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A thulium-doped fiber laser (TDFL) with a dual-active cavity and a directly linked three-coupler triple-ring filter is designed and demonstrated. Its operational principle is analyzed, and a corresponding experimental setup is built. Eleven single-wavelength laser outputs with a single-longitudinal-mode (SLM) output near 2 μm are obtained. The laser output covers a wavelength range from 1933.95 nm to 1971.76 nm, with a continuous switchable output range of 37.81 nm and a minimum center wavelength interval of 0.22 nm. The optical signal-to-noise ratio (OSNR) of the output laser within the tuning range is >48.53 dB, and its maximum OSNR is 70.24 dB. The minimum wavelength fluctuation is 0.03 nm, and the power fluctuation is between 0.15 and 2.61 dB. A single wavelength with a center wavelength of 1933.95 nm is monitored for 75 min, and the radio-frequency spectrum is scanned 27 times within the frequency range of 0 to 400 MHz. The results demonstrate that the TDFL can operate continuously and stably in an SLM state. The linewidth and linewidth fluctuation of the TDFL are measured, and the minimum linewidth, corresponding to a measurement time of 0.001 s, is 65.14 kHz. The experimental results show that the proposed TDFL has a high OSNR and excellent wavelength-switching ability, and its SLM operation is very stable. [ABSTRACT FROM AUTHOR]

• A highly stable single-longitudinal-mode thulium-doped fiber laser. • A linear compound cavity fiber laser utilizing a cascaded dual-coupler double-ring cavity filter. • The peak power fluctuation and wavelength drift over 60 min were less than 0.11 dB and 0.02 nm, respectively. • The minimum linewidth at an integration time of 0.001 s was 8.88 kHz. A linear compound-ring cavity single longitudinal mode (SLM) thulium-doped fiber laser (TDFL) based on a cascaded dual-coupler double-ring cavity filter has been experimentally investigated and is proposed. The cascaded dual-coupler double-ring cavity filter was analyzed theoretically in detail by adjusting the effective free spectral range and transmission bandwidth, which ensures SLM operation and narrow linewidth. The experimental results indicate that the proposed TDFL can generate stable SLM lasing with a high optical signal-to-noise ratio of 69 dB, at 2048.39 nm for more than 60 min. The wavelength drift and peak power fluctuation in that observation time were less than 0.02 nm and 0.11 dB, respectively. The linewidth of the laser was 8.8 kHz at an integration time of 0.001 s. The relative intensity noise was less than −128.88 dB/Hz at frequencies greater than 1 MHz. [ABSTRACT FROM AUTHOR]

• To the best of our knowledge, this is the first report of wavelength tunable NLP output in the all-PM thulium-doped fiber laser. • A temperature-controlled polarization-maintaining fiber filter is proposed, which can be realized not only by co-splicing the polarization-maintaining dispersion compensation fiber and normal polarization-maintaining fiber but also by simply splicing the normal polarization-maintaining fiber with a rotation angle. • The wavelength tunable range of 32.4 nm from 1910.4 nm to 1942.8 nm is realized in the noise-like pulse regime from an all-PM thulium-doped fiber laser. • The wavelength tunable range of 26.6 nm from 1937.7 nm to 1964.3 nm is realized in the continuous-wave regime from an all-PM thulium-doped fiber laser. In this paper, we present both wavelength tunable noise-like pulse (NLP) and continuous-wave (CW) generation in all-polarization-maintaining (all-PM) thulium-doped fiber lasers. By introducing a piece of polarization-maintaining fiber (PMF) whose birefringence changes with temperature in the all-PM thulium-doped fiber laser, a wavelength tunable range of 32.4 nm from 1910.4 nm to 1942.8 nm is realized in NLP regime, and a wavelength tunable range of 26.6 nm from 1937.7 nm to 1964.3 nm is realized in CW regime. The designed laser cavity is configured with all-PM fiber scheme and the special PMF is temperature-controlled, thus the laser owns high environmental stability and repeatability. To the best of our knowledge, this is the first report of wavelength tunable NLP output in the all-PM thulium-doped fiber laser. [ABSTRACT FROM AUTHOR]

A compact single-frequency master oscillator power amplifier laser system composed of three-stage thulium-doped fiber amplifiers was developed. At a repetition rate of 10 Hz, >100-µJ pulse energy at 2050.5-nm wavelength, with ~431-ns pulse width, was achieved successfully. The pulse profile could be actively controlled by adjusting the drive signal of an acoustic-optical modulator. This all-fiber laser system could be utilized as a seeder laser for a solid-state power amplifier system. [ABSTRACT FROM AUTHOR]

Abstract In this work, a tunable dual-wavelength fiber laser (DWFL) with a simple setup is proposed and demonstrated for operation in the 2.0-micron wavelength region. The proposed system employs a ring cavity with a 4-m bi-directionally pumped thulium-doped fiber (TDF) as the linear gain medium, with an inner ring cavity incorporating two tunable bandpass filters (TBPFs) used to generate the desired tunable dual-wavelength output. By fine-tuning the loss of the cavity, peaks of similar intensities for both lasing wavelengths can be obtained by overcoming suppression induced by the homogenous broadening effect, thus producing a stable dual-wavelength output. The widest channel spacing obtained is 183.6 nm, and both lasing wavelengths can be tuned across the 1.8-2.0-micron region by just adjusting the passbands of the TBPFs. The generated dual-wavelength laser has a high signal-to-noise ratio of 66 dB, and its 3-dB bandwidth is measured to be around 0.07 nm. The laser is highly stable, with little-to-none peak fluctuations and no wavelength shift in the lasing wavelengths. The proposed laser is suitable for use in multiple applications near the 2.0-micron region, such as biomedical and industrial applications due to its eye-safe properties. [ABSTRACT FROM AUTHOR]

Demonstrations of dual-wavelength Q-switched fiber lasers in the wavelength regions of 1.0 μm and 1.55 μm have been widely reported but not in the longer wavelength of 2.0 μm region. In this paper, a dual-wavelength Q-switched thulium-doped fiber laser is proposed and demonstrated using an N-doped graphene film as the saturable absorber, while the dual-wavelength mechanism is achieved with the use of a tunable Mach-Zehnder filter. The dual-wavelength Q-switched laser produced consistent outputs at 1922.0 nm and 1961.0 nm with a wavelength spacing of 39.0 nm. The repetition rate of the pulses obtained covers a range from 17.68 kHz to 35.21 kHz corresponding to an increasing pump power of 112.55 mW until 147.78 mW. The narrowest pulse width obtained is 4.4 μs and a pulse energy as high as 25.56 nJ is generated. To the best of our knowledge, this is the first demonstration of a dual‐wavelength Q-switched thulium-doped fiber laser operating in the 2.0 μm wavelength region using a fiber ring cavity design. [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]

ABSTRACT A kind of widely tunable multi-wavelength thulium-doped fiber laser based on nonlinear polarization rotation (NPR) is achieved. Using a ring cavity, 1565 nm laser pump, a 3m long thulium doped fiber, and NPR effect is used as filter. By adjusting the fiber polarization controller, stable 1-5 wavelengths laser output is observed at room temperature, and the side mode suppression ratio is 40-60 dB. The measured results show that the wavelength shift is less than 0.2 nm within one hour and the output peak power fluctuation is less than ±3 dB. The wavelength spacing is about 6.75 nm and the tuning range is 33 nm. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1540-1543, 2016 [ABSTRACT FROM AUTHOR]

Abstract: Narrow-linewidth and linearly polarized operation at high repetition rate of an all-fiber gain-switched Thulium-doped fiber laser is presented. The laser produces stable 135ns pulses with maximum average output power of 960mW at repetition rate of 500kHz, corresponding to maximum pulse energy of 1.92μJ and a slope efficiency of 55.1% with respect to 1.55μm pump power. The center wavelength of 1926.7nm with a spectral bandwidth of <50pm is achieved. [Copyright &y& Elsevier]

ABSTRACT We propose a channel-spacing tunable multiwavelength thulium-doped fiber laser in the 2-μm waveband. Stable multiwavelength operation at room temperature is achieved using four-wave mixing effect in a high nonlinear fiber. The wavelength spacing and number of channels of the multiwavelength fiber laser are adjustable by controlling the effective length of polarization-maintaining fiber in the intracavity Lyot-Sagnac filter. Four channels with 3.0-nm spacing, eight channels with 1.5-nm spacing, and 11 channels with 1.0-nm spacing are experimentally demonstrated. Characteristics of output stability and extinction ratio are also evaluated. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:337-340, 2016 [ABSTRACT FROM AUTHOR]

• A wavelength-interval-switchable MWTDFL based on a NDP-MZI filter is proposed and demonstrated. • Two 20-wavelength operations are obtained and switched between each other flexibly. • The maximum power/wavelength fluctuation of 20-wavelength operation are 0.612 dB/0.04 nm. • 60 lasing wavelengths within a 3-dB bandwidth are obtained by adjusting the PCs. A wavelength-interval-switchable multi-wavelength thulium-doped fiber laser (MWTDFL) is proposed and demonstrated, based on a nonlinear dual-pass Mach-Zehnder interferometer (NDP-MZI) filter for the first time. We investigate the NDP-MZI filter theoretically and experimentally, which has both the transmission characteristics of a dual-pass Mach-Zehnder interferometer (DP-MZI) for wavelength selection and a nonlinear optical loop mirror (NOLM) for suppressing wavelength competition. By tuning two polarization controllers (PCs), two 20-wavelength operations with an opposite phase and a same wavelength-interval of 0.46 nm are obtained and switched between each other flexibly. The maximum power fluctuation and wavelength drift measured are 0.612 dB and 0.04 nm, respectively. In addition, due to the power-equalizing effect resulting from the NOLM, 60 lasing wavelengths within a 3-dB bandwidth with an adjacent wavelength-interval of 0.23 nm are also obtained by adjusting the PCs carefully, and the stability of the MWTDFL is measured experimentally. Furthermore, the performance of the NDP-MZI using an 80 m highly nonlinear fiber has been studied in detail as well. The proposed MWTDFL may find great applications in optical communication and optical sensing. [ABSTRACT FROM AUTHOR]

• A wavelength-switchable thulium-doped fiber laser using two-mode fiber filter was proposed. • The lasing range of the single-wavelength is ~35.7 nm and the maximum lasing range of the dual-wavelength is ~23.38 nm. • The output signal-to-noise-ratio is up to ~60 dB. • The wavelength interval of the dual-wavelength can be adjusted from ~4, to 27.36 nm. A switchable, thulium-doped, isolator-free fiber laser is proposed and demonstrated. The isolator-free configuration, wavelength selective element and stabilization mechanism were achieved by using a theta cavity design, a two-mode fiber filter and nonlinear polarization rotation, respectively. By properly adjusting the polarization controllers to induce polarization-dependent loss, single- and dual-wavelength outputs can be obtained, and the stability of single- and dual-wavelength operations was measured for 30 min in each case. The single wavelength can be switched from 1959.17 to 1994.86 nm in a lasing range of ~35.7 nm with an optical signal-to-noise ratio (OSNR) of up to ~60 dB. When lasing dual-wavelength, the wavelength interval can be changed from ~4 to 27.36 nm with an OSNR higher than 42 dB, and the maximal lasing range of the dual-wavelength is 23.38 nm. In addition, the wavelength drift and power fluctuation of the proposed fiber laser are less than 0.14 nm and 1.976 dB, respectively, at room temperature, which demonstrates that the thulium-doped fiber laser has favorable wavelength and power stability. [ABSTRACT FROM AUTHOR]

Wavelength-tunable thulium-doped fiber laser is demonstrated employing a digital micromirror device (DMD) in combination with a fixed grating. The diffraction property of four typical models of DMDs and its steering efficiency for the laser system are analyzed based on two-dimensional grating theory. By spatially modulating reflective patterns on a DMD, the stable, fast, and flexible tuning of lasing wavelength from 1930 nm to 2000 nm is achieved with wavelength tuning accuracy of 0.1 nm. The side-mode suppression ratio is larger than 50 dB around the 2 μm band with 3 dB linewidth less than 0.05 nm. The wavelength drift and power fluctuation are lower than 0.05 nm and 0.1 dB within 1 h at the room temperature, respectively. [ABSTRACT FROM AUTHOR]