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In this work, mode-locked thulium-doped fiber lasers operating in the 2 µm wavelength region were demonstrated using tantalum aluminum carbide (Ta2AlC)-based saturable absorbers (SAs) utilizing the evanescent wave interaction. The Ta2AlC MAX Phase was prepared by dissolving the Ta2AlC powder in isopropyl alcohol and then deposited onto three different evanescent field-based devices, which were the tapered fiber, side-polished fiber, and arc-shaped fiber. Flame-brushing and wheel-polishing techniques were used to fabricate the tapered and arc-shaped fibers, respectively, while the side-polished fiber was purchased commercially. All three SA devices generated stable mode-locked pulses at center wavelengths of 1937, 1931, and 1929 nm for the tapered, side-polished, and arc-shaped fibers. The frequency of the mode-locked pulses was 10.73 MHz for the tapered fiber, 9.58 MHz for the side-polished fiber, and 10.16 MHz for the arc-shaped fiber. The measured pulse widths were 1.678, 1.734, and 1.817 ps for each of the three SA devices. The long-term stability of the mode-locked lasers was tested for each configuration over a 2-h duration. The lasers also showed little to no fluctuations in the center wavelengths and the peak optical intensities, demonstrating a reliable, ultrafast laser system. [ABSTRACT FROM AUTHOR]

A tunable, passively Q-switched thulium doped fluoride fibre (TDFF) laser using a reduced-graphene oxide-silver (rGO-Ag) thin film as a saturable absorber (SA) for S band operation is proposed and its efficacy demonstrated. Over a pump power range of 91.4 mW up to 158.6 mW, passively generated Q-switched pulses are observed with repetition rates from 20 to 34.5 kHz and pulse widths from 3.1 to 7.1 µs. The highest pulse energy observed is 101.2 nJ with a signal to noise ratio of ∼42 dB. The proposed laser has a tuning range ∼52 nm from 1458 to 1510 nm with a tunable bandpass filter (TBPF) introduced into the cavity. [ABSTRACT FROM AUTHOR]

This paper demonstrates ultrashort pulse generation using molybdenum trioxide (MoO 3) saturable absorber (SA) integrated into a thulium-doped fiber laser. The average particle size of the MoO 3 material was 9.54 µm. The MoO 3 /polydimethylsiloxane composite was prepared and spin-coated on a tapered fiber to fabricate the SA device. It had a modulation depth of 2.89% and demonstrated a high damage threshold, extending beyond 19.34 GW/cm2. From the evanescent light-matter interaction, stable self-starting mode-locked soliton pulses of 1.22 ps duration at 1941.4 nm central wavelength were obtained. The pulse repetition rate was 10.84 MHz with 3.3 nm spectral bandwidth. At 1.15 W pump power, the soliton pulse energy was 0.68 nJ corresponding to a peak power of 492 W. The work exhibited comparable pulse performances in the 2 µm wavelength range while utilizing simple SA fabrication procedures of micro-sized MoO 3 materials. [ABSTRACT FROM AUTHOR]

• Incorporation of rare-earth doped fiber to generate different pulse regimes. • Dark, Q-switched and bright pulses are generated from a common laser cavity. • Optical pulse operation is determined by pump power that leads to flexibility. We demonstrate the generation of dark and bright pulses in a Q-switched laser using an erbium-ytterbium-thulium co-doped fiber. By manipulating pump power while maintaining lasing wavelength at 1571 nm, dark and bright pulses were observed at pump power thresholds 94.1 and 1770 mW with pulse duration of 3 and 71 ns, respectively. Stability of the two regimes were also high across an operating time of 60 min. These findings may be the stepping stone towards realising a laser with flexible operating range at different pulse regimes. [ABSTRACT FROM AUTHOR]

• Graded-index multimode fiber (GMIF) in an optical loop mirror as a saturable absorber. • Core mismatched between GIMF and single-mode fiber induces nonlinear multimodal interference. • The proposed structure functions as a nonlinear absorbing loop mirror. • The proposed structure possesses high thermal damage threshold. This investigation explores the potential use of graded-index multimode fiber (GIMF) in a nonlinear absorbing loop mirror (NAbLM) as an artificial saturable absorber for ultrashort pulse generation. The saturable absorption mechanism of GIMF-NAbLM was based on a combination of nonlinear phase shift and multimodal interference that was satisfied by the asymmetric positioning of the GIMF in the single-mode fiber loop mirror. The proposed saturable absorber was integrated in a mode-locked thulium-doped fiber laser with figure-of-eight cavity. A noise-like pulse of 164 fs spike pulse duration at 1950 nm central wavelength was attained in the net anomalous dispersion with a 10 m long GIMF. The GIMF-NAbLM structure demonstrates immense prospects as an effective saturable absorption device for generating stable ultrashort pulse in the 2 µm region due to its simplicity. [ABSTRACT FROM AUTHOR]

• All-fiber passively mode-locked Erbium-doped fiber using Nb 2 C MXene coated tapered fiber. • Mode-locked pulses were obtained at wavelength of 1559 nm, with a pulse width of 0.77 ps and 3 dB bandwidth 4 nm. • Signal to noise ratio for the signal of 66.5 dB and repetition rate of 14.12 MHz at a pump power of 90.88 mW. • The maximum output power, pulse energy and peak power obtained 3.04 mW, 212.7 pJ and 0.18 kW. In this study, we demonstrated the potential of Nb 2 C MXene, which is a member of the MXene family, as a saturable absorber (SA) material in generating ultrafast laser at C-band wavelength region. The fabricated tapered fiber with a diameter of 3.56 μm was coated with Nb 2 C MXene to realize the interaction of the evanescent field with the material used, hence induced the generation of mode-locked pulses. The investigation on the nonlinear optical properties of the fabricated SA shows that it had a modulation depth and saturation intensity of 12.94% and 1.1 kW/cm2, respectively. The soliton pulse with pulse duration of 0.77 ps at the central wavelength of 1559 nm was successfully generated at the pump power of 90.88 mW upon the insertion of the Nb 2 C MXene SA into the EDF laser cavity. The fundamental mode has a repetition rate of 14.12 MHz within pump power ranging from 90 to 473 mW. The maximum output power, pulse energy and peak power obtained from the mode-locked laser was measured to be 3.04 mW, 212.7 pJ and 0.18 kW, respectively. A signal to noise ratio (SNR) of approximately 66.5 dB was obtained, hence suggests that the generated mode-locked fiber laser possess an excellent stability. The present findings would open a window of opportunity to a new device for Nb 2 C MXene intended for high-performance mode-locked lasers. [ABSTRACT FROM AUTHOR]

• Mode-locking operation at 1075 nm in a DC-YDFL. • A WS 2 -ZnO deposited on a fiber taper as a saturable absorber. • High power mode-locked dissipative solitons with 3.7 nm 3 dB bandwidth. • Repetition rate of 10.98 MHz and Pulse energy of 139.3 nJ. • Higher SA damage threshold due to interaction with evanescent field only. Efficient and stable mode-locking operation at 1075 nm is demonstrated in a double-clad ytterbium-doped fiber laser (DC-YDFL) with WS 2 -ZnO deposited on a fiber taper as a saturable absorber (SA). The WS 2 -ZnO composite is prepared by a simple and cost-effective heating method and deposited onto the fiber taper before being incorporated into the laser cavity. A high power mode-locked normal dispersion output at 1075 nm with a 3 dB bandwidth, repetition rate, pulse width and pulse energy of 3.7 nm, 10.98 MHz, 459 fs and 139.3 nJ respectively are obtained at a pump power of 3.65 W. Due to the interaction of the WS 2 -ZnO nanoparticles with the evanescent field of the propagating signal instead of directly, the SA has a higher laser damage threshold, therefore allowing for higher pulse powers to be obtained. [ABSTRACT FROM AUTHOR]