Chunlei Yu

We demonstrate a mechanism-oriented Surface-Enhanced Raman Scattering (SERS) platform based on a hybrid structure integrating monolayer molybdenum disulfide (MoS₂) and gold nanospheres (AuNSs) on an optical microfiber (MF). The microfiber serves as a whispering-gallery-mode (WGM) microcavity. Monolayer MoS₂, grown directly on the microfiber surface via chemical vapor deposition (CVD), provides a chemically active interface for molecular adsorption and charge-transfer-related chemical enhancement. Subsequently deposited AuNSs couple with the microfiber-supported WGM, leading to the formation of hybrid photonic–plasmonic modes. This coupling results in a narrowed scattering resonance and a localized electromagnetic hotspot near the AuNS–microfiber interface. The combined contribution of electromagnetic enhancement from the microfiber–AuNS hybrid cavity and chemical enhancement from the MoS₂ layer produces discernible Raman enhancement for Rhodamine 6G (R6G) molecules under proof-of-concept measurement conditions. This work provides a useful platform for studying SERS enhancement mediated by hybrid photonic–plasmonic modes and offers guidance for the future development of optimized fiber-based SERS sensors.

Power scaling of neodymium (Nd)-doped single-frequency fiber lasers (SFFLs) operating at approximately 900 nm has been fundamentally constrained by dominant emission of approximately 1060 nm, with previous demonstrations limited to below 3 W. Here, we demonstrate a 910 nm single-mode Nd-doped SFFL system that achieves a record output power of over 30 W employing homemade Nd-doped silica fiber (NDF), while preserving exceptional 49 dB suppression of competing emission of approximately 1060 nm. The laser system originates from a distributed Bragg reflector single-frequency (SF) oscillator with 11 mW output power, which is subsequently amplified to 31.1 W through three polarization-maintaining (PM) amplification stages utilizing PM 10/125 μm NDF. To the best of our knowledge, this represents the highest power achieved for Nd-doped SFFLs in this spectral region. The output exhibits excellent beam quality ( M _x ² = 1.03, M _y ² = 1.05) and narrow linewidth (10.2 kHz). These results validate that the homemade PM 10/125 μm NDF can be employed in intermediate and main amplifiers in all-fiber SF master oscillator power amplifier systems at approximately 900 nm.

Wavefront shaping has revolutionised imaging through multimode fibers, but translating this into a robust sensing modality has been challenging. Here we report a mechanical-sensing platform that combines wavefront shaping with focal-spot feature analysis to convert subtle intermodal coupling changes into quantitative force readouts. Singular value decomposition isolates dominant image features, and Euclidean distance metrics track their evolution under load. Unlike speckle-correlation or SMS sensors that rely on global speckle statistics or dedicated fabrication steps, our approach tracks a wavefront-shaped, localized feature and yields a fabrication-light and linear readout. The sensor delivers a sensitivity of 8.9×10⁻³ N⁻¹, a linear measurement range up to 5 N, and a force resolution of 0.05 N. Spatial mapping reveals that focal spots located midway between the fiber center and periphery offer the highest sensitivity, providing design guidelines for future devices. The approach unites imaging-grade wavefront control with robust feature extraction, opening a path to compact, high-performance fiber sensors for biomedical diagnostics, industrial force monitoring and environmental metrology.

Novel upconversion phosphors of CaLaAl ₃ O ₇ :RE ³⁺ /Yb ³⁺ (RE = Tm, Ho) exhibit exceptional multi-color luminescence under 980 nm laser excitation, making them highly promising for advanced applications such as anti-counterfeiting and laser displays.

Fiber Bragg gratings (FBGs) are widely used in high-radiation environments owing to their high sensitivity, stability, and resistance to electromagnetic interference. In this study, pure and Ge-doped silica core fibers were fabricated using chemical vapor deposition. Based on these fibers, two temperature sensors, FBG-Si and FBG-Ge, were developed using femtosecond laser direct writing combined with metalized armoring. The fibers and sensors were exposed to gamma radiation, and their stability, temperature accuracy, and refractive index were systematically evaluated. Electron paramagnetic resonance and radiation-induced loss were used to investigate the effects of gamma radiation on the fiber materials and temperature sensors at the atomic micro-scale. The results showed that the Bragg center wavelength (λB) of the FBGs linearly redshifted with increasing temperature under non-stressed conditions. After gamma irradiation, at a temperature, λB, redshifted further with increasing radiation dose. The FBG-Si sensor exhibited higher stability and smaller temperature errors than FBG-Ge. Both sensors exhibited a decrease in output power after irradiation. The performance degradation of the FBGs after irradiation is attributed to an increase in the number of color centers and defects within the grating, leading to higher transmission losses. As the radiation dose increased, the concentration of the color centers increased, leading to changes in the refractive index of the gratings. This ultimately resulted in a redshift in λB and caused temperature measurement errors.

We demonstrate a versatile bismuth-doped fiber pulse source that is seeded by a mode-locked fiber laser operating in different regimes with different net dispersions in the same cavity, including the square-wave noise-like pulse regime with anomalous net dispersion at 1331 nm and the multi-pulse soliton regime with normal net dispersion at 1320 nm. The versatile pulse evolutions and the multi-pulse dynamics in these two regimes are investigated under different pump powers or polarization states. The seed pulses are then amplified by a bismuth-doped fiber amplifier, which boosts the pulse energy to 21 nJ with a slope efficiency of 21.3% without power saturation and is anticipated to be useful for practical applications.

In this Letter, a homemade bismuth-doped germane silica fiber (BGSF) with a high gain coefficient is fabricated. Based on this fiber, a single-frequency fiber laser (SFFL) operating at 1440 nm is successfully realized. A ring cavity with a short BGSF of 10 m and two cascaded sub-ring cavities ensures the single-longitudinal-mode (SLM) operation. The maximum SLM laser output power of about 6 mW is obtained with the optical signal-to-noise ratio (OSNR) of more than 75 dB. The linewidth of the stable SLM laser is about 745 Hz, measured by the delayed self-heterodyne method. To the best of our knowledge, this is the first SFFL operating at 1440 nm based on the bismuth-doped fiber (BDF), demonstrating the great potential of BDF in expanding the operating band of SFFL.

Efficient light coupling into the fiber waveguides is important in numerous applications, while the low in‐coupling coefficients of commercially available step‐index fibers significantly narrow their application domains. It is recently introduced that well‐defined periodic nanostructures, such as annulus gratings, allow to substantially boost in‐coupling coefficients. In this study, the genetic algorithm is applied for the optimization of trapezoidal polymer gratings. The experimental data showcase multiply enhanced light coupling at preselected incident angles with respect to a bare fiber. As a breakthrough result, the development of an axial‐asymmetric four‐sector grating, reaching the percentage level of light coupling efficiency in a broad angular range from 0 to 70 that outperforms axial‐symmetric gratings by about order of magnitude. Further, the high average light coupling efficiency is verified in the finite angular intervals at multiple wavelengths of 650, 1000, and 1550 nm. This solution highlights the enhancement of algorithm‐designed structures axially‐asymmetric systems for fiber‐based highly efficient light collections, that will further benefit extensive applications such as wide‐field endoscopies.

Rare-earth-doped silica-based composite glasses (Re-SCGs) are widely used as high-quality laser gain media in defense, aerospace, energy, power, and medical applications. The variable regional chemical environments of Re-SCGs can induce new photoluminescence properties of rare-earth ions but can cause the selective aggregation of rare-earth ions, limiting the application of Re-SCGs in the field of high-power lasers. Here, topological engineering is proposed to adjust the degree of cross-linking of phase-separation network chains in Re-SCGs. A combination of experimental and theoretical characterization techniques suggested that the selective aggregation of rare-earth ions originates from the formation of phase-separated structures in glasses. The decomposition of nanoscale phase separation structures to the sub-nanometer scale, enabled by incorporating Al³⁺ ions, not only maintains the high luminescence efficiency of rare earth ions but also increases light transmittance and reduces light scattering. Furthermore, our investigation encompassed the exploration of the inhibitory mechanism of Al³⁺ ions on phase-separation structures, as well as their influence on the spectral characteristics of Re-SCGs. This work provides a new design concept for composite glass materials doped with rare-earth ions and could broaden their application in the field of high-power lasers.