2-MW peak-power pulses from a dispersion-managed fluoride fiber amplifier at 2.8 µm

Wavelength-tunable spatiotemporal mode-locking in a large-mode-area Er:ZBLAN fiber laser at 2.8 µm

We report a tunable spatiotemporally mode-locked large-mode-area Er:ZBLAN fiber laser based on the nonlinear polarization rotation technique. A diffraction grating is introduced to select the operating wavelength. Under the spectral and spatial filtering effects provided by the grating and spatial coupling respectively, stable ps-level spatiotemporally mode-locked pulses around 2.8 µm with a repetition rate of 43.4 MHz are generated. Through a careful adjustment of the grating, a broad wavelength tuning range from 2747 to 2797 nm is realized. To the best of our knowledge, this is the first wavelength-tunable spatiotemporally mode-locked fiber laser in the mid-infrared region.

Nearly diffraction-limited picosecond pulse amplification from LMA fluoride fiber at 2.8 µm

We demonstrated the generation of a nearly diffraction-limited picosecond pulse from a large-mode-area (LMA) fluoride fiber amplifier. Seeded with a mode-locked fiber oscillator at 2.8 µm, the LMA Er:ZBLAN fiber amplifier delivered the pulse of 16 µJ with a duration of 70 ps at 5 kHz. The nearly diffraction-limited beam was obtained from the 50 µm LMA fiber using the fundamental mode excitation technique, with a measured M2 value of 1.25 for x axis and 1.27 for y axis, respectively. This high-beam-quality high-energy picosecond fiber-based system of 2.8 µm exhibits a great potential in the high-precision biomaterial processing.

All-fiber 3.4-W 2.8-µm ultra-short pulse MOPA system seeded by the soliton self-frequency shift of 2-µm pulses

We report an all-fiber 2.8-µm ultra-short pulse master oscillator power amplifier (MOPA) system seeded by a soliton self-frequency shift from a mode-locked thulium-doped fiber laser. This all-fiber laser source delivers 2.8-µm pulses with an average power of 3.42 W, a pulse width of 115 fs, and a pulse energy of 45.4 nJ. We demonstrate, to the best of our knowledge, the first femtosecond watt-level all-fiber 2.8-µm laser system. A 2.8-µm pulse seed was obtained via the soliton self-frequency shift of 2-µm ultra-short pulses in a cascaded silica and passive fluoride fiber. A novel, to the best of our knowledge, high-efficiency and compact home-made end-pump silica-fluoride fiber combiner was fabricated and used in this MOPA system. Nonlinear amplification of the 2.8-µm pulse was realized, and soliton self-compression was observed accompanied by spectral broadening.

High-energy femtosecond pulse generation from a hybrid mode-locked large-mode-area Er:ZBLAN fiber laser

We report a hybrid mode-locked fiber laser at 2.8 µm based on a large-mode-area Er:ZBLAN fiber. Reliable self-starting mode-locking is achieved via the combination of nonlinear polarization rotation and a semiconductor saturable absorber. Stable mode-locked pulses with a pulse energy of 9.4 nJ and a pulse duration of 325 fs are generated. To the best of our knowledge, this is the highest pulse energy directly generated from a femtosecond mode-locked fluoride fiber laser (MLFFL) to date. The measured M² factors are below 1.13, indicating a nearly diffraction-limited beam quality. Demonstration of this laser provides a feasible scheme for the pulse energy scaling of mid-infrared MLFFLs. Moreover, a peculiar multi-soliton mode-locking state is also observed, in which the time interval between the solitons varies irregularly from tens of picoseconds to several nanoseconds.

Average-power (4.13 W) 59 fs mid-infrared pulses from a fluoride fiber laser system

We report a high-average-power mid-infrared ultrafast laser system consisting of a fluoride fiber mode-locked oscillator and a nonlinear amplifier. A backward pumping scheme was used in the amplifier to simultaneously realize pulse amplification and self-compression. The input signal polarization was demonstrated to play an important role in the self-compression process. Through the optimization of input polarization, a 4.13 W average-power 59 fs pulse at 2.8 µm was achieved, with an estimated pulse energy of 42.2 nJ and a peak power of 715 kW. To the best of our knowledge, this is the highest average-power pulse with sub-100-fs duration generated from a mid-infrared fiber laser system to date.

Recent developments in lanthanide-doped mid-infrared fluoride fiber lasers [Invited]

Mid-infrared fiber sources, emitting between 2.5 µm and 5.0 µm, are interesting for their great potential in several application fields such as material processing, biomedicine, remote sensing and infrared countermeasures due to their high-power, their diffraction-limited beam quality as well as their robust monolithic architecture. In this review, we will focus on the recent progress in continuous wave and pulsed mid-infrared fiber lasers and the components that bring these laser sources closer to a field deployment as well as in industrial systems. Accordingly, we will briefly illustrate the potential of such mid-infrared fiber lasers through a few selected applications.

Dysprosium-doped silica fiber as saturable absorber for mid-infrared pulsed all-fiber lasers

We report on a mid-infrared Q-switched erbium-doped all-fiber laser using a dysprosium-doped silica fiber as saturable absorber for the first time in this wavelength range. Moreover, we demonstrate the use of a highly reflective chirped fiber Bragg grating written in a silica fiber as the input coupler for such lasers. This Q-switched all-fiber laser generates a stable pulse train centered at 2798 nm with a maximum average power of 670 mW at a repetition rate of 140 kHz with a pulse duration of 240 ns and a pulse energy of 4.9 µJ.

Fiber-based source of 500 kW mid-infrared solitons

Fiber-based sources delivering high-energy few-cycle pulses at high repetition rates are currently being developed in the near-infrared spectral range, thanks to the wide availability of telecommunication-grade optical fibers and components. Similar sources in the middle-wave infrared (mid-IR) spectral domain, however, are scarce, although such sources are of high interest for applications such as high-precision frequency metrology and molecular spectroscopy or as a seed source to reach further into the mid-IR via coherent nonlinear processes. Here we report on the design of a fiber-based source of 50-nJ energy 90 fs duration pulses up to 2950 nm, corresponding to 500 kW peak power. To obtain this level of peak power we exploit multi-solitonic fission and soliton self-frequency shift in large mode area fibers excited by picosecond pulses emitted at 2 µm from a megahertz repetition rate fiber laser. We leverage mature silica-based fiber technology up to 2.4 µm and restrict the use of fluoride fiber to the very last frequency-shifting stage. The level of instantaneous power and ultra-short duration achieved in this Letter pave the way to all-fiber format generation of an ultra-broadband coherent continuum in the mid-IR with profound implications for applications such as high-resolution molecular spectroscopy and imaging.