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Recently, plasmonic nanocrystals (NCs) have attracted much attention due to their wide applications in bioimaging, photothermal therapy and photonics devices. Compared to other metal NCs, copper NCs show a weak photo-thermal effect, which shows that the copper NCs are a good candidate for nonlinear optical materials. In this paper, we demonstrated a Q-switched fiber laser at 1 μm wavelength by using Cu1.8S NCs as a saturable absorber (SA). By incorporating the Cu1.8S SA into an ytterbium doped fiber laser cavity pumped by a 980 nm laser diode, stable passive Q-switching at 1038 nm was obtained for a threshold pump power of 63 mW. On gradually increasing the pump power from 64 mW to 160 mW, the repetition rate of a Q-switched laser increases from 25.7 kHz to 54.5 kHz and the pulse duration decreases from 6.7 μs to 2.33 μs. Our results showed that Cu1.8S NCs is an effective SA for constructing pulsed lasers with a broadband operating wavelength.

The S-band polymer-based waveguide amplifier has been fabricated, but how to improve the gain performance remains a big challenge. Here, using the technique of establishing the energy transfer between different ions, we successfully improved the efficiency of Tm3+:3F3→3H4 and 3H5→3F4 transitions, resulting in the emission enhancement at 1480 nm and gain improvement in S-band. By doping the NaYF4:Tm,Yb,Ce@NaYF4 nanoparticles into the core layer, the polymer-based waveguide amplifier provided a maximum gain of 12.7 dB at 1480 nm, which was 6 dB higher than previous work. Our results indicated that the gain enhancement technique significantly improved the S-band gain performance and provided guidance for even other communication bands.

Tm3+ doped fluoroaluminate glass fibers are fabricated by using a rod-in-tube method based on AlF3-BaF2-YF3-MgF2-PbF2 glasses. By using a 1400/1570 nm dual-wavelength upconversion pump technique, lasing at ∼2.3 µm is obtained from a 2.3 m long Tm3+ doped fluoroaluminate glass fiber. The measured maximum unsaturated output power is ∼111 mW for a pump power of 1.5/0.14 W at 1400/1570 nm, and the corresponding slope efficiency is ∼11%. The effect of the gain fiber length on lasing at ∼2.3 µm is also investigated. Our results indicate that Tm3+ doped fluoroaluminate glass fibers are promising gain media for constructing ∼2.3 µm fiber lasers.

We demonstrated broadband S-band (1460–1530 nm) amplification in Tm3+-doped fluorotellurite glass fibers (TDFTFs) by using a 1400/1570 nm dual-wavelength pump technique. TDFTFs based on TeO2-BaF2-Y2O3 (TBY) glass were fabricated by using a rod-in-tube method. For an input signal power of 0 dBm (or 1 mW), a broadband positive net gain ranging from 3+ doping concentration of ∼4000 ppm, as the pump powers of the 1400 nm and 1570 nm lasers were 1.7 W and 0.14 W, respectively. The corresponding bandwidth for a net gain of >20 dB was ∼66 nm (1458–1524 nm), and the measured saturated output power was ∼24.84 dBm at 1490 nm. In addition, numerical simulation was performed by using the parameters of the TDFTFs and the pump lasers, and the noise figure was calculated to be

Optical waveguide amplifiers are essential devices in integrated optical systems. Their gain bandwidths directly determine the operating wavelength of optical circuits. Due to the difficulty of developing wideband gain media, it has been a challenge to fabricate devices with broadband amplification capability, resulting in few reports on multi-band polymer waveguide amplifiers. Here, a polymer waveguide amplifier is demonstrated, which achieves loss compensation covering the whole (S + C) band by using NaYF4:Tm,Yb@NaYF4@NaYF4:Er nanoparticles (NPs)-doped SU-8 as the gain medium. The NPs with a layer-doped core-multishell structure not only provided two emitters required for (S + C)-band amplification, but also reduced the energy transfer (ET) between them. Under 980-nm excitation, the full width at half maximum (FWHM) of the emission peak of NPs reached 119 nm, and the relative gain in the (S + C) band was about 6–8 dB, successfully expanding the operating wavelength from single-band to multi-band.

Optical waveguide amplifiers are essential to improve the performance of integrated communication systems. Previous research has mainly focused on C- and L-bands amplification, but there are few reports on S-band waveguide amplifiers. Here, we introduce a polymer-based waveguide amplifier that uses a NaYF

Ultrathin gold nanowires (UGNWs) with a diameter of ⩽2 nm have attracted much attention because of their high aspect ratios, unusual physical properties and potential applications in nanoelectronics, sensors and photonics. Despite recent advances on UGNWs and the related devices, nonlinear optical properties of UGNWs and their application on photonic devices (e.g. ultrashort pulsed lasers) remain largely unexplored. Here we show that UGNWs can be used as broadband saturable absorbers (SAs) for constructing ultrashort pulsed lasers with an operating wavelength range from near-infrared to mid-infrared (MIR). UGNWs are prepared by using a silane-mediated approach, and then mixed with polyvinyl alcohol to form the UGNWs film. The UGNWs film not only show strong absorption from visible to MIR spectral region (over 25 μm), but also possess the nonlinear saturable absorption properties in the spectral region. As the UGNWs film SA is inserted into an erbium or thulium doped silica fiber laser cavity, stable passively mode-locked lasers at 1562.2 or 1970 nm with a pulse width of a few hundreds of femtoseconds is obtained, respectively. Especially, by inserting the UGNWs film SA into a holmium/praseodymium codoped fluoride fiber laser cavity, stable passively mode-locked laser at 2864 nm is achieved. Our results show that the UGNWs film are promising SAs for constructing broadband ultrashort pulsed lasers.

In this letter, we demonstrate efficient cascaded Raman amplification in fluorotellurite fibers pumped by a 1550 nm nanosecond laser. All-solid fluorotellurite fibers with a core diameter of ∼ 5 µm are fabricated by using a rod-in-tube method. By using a continuous wave (CW) 1765 nm fiber laser as the signal source for first-order Raman amplification, the amplified 1765 nm laser with an average output power of ∼ 190.9 mW and a pulse width of ∼ 3.42 ns is obtained from a 3 m long fluorotellurite fiber for an average pump power of ∼ 519.35 mW and an input signal power of ∼ 1.05 mW, corresponding to a net gain of ∼ 22.6 dB and an optical-to-optical conversion efficiency of 36.76%. Furthermore, a CW 2049.2 nm fiber laser combined with the above 1765 nm laser are used as the signal sources for second-order cascaded Raman amplification. As the power of the 1765 nm and 2049.2 nm lasers are set as 1.05 and 1.00 mW, respectively, the amplified 2049.2 nm laser with an average output power of ∼ 135.35 mW and a pulse width of ∼ 3.36 ns is obtained from the fluorotellurite fiber for an average pump power of ∼ 558.37 mW, corresponding to a net gain of ∼ 21.3 dB and an optical-to-optical conversion efficiency of 24.24%. As the length of the fluorotellurite fiber is increased to 10 m, third-order cascaded Raman amplification is observed by using a 2442.6 nm signal generated by four-wave mixing and the above 1765/2049.2 nm lasers as the signal sources, causing the generation of the amplified 2442.6 nm laser with an average output power of ∼ 18.84 mW. Our results show that fluorotellurite fibers are promising gain media for constructing cascaded Raman fiber amplifiers with a wide range of wavelengths.

Fluorotellurite glasses based on TeO2-BaF2-Y2O3(TBY) with a broadband transmission window of 350–6000 nm, relatively low phonon energy, stable chemical and physical characteristics compared to fluoride glasses have been investigated to develop high-powered mid-infrared (MIR) fiber lasers. In this work, a series of xTeO2-(90-x)BaF2−10Y2O3 (TBYx) (x = 60,65,70,75 mol%) fluorotellurite glasses were prepared with the conventional melting-quenching method in an argon glove box. Then, laser damage characteristics of glass samples under 3000 and 4000 nm MIR femtosecond laser with different pulses was compared and studied. The TBY60 glass has the highest damage threshold, which reaches 1.08 J/cm2 and 0.852 J/cm2 at 4000 nm and 3000 nm, respectively. The femtosecond laser-induced damage threshold (LIDT) of TBY glasses decreased from 1.08 to 0.782 J/cm2 as TeO2 content increased from 60 to 75 mol% at the wavelength of 4000 nm. In addition, the effect of pulse numbers is consistent with exponential defect accumulation model.

In this Letter, we demonstrate a third-order cascaded Raman shift in an all-solid fluorotellurite fiber pumped by a 1550 nm nanosecond laser. The fluorotellurite glass with a composition of TeO2–BaF2–Y2O3 (TBY) has a usable Raman shift of ∼785 cm−1 and a Raman gain coefficient of ∼1.65 × 10−12 m/W at 1550 nm, which is approximately 25.4 times larger than that of silica glass. By using a 5.38 m fluorotellurite fiber as the Raman gain medium and a 1550 nm nanosecond laser as the pump light, a third-order cascaded Raman shift is obtained via spontaneous cascaded Raman amplification in the fluorotellurite fiber, causing the generation of the first-, second-, and third-order Stokes emissions that peak at 1765, 2049, and 2438 nm, respectively. For an average pump power of ∼491.5 mW, the output power of the generated first-, second-, and third-order Stokes light is approximately 14.1, 67.4, and 31.6 mW, respectively. The corresponding conversion efficiency is approximately 2.87%, 13.70%, and 6.43%, respectively. Our results show that fluorotellurite fibers are promising Raman gain media for constructing cascaded Raman fiber lasers with a wide range of wavelengths.

We demonstrate dispersive wave generation at 4 µm in a dispersion-engineered fluorotellurite fiber pumped by a 1.98 µm femtosecond fiber laser. All-solid fluorotellurite fibers with a core diameter of ∼2.6 µm are fabricated by using a rod-in-tube method. The fluorotellurite fibers have two zero-dispersion wavelengths (ZDWs). The first ZDW is 1.328 µm and the second one is 3.551 µm. As the pump laser is launched into the fluorotellurite fiber, firstly, tunable mid-infrared Raman solitons are generated through higher order soliton compression, soliton fission and soliton self-frequency shift. Then, red-shifted dispersive wave at 4 µm is generated as those Raman solitons meet the second ZDW (∼3.551 µm) and soliton self-frequency shift cancellation occurs. Our results show that dispersion-engineered fluorotellurite fibers are promising nonlinear media for constructing all-fiber 4 µm light sources

Optical waveguide amplifiers are essential to improve the performance of integrated communication systems. Previous research has mainly focused on C- and L-bands amplification, but there are few reports on S-band waveguide amplifiers. Here, we introduce a polymer-based waveguide amplifier that uses a NaYF4:Yb3+,Tm3+ nanoparticles–PMMA nanocomposite as gain medium, which can provide loss compensation in the S-band. To obtain the strongest emission luminescence at 1480 nm, we optimized the doping concentration of Yb3+ and Tm3+ to 20% and 1%, respectively. By copolymerizing the nanoparticles and methyl methacrylate monomers, the nanocomposite was synthesized and used as the gain medium to fabricate S-band waveguide amplifiers. A relative gain of 5.6 dB/cm was observed at 1480 nm under the excitation of a 980-nm pump laser. To the best of our knowledge, this is the first time that S-band amplification has been observed in a polymer-based waveguide amplifier. This result is expected to extend the waveband of polymer-based waveguide amplifiers to the S-band.