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• The laser cavity can generate a laser at 1930 nm and 1860 nm. • The cavity employs a Holmium-doped fiber to suppress the amplified spontaneous emission of the Thulium ions. • Passive Q-switching for both wavelengths is achieved using the same Molybdenum Tungsten Disulfide (MoWS 2) film. • The laser at 1860 nm generates a maximum repetition rate of 48.9 kHz as well as narrowest pulse width of 2.3 µs. This work demonstrates an all fiber, passively Q-switched Thulium-doped fiber (TDF) laser with a center operating wavelength at 1860 nm and 1930 nm. The laser initially generates an output at ~1930 nm which is then shifted to ~1860 nm by integrating a Holmium-doped fiber (HDF) into the cavity to serve as an amplified spontaneous emission filter. Q-switching operation is achieved using a molybdenum tungsten disulfide or MoWS 2 thin film acting as a passive optical modulator. At 1930 nm, the generated Q-switched laser has a high repetition rate of 66.3 kHz and a narrow pulse width of 2.1 µs. After the Holmium-filter is employed, the wavelength shifts to 1860 nm while still retaining a modulated output with a maximum repetition rate of 48.9 kHz as well as narrowest pulse width of 2.3 µs. This work demonstrates the use of the absorption characteristics of HDF to access the shorter wavelength region of the TDF. [ABSTRACT FROM AUTHOR]

• Passively Q-switched thulium-doped fiber laser at 1.8 µm. • Modulated by a single-walled carbon nanotube film saturable absorber. • Output with a repetition rate of 67.9 kHz and pulse width of 1.2 µs. • Observed of SNR of 40.0 dB indicates highly stable output. This work demonstrates a simple and reliable passively Q-switched thulium-doped fiber laser capable of generating an output with a peak wavelength at 1.8 µm. Lasing is realized from the shorter wavelength region of a thulium-doped silica fiber gain medium by suppressing lasing at longer wavelengths in combination with a tunable bandpass filter. The laser is modulated by a single-walled carbon nanotube film saturable absorber. The generated Q-switched laser is capable of achieving a high repetition rate of 67.9 kHz and a narrow pulse width of 1.2 µs. As most work on the 1.6–1.8 µm waveband focuses on continuous-wave and mode-locked lasers, to the best of the author's knowledge, this is the first demonstration of a passively Q-switched thulium-doped fiber laser operating at 1.8 µm with an all-silica fiber setup. The demonstrated laser has potential for various applications including biomedical surgery and polymer-based welding applications. [ABSTRACT FROM AUTHOR]

Abstract A passively Q-switched thulium/holmium fiber laser with a gallium selenide (GaSe) saturable absorber (SA) is proposed and demonstrated for the first time. The GaSe based SA is prepared by mechanical exfoliation and inserted into the proposed laser cavity to generate Q-switched pulses. Stable Q-switching operation is achieved at 1986.0 nm, with output pulse repetition rates ranging from 22.9 kHz to 32.3 kHz over a pump power range of 112.0 mW to 235.0 mW. The generated Q-switched pulses have a maximum pulse energy of 120.3 nJ and minimum pulse width of 6.9 μs. The proposed thulium/holmium fiber laser with GaSe SA will be able to cater to multiple applications requiring pulsed laser outputs in the 2.0 μm region. [ABSTRACT FROM AUTHOR]

Highlights • A thin MoWS 2 film as a saturable absorber (SA) in a thulium doped fiber laser. • Few-layer MoWS 2 nanoparticles are embedded in a polymer host to serve as the SA. • Q-switched pulses at repetition rate of 65.79 kHz and pulse width of 1.84 obtained. • Pulses also have maximum energy and power of 35.73 nJ and 13.92 mW. • Broad tuning output of 70 nm from 1927.2 nm to 1996.8 nm with SNR of 50.0 dB. Abstract In this work, a thin Mo 0.8 W 0.2 S 2 film is proposed and fabricated for the use as a saturable absorber (SA) in a thulium-doped fiber laser (TDFL) cavity. The few-layer Mo 0.8 W 0.2 S 2 nanoparticles are obtained through hydrothermal exfoliation as a thin film and suspended in a polymer host, which is then placed between two fiber ferrules to serve as an SA. The proposed laser is capable of generating outputs with a maximum repetition rate of 65.79 kHz and a minimum pulse width of 1.84 µs at the maximum pump power of 168.92 mW, as well as pulse energies andpeak powers as high as 35.73 nJ and 13.92 mW. The laser also has a broad tuning output from 1927.2 nm to 1996.8 nm, giving a tuning band of about 70 nm. The generated pulses are stable with a signal-to-noise ratio of 50.0 dB. The proposed laser has a high potential for operation near the 2000 nm wavelength region, with multiple bio-medical and sensing applications. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate an electro-tunable Thulium-doped Fiber Laser (TDFL) using a voltage-controlled Fabry-Perot Etalon (FPE) filter with passive Q-switching capability, obtained by using a multi-walled carbon-nanotube (MWCNT) thin-film as a saturable absorber (SA). To the best of our knowledge, this is the first demonstration of a wavelength-tunable Q-switched TDFL using an FPE filter. The tunable TDFL has a wavelength-tuning range of 41.95 nm, from 1965.40 nm up to 2007.35 nm. Q-switching operation starts at a pump power of 94.72 mW and destabilizes at a maximum input pump power of 146.39 mW. By varying the pump power, the repetition rate and the pulse width can be tuned with a maximum tuning range of 15.5 kHz and 7.0 µs respectively. The laser also has a maximum pulse energy of 82.6 nJ and a peak power of 27.52 mW. The use of the MWCNT thin-film as an SA generates a stable Q-switching operation, which is verified by its relatively high signal-to-noise ratio at a value of 55.0 dB. [ABSTRACT FROM AUTHOR]

Thulium-doped fiber lasers (TDFLs), operating in the 1.8–2.0 µm wavelength region, have been viewed as an important research topic, due to their potential in various fields of applications. However, the growing need to advance the development of applications in various fields for instance medicine and environment sensor, has led to a deeper and specific study of Q-switched TDFLs with wavelength tunability. In this paper, a stable, tunable Q-switched TDFL operating in a wavelength range near to 1.9 µm by exploiting the use of a multiwall carbon nanotube (MWCNT)-based thin film as a saturable absorber (SA), and the use of an arrayed waveguide grating (AWG) for wavelength tunability, is presented. The tuning range of the Q-switched pulses generated covered a wavelength range that spanned from 1871.6 nm to 1888.8 nm. The repetition rate of the generated Q-switched pulses covers a range of frequency starting from 41.19 kHz to 68.3 kHz with a change in pump power from 242.2 mW until 360.9 mW. [ABSTRACT FROM AUTHOR]