Duanduan Wu

Topological-Insulator Passively Q-Switched Double-Clad Fiber Laser at 2

In this paper, Topological insulator (TI) Bi2Se3 as a saturable absorber (SA) is exploited to Q-switch fiber lasers at 2 μm wavelength for the first time. Few-layer TI:Bi 2Se 3 nanosheets in CS-HAc solution are prepared by the liquid-phase exfoliation method, and the thin 2-D structure with the thickness of 3-5 layers is well characterized. The open-aperture Z-scan experiment shows that the few-layer TI:Bi 2Se 3 has the saturable optical intensity of 41 MW/cm 2 at 800 nm and the modulation depth of 3.7%. The optical deposition technique is used to efficiently assemble the TI:Bi 2Se 3 nanosheets in the solution onto a fiber ferrule, therefore constructing a fiber-compatible TI-based SA (FC-TISA). By further inserting the FC-TISA into a diode-pumped Tm 3+-doped double-clad fiber laser (TM-DCFL), stable Q-switching operation at 1.98 μm is successfully achieved with the shortest pulse width of 4.18 μs and the tunable repetition rate from 8.4 to 26.8 kHz. In particular, the TM-DCFL can deliver large-energy Q-switched pulses with the pulse energy as high as 313 nJ (corresponding to average output power of 8.4 mW). Our results suggest that TI-based SA is suitable for pulsed laser operation in the eye-safe region of 2 μm, and potentially develops as an ultra-broadband photonics device.

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We have demonstrated a high-energy Q-switched double-clad thulium-doped fiber laser (TDFL) using a graphene-oxide-deposited tapered fiber (GODTF) device as a saturable absorber operating at a wavelength of 2 μm for the first time. Because of the side-interaction of the graphene-oxide with the evanescent field on the taper waist, the GODTF devices have potential for offering high laser damage threshold. Using a 788 nm laser diode as the pump source, the TDFL generated stable single transverse mode Q-switched pulses with a single pulse energy of 6.71 μJ (corresponding to an average power of 302 mW) at a wavelength of 2032 nm. This is significantly higher than the highest pulse energy/average power from any rare-earth-doped fiber lasers employing a graphene or graphene-oxide based Q-switch so far. The demonstrated TDFL in this paper represents an encouraging step towards the practical applications of graphene or graphene-oxide based Q-switched 2 μm TDFLs.

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We experimentally confirm that graphene within fiber laser cavities can generate four-wave-mixing (FWM) by observing the laser spectral broadening and the transition from the single-longitudinal-mode oscillation to multiple-longitudinal-mode one. Then, by simultaneously exploiting the graphene-induced nonlinear FWM and its super-broadband saturable absorption, we further achieve for the first time to the best of our knowledge, multiwavelength Q-switched Yb3+- or Er3+-doped fiber lasers at 1 μm and 1.5 μm wavebands, respectively. Simultaneous 23-wavelength Q-switching oscillation with a wavelength spacing of 0.2 nm is stably generated at 1.5 μm waveband. The multiwavelength Q-switched pulses have the minimum pulse duration of 2.5 μs, the maximum pulse energy of 72.5 nJ and a wide range of pulse-repetition-rate (PRR) from 2.8 to 63.0 kHz. At 1 μm waveband, we also obtain five-wavelength simultaneous lasing in Q-switching regime with the pulse duration of ~ 3 μs, pulse energy of 10.3 nJ and PRR between 39.8 and 56.2 kHz.

High-energy passively Q-switched 2 μm Tm 3+ -doped double-clad fiber laser using graphene-oxide-deposited fiber taper

Gold nanoparticle (GNP) possesses saturable absorption bands in the visible region induced by surface plasmon resonance (SPR). We firstly applied the GNP as a visible saturable absorber (SA) for the red Q-switched pulse generation. The GNPs were embedded in polyvinyl alcohol (PVA) for film-forming and inserted into a praseodymium (Pr(3+))-doped fiber laser cavity to achieve 635 nm passive Q-switching. The visible 635 nm Q-switched fiber laser has a wide range of pulse-repetition-rate from 285.7 to 546.4 kHz, and a narrow pulse width of 235 ns as well as the maximum output power of 11.1 mW. The results indicate that the GNPs-based SA is available for pulsed operation in the visible spectral range.

Graphene-Induced Nonlinear Four-Wave-Mixing and Its Application to Multiwavelength Q-Switched Rare-Earth-Doped Fiber Lasers

We experimentally demonstrated compact orange-light passively Q-switched praseodymium (Pr3+)-doped all-fiber lasers utilizing two-dimensional (2D) transition-metal dichalcogenides (TMDs, WS2 and MoS2) as saturable absorbers (SAs). The filmy TMDs SAs are fabricated by evaporating the composite of TMDs nanosheets and polyvinyl alcohol (PVA), and then inserted into an orange-light Pr3+-doped fiber laser cavity, which is designed by coating dielectric mirrors on fiber ends. Stable passively Q-switched orange lasers at 604 nm are successfully achieved. The passive Q-switching generated the short pulse duration of 435 ns and 602 ns, as well as the tunable repetition rate in the range of 67.3 ~132.2 kHz and 50.8 ~118.4 kHz, respectively. This is, to the best of our knowledge, the shortest-wavelength operation of 2D-material-based pulsed fiber lasers.

Gold nanoparticles as a saturable absorber for visible 635 nm Q-switched pulse generation

Passive Q-switching of praseodymium (Pr3+)-doped fiber lasers at 635 nm with topological insulators (TIs) saturable absorbers (SAs) was experimentally demonstrated for the first time. TIs (Bi2Se3, Bi2Te3) nanosheets were embedded in polyvinyl alcohol for film-forming and incorporated into a visible Pr3+-doped fiber laser cavity for Q-switching operation, respectively. The Bi2Se3-based Q-switched fiber laser has a wide range pulse-repetition-rate from 191.6 to 454.5 kHz, and the Bi2Te3 one can be continuously tuned from 164.5 to 403.2 kHz. Both the Q-switching lasers have narrow pulse duration of nanosecond (ns)-level. Our results reveal that the TIs-based SAs are available for pulsed operation in the visible spectral range.

Orange-light passively Q-switched Pr^3+-doped all-fiber lasers with transition-metal dichalcogenide saturable absorbers

We demonstrate the passive synchronization of two large-energy Q-switched all-fiber lasers, operating at 1.06 and 1.53 μm, by sharing a common monolayer graphene Q-switcher. The fiber-compatible Q-switcher is constructed by transferring a monolayer CVD graphene nanosheet onto a fiber ferrule. By exploiting the broadband saturable absorption of graphene and optimizing the cavity designs, both the large-energy Q-switched Yb and Er/Yb double-clad fiber lasers are successfully synchronized. The Q-switching synchronization can be realized in the broad repetition-rate range of 9-20 kHz by adjusting the pump powers of the two lasers. The maximum pulse energies are 5.30 μJ at 1.06 μm and 1.20 μJ at 1.53 μm, respectively, which is, to the best of our knowledge, the largest pulse energy obtained from graphene Q-switched all-fiber laser.

635-nm Visible Pr 3+ -Doped ZBLAN Fiber Lasers Q-Switched by Topological Insulators SAs

In this paper, a compact passively Q-switched praseodymium (Pr3+)-doped fiber laser at the wavelength of 635 nm with black phosphorus (BP) saturable absorber (SA) was first investigated. BP nanoflakes were manufactured by the liquid-phase-exfoliation method and then embedded into polyvinyl-alcohol (PVA) film for the experimental usage and a fiber pigtail mirror (FPM, by coating dielectric film onto the fiber-end face) was applied to realize a compact Pr3+-doped red fiber laser. By transferring a block of the BP-PVA thin film onto the FPM and then incorporating into the compact Pr3+-doped fiber laser, the Q-switched operation at 635 nm was achieved. The pulse-repetition rate of the visible-wavelength Q-switched fiber laser can be widely tuned from 108.8 to 409.8 kHz and the shortest pulse duration of this laser is 383 ns. These results reveal that the BP is an available SA for red-light lasers.

Passive synchronization of 106- and 153-μm fiber lasers Q-switched by a common graphene SA

In this letter, a compact Q-switched red (635.7 nm) praseodymium (Pr3+)-doped fluorozirconate fiber laser using graphene-oxide (GO) as a saturable absorber (SA) is demonstrated experimentally. Furthermore, a silica fiber end coated with a dielectric film was employed to construct the compact resonator. The laser possesses a wide range of pulse repetition rate from 64.1 to 195.3 kHz and the minimum pulse duration of 554 ns. This is the first reported passively Q-switched laser, to the best of our knowledge, at visible region with a GO SA. The experimental results show that the GO can be a promising SA for visible pulsed lasers.

Compact Passive Q-Switching Pr 3+ -Doped ZBLAN Fiber Laser With Black Phosphorus-Based Saturable Absorber

A copper-nanowire (CuNWs)-based saturable absorber (SA) is utilized as a new Q-switcher for pulsed operations in visible regions. The plasmon resonance effect of CuNWs contributes to inducing the saturable absorption property. By incorporating the CuNWs-based SA into a red praseodymium Pr3+-doped ZBLAN fiber laser cavity, the red light shifts from a continuous wave (CW) state to a stable pulsed operation state. When it changes the injected pump power, the pulse repetition rate can be varied from 239.8 to 312.4 kHz. The narrowest pulse duration of this laser is 394 ns. Moreover, the maximum output power under a Q-switching operation is 9.6 mW. The results indicate that a CuNWs-based SA is an available Q-switcher for the red laser, revealing the potential of metal nanomaterials for short-pulse generation in visible regions.