to sense a wide range of metal ions and analytes.

Multiplexed static FBG strain sensors by dual-comb spectroscopy with a free running fiber laser.

We demonstrate a novel and compact FBG interrogation system for multiplexed static strain sensing with a free running mode-locked fiber laser. Multiplexed FBG array in cascading are interrogated by coherent dual-comb pulses generated from a single fiber laser. Dual-comb spectroscopy is achieved with the fiber laser to precisely detect the strain-induced spectral shifts of the FBG sensors. Multi-point strain measurements are performed to characterize the proposed system, where a large dynamic range of 520 µÎµ with 0.5 µÎµ resolution is achieved.

In situ surface-enhanced Raman scattering sensing with soft and flexible polymer optical fiber probes.

Surface enhanced Raman scattering (SERS) fiber sensors have shown great potential in sensitive biosensing and medical diagnostics. However, current SERS fiber probes are most commonly based on stiff silica fibers, which, unfortunately, are not mechanically compliant with soft biological tissues. In addition, the poor biocompatibility of silica fibers sets another barrier that hinders their development for biomedical applications. Here, we present, to the best of our knowledge, the first demonstration of soft-polymer-optical-fiber-based SERS (SPOF-SERS) probes with physio-mechanical properties suitable for implantation, and demonstrate their potential applications for in situ detection of bioanalysts. The SPOFs are made from porous hydrogel materials that are soft, elastic, and biocompatible. The three-dimensional porous structures of the hydrogels enable high loading of metal nanoparticles to provide a large amount of SERS "hot spots" for high sensitivity. We tested the SPOF-SERS sensor for detection and discrimination of rhodamine 6G and 4-mercaptopyridine in situ with detection limits of 10-7 M and 10-8 M, respectively. We also demonstrated the capability of SPOF-SERS probes in multiplexing detection. The soft, biocompatible, and highly sensitive SERS probe is promising for bioanalytical and implantable biomedical applications.

Observation of soliton molecules in a spatiotemporal mode-locked multimode fiber laser.

We report on the first experimental observation, to the best of our knowledge, of soliton molecules in a spatiotemporal mode-locked multimode fiber (MMF) laser. By adjusting the waveplates inside the cavity, not only the spatiotemporal mode-locking state with a stable single pulse but also soliton molecules are observed. Various soliton molecules, including soliton pairs, soliton triplets, and soliton quartets with different pulse separations, are achieved. Transition of different operation states with pump power is given. The results would be beneficial for further understanding of the nonlinear dynamics in spatiotemporal mode-locked MMF lasers.

LINC00511 interacts with miR-765 and modulates tongue squamous cell carcinoma progression by targeting LAMC2.

BACKGROUND: Aimed at underlying the molecular regulatory mechanism and overall biological functions of LINC00511 in tongue squamous cell carcinoma (TSCC). METHODS: The expression level of LINC00511 was examined by QRT-PCR. In particular, Tca-8113 cell line was selected for subsequent experiments, in which the expression level of LINC00511 was the most significant. Meanwhile, the effects of LINC00511 on cells proliferation, cell cycle distribution, and invasion of TSCC cells were explored using RNA knockdown tools with CCK-8, flow cytometry analysis, colony formation, and transwell assay. Further, bioinformatic analysis and the dual-luciferase reporter assay both were conducted to invalidate the ceRNAs regulatory mechanism of LINC00511 in TSCC. RESULTS: LINC00511 was obviously upregulated in TSCC tissues and cell lines. Moreover, it was found that LINC00511 served as a competing endogenous RNA (ceRNA) through sponging miR-765 and ultimately modulated the derepression of laminin subunit gamma 2 (LAMC2). The inhibitory effects of miR-765 on TSCC cells proliferation, invasion as well as cell cycle distribution can be restored by the ectopic overexpression of LINC00511. Additionally, the restored capacity of LINC00511 promoted the expression of LAMC2, which was a downstream target of miR-765 and can be negatively regulated by miR-765. CONCLUSIONS: A novel molecular axis of LINC00511/miR-765/LAMC2 was investigated to regulate the tumor development of TSCC. LINC00511 promoted the expression of LAMC2 via the ceRNA mechanism of sponging miR-765. The ceRNA regulatory network provided a novel understanding of TSCC pathogenesis and also shed light on exploiting the new field of lncRNA-directed therapy against TSCC.