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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.

Mode-division multiplexing (MDM) is a new method of space-division multiplexing (SDM) that can break through the limitation of single-mode transmission capacity and greatly improve the capacity of optical fiber communication. In the case of a few-mode (FM) system, it is possible that each mode can carry its own data steam and transmit long distances owing to a few-mode erbium-doped fiber amplifier (FM-EDFA). In addition, an Er3+-Yb3+ co-doped waveguide amplifier (EYCDWA) based on polymer materials has numerous advantages of miniaturization and flexibility in planar integrated optics compared with the EDFA. This study explored the theory of a few-mode Er3+-Yb3+ co-doped waveguide amplifier (FM-EYCDWA) and established a theoretical model of an FM-EYCDWA with a novel modified overlap integral factor. The differential modal gain (DMG) of the FM-EYCDWA can be reduced or even eliminated by equalizing the modified overlap integral factor of each signal mode. An unprecedented doping configuration adapted to the fabrication process of an optical waveguide was proposed to fill the gap between modal gains, which can be optimized by a genetic algorithm (GA). We investigated two optimization cases of three-mode and five-mode group FM-EYCDWAs to verify the validity of the theoretical model; both cases were optimized to minimize the DMGs under the same limitations, and excellent performance was presented, which demonstrated that the design method of the few-mode amplifiers we presented can offer a referable guideline.

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.

Semiconducting polymer nanoparticles (SPNs) possess many special photophysical and chemical properties. However, little research has been done on the potential of SPNs in laser technology. In this work, we present the ultrafast pulses generation at 1.5 and 2 μm through proposing the deposition of SPNs onto a side-polished fiber (SPF) platform as the nonlinear optical modulator. SPNs are designed and prepared through a combination of density functional theory and nanoreprecipitation method. The prepared SPNs not only exhibit strong linear absorption but also has nonlinear saturable absorption characteristics. Once SPF-SPNs saturable absorber (SA) is integrated into the laser cavity, ultrafast lasers of 1.5 and 2 μm can be achieved with high performance. Our results show that SAs based on the SPNs and SPF are promising nonlinear optical modulators for broadband ultrafast pulse generation.

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

A kHz-linewidth single-frequency laser at 1070 nm was demonstrated based on homemade heavily Yb3+-doped Yb:YAG-derived silica fiber (YDSF), which was fabricated by molten-core fabrication method. Stable single-longitudinal-mode (SLM) lasing operation was achieved by adopting ring cavity configuration, where a piece of un-pumped polarization maintaining Yb3+-doped fiber (PM-YDF) was utilized as a saturable absorber (SA). A maximum output power of the stable single longitudinal mode continuous wave laser up to 40 mW was obtained with a pump power of 542 mW at 976 nm. The optical signal-to-noise ratio (OSNR) was ~60 dB, and the laser linewidth was measured to be less than 4.3 kHz, which is limited by the measurement setup. The fluctuation of center wavelength of the laser was less than 0.1 pm within 10 min. Wavelength tuning from 1069.99 to 1070.42 nm was achieved by controlling the temperature of the fiber Bragg grating (FBG).

Semiconducting polymer dots (Pdots) have attracted much attention due to their outstanding optical properties. However, the potential of Pdots in laser technology is rarely studied. Here, we first report the benzobisthiadiazole (BBT)-based Pdot as a single broadband nonlinear saturable absorber (SA) for passively Q-switched fiber lasers at 1, 1.5, and 2 μm. The Pdot-SA possesses a strong saturable absorption, a broadband nonlinear optical response, and a large modulation depth. Once the Pdot-SA is integrated into the ytterbium-, erbium-, and thulium-doped fiber laser cavities, stable Q-switched operations are observed at the central wavelengths of 1036, 1561, and 1951 nm. Our results verify that the Pdots are promising nonlinear media for Q-switched pulse generation, and highlight the potential of Pdots for relevant nonlinear optical applications.

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.

We report Q-switching and mode-locking operations in a Ho3+/Pr3+ co-doped ZBLAN fiber laser at 3- μ m mid-infrared waveband using a single-walled carbon nanotube saturable absorber (SWCNT-SA). The SWCNTs were produced by catalytic chemical vapor deposition method and then deposited on the surface of a flat gold-coated mirror to form the SWCNT-SA. The modulation depth and saturation intensity of the SWCNT-SA are 16.5% and 1.66 MW/cm2, respectively. Stable Q-switched laser pulses operating at 2865.6 nm were obtained at a launched pump power of 530.6 mW. The resulting pulses have a measured repetition rate and pulse width of 178.6 kHz and 1.21 μs, respectively. The maximum pulse energy is calculated to be 0.36 μJ. By slightly adjusting the position of the SWCNT-SA, stable continuous-wave mode-locked pulses at 2865.2 nm were also achieved. Our work demonstrates that SWCNTs are promising SAs for 3- μ m midinfrared pulsed lasers.

We demonstrated a widely wavelength-tunable mid-infrared mode-locked Ho3+/Pr3+-codoped ZBLAN fiber laser by using single-wall carbon nanotubes (SWCNTs) with a wide diameter distribution as saturable absorber (SA). This laser emits stable mode-locked pulses in the water vapor transmission window with a maximum average output power of 126.6 mW at a repetition rate of 12.5 MHz. The central wavelength of the mode-locked laser can be continuously tuned from 2836.2 to 2906.2 nm. The 70-nm wavelength tuning range represents the widest tuning range ever achieved in mode-locked Ho3+-doped ZBLAN fiber laser oscillators. Our results also indicate that the SWCNTs can be promising broadband SAs for obtaining gain-bandwidth-limited tunable operation for 3- $\mu \text{m}$ Ho3+-doped ZBLAN fiber lasers. Such simple, reliable, wideband tunable, and low-cost mode-locked mid-infrared fiber laser source is highly attractive for molecular spectroscopy, breath analysis, and laser surgery of human tissue.

We alloyed Zn2+ into CsPbI3 perovskite nanocrystals by partial substitution of Pb2+ with Zn2+, which does not change their crystalline phase. The resulting alloyed CsPb0.64Zn0.36I3 nanocrystals exhibited an improved, close-to-unity photoluminescence quantum yield of 98.5% due to the increased radiative decay rate and the decreased non-radiative decay rate. They also showed an enhanced stability, which correlated with improved effective Goldschmidt tolerance factors, by the incorporation of Zn2+ ions with a smaller radius than the Pb2+ ions. Simultaneously, the nanocrystals switched from n-type (for CsPbI3) to nearly ambipolar for the alloyed nanoparticles. The hole injection barrier of electroluminescent LEDs was effectively eliminated by using alloyed CsPb0.64Zn0.36I3 nanocrystals, and a high peak external quantum efficiency of 15.1% has been achieved.

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.

In this Letter, we present the mode-locking operation of a 2.87 µm H o 3 + / P r 3 + codoped fluoride fiber laser, helped by the ultrafast nonlinear optical absorption behavior of gold nanowires (GNWs). The mode locker is fabricated by depositing the GNW solution onto a silver mirror. It has a modulation depth of 14.2%, a saturation intensity of 26.2 M W / c m 2 , and a non-saturation loss of 29.9% at 2.87 µm. With an increased pump power, the laser operates in Q -switched mode-locking, fundamental mode-locking, and harmonic mode-locking (HML) states. This represents the first, to our knowledge, mid-infrared mode-locked laser using gold nanomaterials. Additionally, the HML is also the first observation in a laser in this band using material saturable absorbers, implying the capability of GNWs for high repetition rate generation.

Fluoroindate glass fibers with an

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

We demonstrated the dissipative soliton generation from a passively mode-locked ytterbium-doped fiber laser operating at 1041 nm by using evanescent field interaction with gold nanorods (GNR) saturable absorber (SA) experimentally. The GNRs, which have broadband longitudinal surface plasmon resonance absorption from ~800 to ~1500 nm, are synthesized by a seed-mediated growth method, and then composited with a D-shaped fiber to form the GNRs SA. The GNRs SA shows a modulation depth of 9.7% and low saturation intensity of 0.302 MW/cm2 . With the proposed GNRs SA, a dissipative soliton fiber laser was achieved with pulse duration 162.3 ps, repetition rate of 6.649 MHz at 1041 nm for a pump power of 220 mW. In addition, the signal-to-noise ratio can reach ~77 dB. The experimental result may make inroads for the nonlinear optical applications of the plasmonic nanomaterials.

Highly transparent upconversion (UC) NaYF4-PMMA covalent-linking nanocomposites were synthesized by copolymerization of NaYF4 nanoparticles (NPs) and methyl-methacrylate (MMA). In this technique, the UC NPs functionalized with unsaturated C C bonds were linked to the polymer chains via covalent bonds, making the inorganic UC NPs disperse homogeneously and stably in the NPs-PMMA nanocomposites. Under the near-infrared (NIR) excitation of 980 nm laser, these NPs-PMMA nanocomposites can emit bright visible UC luminescence and the emission colors can be easily controlled by doping or co-doping different UC NPs. Using these transparent NPs-PMMA nanocomposites as display medium, 3D structural UC luminescent images were generated via the computer-controlled 980 nm laser scanning. The visualization and the adjustable color of 3D image endow the potential application of the NPs-PMMA nanocomposites for three dimensional (3D) solid-state multicolor display.

We present the design of fluorotellurite microstructured fibers (FTMFs) with near-zero-flattened dispersion profiles in the wavelength range of 1500–1600 nm for optical frequency comb (OFC) generation. The FTMFs are based on TeO2-BaF2-Y2O3 glass with a zero-dispersion wavelength of ∼2160 nm. The fiber core is surrounded by the two layers of air holes. The addition of large size air holes in the outer layer is to shift the zero-dispersion wavelength of the fiber from ∼2160 nm to the wavelength region of 1500–1600 nm. The addition of small size air holes in the inner layer is to make the dispersion profile of the fiber become flat in the wavelength range of 1500–1600 nm. By optimizing the parameters (the core diameter, the air hole size, the pitch of air holes, etc.) of FTMFs, the fiber with the chromatic dispersion value between −0.5 and 0.3 ps/nm/km in the wavelength range of 1500–1600 nm is achieved. Furthermore, numerical simulations are used to show the potential of the fiber for OFC generation via cascaded four-wave mixing. Flat top OFC extending from 1500 to 1600 nm with tunable mode spacing from 25 to 100 GHz can be generated in a 2-m-long fiber by using a 1550-nm laser with a pulse width of 0.85 ps and a peak power of 49 W as the pump source. The effects of stimulated Brillouin scattering on OFC generation are also investigated.

Ho3+-doped fluoroindate glass fibers (FIGFs) based on InF3-GaF3-ZnF2-BaF2-SrF2-YF3-LiF-PbF2 glasses were fabricated by using a rod-in-tube method. By using a 92-cm-long Ho3+-doped FIGF as the gain medium and a 1120-nm fiber laser as the pump source, lasing at 2875 nm was obtained for a threshold pump power of 278 mW. By further increasing the pump power to 1224 mW, the obtained maximum output power was about 54.5 mW. The corresponding slope efficiency was about 6%. To the best of our knowledge, this is the first time to report lasing at 2875 nm from Ho3+-doped FIGFs.

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.

We investigate coherent broadband mid-infrared supercontinuum generation in all normal dispersion (ANDi) tellurite microstructured fibers through numerical simulations. The proposed tellurite microstructured fibers (PTMFs) have an inverted L-shaped ANDi profile in the wavelength range of < 5.2 μm. By using a 2-μm femtosecond laser as the pump source, the spectral broadening occurs in the PTMF, which is caused by self-phase modulation (SPM) and optical wave breaking. Interestingly, SPM induced spectral broadening is larger on the Stokes side than the antistokes side, since the trailing edge of laser pulse becomes smoother than its leading edge, and the effect of self-steepening (SS) on pulse shape is compensated by the effect of the dispersion in the PTMF. Such a phenomenon is inaccessible in previously reported optical fibers, since the trailing edge of output pulse is steeper than the leading edge of output pulse when SS occurs in previously reported ANDi fibers. As a result, coherent broadband mid-infrared supercontinuum light with long operating wavelength can be generated in the PTMF.

In this paper, a sapphire-derived fiber (SDF) with a core diameter of 10 μm and a cladding diameter of 125 μm is fabricated by the melt-in-tube method, and fiber Bragg gratings (FBGs) with reflectivity over 80% are prepared by the femtosecond laser point-by-point direct writing method. By analyzing the refractive index distribution and reflection spectral characteristics of the SDF, it can be seen that the SDF is a graded refractive index few-mode fiber. In order to study the element composition of the SDF core, the end-face element distribution of the SDF is analyzed, which indicates that element diffusion occurred between the core and the cladding materials. The temperature and stress of the SDF gratings are measured and the highest temperature is tested to 1000 °C. The temperature and strain sensitivities are 15.64 pm/°C and 1.33 pm/με, respectively, which are higher than the temperature sensitivity of the quartz single-mode fiber. As a kind of special fiber, the SDF expands the application range of sapphire fiber, and has important applications in the fields of high-temperature sensing and high-power lasers.

All-solid fluorotellurite fibers with near-zero-flattened dispersion profiles in the wavelength range of 1840–2140 nm are designed for mid-infrared optical frequency comb (OFC) generation. The fiber core materials are TeO2-BaF2-Y2O3 (TBY) glasses. The fiber cladding materials are fluoroaluminate and TBY glasses. By controlling the core diameter and the thickness of the thin annular fluoroaluminate or TBY glass, the fiber with the chromatic dispersion value between −0.3 and 0.32 ps nm km−1 in the wavelength range of 1840–2140 nm is achieved. Furthermore, we perform numerical simulations on mid-infrared OFC generation via four-wave mixing in the designed fiber. By using a 1980 nm laser with a pulse width of 1.28 ps and a peak power of 60 W as the pump source, OFC spectrum expanding from 1127 to 4942 nm is obtained in a 2 m long fiber, and the pulse width of the generated OFC is about 25 fs. By varying the repetition rate of the pump source, mid-infrared OFC with tunable mode spacing is generated in the designed fiber.

In this paper, we demonstrate ∼2 μm lasing in Tm3+-doped fluorotellurite microstructured fibers. The Tm3+-doped fibers are based on TeO2-BaF2-Y2O3 glasses and fabricated by using a rod-in-tube method. Under the pump of a 1570 nm Er3+-doped fiber laser, lasing at 1887 nm is obtained in a ∼42.5 cm long Tm3+-doped fiber with a threshold pump power of 94 mW. As the pump power increases to 780 mW, the obtained maximum unsaturated power reaches up to ∼408 mW with a slop efficiency of ∼58.1%. This result indicates that the Tm3+-doped fluorotellurite fibers are promising gain media for ∼2 μm fiber lasers.

Intense ∼1.2 μm fluorescence is observed in Ho 3+ /Yb 3+ co-doped TeO 2 -BaF 2 -Y 2 O 3 glasses under 915 nm laser diode excitation. The 1.2 μm emission can be ascribed to the transition 5 I 6 → 5 I 8 of Ho 3+ . With the introducing of BaF 2 , the content of OH in the glasses drops markedly, and the 1.2 μm emission intensity increases gradually as increasing the concentration percentage of BaF 2 . Furthermore, microstructured fibers based on the TeO 2 -BaF 2 -Y 2 O 3 glasses are fabricated by using a rod-in-tube method, and a relative positive gain of ∼9.42 dB at 1175.3 nm is obtained in a 5 cm long fiber.

We demonstrate a passively Q-switched Yb3+/Er3+ co-doped fiber (YEDF) laser using a filmy sodium carboxymethylcellulose (NaCMC)-based Cu1.8S nanocrystals (NCs) saturable absorber (SA). Cu1.8S NCs SA exhibit a broad absorption band from 600 nm to more than 2500 nm. By placing Cu1.8S NCs SA into a YEDF laser cavity, stable passively Q-switched laser with a central wavelength of ∼1567.2 nm was achieved at a threshold pump power of ∼1.4 W. On gradually increasing the pump power from 1.4 W to 5.6 W, the repetition rate of Q-switched laser increases from 16.6 kHz to 51.14 kHz and the pulse duration decreases from 8.7 μs to 2 μs. Particularly, we measure the output power of Q-switched lasers based on two types of plasmonic materials, Cu1.8S NCs and gold nanorods (GNRs). The maximum output power of the Q-switched laser based on Cu1.8S NCs SA is 3–4 times higher than that based on GNRs SA owing to weak photothermal effect of Cu1.8S NCs. These results show that Cu1.8S NCs are promising SAs for constructing high power pulse lasers.