Dual-comb ranging (DCR) is a powerful technique for high-precision distance measurement. DCR based on nonlinear asynchronous optical sampling (ASOPS) is practical for field applications, since it does not require mutually coherent optical frequency combs. However, high laser power is usually needed for nonlinear frequency conversion. To alleviate this issue, we introduce a DCR method based on two-color nonlinear ASOPS by utilizing efficient Type-0 phase matching in a periodically poled lithium niobate (PPLN) crystal. In the experiment, a pair of mode-locked Er-fiber lasers centered at 1540 nm and 1580 nm were used to generate a sum frequency signal at 780 nm, which was selected by a narrow bandpass filter for background-free time-of-flight (ToF) measurements. We achieved < 3 µm ranging precision at 100 ms acquisition time with an echoed laser power of 5 µW. The dynamic performance was confirmed by tracking a moving translation stage.

In this article, we present a new phase noise reduction structure for oscillators based on a six-port frequency discriminator (FD) using a multiplexer. In general, the FD for oscillators requires the inputs to be orthogonal, while the proposed FD circuit can operate at any phase condition. In this way, the circuit can be greatly simplified since no phase controls are needed. Unlike previously reported solutions where analog multipliers were used, the proposed FD uses a multiplexer to achieve an infinite phase extraction range. The replacement of multiplier by the multiplexer in FD benefits from a wider power detection range and lower power consumption, which makes it more suitable for integration. An experimental FD prototype for phase noise suppression of a 10.7 GHz dielectric resonator oscillator (DRO) has been carried out and the results show that 30 dB phase noise suppression at close-in offset frequencies (30 Hz–3 kHz) has been achieved.

This study reports a counterintuitive antisymmetric deformation behavior during the electrohydraulic sheet-forming process, which is induced by the positional eccentricity of the electrical explosion. The novelty lies in the antisymmetry between the explosion eccentricity and the position of maximum deformation. When the explosion position is eccentric, the sheet metal becomes naturally eccentric; however, herein the position of maximum deformation was found to be far away from the position of the eccentric explosion, instead of being close to it. Herein, a series of simulations was performed to understand the dynamics involved in such behavior. It was found that the shockwave pressure and the inertial force of water medium are two dominant mechanisms for such an antisymmetric phenomenon. The former tends to accelerate the explosion-side sheet region, and the latter tends to accelerate the explosion-opposite-side sheet region. The much longer duration of the inertial force of water finally results in the observed antisymmetric phenomenon. The experimental results of the high-velocity deformation process obtained by using a high-speed camera confirmed the abovementioned findings. This study may aid in better understanding of the process dynamics in the eccentric explosion electrohydraulic forming, and may also help in the process and equipment design.

Optical solitons have emerged as a highly active research domain in nonlinear fiber optics, driving significant advancements and enabling a wide range of practical applications. This study investigates the dynamics of dark solitons in systems governed by the resonant nonlinear Schrödinger equation (RNLSE). For the RNLSE with third-order (3OD) and fourth-order (4OD) dispersions, the dark soliton solution of the equation in the (1+1)-dimensional case is derived using the F-expansion method, and the analytical study is extended to the (2+1)-dimensional case via the self-similar method. Subsequently, the nonlinear equation incorporating perturbation terms is further studied, with particular attention given to the dark soliton solutions in both one and two dimensions. The soliton dynamics are illustrated through graphical representations to elucidate their propagation characteristics. Finally, modulation instability analysis is conducted to evaluate the stability of the nonlinear system. These theoretical findings provide a solid foundation for experimental investigations of dark solitons within the systems governed by the RNLSE model.

Active feedback has been employed in the context of DFB lasers to generate chirp signals with narrow linewidth. While recent works often adopt heterodyne structures, homodyne structures, despite their simplicity, struggle to stabilize lasers at the in-phase point of delay line frequency discriminators for long term. This study introduces an active feedback method employing a 3 × 3 optical coupler and digital signal processing to break the phase limitation of homodyne delay line frequency discriminators, thus facilitating the generation of arbitrary frequencies. The proposed structure enables precise control of laser frequency with high linearity. This approach also achieves a linewidth reduction in DFB laser from 2.4 MHz to 5.8 kHz. The jitter is reduced from 56 ps to 30 fs (integrated within 10 Hz – 1 MHz). Additionally, the frequency tuning range of laser exceeds 6 GHz and its time response achieves a level on the order of a few hundred nanoseconds.

Millimeter-wave imaging provides a human-body scanning method without potential health damage and has the potential to distinguish objects made of different materials. Therefore, it is a promising technique to realize fast, safe and real-time human-body detection. In this paper, dielectric properties are used to distinguish objects of different materials. Dielectric constants of different targets were calculated through electromagnetic simulation by two methods. The results show that geometric optics approach is more accurate than free-space method in submillimeter-wave band and it has the potential to be used for human screening in the future.