Near‐Infrared Saturable Absorption of Defective Bulk‐Structured WTe₂ for Femtosecond Laser Mode‐Locking

Abstract

Mono‐ and few‐layer transition metal dichalcogenides (TMDCs) have been widely used as saturable absorbers for ultrashort laser pulse generation, but their preparation is complicated and requires much expertise. The possible use of bulk‐structured TMDCs as saturable absorbers is therefore a very intriguing and technically important issue in laser technology. Here, for the first time, it is demonstrated that defective, bulk‐structured WTe2 microflakes can serve as a base saturable absorption material for fast mode‐lockers that can produce femtosecond pulses from fiber laser cavities. They have a modulation depth of 2.85%, from which stable laser pulses with a duration of 770 fs are readily obtained at a repetition rate of 13.98 MHz and a wavelength of 1556.2 nm, which is comparable to the performance achieved using mono‐ and few‐layer TMDCs. Density functional theory calculations show that the oxidative and defective surfaces of WTe2 microflakes do not degrade their saturable absorption performance in the near‐infrared range, allowing for a broad range of operative bandwidth. This study suggests that saturable absorption is an intrinsic property of TMDCs without relying on their structural dimensionality, providing a new direction for the development of TMDC‐based saturable absorbers.

2D Layered Materials: Synthesis, Nonlinear Optical Properties, and Device Applications

“…Interestingly, the number of layers, oxidative and defective surfaces of layered TMDCs do not degrade their saturable absorption performance. For example, the researchers achieved the femtosecond mode‐locking by using the near‐infrared saturable absorption of defective bulk‐structured WTe 2 . These studies indicate that besides graphene and topological insulators, TMDCs are another promising layered materials for mode‐locked lasers.…”

“…Driven by these efforts, mode‐locked fiber lasers based on other layered TMDCs and their derivatives including MoSe 2 , MoTe 2 , WTe 2 , WSe 2 , MoSe 2 , SnS 2 , ReS 2 , In 2 Se 3 , InS, TiS 2 , PtS 2 , PtSe 2 , and HfS 2 , have also developed rapidly, as shown in Table . It can be seen that for these lasers, the minimum pulse width is 67 fs, maximum output power is 212 mW, and maximum repetition rate is 8.82 GHz .…”

Band Alignment of MoTe2/MoS2 Nanocomposite Films for Enhanced Nonlinear Optical Performance

“…[41] This band alignment is important for heterostructure design based on MoTe 2 and MoS 2 for optoelectronic devices, such as solar cell, [42] optical modulator, [10] and saturable absorber. [43] …”

Study on the Energy Band Regulation of Bi2−xSbxTe3 and Its Application as Mode Locking Material in Low Gain Ultrafast Fiber Laser

“…Ultrafast pulsed fiber laser has been widely used in medical, spectral imaging, sensing, and processing fields in recent years by virtue of its high stability, good heat dissipation, and low cost . Passive operation of fiber laser via materials has recently been a hotspot which attracts enormous attention, especially in the field of communication . On the one hand, mode locking based on the artificially saturable absorbers (SA): nonlinear polarization rotation mode‐locking, nonlinear optical (NLO) loop mirror mode‐locking, nonlinear multimode interference mode‐locking, and material‐mode‐locking based on real saturable absorbers .…”