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We experimentally demonstrated a type of tunable and switchable harmonic h-shaped pulse generation in a thulium-doped fiber (TDF) laser passively mode locked by using an ultralong nonlinear optical loop mirror. The total cavity length was ∼3.03 km, the longest ever built for a TDF laser to our best knowledge, which resulted in an ultralarge anomalous dispersion over −200 ps2 around the emission wavelength. The produced h-shaped pulse can operate either in a fundamental or in a high-order harmonic mode-locking (HML) state depending on pump power and intra-cavity polarization state (PS). The pulse duration, no matter of the operation state, was tunable with pump power. However, pulse breaking and self-organizing occurred, resulting in high-order HML, when the pump power increased above a threshold. At a fixed pump power, the order of HML was switchable from one to another by manipulating the PS. Switching from the 8th up to the 48th order of HML was achieved with a fixed pump power of ∼4.15 W. Our results revealed the detailed evolution and switching characteristics of the HML and individual pulse envelope with respect to both the pump power and PS. We have also discussed in detail the mechanisms of both the h-shaped pulse generation and the switching of its HML. This contribution would be helpful for further in-depth study on the underlying dynamics of long-duration particular-envelope pulses with ultralarge anomalous dispersion and ultralong roundtrip time.

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 MoWS2 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.

Q-switched thulium-doped fiber laser (TDFL) is demonstrated using pencil-core flakes as a saturable absorber (SA) for the first time. The SA was fabricated by exfoliating pencil-core flakes on adhesive tape surface, then repeatedly folded over the tape until the flakes homogenously deposited on the tape. A small piece of the tape is sandwiched between two ferrules and incorporated in TDFL cavity to realize a stable Q-switching pulse train. By increasing the 1552-nm pump power from 389 to 431 mW, the repetition rate of the TDFL increases from 14.95 to 34.60 kHz while the pulse width decreases from 6.70 to 4.69 μs. The maximum pulse energy of 46.05 nJ is generated with repetition rate and pulse width of 21.25 kHz and 6.27 μs, respectively. To the best our knowledge, this is a first demonstration SA from mundane object as alternative to commercial bulk graphite for Q-switched fiber laser.

We demonstrate a tunable multi-wavelength thulium-doped fiber laser (TDFL). A Sagnac fiber period filter is employed to achieve the tunable multi-wavelength fiber laser and consists of a 3-dB coupler, a segment of 4 m long polarization maintained thulium-doped fiber (PM-TDF) and a polarization controller (PC). Multi-wavelength laser are observed in the wavelength region of 1.9 μm, and the side-mode suppression ratio (SMSR) of the multi-wavelength fiber laser is over 55 dB with 1 W pump power at 1.56 μm. By adjusting PC, tunable range of output laser spectrum from 1955 to 1962 nm can be obtained with single-wavelength laser. In addition, the linewidth of the laser is narrower due to the use of a fiber loop for suppressing multimode oscillation. This fiber laser around 1.9 μm wavelength are useful mid-infrared laser generation, free space laser communications, medicine and biomedical, coherent laser radar for remote atmospheric sensing, pump for nonlinear frequency conversion based on soliton self-frequency shift and second-harmonic generation.

We demonstrate an all-fiber figure-eight mode-locked thulium-doped fiber laser with a wide tunable range in both pulsewidth and wavelength. A 45-m-long ultrahigh numerical aperture fiber is used to manage the cavity dispersion, and the net cavity dispersion is calculated to be 0.8585 ps2 at 1900 nm. With net-normal dispersion, the experimental laser, operating in a dissipative soliton resonance region, generates stable rectangular pulses. The pulsewidth varies from 480 ps to 6.19 ns with the increasing pump power, and its center wavelength has a 28.95-nm tunable range (from 1940.22 to 1969.17 nm) by properly adjusting the polarization controllers. The maximum of average output power and pulse energy is 60.73 mW and 19.51 nJ, respectively. The rectangular pulses have a clamped peak power of about 3.16 W. The wavelength-tunable fiber laser with high-energy output operating at 2 μm has great potential in various application fields.

We present an efficient method for polarized 963 nm emission based on second-harmonic generation from a high-power, polarized thulium-doped fiber laser using periodically poled MgO:LiNbO3 as the nonlinear material. The maximum 963-nm output power of 710 mW has been achieved with a pulse duration of 34 ns at the repetition rate of 100 kHz and a Gaussian spatial beam profile. The frequency doubling efficiency is up to 56%, and the total optic-to-optic conversion efficiency is more than 12.9%. In addition, third- and fourth-harmonic generations have been observed.

A passively mode-locked thulium-doped fiber (TDF) laser was realized by employing chemical vapor deposited few-layer molybdenum ditelluride (MoTe2) as a saturable absorber (SA). The few-layer MoTe2 film was transferred onto the waist of a microfiber and then incorporated into a TDF laser with a typical all-fiber ring cavity configuration. Stable soliton pulses emitting at 1930.22 nm were obtained with a 3 dB bandwidth of 4.45 nm, a pulse duration of 952 fs, and an average power of 36.7 mW.

We report a study of an all-fiber Tm-doped fiber laser with tunable single wavelength emission and dual-wavelength generation operating in different laser wavelength ranges depending on the Tm-doped fiber (TDF) length. The wavelength selection and tuning for single wavelength laser operation and the adjustment of cavity losses for dual wavelength laser operation is obtained by temperature variations of the high birefringence fiber loop in a fiber optical loop mirror. Stable dual wavelength operation is achieved at the single wavelength tuning limits when cavity losses are balanced to generate two simultaneous laser lines with equal powers. A linear cavity fiber laser setup with TDF lengths of 2, 4, 8 and 12 m is used to obtain tunable single wavelength operation in a range of ~40 nm for each TDF length. A total tuning range of ~110 nm with the four different TDF lengths is achieved. At dual-wavelength laser operation the wavelength separation was ~48 nm. The maximal power efficiency of ~34.9% with a maximum output power of 274 mW was obtained with the use of TDF length of 4 m.

The output characteristics of the mode-locked thulium-doped fiber laser with MoS 2 as saturable absorber are simulated based on rate equation and nonlinear Schrodinger equation. With small signal gain efficient as variable, the effect of pump power, length of gain fiber, doping concentration and other parameters on output characteristics are analyzed. The theoretical results show an optimum doping concentration or fiber length exists to obtain maximum gain and average output power for given doped fiber. In experiment a thulium-doped fiber laser is setup and the experimental output characteristics of the laser are compared with theoretical counterpart, as a result, theoretical results are well in consistence with experimental results.

Pulsed fiber laser operating at 2000 nm is of great interest in applications such as LIDAR system using very low atmospheric absorption bands, material processing for transparent plastics, etc. Thulium- and holmium-doped silicate glass fibers have been the best choice as a gain medium for the fiber lasers. In particular, a holmium-doped fiber laser (HDFL) has drawn much attention because it opened up the possibility to extend the operating wavelength beyond 2100 nm. The pump source of the HDFL has been typically a thulium-doped fiber laser (TDFL) due to the availability of high power at 1950 nm where the HDF has the maximum absorption. A gain-switched HDFL is the pulsed fiber laser built on the same architecture. The pump source, in this case, has been either a Q-switched TDFL pump by a continuous wave (CW) laser at 793 nm or another gain-switched TDFL pumped by a pulsed laser at 1550 nm. Such cascaded pumping scheme leads the laser configuration to be complicated having redundant optical components [1, 2]. We proposed a couple of methodologies for integrating the gain-switched HDFL and the Q-switched TDFL on a single laser cavity. The main idea here is to let the HDF, the saturable absorber of the Q-switched TDFL, be the gain at the same time in the cavity, thereby being a gain-switched HDFL. One of proposed methods to realize the idea appears in Fig. 1(a). The laser consists of a ring cavity with a linear section. The TDF and HDF are in the ring cavity, and a fiber Bragg grating (FBG, reflection at 1950 nm), a variable optical attenuator and a fiber mirror are in the linear section. In the Q-switched TDFL configuration, the HDF functions as a saturable absorber. The FBG determines the lasing wavelength of 1950 nm at the highest level of attenuation (no reflection from the fiber mirror), which is for case (i) in Fig. 1(b). Very stable output pulses are observed in this case. The lasing wavelength jumps up to the wavelength of 2008 nm at the middle level of attenuation, which corresponds to case (ii) in Fig. 2(b). This is because the effective thulium gain at 2008 nm gets higher than that at 1950 nm. In the meantime, output pulses become unstable due to the low modulation depth of the HDF at the wavelength. At the lowest level of attenuation, the laser operates at two different wavelengths as shown in case (iii) in Fig. 2(b): one is at 1987 nm and the other is at 2013 nm. The attenuator can control the distance of separation, which can be understood by considering the spectral emission and absorption profiles of TDF and HDF. The shorter wavelength (1987 nm) is expected to be from the Q-switched TDFL and the longer wavelength (2013 nm) the gain-switched HDFL. In this presentation, we will introduce two methods for integrating gain-switched holmium-doped fiber laser and Q-switched thulium-doped fiber laser and describe their experimental results.

The high power infrared 2μm lasers have been extensively investigated for a number of commercial, scientific and engineering applications, such as remote chemical sensing, medical diagnostics, eye-safe laser radar, and environmental monitoring. Furthermore, high-power 2μm lasers are effective pump sources of optical parametrical oscillators and optical parametrical amplifications to generate mid-infrared 3-5μm laser. In recent years, Ho:YAlO3(Ho:YAP) crystal has drawn great attention as a promising efficient laser material for its long emission wavelength at 2118nm. An acoustic-optical Q-switched Ho:YAP laser pumped by an all fiber thulium-doped fiber laser is demonstrated. The all fiber thulium-doped fiber laser can emit 80W output power, and the output laser wavelength is 1915nm. By using this 1915nm laser to end pump the AO Q-switched Ho:YAP laser system, 2118nm laser with 30W average power and 45ns pulse width at 20kHz repetition rates was obtained.

A novel optofluidically tunable Thulium-doped fiber laser (TDFL) based on a multimode interference (MMI) fiber filter is experimentally demonstrated with a wide tuning range from 1813.52 to 1858.70 nm. The wavelength tuning of the TDFL is achieved by employing an MMI fiber filter which is formed by splicing a segment of a special no-core fiber that is an all silica fiber without fiber core to single mode fibers. The no-core fiber with a large diameter of 200 μm is gradually vertically covered by refractive index matching liquid, which leads to a wavelength tuning of the transmission peak of the MMI fiber filter. The relationship between the refractive index of the refractive index matching liquid and the peak wavelength shift of the MMI fiber filter is also discussed. Using the MMI fiber filter, a Thulium-doped fiber laser with a tuning range of 45.18 nm, a side-mode suppression ratio better than 40 dB, and a 3 dB bandwidth less than 0.16 nm is demonstrated.

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.

We report a linear cavity all-fiber passive Q-switched thulium-doped fiber laser operating at the 2 μm wavelength range. The laser configuration is based on a thulium-doped fiber used as a gain medium and an unpumped segment of holmium-doped fiber which acts as a fiber saturable absorber. The cavity is formed by a fiber optical loop mirror and the flat end facet of the holmium-doped fiber. The fiber segments as saturable absorber is a 1-m long single mode doubleclad holmium-doped fiber. Q-switched pulses are obtained at the wavelength of 2024.5 nm with a pulse width of 1.1 μs. The pulse repetition rate increases as a linear function of the applied pump power. The maximum pulse repetition rate of 100 kHz was obtained with a pump power of 2.4 W.

We experimentally demonstrate the use of a high-speed, solid-state optical switch as an efficient Mid-IR Q-switch. The switch could be modulated upto 2.2 MHz and its rising and falling time were measured to be 160 ns and 140 ns, respectively. Using the optical switch, stable actively Q-switched pulses were readily generated from a thulium doped-fiber laser cavity. The minimum pulse width of the pulses was measured to be 160 ns at 100 kHz with the average output power of 0.5 mW.

We reported dissipative soliton resonance effects passively mode-locked figure-eight thulium doped fiber laser. At maximum pump power was achieved 85.18 ns pulse duration, a pulse energy of 206 nJ, a repetition rate of 1.19 MHz.

We report 209 MHz harmonic mode-locking of a 2420 nm Cr: ZnSe laser synchronously pumped by a 1935 nm, 104.5 MHz, 112 ps thulium doped fiber laser. Self-starting behavior was investigated by a chopper wheel.

We demonstrate a gain-switched thulium-doped fiber laser with electrically wavelength tuning in the 1.7-μm band. The achieved stable laser pulses with an energy of 1.6 μJ are exploited to implement spectroscopic photoacoustic microscopy of lipid.

Tunable dual-wavelength emission of a Tm-doped fiber laser based on two fiber Bragg gratings (FBGs) is experimentally demonstrated. By using two FBGs with central wavelengths at 2069.30 and 2069.44 nm, stable dual-wavelength laser generation in the 2 ?m wavelength region is achieved by adjusting the differential loss of the two wavelengths in the laser cavity. Strain applied on the FBG allows independent tuning of the simultaneously generated wavelengths with separation between the laser lines in a range from 0.54 to 9 nm. The laser has output power fluctuations less than 0.093% for an output power of 77.3 mW.

We demonstrate a gain-switched thulium-doped fiber laser with electrically tuning at 1690–1765 nm. Stable laser pulse with duration of 190 ns, average power of 654 mW, and pulse energy of 2.2 μJ is achieved.

A switchable multi-wavelength thulium-doped fiber laser based on non-adiabatic tapered fibers is experimentally demonstrated. The laser is switched from single to multi-wavelength by curving the tapers showing high stability output near 2 μm region.

This study describes a proposal and experimental demonstration of a tunable thulium-doped fiber laser with a multi-wavelength output operating at 1.8 μm. The introduction of a multi-mode non-adiaba...

We report, for the first time to our knowledge, the usage of CVD-grown few-layer WSe 2 as a saturable absorber for the mode locking of a thulium-doped fiber laser. The WSe2 saturable absorber was deposited on the waist of the tapered fiber. By employing the WSe 2 saturable absorber, we demonstrate a passively mode-locked fiber laser operating at 1863.96 nm with a 3 dB spectral bandwidth of 2.89 nm. The fundamental repetition rate was 11.357 MHz with a signal-to-noise ratio of 85 dB.

We demonstrate a high-energy all-fiber short wavelength gain-switched thulium-doped fiber laser for volumetric photoacoustic (PA) imaging of lipids. The laser cavity is constructed by embedding a short piece of gain fiber between a pair of fiber Bragg gratings (FBGs). Through using three pairs of FBGs with operation wavelengths at 1700, 1725, and 1750 nm, three similar lasers are realized with a cavity length of around 25 cm. Under a maximum pump energy of 300 μJ at 1560 nm, laser pulse energies of 58.2, 66.8, and 75.3 μJ are, respectively, achieved with a minimum pulse width of < 16.7 ns at a repetition rate of 10 kHz. Volumetric imaging of lipids is validated through scanning a fat beef slice with a PA microscopy system incorporated with the newly developed source, and a lateral resolution of 18.8 μm and an axial resolution of 172.9 μm are achieved. Moreover, the higher shooting speed of the developed source can potentially allow for increasing at twice the frame rate of current intravascular PA imaging.

A novel tunable dual-wavelength thulium-doped fiber laser is demonstrated experimentally. The wavelength-tuning by employing a high birefringence fiber Bragg grating is proposed in 2-μm band lasing for the first time. By adjusting the polarization controller, stable dual-wavelength operation at the wavelengths of 1941.40 and 1942.21 nm is obtained. The optical signal-to-noise ratio is better than 48 dB. A 15.5% slope efficiency is achieved using a 90% output coupling ratio for laser extracting. The wavelength-tuning range in dual-wavelength operation is as wide as 6.93 nm.

Herein, we present a fundamental and harmonic mode-locked figure-of-9 thulium-doped fiber laser using a nonlinear amplifying loop mirror. The generated fundamental mode-locked h-shaped pulse is centered at 1889 nm with an average output power reaching 282 mW and a pulse energy up to 1.23 µJ, which is the highest power and pulse energy of an h-shaped pulse. In the harmonic mode-locked regime, up to the 8th harmonic h-shaped pulse is obtained. The detailed characteristics of the h-shaped pulse are discussed. The proposed study shows that the figure-of-9 fiber laser can generate h-shaped pulses and also allows the generation of nanosecond pulses with a µJ-level pulse energy.

We demonstrate a passive Q-switched all-fiber ring configuration in thulium-doped fiber laser (TDFL) cavity using a bismuth-doped fiber (BDF) as a saturable absorber (SA). A piece of 20 cm long BDF was spliced and incorporated in the laser cavity for Q-switching pulse generation. By raising the pump power from 454 mW to 564 mW, the repetition rate of the laser is tunable within a range from 18.10 kHz to 25.22 kHz while the pulse width reduces from 9.04 µs to 6.98 µs. At maximum pump power, the Q-switched TDFL has output power, a slope efficiency, pulse energy and peak power of 5 mW, 3.53 %, 0.2 µJ and 28.40 mW, respectively.

We experimentally demonstrate the use of Fe3O4-based saturable absorber (SA) to generate self-starting, passively Q-switched pulses at 1943 nm. The Fe3O4 particles were characterized with scanning electron microscopy with energy dispersive spectroscopy. The size distribution of Fe3O4 particles was varied from ∼150 nm to 980 nm. The proposed SA was fabricated with combination of a side-polished fiber and the Fe3O4 particle by using evanescent field interaction between the side-polished fiber and the Fe3O4 particle. The insertion loss and polarization dependent loss of the proposed SA were measured as ∼4 dB and 0.3 dB, respectively at a wavelength of 1930 nm. The stable passively Q-switched pulses were readily generated from thulium-doped fiber laser incorporating the proposed SA at 1943 nm. The pulse width was changed from ∼8.1 μs to ∼880 ns while the repetition rate was changed from ∼61 kHz to ∼87 kHz. The tuning capability of both pulse width and repetition rate was also shown according to pump power.

We reported on a passively Q-switched double-clad thulium-doped fiber laser by using oxygen vacancies (OVs) enriched with MoO3-x as a saturable absorber (SA). The MoO3-x was successfully embedded in polyvinyl alcohol and acted as the SA for a stable Q-switching operation in the 2 µm wavelength region. Stable Q-switched pulses were obtained at a central wavelength of ∼1992.1 nm with a maximum output power of ∼62.7 mW, maximum pulse energy of ∼1.63 µJ and a minimum pulse duration of ∼2 µs. The repetition rate of the pulses can be tuned from ∼15.5 kHz to ∼38.5 kHz with increasing the pump power. Our experiment was the first demonstrated use of MoO3-x as a SA for pulse laser generation, in which OVs were considered as the original reason for the optical saturable absorption. Moreover, it provides a novel idea for optical SA preparation by controlling the vacancy defects in such materials.

Using the novel 45°-plane-by-plane-tilted fiber grating inscribed by a femtosecond laser as an in-line fiber polarizer, we demonstrate an all-fiber passively mode-locked thulium-doped fiber laser. We characterize the grating for polarization-dependent loss, indicating high contrast and broad operating wavelength. The 45°-tilted fiber grating together with polarization controller act as an artificial saturable absorber suitable for mode-locking through nonlinear polarization rotation. By properly pre-adjusting the polarization controller, stable mode-locking is achieved for a pump power in the range of 300 mW-400 mW at 1565 nm. Owing to the net anomalous dispersion, a stable mode-locked soliton pulse centered at 1870 nm with a pulse width of 862 fs is reported at a fundamental repetition rate of 22.34 MHz. A long-term stability test reveals that the laser is quite stable for 24 h under laboratory conditions, confirming the capabilities of the 45°-tilted fiber grating for stable laser operation.

We report an efficient thulium-doped fiber offering a laser efficiency >70% with respect to the absorbed pump power over a wide wavelength band of 1890 to 2080nm when cladding pumped at 793nm.

In this contribution we report and discuss the results of laser characterizations of experimental thulium-doped optical fibers. These active fibers were fabricated in house and were tested in two laser systems to verify their characteristics. The first one, a monolithic fiber laser, was of great interest to us due to its potentially lower overall resonator losses, improved laser lifetime and better robustness. The compact laser cavities with a Bragg gratings inscribed directly into the active optical fiber differs to the second laser system where the Bragg gratings were inscribed into a passive fiber which had to be spliced to the active fiber. The tested fibers were manufactured by the modified chemical vapor deposition method and a solution-doping of thulium ions with Al2O3 or alumina nanoparticles, respectively. We focused on comparison of laser output powers, slope efficiencies, and laser thresholds for particular thulium-doped fiber in different laser configurations.

Dissipative soliton resonance (DSR) exists in a dissipative system with narrow cavity parameter space in mode-locked fiber lasers. In this work, DSR generation with >800ns pulse width and >84% duty cycle is demonstrated in a mode-locked TDFL. To the best of our knowledge, this result presents the longest DSR pulse duration for 2μm fiber lasers, and the highest pulse duty cycle that has been achieved for any fiber laser operating in the DSR regime.

A monolithic widely wavelength-tunable TDFL mode-locked by SESAM is experimentally demonstrated in our contribution. The laser features a broad wavelength tuning range of 121 nm (1862 - 1983 nm). The central wavelength is tuned by a grating-based tunable filter in the ring laser cavity. To the best of our knowledge, this is so far the most widely wavelength-tunable TDFL mode-locked by SESAM.

Dissipative soliton resonance (DSR) fiber mode-locked lasers (MLL) are attracting a steadily growing interest over the recent years, due to their ability to generate relatively long (ns-scale), strongly chirped and large energy pulses directly inside a main oscillator. Thulium-doped fiber (TDF) DSR MLLs, optionally enhanced with amplification and compression stages, are in high demand in various application areas in 2-μm spectral region, like surgery, LIDAR and remote sensing, microscopy, etc. Figure-8 (F8) TDF laser, emitting 20 nJ pulses from net-normal-dispersion cavity, was demonstrated [1]. More advanced total-anomalous-dispersion F8 cavity, involving double-clad (DC) TDF and two-stage post-amplification, was used to obtain a pulse energy of 66 μJ [2]. The nonlinear amplifiying loop mirror (NALM) was exploited in both experiments as a mode-locking element. Being mainly fiber-based, above-mentioned configurations include some inherently free-space components, such as isolators, which have lower damage threshold, comparing to all-fiber elements. In this paper, we demonstrate the first truly all-fiber figure-9 (F9) DSR TDF laser that emits nanosecond pulses with energies up to 400 nJ, which is to the best of our knowledge a record value of the energies, extracted directly from the DSR oscillator at 2 μm.

We report the generation of high energy 2 μm picosecond pulses from a thulium-doped fiber master oscillator power amplifier system. The all-fiber configuration was realized by a flexible large-mode area photonic crystal fiber (LMA-PCF). The amplifier output is a linearly-polarized 1.5 ns, 100 kHz pulse train with a pulse energy of up to 250 μJ. Pulse compression was achieved with (2+2)-pass chirped volume Bragg grating (CVBG) to obtain a 2.8 ps pulse width with a total pulse energy of 46 μJ. The overall system compactness was enabled by the all-fiber amplifier design and the multi-pass CVBG-based compressor. The laser output was then used to demonstrate high-speed direct-writing capability on a temperature-sensitive biomaterial to change its topography (i.e. fabricate microchannels, foams and pores). The topographical modifications of biomaterials are known to influence cell behavior and fate which is potentially useful in many cell and tissue engineering applications.

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

We experimentally demonstrate a passively mode-locked thulium doped fiber laser using a bismuth telluride deposited multimode interference (MMI) fiber at a wavelength of 1958 nm. Our MMI based saturable absorber was fabricated by fusion splicing with single mode fiber and null core fiber. The center wavelength and insertion loss of MMI fiber were measured to be ~ 1958 nm and 3.4 dB. We observed a passively mode locked thulium doped fiber laser operating at a wavelength of 1958 nm. The temporal pulse width of output pulses is 4.2 ps with repetition rate of 22.7 MHz.

A continuous wave (CW) wavelength-tunable Tm3+-doped fiber laser with two sampled fiber Bragg gratings (SFBGs) has been proposed and demonstrated. This proposed laser is stable operating with a significant 14.44 nm wavelength range from 1942.09 nm to 1956.53 nm due to the Vernier effect. The laser OSNRs of different wavelengths ranged from 45 dB to 58 dB at a launched pump power of 3.67 W. The wavelength shift and power fluctuation were less than 0.03 nm and 0.46 dB, respectively. An 8.62% slope efficiency was achieved using a grating for laser extracting. To the authors’ knowledge, this is the first time that a wavelength-tunable Tm3+-doped fiber laser with two SFBGs has been demonstrated.

We present a continuously tunable thulium(Tm)-doped fiber laser operating in the important 2.1 μm region, which is tandem-pumped by another Tm-doped fiber laser at 1908 nm. The advantages of pumping a Tm-doped fiber laser at the long-wavelength absorption tail (>1900 nm) of the fiber include a reduced quantum-defect, and efficient suppression of the amplified spontaneous noise (and potential parasitic lasing) at the short-wavelength region. This facilitates attainment of stable lasing operation in the long-wave emission tail of the Tm fiber at ~2.1 μm. By rotating a diffraction grating inside the Tm fiber laser cavity, we experimentally achieved a wavelength-tuning range of 2000-2172 nm. At central wavelengths of 2050 nm, 2150 nm, and 2172 nm, the slope efficiencies were 23%, 16%, and 9.9%, respectively. To the best of our knowledge, this is the first demonstration of long-wavelength operation of a Tm fiber laser system tandem-pumped at >1900 nm.

We report on an all-fiber, actively mode-locked, tunable, Thulium-doped, fiber laser based on a 20-GHz bandwidth electro-optic intensity modulator (EOM) and a voltage driven 2-μm, intra-cavity, fiber-coupled, Fabry-Perot tunable filter (FFP-TF). The repetition rate of output pulses was 47 MHz and the shortest measured output pulse width was 445 ps. A continuous tuning range of 88 nm has been achieved from 1954 to 2042 nm with a spectral linewidth ≤0.14 nm and an optical signal-to-noise ratio

We demonstrate a short wavelength harmonically mode-locked thulium-doped fiber laser based on nonlinear polarization rotation. Stable soliton pulsing with record short wavelength of 1787 nm and FWHM of 6.5 nm is achieved.

A 1901.6-nm laser is demonstrated using the newly developed double-clad ytterbium-thulium-doped fiber (YTDF) samples in conjunction with 931-nm pumping through the transition of thulium ion from 3F4 to 3H6 with the assistance of ytterbium to thulium-ion energy transfer. The YTDF used was drawn from a D-shape preform, which was fabricated using the modified chemical vapor deposition and solution-doping technique. The laser operates at 1901.6 nm with an efficiency of 2.47% using 2-m-long YTDF in a Fabry-Perot cavity with two fiber Bragg gratings. It is found that the higher ytterbium-to-thulium concentration ratio contributes to more efficient energy transfer between the sensitizer and acceptor ions in YTDF, which in turn lowers the threshold of the proposed ytterbium-thulium-doped fiber laser (YTFL). The lowest threshold pump power of the proposed YTFL is around 961 mW. The use of multimode pump with a wavelength slightly lower than 931 nm is also observed to improve both the laser's threshold and efficiency of the YTFL.

We demonstrate an all-fiber gain-switched thulium-doped fiber laser (TDFL) producing nanosecond pulses with variable wavelength in the 2 μm waveband. The laser features tunable operation in an ultra-wide spectral region of 1765 – 2055 nm (24 THz). The nearly 300 nm tunability doubles the record tuning range of existing gain-switched fiber lasers, and to the best of our knowledge, presents the broadest tuning range that has been reported for a monolithic pulsed rare earth doped fiber laser to date. The TDFL can operate at a repetition rate of 5 – 100 kHz with a pulse width as short as ~200 ns. A modest compromise in the tuning range allows pulse width reduction to sub-100 ns.

In this paper, we demonstrate a dual-wavelength mode-locked thulium-doped fiber laser. The single-wall carbon nanotube is used as the mode-locker due to its large and ultrafast nonlinear optical responses. By tuning the pump power and adjusting the PC properly, stable dual-wavelength output can be achieved. The center wavelength of the dual-wavelength pulses are 1894 nm and 1907 nm, respectively. The repetition rate is about 17.64 MHz which exactly corresponds to the total length of the ring cavity. The signal-to-noise ratio is over 30 dB. It is a reliable method to realize dual-wavelength mode-locking operating at the range of 2 µm.

A high-power, wavelength-tunable, all-fiber integrated thulium-doped fiber laser (TDFL) at 2 μm is presented. The TDFL has a compact configuration which only consists of a low power seed oscillator and a stage of fiber power amplifier. The seed oscillator adopts a tunable band-pass filter as the wavelength selective element, matching the gain spectrum of thulium-doped fiber. It can provide ~5 W single-mode seed laser with superb spectral characteristics, and the lasing wavelength is adjustable from 1890 to 2050 nm. The fiber power amplifier provides a total gain of ~17 dB at 2 μm which boosts the signal power to the 300 W-level. The maximum average power reaches 327.5 W at 1930 nm with the highest slope efficiency of 57.4%. This TDFL can afford >270 W lasing operation over the whole tuning range of 140 nm spanning from 1910 to 2050 nm, together with high spectral quality and power stability. This is the first demonstration, to the best of our knowledge, on an all-fiber integrated wavelength-widely-tunable TDFL at 2 μm with output power at the 300 W-level. The results are of great interest for many applications.

A Q-switched Thulium-doped Fiber Laser (TDFL) operating at approximately 2 μm wavelength is successfully generated by using four different saturable absorbers (SAs) which are nitrogen-doped graphene in PVA (NG:PVA), nitrogen-doped graphene in PEO (NG:PEO), single-walled carbon nanotube in PVA (SWCNT:PVA), and high pressure carbon monoxide carbon nanotube in PVA (CNTHiPCO:PVA). The SAs integrated in the cavity were able to provide the real saturable absorption in modulating the intra-cavity losses. SWCNT gives the best results with the highest repetition rate and lowest pulse width of 57.45 kHz and 1.958 nJ correspondingly as compared to the other three SAs.