Implementing compact, efficient, and reliable passive pulsed lasers at visible wavelengths is attractive. This paper systematically investigated the thickness-dependent optical absorption characteristics of two-dimensional materials, including graphene, transition-metal dichalcogenides, and dye films at the 532 nm wavelength band, and revealed the effects of thickness on different optical absorption parameters. The results suggested that dye films are more suitable for loss-sensitive pulsed lasers and graphene is more suitable for modulation depth-sensitive pulsed lasers, while transition-metal dichalcogenide samples have intermediate performance. It can provide guidance for the rational selection of saturable absorbers in pulsed all-fiber lasers to optimize the optical pulse performance in the visible-wavelength band.

Broadband and tunable microwave signals are widely used in modern communication systems and sensing systems. In this work, we demonstrate a stable and tunable optoelectronic oscillator (OEO) scheme based on external low-power beat note injection of the stimulated Brillouin signal and a phase modulation sideband of the original pump signal. The injection-locked system reduces the high-frequency disturbance induced by the beat note signal, and thus the power required only meets the OEO locking threshold requirement. In addition, the external stimulated Brillouin signal generator avoids the excessive length of the resonant cavity and guarantees the frequency stability, especially the mode stability in the OEO with a total path length of ~12 m. By varying the stimulated Brillouin signal frequency and selecting different pump modulation sidebands, a continuously tuned beat note is generated, and a beat note injected OEO with a maximum frequency up to 11.5 GHz is achieved, which is the intrinsic upper frequency limit of the devices used, even for an injection beat frequency power as low as -14 dBm ( ~ 40 μ W). Our work provides an important solution for the realization of widely tunable microwave systems.

By using an external injection locking method, for what we believe to be the first time, we experimentally demonstrate continuous ultra-wideband signal regeneration in random optoelectronic oscillators, achieving more adaptable signal processing capabilities than self-oscillation methods. Supported by theoretical analysis and experimental evidences, this system can regenerate any signal with sufficient gain in a random-feedback cavity, independent of cavity filters. Remarkably, enhanced phase noise performance with over 35.2 dB side mode suppression and a phase noise better than −86 dBc@1 kHz at higher injecting powers are demonstrated. Additionally, we successfully process complex multi-frequency communication signals, indicating potential applications in radar, remote sensing, and data communications.

Experimental near‐field analysis of the output beams from the end faces of micro/nano‐waveguide is very necessary, because important information such as spatial intensity distributions, mode orders, and divergence angles can be obtained, and are very important for investigating and designing nanophotonic devices. However, as far as we know, it has not been demonstrated yet. In this work, we experimentally demonstrate a plasmonic‐nanowire near‐field beam analyzer, utilizing a single Au nanowire (AuNW) as the probe to scan the spatial near‐field distributions of emitted beams from micro/nano‐waveguide end‐faces. Our analyzer can resolve the trade‐off between high measurement resolution and light collection efficiency in conventional beam analyzers by a reverse nanofocusing process, achieving a probe resolution of 190 nm (< λ /8) and a simulated collection efficiency of ∼47.4 % at λ = 1596 nm. These attractive advantages allow us to obtain three‐dimensional (3D) scanning in a large range from the plasmonic hotspot region to the far‐field region, characterizing the 3D spatial distribution evolution from a metal nanowire output beam for the first time, with an M ² factor lower than that of the ideal Gaussian beam ( M ² = 1). In addition, the analyzer also demonstrates simultaneous characterization of multimodes in irregular and large‐sized nanoribbons, further verifying its ability to selectively explore complex multimodes that are difficult to be predicted by numerical simulations. Our results suggest that this plasmonic‐nanowire beam analyzer may hold promise for diverse near‐field applications for micro/nano‐waveguides such as nanolasers and biosensing, and offer a new method for understanding nanophotonic structures.

In this paper, we propose a passive near-field scanning imaging system by using the structure of cadmium sulfide (CdS) nanowire/tapered microfiber probe, which combines the near-field scanning structure and the nanowire/microfiber coupling technology. In the passive near-field scanning imaging system, a passive nanoprobe is adopted to detect the intensity change of the reflected light field on the sample surface, which not only retains the advantage of the nanoprobe for the strong restriction of the reflected light on the sample surface, but also reduces the interference of strong excitation light during detection. Through the high efficiently evanescent field coupling between the CdS nanowire and the tapered microfiber, the collected light signal is transmitted to the photodetector in the far field, and finally the imaging of the target sample morphology can be realized.At first, the light field model of the nanowire/tapered microfiber probe structure is verified by the finite element analysis method. The calculated collection efficiency from the sample to the probe is about 4.65‰ and the transmission efficiency from the nanowire to the tapered microfiber is about 74.47%. The collection efficiency is improved by an order of magnitude compared with traditional metal-coated near-field probe. In the experiments, a scanning step of 20 nm and a probe-sample distance of 230 nm are selected. The nanowire/tapered microfiber probe and traditional tapered fiber probe are both used to measure the widths of different CdSe nanoribbons samples, and the atomic force microscopy measurement is used as the benchmark to calculate their measurement error, which is increased about 3 times. By changing the angle θ between the probe and the sample, it is found that the resolution obtained using the designed nanowire/microfiber probe is always higher than only using the tapered microfiber probe. Comparing with the tapered microfiber probe scheme, the measurement error is reduced to a value less than 7.2%.In addition, compared with the active luminescence probe scheme, this passive near-field scanning scheme reduces the preparation complexity of the optical probe and the detection structure complexity of the optical system. The large microscopic illumination area can avoid the influence of the small laser spot size on imaging, and the imaging range is determined only by the travel distance of the linear stage. Therefore, our work may provide an attractive approach for developing new near-field scanning microscopy systems in the future.