All-fiber short-wavelength tunable mode-locked fiber laser using normal dispersion thulium-doped fiber

Raman dissipative soliton source of ultrashort pulses in NIR-III spectral window

We present a novel fiber source of ultrashort pulses at the wavelength of 1660 nm based on the technique of external cavity Raman dissipative soliton generation. The output energy of the generated 30 ps chirped pulses is in the range of 0.5-3.6 nJ with a slope efficiency of 57%. Numerical simulations are in excellent agreement with the experimental results and the shape of the compressed pulses. The compressed pulses consist of a central part with a duration of 300 fs and a weak pedestal. Our results clearly demonstrate the potential to extend the spectral range of the Raman-assisted technique for generating ultra-short pulses to new frequency regions, including biomedical windows. This paves the way for the development of new dissipative soliton sources in these bands.

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.

1.8-µm laser operation based on femtosecond-laser direct written Tm:YVO4 cladding waveguides

In this work, we have demonstrated tunable 1.8-µm laser operation based on a Tm:YVO₄ cladding waveguide fabricated by means of femtosecond laser direct writing. Benefiting from the good optical confinement of the fabricated waveguide, efficient thulium laser operation, with a maximum slope efficiency of 36%, a minimum lasing threshold of 176.8 mW, and a tunable output wavelength from 1804 to 1830nm, has been achieved in a compact package via adjusting and optimizing the pump and resonant conditions of the waveguide laser design. The lasing performance using output couplers with different reflectivity has been well studied in detail. In particular, due to the good optical confinement and relatively high optical gain of the waveguide design, efficient lasing can be obtained even without using any cavity mirrors, thereby opening up new possibilities for compact and integrated mid-infrared laser sources.

Tunable dissipative soliton Tm-doped fiber laser operating from 1700 nm to 1900 nm

In this Letter, we demonstrate an ultrabroadband (1700-1900 nm) tunable Tm-doped fiber laser (TDFL) generating dissipative solitons in the net-normal dispersion regime. The laser delivers pulses with spectral widths ranging from 10 nm to 23 nm and pulse durations from 8.7 ps to 18.3 ps. Stretched-free pulse amplification at the gain edge (1708 nm) and gain peak (1807 nm) is implemented to demonstrate the range of further power scalability of the laser signal. The maximum achieved power in a one-stage Tm-doped amplifier is 140 mW with a compressed pulse duration of 478 fs. Considering the diverse utility of this wavelength band, this laser is highly desirable for applications such as optical sensing, biological imaging, and industrial machining.

1.7 µm - 1.73 µm tunable ultrafast Raman fiber laser pumped by 1.6 µm dissipative soliton pulses

Here, we report an all-fiber tunable ultrafast Raman laser synchronously pumped by a home-made 1.6 µm dissipative soliton (DS) picosecond (ps) laser, which produces Stokes light beyond 1.7 µm. The Raman gain medium is a segment of highly germanium-doped (Ge-doped) fiber offering a high Raman gain coefficient at the target wavelength. Once the Raman conversion cavity is synchronized with the pump light, a stable 1.7 µm Raman laser (the first Stokes light) can be obtained at a low pump threshold. The maximum output power of the 1.7 µm Raman laser can reach ∼ 22.62 mW. The wavelength tuning operation is independent of tunable pump source and intra-cavity filter. By adjusting the intra-cavity delay line simply, the different spectral component within the broad Raman gain bandwidth can be selectively synchronized with the pump light so that the Raman laser wavelength can be tuned continuously from 1702.6 nm ∼ 1728.84 nm. This tunable 1.7 µm waveband ultrafast laser will have potential applications in multiphoton microscopy for e.g. deep bio-imaging.

1.7 µm figure-9 Tm-doped ultrafast fiber laser

The evolution of multiphoton microscopy is critically dependent on the development of ultrafast laser technologies. The ultrashort pulse laser source at 1.7 µm waveband is attractive for in-depth three-photon imaging owing to the reduced scattering and absorption effects in biological tissues. Herein, we report on a 1.7 µm passively mode-locked figure-9 Tm-doped fiber laser. The nonreciprocal phase shifter that consists of two quarter-wave plates and a Faraday rotator introduces phase bias between the counter-propagating beams in the nonlinear amplifying loop mirror. The cavity dispersion is compensated to be slightly positive, enabling the proposed 1.7 µm ultrafast fiber laser to deliver the dissipative soliton with a 3-dB bandwidth of 20 nm. Moreover, the mode-locked spectral bandwidth could be flexibly tuned with different phase biases by rotating the wave plates. The demonstration of figure-9 Tm-doped ultrafast fiber laser would pave the way to develop the robust 1.7 µm ultrashort pulse laser sources, which could find important application for three-photon deep-tissue imaging.

Wavelength-stabilized tunable mode-locked thulium-doped fiber laser beyond 2 µm

We report the development of a widely tunable mode-locked thulium-doped fiber laser based on a robust chirped fiber Bragg grating (CFBG). By applying mechanical tension and compression to the CFBG, an overall tunability of 20.1 nm, spanning from 2022.1 nm to 2042.2 nm, was achieved. The observed mode-locked pulse train from this fiber laser has a repetition rate of 9.4 MHz with an average power of 12.6 dBm and a pulse duration between 9.0 ps and 12.8 ps, depending on the central wavelength. To the best of our knowledge, this is the first demonstration of a tunable mode-locked thulium-doped fiber laser operating beyond 2 µm using a CFBG as a wavelength-selective element.

1.7 µm Tm-fiber chirped pulse amplification system with dissipative soliton seed laser

We report on a 1.7 µm Tm-fiber chirped pulse amplification (CPA) system by virtue of a broadband dissipative soliton seed laser. The seed oscillator delivers the dissipative soliton with 10 dB spectral bandwidth of 23 nm and an average power of 4 mW. The duration of the seed pulse is directly stretched to ∼60ps by a segment of 50 m normal dispersion fiber. Using a two-stage fiber amplifier, the average power of the pulse is amplified to 1.95 W with a slope efficiency of 40.3%. The amplified pulse is then compressed to 348 fs by a pair of fused silica transmission gratings. The compressed average power of 1.3 W and peak power of 155 kW are achieved. These experimental results would pave the way to achieve a high-power femtosecond laser source at 1.7 µm, which could find important applications in fields such as three-photon deep-tissue imaging and material processing.

W-type normal dispersion thulium-doped fiber-based high-energy all-fiber femtosecond laser at 1.7 µm

We propose a parabolic W-type thulium-doped fiber for the 1.7 µm high-energy femtosecond pulsed laser. Despite its attractive normal dispersion, the fiber offers high gain in 1.7 µm region thanks to its distributed short-pass filtering effect. With a proper dispersion management in an all-fiber chirped pulse amplification (CPA) scheme, we demonstrate so far the highest pulse energy of 128.0 nJ in a stable pulse of 174 fs in the 1.7-1.8 µm region, which marks above an order of magnitude improvement in pulse energy while exhibiting the shortest pulse duration among fiber-based CPA works at 1.7 µm. Hence, we provide a pathway to an energy scalable and efficient femtosecond laser at 1.7 µm via a compact and elegant all-fiber solution.

High-repetition-rate mid-IR femtosecond pulse synthesis from two mid-IR CW QCL-seeded OPAs

Coherent pulse synthesis in the mid-infrared (mid-IR) domain is of great interest to achieve broadband sources from parent pulses, motivated by the advantages of optical frequency properties for molecular spectroscopy and quantum dynamics. We demonstrate a simple mid-IR coherent synthesizer based on two high-repetition-rate optical parametric amplifiers (OPAs) at nJ-level pump energy. The relative carrier envelope phase between the two OPAs was passively stable for a shared continuous wave (CW) quantum cascade laser (QCL) seed. Lastly, we synthesized mid-IR pulses with a duration of 105 fs ranging from 3.4 to 4.0 µm. The scheme demonstrated the potential to obtain broader mid-IR sources by coherent synthesis from multiple CW QCL-seeded OPAs.