In this paper, we studied the dynamics of a dispersion-tuned swept-fiber laser both experimentally and theoretically. By adding a dispersion compensation

In this paper, we studied the dynamics of a dispersion-tuned swept-fiber laser both experimentally and theoretically. By adding a dispersion compensation fiber and an electro-optic modulator in the laser cavity, an actively mode-locked laser was obtained by using intensity modulation, and wavelength sweeping was realized by changing the modulation frequency. Using a high-speed real-time oscilloscope, the dynamic behaviors of the swept laser were investigated during wavelength switching, static-sweeping cycle, and continuous sweeping, respectively. It was found that the laser generates relaxation oscillation at the start of the sweeping mode. The relaxation oscillation process lasted for about 0.7 ms, and then the laser started to operate stably. Due to the nonlinear effect, new wavelengths were generated in the relaxation oscillation process, which is not beneficial for applications. Fortunately, relaxation oscillation disappears if the laser starts up and operates in the continuous sweeping mode, and the good sweeping symmetry between the positive sweep and negative sweep increases the application potential of the laser. In addition, the instantaneous linewidth is almost the same as that in the static state. These results describe the characteristics of the laser from a new perspective and reveal, to the best our knowledge, the intensity dynamics of such lasers for the first time. This paper provides some new research basis for understanding the establishment process of dispersion-tuned swept-fiber lasers and their potential application in the future.show less

Fifth-generation (5G) communication requires spatial multiplexing multiple-input multiple-output systems with integrated hardware. With the increase in th

Fifth-generation (5G) communication requires spatial multiplexing multiple-input multiple-output systems with integrated hardware. With the increase in the number of users and emergence of the Internet of Things devices, complex beamforming devices have become particularly important in future wireless systems to meet different communication requirements, where independent amplitude and phase modulations are urgently required for integrated beamforming devices. Herein, by utilizing the constructive interference between multiple geometric-phase responses, the mathematical relation for decoupling amplitude and phase modulations in the radiation-type operational mode is derived. Based on this strategy, complex-amplitude radiation-type metasurfaces (RA-Ms) are implemented, with an integrated feeding network. Such metasurfaces exploit full 2π phase modulation and tailorable radiation amplitude in the circular polarization state. Meanwhile, a complex-amplitude retrieval method is developed to design the RA-Ms, enabling precise beamforming performances. On this basis, several functional devices based on the complex-amplitude RA-Ms, including energy-allocable multi-router, shape-editable beam generator, and complex beamformer, are demonstrated in the microwave region. The amplitude-phase decoupling mechanism with the retrieval method merges amplitude and phase modulations, and energy distribution into one compact and integrated electromagnetic component and may find applications in multi-target detection, 5G mobile communication, and short-range ground-to-sea radar.show less

Two-color plasma, induced by two lasers of different colors, can radiate ultra-broadband and intense terahertz (THz) pulses, which is desirable in many te

Two-color plasma, induced by two lasers of different colors, can radiate ultra-broadband and intense terahertz (THz) pulses, which is desirable in many technological and scientific applications. It was found that the polarization of the emitted THz depends on the phase difference between the fundamental laser wave and its second harmonic. Recent investigation suggests that chirp-induced change of pulse overlap plays an important role in the THz yield from two-color plasma. However, the effect of laser chirp on THz polarization remains unexplored. Hereby, we investigate the impact of laser chirp on THz polarization. It is unveiled that the chirp-induced phase difference affects THz polarization. Besides, positive and negative chirps have opposite effects on the variation of the THz polarization versus the phase difference. The polarization of THz generated by a positively chirped pump laser rotates clockwise with an increasing phase difference, while it rotates anticlockwise when generated by a negatively chirped pump laser.show less