In recent years, two-dimensional materials have been widely used in the field of optics due to their unique nonlinear optical properties, broadband saturation absorption and ultrafast recovery time. MXene Ti 3 C 2 T x is a kind of emerging two-dimensional materials with large modulation depth, high damage threshold, and excellent electrical conductivity with near zero bandgap structure. However, MXene has seldom been applied in ultrafast photonics, especially the generation of ultrastable soliton molecules. In this paper, MXene is prepared and applied in the erbiumdoped fiber laser. The nonlinear optical properties of MXene Ti 3 C 2 T x are studied experimentally. The center wavelength, 3-dB bandwidth, fundamental frequency and the pulse duration of the conventional soliton are 1566.1 nm, 1.21 nm, 6.09 MHz and 993 fs, respectively. By adjusting the polarization state and pump power, the soliton molecules can be obtained in the laser cavity. Especially, two kinds of soliton molecules with CW peak and without CW peak are observed, respectively. Experimental results show that MXene saturable absorber (SA) can bear a high pump power. This work demonstrates that MXene Ti 3 C 2 T x can be used as an excellent SA. Hence, we believe that this kind of optical material has many applications such as optical communication, optical logic gates and nonlinear devices, etc.

Two-dimensional materials have attracted increasing attention because of their excellent mechanical, thermodynamic, magnetic, electrical and optical properties. Here, a new two-dimensional material of tin sulfide (SnS) is experimentally prepared. It is layered like black phosphorus and owns distinct optoelectronic properties, but eliminates the disadvantage of instability. The nonlinear saturable absorption characteristics of the SnS nanosheets is investigated at 1563.3 nm by the double-balanced detection method. The obtained modulation depth and saturation intensity are 5.4% and 66.3 MW/cm 2 , respectively. A passively harmonic mode-locked erbium-doped fiber laser based on the SnS saturable absorber (SA) has been demonstrated. The results show that mode-locking with fundamental frequency of 5.47 MHz is realized at pump power of 28.38 mW. With the increase of pump power, the laser can operate from fundamental frequency to high-order harmonic mode-locking. The maximum repetition rate of 412.73 MHz has been obtained, which is equivalent to the 76th harmonic mode-locking. This work reveals that SnS nanosheets is a novel and efficient SA with high damage threshold, which will find potential applications in optical communication, photoelectric detection, laser medicine, etc.

Two-dimensional materials with a sheet structure have excellent optical, electrical and mechanical properties, and have attracted much attention in recent years, especially In 2 Se 3 (the N-type semiconductor compound), which has a rapid development in the fields of materials science and optical communication. In this paper, the nonlinear saturation absorption characteristics of In 2 Se 3 are studied. The In 2 Se 3 nanosheet dispersion can be used in ultrafast photonics applications. The nonlinear absorption is measured by power dependent method, and the modulation depth and saturation intensity are 3.8% and 246.6 MW cm −2 , respectively. More importantly, In 2 Se 3 is used as a saturable absorber (SA) in a passively mode-locked erbium-doped fiber laser. The proposed mode-locked fiber laser is demenstrated with a center wavelength of 1529.4 nm, a fundamental frequency of 5.9 MHz, a spectral width of 3.96 nm, a pulse width of 1.38 ps, and a signal-to-noise ratio of 55 dB. For the first time, harmonic mode-locking with a high-repetition rate of 431 MHz is achieved when the pump power is 360 mW corresponding to 73rd-order harmonic mode locking. It can be seen that In 2 Se 3 is indeed a new excellent photonic material, which can be used in fiber optic communication, SAs photonics, laser material processing and light modulators.

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.