We propose and demonstrate a widely tunable passively $Q$-switched ${\mathrm{Ho}}^{3+}/{\mathrm{Pr}}^{3+}$-codoped ${\text{ZrF}}_4$-${\text{Ba}\text{F}}_2$-${\text{LaF}}_3$-${\text{AlF}}_3$-NaF fiber laser operating in the 2.8 μm mid-infrared (MIR) waveband based on a single-walled carbon nanotube (SWCNT) saturable absorber (SA). The SWCNTs have diameters ranging from 1.4 to 1.7 nm. The modulation depth and saturation intensity of the SWCNT SA measured at 2850 nm are 16.5% and $1.66\mathrm{MW}/{\mathrm{cm}}^2$, respectively. Stable $Q$-switched pulses with the shortest pulse duration of 1.46 μs and the maximum pulse energy of 0.43 μJ are achieved at a launched pump power of 445.6 mW. The combined use of a broadband SWCNT SA and a plane ruled grating ensures a broad continuously tuning range of 55.0 nm from 2837.6 to 2892.6 nm. The output powers, emission spectra, repetition rates, and pulse durations at different tuning wavelengths are also characterized and analyzed. Our results indicate that SWCNTs can be excellent broadband SAs in the 3 μm MIR region. To the author’s knowledge, this is the first demonstration of a widely tunable carbon-nanotube-enabled passively $Q$-switched fiber laser operating in the 2.8 μm MIR waveband.

In this Letter, we present the mode-locking operation of a 2.87 µm H o 3 + / P r 3 + codoped fluoride fiber laser, helped by the ultrafast nonlinear optical absorption behavior of gold nanowires (GNWs). The mode locker is fabricated by depositing the GNW solution onto a silver mirror. It has a modulation depth of 14.2%, a saturation intensity of 26.2 M W / c m 2 , and a non-saturation loss of 29.9% at 2.87 µm. With an increased pump power, the laser operates in Q -switched mode-locking, fundamental mode-locking, and harmonic mode-locking (HML) states. This represents the first, to our knowledge, mid-infrared mode-locked laser using gold nanomaterials. Additionally, the HML is also the first observation in a laser in this band using material saturable absorbers, implying the capability of GNWs for high repetition rate generation.

We demonstrated passively $Q$-switched mid-infrared (mid-IR) erbium-doped fiber lasers by using gold nanostars (GNSs) as the $Q$-switcher. The nonlinear optical responses of the GNSs synthesized via the seed-mediated method have been characterized via a Z-scan technique, and the modulation depth and saturation intensity of the GNSs are measured to be 25% and $15.75\mathrm{kW}/{\mathrm{cm}}^2$, respectively. The $Q$-switched fiber laser can deliver a maximum average power of 454 mW with corresponding pulse energy of 3.6 μJ and pulse duration of 536 ns at a repetition rate of 125 kHz under the incident pump power 3.5 W. To the best of our knowledge, this is the first Letter that reports that the GNSs can act as a $Q$-switcher for the mid-IR erbium-doped ZBLAN fiber lasers. This Letter can deepen the understanding of the nonlinear optical behavior of the gold nanomaterials and may make inroads for the excellent mid-infrared optoelectronic devices.

Mid-infrared pulsed lasers operating around the 3 μm wavelength regime are important for a wide range of applications including sensing, spectroscopy, imaging, etc. Despite the recent advances in technology, the lack of a nonlinear optical modulator operating in the mid-infrared regime remains a significant challenge. Here, we report the third-order nonlinear optical response of gold nanorods (GNRs) ranging from 800 nm to the mid-infrared regime (2810 nm) enabled by their size and overlapping behavior-dependent longitudinal surface plasmon resonance. In addition, we demonstrate a wavelength-tunable ${\mathrm{Er}}^{3+}$-doped fluoride fiber laser modulated by GNRs, which can deliver pulsed laser output, with the pulse duration down to 533 ns, tunable wavelength ranging from 2760.2 to 2810.0 nm, and spectral 3 dB bandwidth of about 1 nm. The experimental results not only validate the GNRs’ robust mid-infrared nonlinear optical response, but also manifest their application potential in high-performance broadband optoelectronic devices.

We report Q-switching and mode-locking operations in a $\rm Ho^{3+}/Pr^{3+}$ co-doped ZBLAN fiber laser at 3-μm mid-infrared waveband using a single-walled carbon nanotube saturable absorber (SWCNT-SA). The SWCNTs were produced by catalytic chemical vapor deposition (CVD) method and then deposited on the surface of a flat gold-coated mirror to form the SWCNT-SA. The modulation depth and saturation intensity of the SWCNT-SA are 16.5% and $\rm 1.66 MW/cm^2$ , respectively. Stable Q-switched laser pulses operating at 2865.6 nm was obtained at a launched pump power of 530.6 mW. The resulting pulses have a measured repetition rate and pulse width of 178.6 kHz and 1.21 μs, respectively. The maximum pulse energy is calculated to be 0.36 μJ. By slightly adjusting the position of the SWCNT-SA, stable continuous-wave mode-locked pulses at 2865.2 nm were also achieved. Our work demonstrates that SWCNTs are promising SAs for 3-μm mid-infrared pulsed lasers.

We demonstrated that gold nanowires (GNWs), as a new kind of saturable absorber (SA), could be used to construct all-fiber passively Q-switched thulium-doped fiber lasers (TDFL). The GNWs were mixed with polyvinylpyrrolidone (PVP) to form the GNWs-PVP SA film. It exhibited a broad absorption band covered from 300 nm to 2500 nm, which was induced by the surface plasmon resonance (SPR) absorption of GNWs. When the GNWs-PVP SA film was inserted into the TDFL cavity pumped by a 1570 nm fiber laser, a stable passively Q-switched laser at ∼1940nm was obtained when the threshold of pump power exceeded ∼800 mW. Furthermore, ∼2.4 µs pulses with a repetition rate of 52.75 kHz were also obtained at the pump power of ∼1500 mW.