Results and Discussions Tellurene nanoflakes were prepared using a bottom-up approach and then comprehensively characterized. The thickness of the as-grown tellurene nanoflakes was about tens of nanometers and the maximum transverse size was 80 μm. The E₁ (transverse to mode), A₁, and E₂ active Raman phonon modes of tellurium were found consistent with their typical characteristic peaks reported previously. The characteristic crystal plane is consistent with the PDF card (JCPDS # 36-1452). Furthermore, the high-resolution transmission electron microscopy image showed a clear atomic image. The prepared tellurene nanoflakes have high elemental purity. All characterization methods confirmed that the tellurene nanoflakes have high crystalline quality. The saturated absorption characteristic was studied with a double arm detection system. By fitting the saturable absorption curve to the data, the modulation depth, saturation strength, and unsaturated loss were found to be 0.5%, 0.66 GW/cm², and 99.16%, respectively. Benefiting from the excellent nonlinear saturation absorption property of tellurene, a stable passively Q-switched laser was realized. The Q-switched pulses are achieved at a communication band with a center wavelength of ~1558 nm and pulse duration of 1.44 μs, and the repetition frequency is adjustable from 87 to 133 kHz. Additionally, the signal-to-noise ratio is ~53.96 dB, indicating good pulse stability. The reported results point out a potential way to achieve tunable pulsed lasers.

In recent years, low-dimensional materials have received significant attention in optics and demonstrated excellent application prospects. In the previous studies, numerous carbon, nitrogen, and oxygen group single element films, such as arsenic, antimony, and tellurium, have been obtained. Tellurene is a basic material of the oxygen group with a helical chain structure. It may form various morphologies, such as nanowires, nanorods, nanotubes, or nanoribbons. On the one hand, preparing a thin layer of single tellurene crystal remains a challenge. On the other hand, as one of the chalcogenide elements (group Ⅵ materials), tellurene is a promising material for infrared optical applications because of its wideband absorption, high mobility, and unique topological properties. The electrical and topological properties of tellurene single crystals have been systematically studied. A second harmonic property in the optical nonlinear characteristics has also been observed. However, nonlinear applications, especially an ultrafast pulsed fiber laser based on the saturable absorption of tellurene, require further studies. In the present study, tellurene nanoflakes with high crystallinity were prepared by adopting the chemical vapor transport method. Using the precise transfer technology, the tellurium nanoflakes were integrated into the tip of the optical fiber as fiber-compatible saturable absorbers. The nonlinear saturation absorption property enabled achieving stable passively Q-switched laser pulses. It is envisaged that the present work will extend the range of applications of novel tellurene nanomaterials and provide a potential means of obtaining tunable pulsed lasers.

A tellurene-based saturable absorber was prepared using a bottom-up approach and then used for laser pulse generation. Firstly, tellurium powder and mica substrate were placed on each side of the middle-necked quartz tube. The quartz tube was sealed under vacuum and then placed in a double temperature zone furnace. By executing an appropriate temperature program, the source material was vaporized, transported, and recrystallized. The as-grown nanoflakes were characterized using optical microscope, atomic force microscope, electron microscope, and a Raman spectrometer. Then, the tellurium nanoflakes were integrated into the tip of the optical fiber as fiber-compatible saturable absorbers using our polydimethylsiloxane (PDMS)-assisted accurate transfer method. Finally, the fiber-compatible saturable absorbers were integrated into an in-house erbium-doped fiber laser ring cavity for laser pulse generation.

Tellurene nanoflakes have been prepared using a bottom-up approach adopting chemical vapor transport. After comprehensive physical and chemical characterization, it was confirmed that the tellurene nanoflakes had a high crystallinity and environmental stability. The nanoflakes were transferred using the PDMS-assisted dry transfer method onto the end cap of the optical fiber with a high coverage over the core area. Benefiting from the nonlinear saturation absorption property of tellurene, stable passive Q-switched laser pulses were achieved in the communication band with a center wavelength of 1558 nm and pulse duration of 1.44 μs. The repetition frequency was adjustable from 87 to 133 kHz. The results extend the application scenarios of novel tellurene nanomaterials and provide a potential pathway to obtaining tunable pulsed lasers.