Ultrafast, stretched-pulse thulium-doped fiber laser with a fiber-based dispersion management

Bound-State Soliton and Noise-Like Pulse Generation in a Thulium-Doped Fiber Laser Based on a Nonlinear Optical Loop Mirror

We demonstrate a thulium-doped, mode-locked, all-fiber laser capable of operating in two generation regimes: dispersion-managed soliton and noise-like pulse (NLP). Employing a nonlinear optical loop mirror as an artificial saturable absorber, the oscillator generated optical pulses with a fundamental pulse repetition frequency of ~15.795 MHz. The total net dispersion of the laser cavity had a slightly anomalous group delay dispersion value of −0.016 ps2. After appropriate adjustment of a polarization controller, bound states of a dispersion-managed soliton composed of three pulses with fixed soliton separations were also observed. NLP generation, tunable over 35 nm from 1943.5 to 1978 nm, was also presented in the same laser setup. To our knowledge, this is the first report of the generation of tunable NLPs in a mode-locked thulium-doped fiber laser based on a nonlinear loop mirror saturable absorber.

Passively mode locked thulium and thulium/holmium doped fiber lasers using MXene Nb2C coated microfiber

As a result of the emergence of two-dimensional (2D) materials for various opto-electronics applications, a new class of materials named MXenes have been attracting interests due to their outstanding nonlinear properties. In this work, an MXene niobium carbide (Nb2C) was proposed and demonstrated as a saturable absorber to induce mode-locking in thulium- and thulium/holmium-doped fiber lasers. The Nb2C solution was first prepared using the liquid exfoliation technique, and then deposited onto a microfiber for integration into the laser cavity. Stable mode-locking operation was observed in both laser cavities, where the center wavelengths of the laser were recorded at 1944 nm for the TDFL and 1950 nm for the THDFL. The generated pulses in the TDFL and THDFL had repetition rates of 9.35 and 11.76 MHz respectively, while their corresponding pulse widths were 1.67 and 1.34 ps. Both of the lasers were highly stable, having SNR values of more than 52 dB and showed no major fluctuations when tested for their long-term stabilities. The results demonstrate an excellent performance of the Nb2C as a saturable absorber, offering opportunities to further explore MXenes for future photonics devices.

Numerical model of hybrid mode-locked Tm-doped all-fibre laser

Ultrafast Tm-doped fibre lasers have been actively studied for the last decade due to their potential applications in precise mid-IR spectroscopy, LIDARs, material processing and more. The majority of research papers is devoted to the comparison between a numerical modelling and experimental results; however, little attention is being paid to the comprehensive description of the mathematical models and parameters of the active and passive components forming cavities of Tm-doped all-fibre lasers. Thus, here we report a numerical model of a stretched-pulsed Tm-doped fibre laser with hybrid mode-locking and compare it with experimental results. The key feature of the developed numerical model is employment of the experimentally measured dispersion coefficients and optimisation of some model parameters, such as the bandwidth of the spectral filter spectral filtering and the saturation power of the active fibre, for a conformity with the experiment. The developed laser emits 331.7 fs pulses with a 23.8 MHz repetition rate, 6 mW of average power, 0.25 nJ of pulse energy, and a 21.66 nm spectral bandwidth at a peak wavelength of 1899.5 nm. The numerical model characteristics coincide with experimentally achieved spectral width, pulse duration, and average power with inaccuracy of 4.7%, 5.4%, and 22.9%, respectively. Moreover, in the discussion of the work the main possible reasons influencing this inaccuracy are highlighted. Elimination of those factors might allow to increase accuracy even more. We show that numerical model has a good agreement with the experiment and can be used for development of ultrafast Tm-doped fibre laser systems.

All-fiber frequency-resolved optical gating pulse characterization from chalcogenide glass

We report, to the best of our knowledge, the first all-fiber frequency-resolved optical gating device from nonlinear processing in chalcogenide glass. The strong four-wave mixing efficiency of an 11 cm long chalcogenide microwire enables a high sensitivity characterization of pulses in the 2 μm wavelength band. The amplitude and phase of chirped and unchirped picosecond pulses are accurately characterized with a high sensitivity of 0.16  mW².

Multistate passively mode-locked thulium-doped fiber laser with nonlinear amplifying loop mirror

In this paper, a multistate passively mode-locked thulium-doped fiber laser with nonlinear amplifying loop mirror is reported. An ultra-high numerical aperture fiber is employed to compensate the cavity abnormal dispersion, and the net cavity dispersion value is fixed at -0.046  ps². By changing the pump power, three different mode-locked regions, namely Q-switched mode-locking operation, mode-locking operation, and dual-wavelength mode-locking operation, are observed sequentially. When the pump power is raised to the threshold of 1.60 W, the transition state of the Q-switched mode locking begins to be observed. When the pump power increases from 2.88 W to 8.75 W, stable single-wavelength mode-locking operation is obtained. And the center wavelength is 1988.73 nm corresponding to the 3 dB spectral bandwidth of 11.21 nm. As the pump power is raised beyond 8.75 W, dual-wavelength mode-locking operation is developed, where the dual wavelengths are 1969.70 nm and 1984.12 nm with the 3 dB spectral bandwidth of ∼4.11  nm and ∼6.14  nm, respectively.

High-order soliton evolution and pulse breaking-recovery in stretched ultrafast fiber lasers

We present a new pulse regime in a stretched ultrafast fiber laser based on numerical simulations. The pulse breaking due to high-order soliton evolution in the passive fiber is recovered to a smooth pulse in the gain fiber with normal dispersion. The new pulse regime formed by the two nonlinear processes makes the ultrafast fiber laser generate ultra-broadband, ultrashort duration, high energy and large breathing ratio pulses. Our work gives insights into the nonlinear dynamics in fiber lasers and has potential for a better design of the stretched fiber lasers.

Mode-locked Ho-doped laser with subsequent diode-pumped amplifier in an all-fiber design operating at 2052 nm

We present a mode-locked holmium-doped all-fiber soliton laser operating in the 2052 nm wavelength range. The ultrashort pulse oscillator is simultaneously self-providing 1950-nm radiation for efficient in-band pumping in a subsequent thulium-/holmium-doped fiber tandem amplifier. More than 76 nJ-pulses for Ho:YLF or Ho:YVO₄ amplifier seeding have been achieved.

Quantized pulse separations of phase-locked soliton molecules in a dispersion-managed mode-locked Tm fiber laser at 2 μm

We report, for the first time to the best of our knowledge, the discovery of quantized pulse separations between phase-locked soliton pairs in a thulium-doped fiber laser at the wavelength range of 2 μm. The soliton pairs are formed by the nonlinear binding interaction between the solitons and dispersive waves, and the two lowest-order Kelly sidebands drive the interaction in these soliton pairs and fix the pulse separations of the soliton pairs to a discrete set of values. Our experimental observations are well confirmed by numerical simulations.

1 μJ, sub-300 fs pulse generation from a compact thulium-doped chirped pulse amplifier seeded by Raman shifted erbium-doped fiber laser

We present a compact thulium-doped chirped pulse amplifier producing 241 fs pulses with 1 μJ energy. The system is seeded with the Raman shifted soliton generated by the combination of an erbium-doped femtosecond laser and a nonlinear fiber. The Tm-doped large mode area fiber yields output power of 71 W, corresponding to pulse energy of 2.04 μJ, with a slope efficiency of 52.2%. The amplified pulses have been compressed to a duration time of 241 fs, using a folded Treacy grating setup. The pulse energy is measured to be 1.02 μJ, corresponding to a peak power of ~3 MW. To the best of our knowledge, this is the highest average power and pulse energy generated from an all-fiber, Raman shifted soliton seeded thulium-doped chirped pulse amplifier system.

Dispersion-compensation-free femtosecond Tm-doped all-fiber laser with a 248 MHz repetition rate

In this Letter, we report a dispersion-compensation-free ultrafast thulium-doped all-fiber laser based on nonlinear polarization evolution (NPE) mode locking, delivering 330 fs soliton pulses at 1950 nm. A multifunctional hybrid fiberized device was applied in the oscillator to minimize the physical cavity length to ∼80  cm with a total dispersion of -0.045  ps², enabling a state-of-the-art fundamental mode-locking repetition rate of 248 MHz in an NPE-based oscillator at ∼2  μm.

152 fs nanotube-mode-locked thulium-doped all-fiber laser

Ultrafast fiber lasers with broad bandwidth and short pulse duration have a variety of applications, such as ultrafast time-resolved spectroscopy and supercontinuum generation. We report a simple and compact all-fiber thulium-doped femtosecond laser mode-locked by carbon nanotubes. The oscillator operates in slightly normal cavity dispersion at 0.055 ps², and delivers 152 fs pulses with 52.8 nm bandwidth and 0.19 nJ pulse energy. This is the shortest pulse duration and the widest spectral width demonstrated from Tm-doped all-fiber lasers based on 1 or 2 dimensional nanomaterials, underscoring their growing potential as versatile saturable absorber materials.

Comparison between Tm:YAP and Ho:YAG ultrashort pulse regenerative amplification

We compare the performance characteristics of Tm:YAP and Ho:YAG in ultrashort pulse regenerative amplification. Both systems follow the same amplification concept and use nearly the same experimental setup reaching similar output energies of >700 µJ.

Ultra-broadband dissipative soliton and noise-like pulse generation from a normal dispersion mode-locked Tm-doped all-fiber laser

We report generation of ultra-broadband dissipative solitons and noise-like pulses from a simple, fully fiberized mode-locked Tm-doped fiber laser. The oscillator operates in the normal net dispersion regime and is mode-locked via nonlinear polarization evolution. Depending on the cavity dispersion, the laser was capable of generating 60 nm or 100 nm broad dissipative solitons. These are the broadest spectra generated from a normal dispersion mode-locked Tm-doped fiber laser so far. The same oscillator might also operate in the noise-like pulse regime with extremely broad emission spectra (over 300 nm), which also significantly outperforms the previous reports.

260 fs and 1 nJ pulse generation from a compact, mode-locked Tm-doped fiber laser

We report on generation of 260 fs-short pulses with energy of 1.1 nJ from a fully fiberized, monolithic Tm-doped fiber laser system. The design comprises a simple, graphene-based ultrafast oscillator and an integrated all-fiber chirped pulse amplifier (CPA). The system generates 110 mW of average power at 100.25 MHz repetition rate and central wavelength of 1968 nm. This is, to our knowledge, the highest pulse energy generated from a fully fiberized sub-300 fs Tm-doped laser, without the necessity of using grating-based dispersion compensation. Such compact, robust and cost-effective system might serve as a seed source for nonlinear frequency conversion or mid-infrared supercontinuum generation.

Compact polarization-maintaining 2.05-μm fiber laser at 1-MHz and 1-MW peak power

We report on a compact all-polarization-maintaining 2.05-μm chirped pulse fiber amplifier system emitting pulses at up to 1-MW peak power level at 371-fs pulse duration. The seed pulse repetition rate provided by an inhouse-built oscillator is reduced to around 1 MHz using a pulse picker. In combination with a two stage fiber amplifier, output pulse energies up to 570 nJ are obtained without the need of a high-power large-mode area amplifier. Both temporal stretching and compression of the chirped pulse amplifier design are achieved using a single chirped volume Bragg grating.

Mode-locked, 1.94-μm, all-fiberized laser using WS₂ based evanescent field interaction

We demonstrate the use of an all-fiberized, mode-locked 1.94 μm laser with a saturable absorption device based on a tungsten disulfide (WS2)-deposited side-polished fiber. The WS2 particles were prepared via liquid phase exfoliation (LPE) without centrifugation. A series of measurements including Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) revealed that the prepared particles had thick nanostructures of more than 5 layers. The prepared saturable absorption device used the evanescent field interaction mechanism between the oscillating beam and WS2 particles and its modulation depth was measured to be ~10.9% at a wavelength of 1925 nm. Incorporating the WS2-based saturable absorption device into a thulium-holmium co-doped fiber ring cavity, stable mode-locked pulses with a temporal width of ~1.3 ps at a repetition rate of 34.8 MHz were readily obtained at a wavelength of 1941 nm. The results of this experiment confirm that WS2 can be used as an effective broadband saturable absorption material that is suitable to passively generate pulses at 2 μm wavelengths.

700 MW peak power of a 380 fs regenerative amplifier with Tm:YAP

We report on a high power ultrashort pulse regenerative amplifier system, entirely based on thulium-doped laser materials operating around 1.94 μm. At a repetition rate of 1 kHz the Tm:YAP regenerative amplifier emits pulse energies > 700 μJ, only limited by the damage threshold of the Tm:YAP crystal. The pulses can be compressed to 380 fs at an efficiency of 50 %. Purging of the regenerative amplifier cavity with nitrogen is necessary due to atmospheric absorptions causing long ps pedestals in the autocorrelation.

Stretched-pulse and solitonic operation of an all-fiber thulium/holmium-doped fiber laser

Stretched-pulse operation of a mode-locked thulium/holmium-doped fiber laser has been demonstrated using a high numerical aperture (NA) fiber inside the laser cavity for intracavity dispersion compensation. The high NA fiber exhibits normal group-velocity dispersion allowing for the net-cavity dispersion to be positive. We experimentally investigate the laser dynamics as a function of the net-cavity dispersion, observing the transition from stretched-pulse to solitonic operation as the length of high NA fiber was reduced. In the stretched-pulse regime the laser produced pulses with a bandwidth of 30 nm and duration of 450 fs. Methods for compensating the third-order dispersion using high NA fibers are proposed.

Sub-100 fs passively mode-locked holmium-doped fiber oscillator operating at 2.06 μm

We demonstrate a simple and compact Holmium-doped fiber femtosecond oscillator, in-band pumped by a commercial Tm-doped fiber laser. The oscillator operates in the dispersion managed soliton regime at net zero intracavity dispersion and delivers >1  nJ pulse energy at 35 MHz repetition rate. The pulse duration directly at the oscillator output is 160 fs FWHM, close to the Fourier-limit of 145 fs FWHM. Using an additional nonlinear compressor stage, sub-100 fs FWHM pulse durations could be achieved. The nonlinear fiber compressor is implemented by a solid core highly nonlinear fiber for spectral broadening and a single mode fiber for pulse compression.

Fiber chirped pulse amplifier at 2.08 μm emitting 383-fs pulses at 10 nJ and 7 MHz

An all-polarization maintaining (PM) fiber chirped pulse amplifier system at 2.08 μm based on thulium:holmium codoped gain fibers is reported. An inhouse built oscillator emits pulses at a repetition rate of 7 MHz with a spectral full width at half-maximum (FWHM) bandwidth of 23.5 nm at 2.8 mW average output power. The pulses are temporally stretched and subsequently amplified in a double-stage amplifier setup. The stretched pulses are compressed to 383 fs by use of a Martinez-style setup at an output pulse energy of 10.2 nJ. By neglecting temporal stretching, high peak powers in a single amplifier stage led to Raman soliton formation at 2.3 μm.

152 W average power Tm-doped fiber CPA system

A high-power thulium (Tm)-doped fiber chirped-pulse amplification system emitting a record compressed average output power of 152 W and 4 MW peak power is demonstrated. This result is enabled by utilizing Tm-doped photonic crystal fibers with mode-field diameters of 35 μm, which mitigate detrimental nonlinearities, exhibit slope efficiencies of more than 50%, and allow for reaching a pump-power-limited average output power of 241 W. The high-compression efficiency has been achieved by using multilayer dielectric gratings with diffraction efficiencies higher than 98%.

Sub-50-fs pulse generation from thulium-doped ZBLAN fiber laser oscillator

An ultrafast, passively mode-locked fiber laser oscillator has been realized using thulium-doped ZBLAN fibers. Very low dispersion of ZBLAN glass fibers enabled generation of pulses with broad spectra extending from 1730 nm to 2050 nm. Pulses are obtained with the average power of 13 mW at the repetition rate of 67.5 MHz when the pump power is 140 mW. The output pulses are compressed with a pair of SF10 prisms and their durations are measured with SHG FROG, from which we obtained the pulse duration as short as 45 fs.

Mode-locked pulse generation from an all-fiberized, Tm-Ho-codoped fiber laser incorporating a graphene oxide-deposited side-polished fiber

An in-depth experimental investigation was conducted into the use of a graphene oxide-based saturable absorber implemented on a side-polished fiber platform for femtosecond pulse generation in the 2 μm region. First, it was experimentally shown that an all-fiberized thulium-holmium (Tm-Ho)-codoped fiber ring laser with reduced cavity length can produce stable femtosecond pulses by incorporating a graphene oxide-deposited side-polished fiber. Second, the measurement accuracy issue in obtaining a precise pulse-width value by use of an autocorrelator together with a silica fiber-based 2 μm-band amplifier was investigated. It showed that the higher-order soliton compression effect caused by the combination of anomalous dispersion and Kerr nonlinearity can provide incorrect pulse-width information. Third, an experimental investigation into the precise role of the graphene oxide-deposited side-polished fiber was carried out to determine whether its polarization-dependent loss (PDL) can be a substantial contributor to mode-locking through nonlinear polarization rotation. By comparing its performance with that of a gold-deposited side-polished fiber, the PDL contribution to mode-locking was found to be insignificant, and the dominant mode-locking mechanism was shown to be saturable absorption due to mutual interaction between the evanescent field of the oscillated beam and the deposited graphene oxide particles.

A stable polarization switching laser from a bidirectional passively mode-locked thulium-doped fiber oscillator

We report on a novel polarization switching laser from a bidirectional passively mode-locked thulium(Tm)-doped fiber oscillator, which was characterized by the periodical change of polarization state of every pulse. The switching laser was created by combing two orthogonally stable vector solitons, which were found to be wave-breaking-free pulses in the all-anomalous-dispersion regime. The measured repetition rates of switching laser and the corresponding vector solitons were 49.596 MHz, 24.798 MHz, and 24.798MHz. By controlling wave plates, either of the polarized pulse trains can be switched on or off. To our knowledge, this is the first report of polarization switching laser with vector solitons in Tm fiber oscillators.