Thulium-doped Fiber Laser Research Articles

Dispersion managed thulium-doped fiber laser mode-locked by the nonlinear loop mirror

Intracavity dispersion management in a passively mode-locked thulium-doped all-fiber laser, based on a nonlinear optical loop mirror (NOLM) saturable absorber is reported. Fundamental soliton and stretched pulse soliton generation are demonstrated, when the oscillator operates with anomalous net dispersion. Gaussian pulses with a duration of 253 fs and 26.4 nm spectral bandwidth centered at wavelength of 1967 nm were generated with a fundamental pulse repetition frequency of ~15.8 MHz. In soliton mode-locking regime the oscillator delivering optical solitons with a 3 dB spectral width of 7.96 nm and duration of 675 fs. To the best of our knowledge, this is the shortest fundamental soliton generated from thulium-doped fiber laser with all anomalous dispersion based on a nonlinear fiber loop mirror saturable absorber reported till date.

Passively mode-locked thulium doped fiber laser based on SnSe nanoparticles as a saturable absorber

In this paper, tin selenide (SnSe) nanoparticles (NPs) are employed as a saturable absorber (SA) in a passively mode-locked thulium (Tm)-doped fiber laser for the first time. The mode-locked pulse has a central wavelength of 1963 nm and a 3-dB bandwidth of 4.3 nm. The repetition rate is 24.59 MHz and the full width at half maximum (FWHM) of the pulse is 1.2 ps. Harmonics from the second order to the eighth order are observed. Our results prove that the SnSe have excellent nonlinear saturable absorption properties and could have wide potential applications on ultrafast photonics in mid-infrared waveband.

High repetition rate gain-switched thulium-doped fiber laser pumped by 1.6 μm noise-like pulses

We demonstrate a watt-level 2 μm high repetition rate gain-switched thulium-doped fiber laser (TDFL) pumped by 1.6 μm noise-like pulses (NLPs). Served as pump pulses, the hundred nanoseconds level NLPs from a mode-locked fiber laser are amplified to ~8 μJ by an Er:Yb co-doped fiber amplifier. Referring to simulative and experimental results of the gain-switched TDFL, the cavity parameters are adapted for the performance of the gain-switched pulse. The TDFL generates 1940 nm gain-switched pulses with the minimum pulse duration of 14.7 ns in the cavity length of 14 cm. The maximum output power reaches 2.44 W. The research firstly reports a gain-switched TDFL pumped by noise-like pulses and provide a method to generate high repetition rate gain-switched short pulse.

Ultrashort pulse formation from a thulium-doped fiber laser: Self-characterization and mapping

We have performed an automatic characterization of a mode-locked thulium-doped fiber laser in soliton regime based on a versatile scheme of nonlinear polarization rotation (NPR) mode-locking. The cavity includes three fiber loop waveplates for adjusting the oscillation states of the cavity. The polarization controllers are equipped with servo motors that allow for automated stepping through a large number of polarization controller settings. The optical spectra and the radio frequency spectra of the cavity output are recorded at each polarization controller setting to extract key laser parameters from the data, automatically. Analyzing the large data sets, not only provides maps of the laser operation in various modes, but also it identifies the polarization controller settings leading to optimal mode-locking, consequently. Such method allows a detailed self-characterization of the fiber laser cavity which paves the way to achieve smart fiber lasers. This approach facilitates applications of fiber lasers and improves their reliability for practical purposes, where environmental instabilities might limit their performances.

Optimization and Application of High Power Thulium-Doped Fiber Laser

In recent years, with the continuous progress of laser technology, fiber laser has been developed rapidly. Compared with the traditional laser, fiber laser has the advantages of good beam quality, small volume, easy integration, high luminous efficiency, strong anti-interference ability and good heat dissipation. As a kind of fiber laser, thulium doped fiber laser not only inherits the above advantages, but also has the rich energy level structure and spectral characteristics of thulium ion, which determines that thulium doped fiber laser plays an important role in the research field of long wavelength fiber laser. This paper discusses the influence of the length and concentration of doped fiber on the output of high power laser system. For a given laser system, all parameters have an optimal value. In order to make the high power thulium doped fiber laser work in the best state, we need to carefully select these parameters. Based on the rate equation, the relationship between the dopant concentration and the length of the optical fiber is given in theory. The experimental results show that the optimal fiber length is different for different pump power. The higher the pump power, the larger the optimal fiber length. The experimental results have guiding significance for the manufacturing technology of high power fiber lasers.

Wavelength-Switchable Single-Longitudinal- Mode Thulium-Doped Fiber Laser With Sampled Fiber Bragg Grating

A wavelength-switchable single-longitudinal-mode thulium-doped fiber laser using a sampled fiber Bragg grating is proposed in this study. The laser can be switched between three single-wavelength and three dual-wavelength modes of operation. For the single-wavelength mode of operation, the maximum power and wavelength fluctuations in 50 min were ±0.404 dB and ±0.01 nm, and the linewidths at three wavelengths were 0.39, 1.88, and 0.89 kHz, respectively. For the dual-wavelength mode of operation, the maximum power and wavelength fluctuations in 20 min were ±0.926 dB and ±0.03 nm, respectively. The proposed thulium-doped fiber laser will find useful application in optical communication and free-space optical detection and sensing.

Tunable Multiwavelength Thulium-Doped Fiber Laser Based on Parallel Lyot Filter

This paper demonstrates a tunable wavelength spacing of thulium-doped fiber laser (TDFL) based on a parallel Lyot filter. An intensity-dependent loss (IDL) mechanism acts as an amplitude equalizer to flatten and stabilize the multiwavelength spectrum. The IDL mechanism is obtained at a certain polarization state from the combination of highly nonlinear fiber and polarizer. The wavelength spacing of the TDFL can be tuned to either 0.9 nm or 1.8 nm when the polarization controllers (PCs) in each branch of the parallel Lyot filter are adjusted. The wavelength spacing is tuned by adjusting both PC2 and PC3 to suppress or transmit the light at each branch. Up to 4 and 9 lasing lines are generated based on wavelength spacing of 0.9 nm and 1.8 nm, respectively. Lower pump power has disappeared lasing lines, while different half-wave plate angle of PC has shown variation the laser performances.

2.04 µm harmonic noise-like pulses generation from a mode-locked fiber laser based on nonlinear polarization rotation

We report the generation of harmonic noise-like mode-locked pulses in a thulium-doped fiber laser. In this laser, mode-locking can be realized through the nonlinear polarization rotation (NPR) technique. The ring cavity configuration uses 5 m of a Tm-doped dual-cladding fiber, as a gain medium, pumped by a 793 nm diode laser. The cavity uses a couple of polarization controllers (PCs) and polarization-dependent isolator to form a nonlinear polarization-rotating saturable absorber. By carefully adjusting of the PCs, the laser generates noise-like mode-locked pulses at the 2.04 µm band. With the increase of the pump power, the laser generates harmonics of the mode-locking fundamental repetition frequency of 6.88 MHz, from which we can obtain the second harmonic in a controlled mode. The obtained results may be useful for enhancing the understanding of the mechanism and characteristics of noise-like pulse at the 2 µm band.

1.56 µm and 1.93 µm synchronized mode-locked fiber laser with graphene saturable absorber

Ultrafast pulse with short duration ranging from picosecond to femtosecond has extensive industrial and scientific applications. The laser cavity generates this ultrafast pulse, however, was typically designed to emit the light at wavebands such as at approximately 1.5–1.6 µm or 1.9–2.0 µm. This could be limited by the bandgap of certain saturable absorber material to conduct ultra-broadband laser emission. Graphene, a 2D material with gapless band structure contributes to the optical resonant excitation to emit at any wavelength. The graphene was employed as the saturable absorber and positioned in a laser cavity consisting of both erbium and thulium-doped fiber laser. A synchronized mode-locked fiber laser was generated at a centre wavelength of 1563.5 nm and 1931.9 nm, giving a pulse duration of 700 fs and 1.77 ps at a constant pulse repetition rate of 12.905 MHz. The success of this work will provide a better insight by developing the optimum utilization of a saturable absorber in generating multiple mode-locked lasers with different yet far wavelength in near-infrared red region.

Single-longitudinal Mode Thulium-doped Fiber Laser Based on Fabry-Pérot Fiber Bragg Grating Filter and Passive Compound Double-rings Cavity

Single-longitudinal Mode Thulium-doped Fiber Laser Based on Fabry-Pérot Fiber Bragg Grating Filter and Passive Compound Double-rings Cavity

High-power Thulium-doped Fiber Laser and Its Application in Biological Tissue Cutting

High-power Thulium-doped Fiber Laser and Its Application in Biological Tissue Cutting

Generation of Q-switched fiber laser at 1.0-, 1.55- and 2.0-µm employing a spent coffee ground based saturable absorber

Spent coffee ground (SCG) was demonstrated as saturable absorber (SA) for Wideband Q-switched fiber lasers generation. The SCG SA has a broad linear absorption that covers from 1000 nm to 2000 nm wavelength and a modulation depth of 30% at 1.55-µm region. Through purification process, the finer SCG powder is obtained, and be embedded with a polyvinyl alcohol for thin film formation. To realize Q-switching operation lasers, a fabricated SCG film was integrated into three different fiber laser cavities including ytterbium-doped fiber laser, erbium-doped fiber laser, and thulium-doped fiber laser. A peak wavelength has obtainable at 1031 nm, 1563 nm, and 1976 nm for 1-, 1.55-, and 2- µm regions, respectively. The shortest pulse width of 4.80 µs and maximum pulse energy of 0.152 µJ are observed from the YDFL cavity. RF spectrum shows the signal-to-noise ratio for all regions is above 35 dB, indicates a stable pulsing generation. Our technique opens the door for unlimited materials SA from environmentally friendly resources which contribute to sustainable effort.

Switchable dissipative soliton resonance and noise like pulses regimes in a mode-locked double-clad thulium doped fiber laser

We report an experimental study of switchable rectangular pulses generation in a passively mode-locked double-clad thulium-doped fiber laser operating in the anomalous dispersion regime. A fiber loop mirror and a polarization imbalanced nonlinear optical loop mirror (NOLM) forms the linear cavity. The loop in the NOLM includes a quarter-wave retarder, which allows switching between two regimes of rectangular pulse generation. The laser generates rectangular noise-like pulses (NLPs) or dissipative soliton resonance (DSR) pulses with 1.18 MHz repetition rate at ∼1990 nm. At the maximum pump power of 10 W, rectangular pulses with energy of up to 540 nJ in DSR operation and 482 nJ in NLP operation were obtained with output average power of 640 mW and 571 mW, respectively.

Sub-picosecond passively mode-locked thulium-doped fiber laser by ReS2 nanoparticles

Passively mode-locked pulses generated in a thulium-doped fiber laser was demonstrated by the ReS2 nanoparticles. The ReS2 nanoparticles are introduced into the laser cavity on a side polished fiber through optical deposition method, which works as a saturable absorber. Self-starting mode-locking can be established quickly when the pump power is higher than 700 mW. The central wavelength and the 3 dB bandwidth of single pulse operation are 1970.65 and 5.05 nm, respectively. The pulse repetition is 26.1 MHz and the full width at half maximum is 893 fs with the time-bandwidth product of 0.348.

Generation of cavity-birefringence-dependent multi-wavelength bright–dark pulse pair in a figure-eight thulium-doped fiber laser* *Project supported by the National Natural Science Foundation of China (Grant No. 6170031626) and the Natural Science Foundation of Chongqing City, China (Grant Nos. cstc2018jcyjAX0585 and cstc2017zdzxX0011).

We experimentally demonstrated a stable multi-wavelength bright–dark pulse pair in a mode-locked thulium-doped fiber laser (TDFL). The nonlinear polarization rotation (NPR) and nonlinear optical loop mirror (NOLM) were employed in a figure-eight cavity to allow for multi-wavelength mode-locking operation. By incorporating different lengths of high birefringence polarization-maintaining fiber (PMF), the fiber laser could operate stably in a multi-wavelength emission state. Compared with the absence of the PMF, the birefringence effect caused by PMF resulted in rich multi-wavelength optical spectra and better intensity symmetry and stability of the bright–dark pulse pair.

Broadband Fe3O4 nanoparticles saturable absorber for Q-switched fiber lasers

We demonstrated passively Q-switched 1-, 1.5-, and 2-μm fiber lasers by exploiting ferroferric-oxide nanoparticles (FONPs) as a broadband saturable absorber (SA). FONPs were prepared by a method of thermal decomposition, and then were mixed with sodium carboxymethylcelluose (NaCMC) to form a FONPs film. The FONPs film was sandwiched between two fiber ferrules to fabricate the FONPs SA, which had a broadband absorption from 800 to 2000 nm and nonlinear saturable absorption at 1-, 1.5-, and 2-μm. By inserting the same FONPs SA into the ytterbium, erbium and thulium doped fiber laser cavities, the stable passively Q-switching operation at 1039, 1560 and 1982 nm was realized for a threshold pump power of ∼82 mW, ∼62 mW and ∼830 mW, respectively. To the best of our knowledge, it is the first demonstration of the use of a single SA based on FONPs for wide-band Q-switching operation of fiber lasers from 1 to 2 μm.

Stable Multi-Wavelength Thulium-Doped Fiber Laser With Two Cascaded Single-Mode-Four-Mode-Single-Mode Fiber Interferometers

We propose and experimentally demonstrate a multi-wavelength thulium-doped fiber laser using two cascaded single-mode-four-mode-single-mode (SFS) fiber interferometers and a 150-m-long highly nonlinear fiber. The transmission properties of SFS fiber interferometers with two different four-mode fiber (FMF) lengths are analyzed theoretically. The interferometer with a longer FMF is used to select specific wavelengths, and the one with a shorter FMF is used to stimulate more laser lines. By adjusting the polarization controller and increasing the pump power, the number of output laser channels and the wavelength spacings can be changed and switched. By selecting the proper length of the FMFs, 31 lasing lines are achieved with covering a wavelength range of $\sim 22$ nm. The power fluctuation and the wavelength drift of the 31-wavelength operation for the proposed fiber laser are within 0.706 dB and 0.02 nm, respectively.

Six-wavelength-switchable narrow-linewidth thulium-doped fiber laser with polarization-maintaining sampled fiber Bragg grating

A compound-cavity-based six-wavelength-switchable single-longitudinal-mode (SLM) thulium-doped fiber laser (TDFL) with a homemade polarization-maintaining sampled fiber Bragg grating (PM-SFBG) is proposed and demonstrated. The PM-SFBG in the 2 μm band is studied theoretically and experimentally, and is utilized as a polarization-dependent multi-channel reflecting filter in a multi-wavelength-switchable fiber laser, both for the first time. The SLM lasing in each channel is guaranteed by using a tri-ring sub-cavity. 6 single-wavelength operations are easily obtained and switched each other, and the maximum power and wavelength fluctuations are as low as 0.71 dB and 0.02 nm, respectively. The frequency noise of each lasing wavelength is measured through an unbalanced Michelson interferometry system, and the linewidths for all six lasing wavelengths are among 0.60–1.08 kHz, calculated by the β-separation line method on the basis of the measured frequency noise spectra. Benefiting from the enhanced polarization hole burning effect formed in the gain fiber, 9 switchable dual-wavelength operations with different wavelength intervals and orthogonal polarizations at two lasing wavelengths are obtained with the maximum power and wavelength fluctuations of only 0.95 dB and 0.03 nm, respectively. We believe the proposed TDFL will find great applications as an ideal light source in free space optical communication and optical sensing.

Wavelength-Flexible Thulium-Doped Fiber Laser Based on Digital Micromirror Array

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.

Mode-locked thulium doped fiber laser utilizing tungsten trioxide saturable absorber

Stable mode-locked thulium-doped fiber laser (TDFL) is demonstrated using tungsten trioxide (WO3) deposited on a microfiber as a passive saturable absorber. The WO3 composite was prepared and deposited onto the microfiber before being integrated into the laser cavity. Owing to the interaction of WO3 nanoparticles with the evanescent field of the propagating light, a stable soliton mode-locked TDFL at 1955.3 nm with 3 dB bandwidth of 3.22 nm, repetition rate of 10.98 MHz, and pulse width of 1.26 ps was obtained. The pulse energy and peak power were then calculated to be 0.59 nJ and 419 W respectively, with a signal-to-noise ratio of 54.8 dB. The microfiber WO3 saturable absorber showed no sign of deterioration even though the laser cavity was pumped at 1.15 W power. The findings indicate that WO3 could be an excellent candidate as saturable absorber for mode-locking generation at mid-infrared fiber lasers.