Optical Nonlinearity of ZrS₂ and Applications in Fiber Laser

Switchable Single- to Multiwavelength Conventional Soliton and Bound-State Soliton Generated from a NbTe2 Saturable Absorber-Based Passive Mode-Locked Erbium-Doped Fiber Laser

As a member of transition metal dichalcogenides (TMDs), NbTe2 has a work function of 5.32 eV and a band gap of 0 eV at the Fermi level, which enables it to possess broadband absorption characteristics and has huge potential in optoelectronic devices. In this work, a combination of liquid phase exfoliation (LPE) and optical deposition methods (ODMs) were used to fabricate a NbTe2 saturable absorber (SA). Based on the NbTe2 SA, a ring passive mode-locked erbium-doped fiber laser (PML-EDFL) was constructed by adding NbTe2 SA into the laser cavity. A switchable single- to multiwavelength (dual/triple/quadruple) conventional soliton (CS) and a bound-state soliton (BS) were observed for the first time. The results reveal that NbTe2 SA has excellent saturable absorption characteristics (modulation depth of 2.6%, saturation intensity of 177.4 MW/cm2, and unsaturated loss of 63.8%) and can suppress mode competition and stabilize multiwavelength oscillation. This study expands the applications of NbTe2 nanosheets in ultrafast optoelectronics. The proposed switchable PML-EDFL has extensive applications in high-capacity all-optical communication, high-sensitivity optical fiber sensing, high-precision spectral measurements, and high-energy-efficiency photon neural networks.

Room temperature sensing of primary alcohols via polyaniline/zirconium disulphide

Among the primary alcohols, ethanol is referred to as a heavy chemical due to its many applications in a variety of industries. Detection of primary alcohols can be deployed as a non-invasive method in medical diagnosis and safety measures in food processing companies. Zirconium disulphide is a novel 2D layered material with exotic features when in mono or few layers, which include fast electron transport, high carrier mobility and sizeable band gap. ZrS₂ and PANI were fabricated using liquid exfoliation and chemical polymerization methods respectively. Functionalization of the conducting polyaniline with ZrS₂ was done using facile sonication process. The sensor showed good sensitivities (43%, 58% and 104%) which were estimated from slopes of the linear fitted plots with fast response-recovery times of 8 s and 27 s (111 ppm); 12 s and 130 s (77 ppm); and 58 s and 88 s (58 ppm). Good reproducibility at three repeated measurements (111 ppm, 77 ppm and 58 ppm) was also observed for methanol, ethanol, and isopropanol vapours respectively. Meanwhile, the sensor displayed more linearity and sensitivity towards isopropanol compared to methanol and ethanol. The sensor showed good performance even at RH values close to 100% making it a potential alcohol breath analyser.

Few-layer metal monochalcogenide saturable absorbers for high-energy Q-switched pulse generation

Two-dimensional layered materials have been widely utilized as nonlinear absorption materials to transfer continue-wave into pulse trains in fiber laser systems. Here, we prepare robust GaSe/GeSe composites with high power bearing capacity as saturable absorbers (SAs) and then investigate their nonlinear optical properties via broadband Z-scan measurement at 800 nm and 1550 nm, respectively. The modulation depths of GaSe/GeSe based SAs are measured to be 11.97% and 7.69% at 1550 nm. After incorporating the GaSe/GeSe SAs into an Erbium-doped fiber laser cavity, passively Q-switched pulse trains could be obtained with repetition rates changing from 83.58 to 136.78 kHz (70.41 to 161.65 kHz). The maximum output power and pulse energy are 52.1 mW/370.67 nJ (GaSe) and 21.6 mW/133.74 nJ (GeSe) under the maximum pump power of 600 mW. The results indicate that GaSe and GeSe possess outstanding thermal stability and could be employed as remarkable saturable absorption materials for high-energy pulses generation.

Niobium disulfide as a new saturable absorber for an ultrafast fiber laser

Group VB transition metal dichalcogenides (TMDCs) are emerging two-dimensional materials and have attracted significant interests in the fields of physics, chemistry, and material sciences. However, there are very few reports about the optical characteristics and ultrafast photonic applications based on group VB TMDCs so far. In this work, we have calculated the niobium disulfide (NbS2) band structure by the density functional theory (DFT), which has revealed that NbS2 is a metallic TMDC. In addition, we have prepared an NbS2-microfiber device and the nonlinear optical characteristics have been investigated. The modulation depth, saturation intensity and non-saturable loss have been measured to be 13.7%, 59.93 MW cm-2 and 17.74%, respectively. Based on the nonlinear optical modulation effect, the Er-doped fiber (EDF) laser works in the soliton mode-locking state with the pump power of 94-413 mW. The pulse duration of 709 fs and the maximum average output power of 23.34 mW have been obtained at the pump power of 413 mW. The slope efficiency is as high as 6.79%. Compared to the recently reported studies based on TMDCs comprehensively, our experimental results are better. These experimental results demonstrate that NbS2 with excellent nonlinear optical properties can be used as a promising candidate to advance the development of ultrafast photonics.

Q-switched ytterbium-doped fiber laser based on evanescent field interaction with lutetium oxide

We demonstrated lutetium oxide (${\textrm{Lu}_2}{\textrm{O}_3}$Lu₂O₃) deposited onto D-shaped fiber producing Q-switched ytterbium-doped fiber laser (YDFL) with an operating wavelength of 1037 nm. D-shaped fiber ${\textrm{Lu}_2}{\textrm{O}_3}$Lu₂O₃ as a saturable absorber (SA) was prepared using a polishing-wheel technique by polishing 2 times to establish an excellent evanescent field interaction between material and light on the surface of the polished region. The SA was deployed into a YDFL to generate Q-switching. The proposed D-shaped fiber ${\textrm{Lu}_2}{\textrm{O}_3}$Lu₂O₃ initiated pulses as short as 3.6 µs, with the highest repetition rate of 65.8 kHz. Stability of the SA is proven, as it produced stable pulses within the pump power of 99 to 133 mW with an SNR of 62.13 dB. Q-switched YDFL generates pulses with an output power of 0.93 to 1.99 mW and pulse energy of 17 to 30 nJ. We obtained a laser cavity with the optical-to-optical efficiency of 3.33%, which was the highest among D-shaped fiber-deposited SA materials in YDFL. Therefore, ${\textrm{Lu}_2}{\textrm{O}_3}$Lu₂O₃ deposited onto D-shaped fiber can be deployed as an SA in YDFL for a portable Q-switched laser source.

Ferromagnetic insulator Cr2Ge2Te6 as a modulator for generating near-infrared bright-dark soliton pairs

Novel two-dimensional (2D)-materials-based ultra-fast modulators exhibit significance in extending the fundamental investigations and practical applications of mode-locked fiber lasers. In our work, employing the liquid-phase exfoliation method, a ${{\rm Cr}_2}{{\rm Ge}_2}{{\rm Te}_6}$Cr₂Ge₂Te₆ (CGT) optical modulator with a modulation depth and a saturable intensity of 1.64% and ${6.31}\,\,{{\rm MW/cm}^2}$6.31MW/cm² was fabricated. Due to its suitable modulation properties and high nonlinear coefficient, a stable bright-dark soliton pair was successfully achieved within an Er-doped fiber laser. Under the pump power of 560 mW, the maximum average output power was 5.36 mW with a pulse repetition rate of 1.835 MHz. Our results fully present the capacity of CGT in designing bright-dark soliton operations and provide a meaningful reference for promoting the ultra-fast modulation applications of ferromagnetic insulators.

1.34 µm Q-Switched Nd:YVO4 Laser with a Reflective WS2 Saturable Absorber

In this work, a Tungsten disulfide (WS₂) reflective saturable absorber (SA) fabricated using the Langmuir–Blodgett technique was used in a solid state Nd:YVO₄ laser operating at 1.34 µm. A Q-switched laser was constructed. The shortest pulse width was 409 ns with the repetition rate of 159 kHz, and the maximum output power was 338 mW. To the best of our knowledge, it is the first time that short laser pulses have been generated in a solid state laser at 1.34 µm using a reflective WS₂ SA fabricated by the Langmuir–Blodgett method.

Nonlinear Optical Response of Graphene Oxide Langmuir-Blodgett Film as Saturable Absorbers

Two-dimensional (2D) materials as saturable absorbers (SAs) have attracted intense interest for applications in pulsed laser generation because of their distinguishing optical properties. However, the existing methods of preparing SAs were insufficient. Here, we fabricated graphene oxide (GO) SAs by Langmuir-Blodgett (LB) methods for passively Q-switched Nd:YAG laser. The GO sheets were deposited on a quartz plate using the LB method. Two different LB-GO SAs grown under the surface pressure of 22 and 38 mN/m were obtained. Compared with the drop coating method, LB-GO SA exhibited more excellent uniformity, larger nonlinear performance and higher optical transparency. By inserting LB-GO SA into the Nd:YAG laser linear cavity, the short pulse duration of 156 ns and the average output power of 1.313 W were obtained. The slope efficiency was as high as 43.7%, due to low loss of the LB-GO SA. Our results illustrated a new way for preparing the SA using the LB technique.