Thulium-doped Fiber Laser Research Articles

Monolithic ultrashort-cavity DBR gain-switched thulium doped fiber laser made by high-precision femtosecond laser direct-writing

We demonstrate a novel monolithic ultrashort-cavity distributed Bragg reflector (DBR) gain-switched thulium doped silica fiber laser. Commercial heavily thulium doped non-polarization-maintaining silica fiber was selected as the gain medium. Monolithic linear laser resonator, which includes a pair of uniform fiber Bragg gratings (FBGs) with a space of 1.0-mm inbetween, was inscribed in the thulium fiber by femtosecond-laser point-by-point (PbP) writing method. The reflectivity of either FBG is close to 100 % and the effective cavity length is calculated to be 3.5 mm. Such an ultrashort-DBR-cavity fiber laser exhibited high Q factor and low cavity loss, allowing the efficient utilization of pump power within the millimeter-long cavity. Single-longitudinal, linearly polarized, gain-switched TDFL at 2003 nm, with a recorded shortest pulse duration of 4.3 ns, a repetition rate of 50 kHz, a maximum peak power of 500 W, and single pulse energy of 2.14 μJ, has been realized, benefitted from the ultrashort cavity length.

Ultra-short wavelength of 1.7 μ m ultrafast Tm-doped fiber laser

Thulium-doped fiber lasers (TDFLs) operating at 1.7 μm have immense potential for multiphoton microscopy and imaging applications. However, further research and development are needed, particularly in the ultra-short wavelength range below 1720 nm. Herein, we demonstrate the mode-locked TDFL at 1.7 μm, utilizing a microfiber InSb saturable absorber. By employing intracavity filters, optimizing the gain fiber length, and incorporating a broadband evanescent field absorber, we achieve high-performance ultra-short wavelength solitons in the TDFL. The solitons exhibit a central wavelength of 1707 nm, a pulse width of 895 fs, a repetition rate of 23.36 MHz, and a single pulse energy of 1.7 nJ. Moreover, our experiments demonstrate the generation of diverse soliton states, including high-order harmonic and bound solitons. We also explore the dynamics of mode-locking through experimental investigations. Our findings establish a solid foundation for the research and control of diverse 1.7 μm mode-locked operation state, advancing the field of ultrafast fiber lasers in this wavelength band.

Broadly tunable dual-wavelength thulium-doped fluoride fiber laser covering S-band region from 1472 to 1506 nm

Dual-wavelength fiber lasers have gained the interest of researchers in practical applications such as fiber-optic sensors and optical telecommunication. This work demonstrated a broadly tunable dual-wavelength thulium-doped fluoride fiber laser (TDFFL) at the S-band region. Two tunable-bandpass filters (TBPFs) were incorporated in the TDFFL cavity to achieve dual-wavelength fiber laser (DWFL) operation. Two identical peaks with a balanced signal-to-noise ratio (SNR) were acquired by tuning TBPFs and an attenuator within the cavity. The DWFL covers a significant portion of S-band TDFFL gain from 1472.9 to 1506.5 nm with a wide tunability in wavelength spacing from 0.95 to 33.6 nm. The narrowest possible DWFL was achieved with the spacing of 0.95 nm at the operating wavelengths of 1489.2 and 1490.15 nm, with a frequency bandwidth of 128 GHz. The broadest spacing of 33.6 nm was achieved at operating wavelengths of 1472.9 and 1506.5 nm, with a frequency bandwidth of 4.79 THz.

Switchable noise-like pulse generation in an all-polarization-maintaining thulium-doped fiber laser

In this paper, a tuning method based on temperature control of a piece of polarization-maintaining dispersion compensation fiber (PMDCF) is proposed in an all-polarization-maintaining (all-PM) thulium-doped fiber laser. The proposed tuning method simplifies the tuning parameter of the all-PM fiber laser, and various patterns of noise-like pulse (NLP) output can be realized only by adjusting the temperature of the PMDCF. The rectangular-shaped NLP, NLP bunches, the coexistence of rectangular-shaped NLP and NLP bunches, double rectangular-shaped NLP, and the switching between them are observed only through changing the temperature of the PMDCF, which helps to improve the research on the underlying physical mechanism of NLP. To the best of our knowledge, this is the first report of various patterns of NLP and their switching phenomena in an all-PM thulium-doped fiber laser.

Soliton ultrafast fiber laser with V4AlC3 MAX phase in 2 µm region

We demonstrate a mode-locked thulium-doped fiber laser (TDFL) using a new vanadium aluminum carbide (V4AlC3) as a saturable absorber (SA). Using the embedding method, we prepared a thin film containing V4AlC3 powders into polyvinyl alcohol (PVA). SA film was placed in a TDF laser cavity to produce a mode-locked laser. The mode-locked TDFL was operating at 1976.2 nm with a 3 dB bandwidth of 3.44 nm, respectively. At the input power of 850 mW, the laser generated the maximum output power of 12.2 mW, a pulse duration of 1.65 ps, a repetition rate of 34.65 MHz, a signal-to-noise ratio of 57 dB, and a pulse energy of 0.35 nJ. To our knowledge, this is the first time utilizing V4AlC3 PVA as SA to produce pulses in the 2-μm region.

Ultrafast dissipative soliton generation in anomalous dispersion achieving high peak power beyond the limitation of cubic nonlinearity

The maximum peak power of ultrafast mode-locked lasers has been limited by cubic nonlinearity, which collapses the mode-locked pulses and consequently leads to noisy operation or satellite pulses. In this paper, we propose a concept to achieve mode-locked pulses with high peak power beyond the limitation of cubic nonlinearity with the help of dissipative resonance between quintic nonlinear phase shifts and anomalous group velocity dispersion. We first conducted a numerical study to investigate the existence of high peak power ultrafast dissipative solitons in a fiber cavity with anomalous group velocity dispersion (U-DSAD) and found four unique characteristics. We then built long cavity ultrafast thulium-doped fiber lasers and verified that the properties of the generated mode-locked pulses match well with the U-DSAD characteristics found in the numerical study. The best-performing laser generated a peak power of 330 kW and a maximum pulse energy of 80 nJ with a pulse duration of 249 fs at a repetition rate of 428 kHz. Such a high peak power exceeds that of any previous mode-locked pulses generated from a single-mode fiber laser without post-treatment. We anticipate that the means to overcome cubic nonlinearity presented in this paper can give insight in various optical fields dealing with nonlinearity to find solutions beyond the inherent limitations.

Acousto-Optic Q-Switched Ho:YLF Ring Laser Based on Anti-Misalignment Resonant Cavity

An acousto-optic Q-switching Ho:YLF ring oscillator at 2066.33 nm with two anti-misalignment corner cube reflectors (CCRs) pumped by a 1940 nm thulium-doped fiber laser is demonstrated. The depolarization effect of the CCR is expressed in the form of equivalent transmission, and the transmission from two output directions of the oscillator is changing synchronously and periodically as the waveplate angle changes. In the experiment, under the pump power of 21.76 W, the optimum bidirectional energy of 3.13 mJ for a pulse duration of 122 ns at a repetition rate of 50 Hz is realized. The pulse energy reduction percentage at 50 Hz is 8% by changing the horizontal drift angle of one of the CCRs to 4.5°. The beam quality factor M2 is calculated to be about 1.10, revealing that the Ho laser is working in a fundamental transverse mode.

Wavelength tunable actively mode-locked Tm3+ doped fiber laser with GHz repetition rate

Using a phase modulator to synchronize the longitudinal modes in an all-fiber cavity, we demonstrate a wavelength tunable (1955–2045 nm) diode pumped actively mode-locked Thulium doped fiber laser with tunable repetition rate up to 10 GHz with the shortest measured pulse width of 42 ps and average output power of 5 mW. We have performed a detailed analysis of the stable mode-locking regimes, including the self mode-locking condition that challenges the harmonic mode-locked operation. We demonstrate a supermode suppression ratio of > 50 dB across the entire wavelength band of operation while maintaining a pulse width and timing jitter of < 50 ps and < 1 ps, respectively.

Modeling and numerical simulation optimization of output spectrum of thulium-doped broadband fiber optic light source

In this research, the performance of thulium-doped fiber lasers is analyzed and a mathematical model is established. Thulium-doped fiber amplifiers are the focus of this article. A large number of simulations have been carried out in the MATLAB simulation environment, and the main work and innovation points are as follows: firstly, the energy level structure characteristics of thulium were studied, and its spectral characteristics were analyzed. After consulting some information, 3H4 to 3H6 energy level has been selected in modeling. Secondly, use the rate equations and the power propagation equations to provide a theoretical analysis of the pumping mode of thulium-doped fiber lasers. And a mathematical model of a thulium-doped fiber laser was established. The parameters such as fiber length and doping concentration in the model are discussed. Finally, to find the appropriate parameters, the genetic optimization algorithm is used to optimize the fiber length and doping concentration, and then we can get the parameters corresponding to the maximum output power of the thulium-doped fiber amplifier.

Temporal soliton dynamics of synchronised ultrafast fibre lasers.

Synchronised ultrafast soliton lasers have attracted great research interest in recent decades. However, there is a lack of comprehensive understanding regarding the buildup mechanism of synchronised pulses. Here, we report a dynamic analysis of independent and synchronised solitons buildup mechanisms in synchronised ultrafast soliton lasers. The laser comprises an erbium-doped fibre cavity and a thulium-doped fibre cavity bridged with a common arm. Pulses operating at two different wavelengths formed in the cavities are synchronised by cross-phase modulation-induced soliton correlation in the common fibre arm. We find that the whole buildup process of the thulium-doped fibre laser successively undergoes five different stages: continuous wave, relaxation oscillation, quasi-mode-locking, continuous wave mode-locking and synchronised mode-locking. It is found that the starting time of the synchronised solitons is mainly determined by the meeting time of dual-color solitons. Our results will further deepen the understanding of dual-color synchronised lasers and enrich the study of complex nonlinear system dynamics.

Thulium-doped fiber laser with bidirectional single-longitudinal-mode output using a cascaded triple-ring cavity filter

Single-longitudinal-mode (SLM) fiber lasers play important roles in optical fiber communication. However, there has been little reported research on bidirectional SLM output, especially in the 2-μm band. In the work reported here, a bidirectional SLM output thulium-doped fiber laser (TDFL) using a cascaded triple-ring cavity (CTRC) filter was proposed and investigated. To realize bidirectional output, the proposed TDFL had a simple structure, using only two 2 × 2 optical couplers. To realize SLM output, the transmission spectrum, as well as the reversibility of the CTRC filter were discussed and investigated in detail. The direction-switchable SLM output was realized by polarization-dependent loss. By tuning the polarization controller carefully, each direction could generate SLM output with an optical signal-to-noise ratio (OSNR) > 72 dB. The maximum wavelength and peak power fluctuation over 60 min were, respectively, 0.01 nm and 0.48 dB. The variation of output power with pump power, linewidth, relaxation oscillation, and relative intensity noise were also investigated. To the best of our knowledge, this is the first time that a sub-ring cavity filter has been used to realize bidirectional SLM output.

Generation of bright-dark pulses in a Q-switched thulium-doped fiber laser by using 8-HQCdCl2H2O

Generation of bright-dark pulses in a Q-switched thulium-doped fiber laser by using 8-HQCdCl2H2O

Raman amplification at 2.2 μm in silicon core fibers with prospects for extended mid-infrared source generation

Raman scattering provides a convenient mechanism to generate or amplify light at wavelengths where gain is not otherwise available. When combined with recent advancements in high-power fiber lasers that operate at wavelengths ~2 μm, great opportunities exist for Raman systems that extend operation further into the mid-infrared regime for applications such as gas sensing, spectroscopy, and biomedical analyses. Here, a thulium-doped fiber laser is used to demonstrate Raman emission and amplification from a highly nonlinear silicon core fiber (SCF) platform at wavelengths beyond 2 μm. The SCF has been tapered to obtain a micrometer-sized core diameter (~1.6 μm) over a length of 6 cm, with losses as low as 0.2 dB cm−1. A maximum on-off peak gain of 30.4 dB was obtained using 10 W of peak pump power at 1.99 μm, with simulations indicating that the gain could be increased to up to ~50 dB by extending the SCF length. Simulations also show that by exploiting the large Raman gain and extended mid-infrared transparency of the SCF, cascaded Raman processes could yield tunable systems with practical output powers across the 2–5 μm range.

Thulium-doped multi-wavelength and mode-locked fiber laser based on multimode interference

We demonstrate a thulium-doped multi-wavelength mode-locked fiber laser with a single-mode-gradient refractive index multimode-single-mode fiber (SMF-GIMF-SMF) structure which acts as both a filter and a saturable absorber. Based on the multimode interference effect (MMI) filtering, wavelength-tunable operation with a tunable range of up to 15.69 nm can be obtained in the fiber laser. Moreover, tunable multi-wavelength continuous wave (CW) laser output of up to four wavelengths can be obtained by properly adjusting the pump power and polarization controller. Owing to mode interference and phase modulation, the SMS structure also plays a role as a saturable absorber (SA), which leads to the multi-wavelength output of the fiber laser accompanied by mode-locking. The state of dual-wavelength mode locking and the state of coexistence of continuous wave and mode-locking pulses at different wavelengths were observed in the laser. These results suggest that the all-fiber SMF-GIMF-SMF structure is a key device for fiber lasers to achieve multi-wavelength and mode-locked pulse output, which may find potential applications in nonlinear microscopy, biodegradable material processing, and terahertz spectroscopy.

Noise-like pulse generation in 1.95 µm region using bulk α-alumina saturable absorber

This work presents a tapered fiber decorated with bulk α-alumina with 4.08% modulation depth and 21.67 MW/cm2 saturation intensity which was responsible to induce noise-like pulse (NLP) in an “eye-safe” wavelength region. The light-matter interaction within evanescent field of ultrathin tapered fiber established NLP in a ring configuration of thulium-doped fiber laser with a broad spectral bandwidth of 45 nm centered at 1948 nm wavelength. The NLP was emitted at 11.36 MHz repetition rate in a net anomalous laser cavity. The generated pulse had a maximum pulse energy of 2.46 nJ at 1587 mW pumping power. The robustness of the NLP performance was validated with 3 h stability test, which opens new possibilities for future research of this material in the wavelength of exceeding 1.9 μm.

1.7 µm sub-200 fs vortex beams generation from a thulium-doped all-fiber laser.

The pulsed 1.7 µm vortex beams (VBs) has significant research prospects in the fields of imaging and material processing. We experimentally demonstrate the generation of sub-200 fs pulsed VBs at 1.7 µm based on a home-made mode-selective coupler (MSC). Through dispersion management technology in a thulium-doped fiber laser, the stable linearly polarized VBs pulse directly emitting from the cavity is measured to be 186 fs with central wavelength of 1721.2 nm. By controlling the linear superposition of LP11 modes, cylindrical vector beams (CVBs) can also be obtained. In addition, a variety of bound states pulsed VBs at 1.7 µm can also be observed. Our finding provides an effective way to generate ultrashort pulsed VBs and CVBs at 1.7 µm waveband.

Thulium-Doped Fiber Laser and Its Application in Urinary Lithotripsy

Thulium-Doped Fiber Laser and Its Application in Urinary Lithotripsy

Generation of bright‐dark Q‐switched pulse pair in thulium‐doped fiber laser cavity with titanium aluminum carbide absorber

AbstractThe proposed titanium aluminum carbide (Ti3AlC2) film‐based saturable absorber (SA) for Q‐switching in thulium‐doped fiber laser (TDFL) cavity offers a cost‐effective and practical alternative to conventional SA materials such as graphene or semiconductor. The Ti3AlC2 film was produced using a simple and low‐cost casting approach with polyvinyl alcohol as a binder. The SA was devised from the film using a sandwich‐structured fiber‐ferrule platform and integrated into a TDFL ring cavity. The generated Q‐switched pulses were stable and had a repetition rate of up to 20.82 kHz with a minimum pulse width of 3.167 µs and a maximum pulse energy of 58.12 nJ. The Q‐switched laser produced the bright‐dark pulse pair. These results demonstrate the potential of Ti3AlC2 as a promising SA material for practical applications in the field of fiber lasers.

MAX phase V4AlC3 for generating Q-switched pulses in 2 µm region

A stable Q-switched Thulium-doped fibre laser (TDFL) operating at 1978.14 nm is demonstrated using a MAX phase thin film as a saturable absorber (SA). The MAX phase film is fabricated by embedding the Vanadium Aluminium Carbide (V4AlC3) compound into polyvinyl alcohol (PVA) via a drop-casting technique. The MAX Phase V4AlC3 thin film is characterized to has a saturable absorption, non-saturable loss, and saturation intensity of about 30 %, 45 %, and 0.07 MW/cm2, respectively. It is sandwiched between two fibre ferrules and integrated into TDFL cavity to induce Q-switching. The pulse train generated records the highest pulse energy of 161.33 nJ, narrowest pulse duration of 2.14 µs, and a maximum repetition rate of 58.45 kHz at the maximum input power of 750 mW. The corresponding signal-to-noise ratio (SNR) of the fundamental frequency is obtained at 55 dB, which indicates a stability of the pulse. The results indicate the MAX phase material has a great potential to serve as SA in future photonics systems.

Widely-tunable all-fiber Tm doped MOPA with > 1 kW of output power.

In this paper, we report on a high-power and widely tunable thulium-doped fiber laser (TDFL) based on a monolithic master oscillator power amplifier (MOPA) system. The master oscillator is a Tm fiber ring laser incorporating a tunable bandpass filter to realize narrow linewidth and wavelength tunable operation. The MOPA generated 1010 W ∼1039 W of output power over a tuning range of 107 nm from 1943 to 2050nm with slope efficiencies of more than 51% and spectra linewidth of ∼0.5 nm. Power stability (RMS) in ∼10 min scale is measured to be ∼0.52%. A diffraction-limited beam quality factor M2 of ∼1.18 is measured at 920 W of laser output. Output power is pump-limited without the onset of parasitic oscillation or amplified spontaneous emission (ASE) even at the maximum power level. This is the first demonstration, to the best of our knowledge, on an all-fiber integrated wavelength-tunable TDFL at 2 µm with output power exceeding 1 kW.