In recent years, the photoelectric properties and nonlinear optical properties of layered metal chalcogenides (LMCs) have attracted extensive attentions. Because of lower phonon thermal conductivity, larger energy storage rate, and larger electron mobility, LMCs are widely studied in the fields of thermoelectric energy conversion, battery electrode materials, and semiconductor devices. As 2D LMCs, SnSe2 nanosheets (Ns) are connected to each other by van der Waals force, which makes it possible to use electrochemical methods to help peel off the thin layer structure. Two-dimensional SnSe2 has obvious adjustable band gap characteristics. Its thickness can be controlled to keep it on the desired band gap. In this article, we prepared a thin layer of SnSe2 by electrochemical methods and detected its nonlinear optical characteristics. It shows that our prepared materials have good optical absorption characteristics; it has a modulation depth of 15% and a saturation intensity of 61 MW/cm2. To investigate the nonlinear effects of SnSe2 in short and long cavities, the Q-mode-locking phenomenon was first achieved in a fiber laser with cavity length of 6 m. After increasing the cavity length to 56 m, the pump power is adjusted to achieve an adjustable repetition frequency from MHz to GHz in turn in an Er-doped fiber laser through utilizing an SnSe2 incorporating a tapered fiber as a saturable absorber (SA). The nonlinear optical properties of thin layer SnSe2 are fully proven, which opens a new way for advanced photonics, optical communication, laser measurement, and other fields.
Two-dimensional layered metal chalcogenides (LMCs) are widely used in battery anode materials, energy conversion, and semiconductor devices, because of their high energy storage characteristics, high thermoelectric characteristics, and large electron mobility. SnSe2 as a kind of LMC has strong nonlinear optical characteristics. However, its research on dissipative system dynamics as a saturable absorber has not been studied. In this work, we obtained SnSe2 nanosheets using lithium ion intercalation and we reported a passively mode-locked fiber laser with SnSe2 as a saturable absorber to achieve the dissipative soliton in a dissipative system. Due to the high third-order nonlinearity of SnSe2, the evolution of square wave pulses from 2 to 16 ns was obtained in a fiber ring cavity. Through adjusting the polarization state, the evolution phenomenon of soliton rain, the soliton rain phenomenon with a spectrum of dual-wavelengths, and a bound state harmonic phenomenon with a frequency of 313 MHz were obtained. Therefore, the strong nonlinear fiber laser based on SnSe2 provides a good platform for study the pulsation, explosion, rainfall and other phenomena.
Three-dimensional (3D) materials are widely used in optoelectronics, thermodynamics and ultrafast fiber lasers because of their excellent nonlinear optical properties. Silver sulfide (Ag 2 S) is a kind of 3D material with a unique cubic structure and large absorption coefficient. In this paper, a double-balance detection system is used to measure the saturation absorption intensity of Ag 2 S as 226.6 MW cm −2 and the modulation depth as 13.9%. In the ring fiber laser, Ag 2 S is used as a saturable absorber (SA) to obtain a stable dual-wavelength mode locking. The center wavelengths of the mode locking are 1536.9 and 1544.5 nm, and the corresponding 3 dB bandwidths are 1.3 and 1.5. nm. By adjusting the polarization controller, a tuning process from two wavelengths to multiple wavelengths is realized, and the tunable width is 13.1 nm. This phenomenon is due to the combined effect of birefringence and nonlinear effects in the cavity. To our knowledge, this is the first report of a multiplexed fiber laser with Ag 2 S as a SA. The emergence of this result provides a valuable reference information for the multifunctional compact fiber laser, and the formed system can be applied in the fields of fiber sensing, telecommunications and optical communication.
In this study, based on the single-layer metasurface structure, a dual-wavelength polarization multiplexing metalens is designed at the communication wavelengths of 1310 nm and 1550 nm, respectively. Using the dual-phase modulation method, a single-wavelength polarization multiplexing metalens is proposed, which can simultaneously control left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP). Furthermore, the cross superposition method is used to combine them to achieve the dual-wavelength polarization multiplexing metalens. The results show that the system can achieve polarization multiplexing at the two wavelengths of 1310 nm and 1550 nm, which is consistent with the expected results, and the focusing efficiency reached 61%. With the increase of the numerical aperture, the focusing intensity of the left and right focal points gradually approaches, and the difference between the full width at half maximum of the two focal points also decreases accordingly. It provides a new way for the optical imaging, information detection and the realization of multifunctional ultra-surface devices.
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