Terahertz (THz) scattering-type scanning near-field optical microscopy (s-SNOM) is an important means of studying and revealing material properties at the nanoscale. The nanotip is one of the core components of THz s-SNOM, which has a decisive impact on the resolution of the system. In this paper, we focus on the theory and design of the nanotip and conduct comprehensive research on it through simulation. The theoretical model is based on full-wave numerical simulation and dipole moment analysis, which can describe the overall nanotip electromagnetic response under the incident field. A comprehensive design model of nanotip geometry, sample materials, and incident field is established to significantly improve the near-field coupling efficiency and spatial resolution to achieve optimal performance.

In this study, we proposed and experimentally demonstrated an electro-optic modulator with a small footprint and high modulation efficiency, achieved through the utilization of a mode-folded phase shifter with lumped electrodes. The three-mode phase shifter recycles the light three times with different waveguide modes while leading to a pronounced tightening of the optical field confinement. We experimentally obtained a 3.7-times improvement in the modulation efficiency. A low VπL for thin-film lithium niobate (TFLN) Mach–Zehnder modulators of 1 V·cm is realized with a device footprint of 2.7 mm × 0.6 mm (0.5 mm for the phase shifter). Even greater improvements in modulation efficiency can be expected through the incorporation of additional modes.

Microwave photonics (MWP) studies the interaction between microwaves and light waves, including the generation, transmission, and processing of microwave signals. Integrated MWP using photonic integrated circuits (PICs) can achieve compact, reliable, and green implementation. However, most PICs have recently been developed that only contain one or a few devices. Here, we propose a multi-channel PIC that covers almost all devices in MWP. Our PIC integrates lasers, modulators, amplifiers, and detectors in the module, successfully manufacturing an eight-channel array transceiver module. We conducted performance tests on the encapsulated transceiver module and found that the cascaded bandwidth of the eight-channel transceiver module was greater than 40 GHz, and the spurious-free dynamic range (SFDR) of the broadband array receiver module was greater than 94 dBm · Hz2/3. The noise figure (NF) is less than -35 dB and the link gain is greater than -26 dB. The success of multi-channel PIC marks a crucial step forward in the implementation of large-scale MWP.

In recent years, thin-film lithium niobate (TFLN) electro-optic (EO) modulators have developed rapidly and are the core solution for the next generation of microwave photonics (MWP) problems. We designed and fabricated a dual-parallel Mach–Zehnder modulator (DPMZM) based on TFLN, achieving a 3 dB electro–electro (EE) bandwidth of 29 GHz and a low drive voltage (Vπ = 6 V). The device we manufactured is metal-encapsulated. It is noteworthy that we proposed a single-channel Doppler frequency shift (DFS) measurement system based on this device and conducted verification experiments. We coupled light from an external laser into the chip and passed it through each of the two sub-MZMs of the DPMZM. These lights were modulated by echo signals and reference signals. By measuring the frequency of the output signal, we can obtain a DFS value without directional ambiguity. The success of this experiment marks a key step in the practical application of TFLN modulators in MWP.

We have developed a remote sea salt aerosol fluorescence spectroscopy system integrating a high-power industrial-grade femtosecond laser to enhance detection sensitivity and precision in complex environments. This system successfully detects sea salt aerosol particles, achieving a detection limit of 0.015 ng/m3 for neutral Na element (Na I) at 589 nm, with a detection range of 30 m. Our findings demonstrate significant improvements in remote aerosol monitoring, addressing previous challenges in long-range and high-precision sensing with a detection accuracy previously unattainable below 10 ng/m3.

In this Letter, we propose a scheme to generate helical optical fields with multi-freedom controllable features. High-quality helical lobes with adjustable radii, chirality, and lobe numbers can be generated by tuning the phase term of two paired high-order Bessel beams. Furthermore, the pitch of the helical beam can be controlled by combining another rotational phase term. The validity of our scheme is demonstrated in both simulations and experiments. Our scheme is promising to facilitate the rapid fabrication of helical structures with diverse parameters, which are critical in various applications, such as optical metamaterials, biology, and particle transport.

In this Letter, waveguide beam splitters (1 × 3) with type I modifications are fabricated in a LiNbO3 crystal by femtosecond laser direct writing. The influence of the relative positions of three sub-waveguides on power splitting ratios are investigated in detail and the corresponding output intensities as functions of the relative positions in the numerical simulation are plotted, which are in good accordance with the experimental results. In addition, the waveguide beam splitter with a 1:1:1 splitting ratio is fabricated by changing the relative widths of the three branch-waveguides. Guiding performances at 532 nm are measured and analyzed by a typical end-face coupling system. The simulation and experimental results demonstrate that the beam splitting ratio of the waveguide splitter can be precisely regulated by the positions and widths of the sub-waveguides.

We proposed an approach for the generation of interference-pattern helico-conical beams (HCBs) both theoretically and experimentally. The HCBs exhibiting intricate fringe structures are obtained by exploiting amplitude modulation and interference techniques. To precisely control the optical field distributions, we manipulate the azimuthal term within the helico-conical phase expression, presenting several illustrative cases that highlight the versatility of our approach. Through further combinations, more sophisticated comprehensive HCB patterns are investigated. This study deepens our knowledge about spiral-like optical patterns and paves a new avenue for potential applications, especially in the fields of particle manipulation, nanostructure fabrication, and optical metrology.

Due to the promising applications of femtosecond laser filamentation in remote sensing, great demands exist for diagnosing the spatiotemporal dynamics of filamentation. However, until now, the rapid and accurate diagnosis of a femtosecond laser filament remains a severe challenge. Here, a novel filament diagnosing method is proposed, which can measure the longitudinal spatial distribution of the filament by a single laser shot-induced acoustic pulse. The dependences of the point-like plasma acoustic emission on the detection distance and angle are obtained experimentally. The results indicate that the temporal profile of the acoustic wave is independent of the detection distance and detection angle. Using the measured relation among the acoustic emission and the detection distance and angle, a single measurement of the acoustic emission generated by a single laser pulse can diagnose the spatial distribution of the laser filament through the Wiener filter deconvolution (WFD) algorithm. The results obtained by this method are in good agreement with those of traditional point-by-point acoustic diagnosis methods. These findings provide a new solution and idea for the rapid diagnosis of filament, thereby laying a firm foundation for femtosecond laser filament-based promising applications.

Light detection and ranging (lidar) has attracted significant interest as a sensing technology for its ability to achieve high-resolution imaging and wide-angle perception. However, conventional lidar systems, built with separate components, are often bulky, expensive, complex, and prone to instability. In contrast, solid-state lidar, based on silicon photonics technology, offers a solution with its compact size, less expense, low energy consumption, and improved reliability. However, achieving precise beam steering remains a critical challenge for integrated lidar systems. Various methods have been demonstrated for beam steering, which is one of the simplest and most efficient approaches that utilize wavelength tuning with a grating coupler antenna. In this review, we introduce the fundamental principle of optical phased array for beam steering and provide an overview of the recent advancements in integrated solid-state lidars utilizing orthogonal polarizations and counterpropagation to enhance beam-steering range and angular resolution.