Co-doped Fiber Research Articles

414.9 W in-band pumped Er/Yb co-doped fiber amplifier seeded by a random fiber laser.

We demonstrated a 414.9 W large-mode-area Er/Yb co-doped fiber amplifier with a good time-domain stability, seeded by a 1568 nm random fiber laser (RFL) seed with a half-open cavity. We believe this to be the highest output power of the RFL in a 1.5 µm band to date. At the maximum output power, the optical efficiency was 36.9% and the 3 dB linewidth was 0.69 nm. The 1535 nm fiber lasers were used as the pumping source of the main amplifier to avoid the parasitic lasing of Yb ions. The spectral linewidth broadening was suppressed during the amplification process due to the stable temporal output of the RFL seed. The M2 factor increased from 2.28 at 145.7 W to 2.83 at 280.8 W. Our research provides a robust approach for achieving high-power and high-spectral-purity RFLs in the 1.5 µm band.

Conventional soliton and noise-like pulse emissions at 1.98μm utilizing tungsten trioxide as mode-locker

In this paper, we experimentally demonstrate the dual pulse emissions of conventional soliton (CS) and noise-like pulse (NLP) in thulium-holmium co-doped fiber laser using tungsten trioxide saturable absorber (WO3-SA). The CS pulse delivered 2[Formula: see text]ps width, centered at 1982.8[Formula: see text]nm. Increasing the pump power and alteration of polarization states switched the CS to the NLP regime with 1990.0[Formula: see text]nm central wavelength, 17.2[Formula: see text]nm spectral bandwidth, and 396[Formula: see text]fs spike width riding on top of a wide picosecond pulse pedestal in the time domain. This work suggests the capability of WO3-SA as a pulse initiator for future dual-source ultrashort pulses based on an all-fiber laser cavity design.

N, O and P co-doped hierarchically porous carbon fiber for high performance Zinc-ion hybrid capacitors

Multi-heteroatoms co-doped hierarchically porous carbon-based electrode is an effective strategy to solve the low energy density and poor cycle stability of Zn-ion hybrid capacitors (ZHCs). Herein, N/O/P co-doped porous carbon nanofiber (N-P-PCF) was prepared, which displays fibrous network hierarchically porous structure to fast electron/ Zn2+ transport and enhance Zn2+ adsorption sites. Meanwhile, rich N (9.47 at.%), O (11.29 at.%) and P (1.29 at.%) co-doping can be beneficial for the infiltration of electrode–electrolyte interface and provide an additional pseudocapacitance. The N-P-PCF based ZHCs can yield a large specific capacitance (205 mAh g−1 at 1 A g−1), high energy density (173 Wh kg−1 at 823 W kg−1) and excenllent cycle stability for 10,000 cycles (98.6 % capacity retention), which provides a reliable multi-heteroatoms co-doped porous carbon fiber for high-performance ZHCs.

145 W single-frequency fiber laser at 1607 nm with the seed and MOPA configuration

In this paper, high Er3+ concentration erbium doped fiber (EDF) and erbium-ytterbium co-doped fiber (EYDF) were fabricated for the seed and master oscillator power amplifier (MOPA) system of the single-frequency fiber laser. An in-band pumping source with the wavelength of 1535 nm was proposed to improve the efficiency in the ring-cavity. A slope efficiency of 23.8% with an output power of 49 mW was achieved and the laser linewidth was measured to be 800 Hz. In the MOPA system, a piece of EYDF was used firstly to absorb the backward 1 µm amplified spontaneous emission (ASE) and amplified the signal from the seed. Based on the above methods, an output power of 145 W was achieved at 1607.75 nm. Because of the self-phase modulation, the laser linewidth was expanded to be 10.75 kHz at the output power of 132 W. To the best of our knowledge, this is the highest efficiency and output power of the seed and the highest output power of the 1.6 µm single-frequency fiber laser.

Suppression of intensity noise and phase noise for thulium-holmium co-doped fiber laser by self-injection locking

The present study proposes and demonstrates a narrow-linewidth thulium-holmium co-doped fiber laser based on self-injection locking. The laser with single-longitudinal-mode operation is realized using a fiber Bragg grating as a wavelength-selection component and a dual-ring compound cavity as a mode-selection filter. The linewidth was compressed by increasing the photon lifetime by utilizing delay fibers of different lengths in the feedback cavity. The results show that the optical signal-to-noise ratio of the output laser is 57.2 dB, and the relative intensity noise is -130.43 dB/Hz with self-injection locking. The intrinsic linewidth is compressed from 39.45 kHz to 3.21 kHz, a reduction of nearly an order of magnitude. The linewidth compression mechanism solves the problems associated with deep linewidth compression in fiber lasers with long ring cavities and fosters the development of practical and reliable all-fiber structures. The laser source is characterized by low cost, high coherence, and low noise, which are highly desirable features in coherent optical detection, high-resolution spectrometers, microwave photonics, and optical sensing.

Er3+/Yb3+ Co-Doped Fluorotellurite Glass Fiber with Broadband Luminescence.

In order to address the 'capacity crisis' caused by the narrow bandwidth of the current C band and the demand for wide-spectrum sensing sources and tunable fiber lasers, a broadband luminescence covering the C + L bands using Er3+/Yb3+ co-doped fluorotellurite glass fiber is investigated in this paper. The optimal doping concentrations in the glass host were determined based on the intensity, lifetime, and full width at half maximum (FWHM) of the fluorescence centered at 1.5 µm, which were found to be 1.5 mol% Er2O3 and 3 mol% Yb2O3. We also systematically investigated this in terms of optical absorption spectra, absorption and emission cross-sections, gain coefficients, Judd-Ofelt parameters, and up-conversion fluorescence. The energy transfer (ET) mechanism between the high concentrations of Er3+ and Yb3+ was summarized. In addition, a step-indexed fiber was prepared based on these fluorotellurite glasses, and a wide bandwidth of ~112.5 nm (covering the C + L bands from 1505.1 to 1617.6 nm) at 3 dB for the amplified spontaneous emission (ASE) spectra has been observed at a fiber length of 0.57 m, which is the widest bandwidth among all the reports based on tellurite glass. Therefore, this kind of Er3+/Yb3+ co-doped fluorotellurite glass fiber has great potential for developing broadband C + L band amplifiers, ultra-wide fiber sources for sensing, and tunable fiber lasers.

Highly active nitrogen-phosphorus co-doped carbon fiber@graphite felt electrode for high-performance vanadium redox flow battery

Heteroatom-doped electrodes offer promising applications for enhancing the longevity and efficiency of vanadium redox flow battery (VRFB). Herein, we controllably synthesized N, P co-doped graphite fiber electrodes with conductive network structure by introducing protonic acid and combining electrodeposition and high temperature carbonization. H2SO4 and H3PO4 act as auxiliary and dopant, respectively. The synergistic effect between N and P introduces additional defect structures and active sites on the electrodes, thereby enhancing the reaction rate, as confirmed by density functional theory calculations. Furthermore, the conductive network structure of carbon fibers improves electrode-to-electrode connectivity and reduces internal battery resistance. The optimized integration of these strategies enhances VRFB performance significantly. Consequently, the N, P co-doped carbon fiber modified graphite felt electrodes demonstrate remarkably high energy efficiency at 200 mA cm−2, surpassing that of the blank battery by 7.9 %. This integrated approach to in-situ controllable synthesis provides innovative insights for developing high-performance, stable electrodes, thereby contributing to advancements in the field of energy storage.

Enhanced radiation resistance of Er3+/Yb3+ co-doped high-phosphorus silica glasses and fibers via phase-interface engineering

Enhanced radiation resistance of Er3+/Yb3+ co-doped high-phosphorus silica glasses and fibers via phase-interface engineering

Tm–Ho co-doped hybrid mode-locked fiber laser based on Ti3CNTx saturable absorber

We proposed a thulium-holmium (Tm–Ho) co-doped hybrid mode-locking fiber laser utilizing few-layer Ti3CNTx MXene saturable absorber. The Ti3CNTx material exhibits superior optical properties with a saturation intensity of 25 mW and a modulation depth of 18.32%. By integrating nonlinear polarization rotation (NPR) technology with Ti3CNTx-SA, we achieved a self-starting, low threshold, ultra-stable and, efficient hybrid mode-locking pulse. The pulses are generated at a central wavelength of 1959.23 nm, with a 3 dB bandwidth of 5.34 nm and a pulse width of 766 fs. Compared to the single NPR technology, the structure reduces the self-starting threshold for mode-locking, compresses the pulse width by at least 21 fs, and significantly improves the signal-to-noise ratio. The proposed laser underscores the potential application and broad prospects of Ti3CNTx-SA in the 2-μm field of ultrafast fiber lasers.

Tunable high energy pulse generation in the range of 2.9-3.6 μm enabled by an actively Q switched Er3+/Dy3+ codoped fluoride fiber oscillator.

We demonstrate, for the first time, an actively Q switched red-diode-clad-pumped Er3+/Dy3+ codoped fluoride fiber oscillator. Its wavelength can be continuously tuned over the range of 2.906-3.604 μm (698 nm), representing the widest tuning span of pulsed fluoride fiber oscillators in the mid-infrared. In addition, the achieved pulse energy at each wavelength of >2.95 μm is also higher than that of a previously reported pulsed fluoride fiber oscillator at the corresponding wavelength, to the best of our knowledge. By tuning the wavelength to 3.204 μm, the highest pulse energy of 82 μJ has been gotten with a pulse width of 520 ns at a repetition rate of 500 Hz.

Exploring the potential of a bismuth-erbium-vanadium co-doped optical fiber as a stable Q-switcher in the 1550 nm region

This paper experimentally demonstrates the ability of a bismuth-erbium-vanadium co-doped optical fiber as a saturable absorber (BEV-FSA) to generate stable Q-switched pulses in the 1550 nm region. The laser cavity delivered passively Q-switched pulses exploiting an erbium-ytterbium co-doped double-clad fiber (DC-EYDF) as the laser gain medium while maintaining an all-fiber cavity configuration. The output parameters of the laser such as output power, repetition rate, pulse duration, and pulse energy have been studied in detail with the variation of pump power. The output spectrum centered at 1550.86 nm throughout the experiment. The system produced stable pulses with a minimum pulse width of 1.83 µs with a pulse energy≈0.4µJ at the highest pump power of 2.31 W. The highest achievable repetition rate was 47.5 kHz with an of SNR≈53dB.

Efficiency improvement for Ho3+/Pr3+co-doped 3 μm fiber laser in AlF3-based glass fiber

Over the past few decades, significant advancements have been made in the development of 3 μm fiber lasers utilizing Ho3+/Pr3+ doped fluoride fiber, particularly in terms of slope efficiency and output power. While achieving an efficiency of ∼15 % for the 3 μm laser in AlF3 fiber with a Ho3+/Pr3+ doping ratio of ∼10:1, further improvements are necessary to approach the Stokes efficiency limit of ∼40 %. Our study focused on the influence of the Ho3+/Pr3+ doping ratio on 3 μm laser efficiency. We conducted experiments on Ho3+/Pr3+ co-doped glass and fiber with doping ratios ranging from 1:0.01 to 1:1. Luminescence decay lifetime tests of the Ho3+: 5I6 and 5I7 energy levels in the Ho3+/Pr3+ doped AlF3 glass samples revealed the primary energy transfer progress that affected the 3 μm laser efficiency. When pumped by a 1150 nm Raman fiber laser, a maximum slope efficiency of 29.3 % at 3 μm was obtained in a 1mol%Ho3+/0.6mol%Pr3+ co-doped AlF3 Fiber.

Ag/MXene as Saturable Absorber for Tm:Ho Co-Doped Q-Switched Fiber Laser.

Q-switched fiber lasers have become reliable light sources for generating high-energy pulses, which can be passively modulated by saturable absorbers with excellent nonlinear optical properties. The composite combining Ag and MXene exhibits a broadband nonlinear response and high modulation depth, making it a promising candidate for saturable absorbers in pulsed lasers. Herein, we demonstrate a Q-switched Tm:Ho co-doped fiber laser centered at 2 µm, where the Ag/MXene composite serves as a saturable absorber to generate pulses. The typical spectrum, pulse train, and radio frequency spectrum of Q-switched pulses were observed, in which the 60 dB signal-to-noise ratio was higher than that of 2 µm Q-switched fiber lasers based on other materials, demonstrating the stability of the output pulses. Additionally, the long-term stability of the laser was evaluated over 2 h, where the well-maintained central wavelength and output power also indicated the robustness of the Q-switched laser. Furthermore, the influence of the pump power on the parameters of Q-switched pulses was also investigated, which is conducive to control the output characteristics of lasers. Specifically, the pulse width of the Q-switched pulse decreased, while the repetition rate, output power, and single pulse energy all increased with the increase in pump power. These experimental results demonstrate the ability of Ag/MXene as a saturable absorber and show its potential for generating high-performance pulses in ultrafast lasers.

High-sensitivity ratiometric thermometers of Yb3+/Er3+/Tm3+ co-doped LuScO3 single crystal fibers based on non-thermally coupled energy levels

Fluorescence thermometry manifests tremendous attention for their potential applications in the temperature sensing, especially for combining wide operating temperature range with high sensitivity. However, the use of thermally coupled energy levels (TCLs) for temperature measurement has strict requirements for energy difference, which limits the sensitivity of detection. In order to satisfy higher sensitivity sensing, the pair of non-thermally coupled energy levels (NTCLs) of 4S3/2 and 3H4 has been innovatively designed. Herein, the sesquioxide Yb,Er,Tm co-doped LuScO3 single crystal fibers (SCFs) had been delicately grown by Laser Heated Pedestal Growth (LHPG) method. The fluorescence intensity ratio (FIR) thermometry was realized based on the Er3+:4S3/2→4I15/2 (545–593 nm) and Tm3+:3H4→3H6 (750–850 nm) NTCLs. Such an obvious FIR-temperature change through the NTCLs presents an outstanding optical thermometric performance, yielding the high temperature sensing with wide range. The maximum value of absolute sensitivity was 2 orders of magnitude higher than the temperature measurement using TCLs. More importantly, the sesquioxide Yb,Er,Tm:LuScO3 SCFs exhibit superior thermal stability that will be helpful to obtain high precision temperature measurement. Hence, our findings might offer some useful inspiration for exploring high-sensitivity luminescent thermometers and enriching the research of temperature measuring materials.

Experimental study on activating bismuth active centers in bismuth/erbium co-doped optical fiber by ionizing radiations

Post-treatments by ionizing radiations have been proposed previously for regulating the properties of bismuth/erbium co-doped optical fiber (BEDF). In this work, the effects of common ionizing radiations (i.e. gamma ray, electron beam and mixed γ/neutron) on Bismuth Active Centers (BACs) in BEDF have systematically been investigated. Our experimental results show obvious BAC activation by ionizing radiation – evident from the increase in saturable absorption at 830 nm that is closely associated with the BAC responsible for the desirable near infrared (NIR) emissions. This radiation induced BAC activation has been confirmed from the emission of BAC associate with silica (BAC-Si). The saturation pump power of the BAC-Si emission in all irradiated samples is found higher than that in pristine (or non-irradiated) samples. In addition, the effect on emission by different radiation is found in the order of gamma ray > mixed gamma/neutron > electron beam. On the other side, we have also observed significant radiation induced unsaturable loss that can affect the pumping efficiency and Figure of Merit (FOM).

N, O-codoped porous carbon fiber cloth synthesized by molecular dispersed CaCl2·6H2O in situ activation for high performance supercapacitors

In this study, a nitrogen/oxygen co-doped carbon fiber cloth with a hierarchical porous structure was synthesized by one-step carbonization and in situ activation method and acted as binder-free electrode materials for supercapacitors. Cotton fiber cloth served as the carbon precursor, while molecular dispersed CaCl2·6H2O and urea functioned as activator and N dopant, respectively. The influence of molar concentration of CaCl2·6H2O and urea on the microstructure and capacitive performance of the resulting products were investigated. CaCl2·6H2O has an expansion effect on pores, resulting in reduction of micropores. Hence, the specific surface area of the resulting porous carbon increased first and then decreased with the increase of CaCl2·6H2O concentration. In addition, the erosion of NH3 and CO2 (produced by the decomposition of urea) at high temperature on the surface of the samples promoted the formation of porous structure. Urea plays the dual role of doping and activation agent. The morphology and structure analysis shown that the activated samples exhibited hierarchical pore structure, large specific surface area, and high heteroatom content. The optimal sample NAC-20 exhibited good capacitive performance, including high specific capacitance of 260.9 F g−1 at 0.1 A g−1 and good rate performance. Moreover, the symmetric supercapacitor exhibited a maximum energy density and power density of 16.2 Wh kg−1 and 19.0 kW kg−1, respectively, in 6 M KOH electrolyte. In this work, a green, low-cost molten salt activation method was proposed to synthesis biomass derived porous carbon materials for energy storage devices.

Dipole-induced hydrogen bonds enhanced P/O co-doped Lyocell-based porous carbon fiber cloth for hydrogen storage under ambient pressure

Currently, the hydrogen storage application of carbon-based adsorbent materials is mostly implemented under the pressure conditions of 30–300 bar, while there is few targeted studies conducted on the unsaturated adsorption under ambient pressure conditions. Therefore, based on industrialized Lyocell biopolymer fiber precursors and the enhancement effects of dipole-induced hydrogen bonds (DIHB), this work presents a facile construction strategy for P/O co-doped Lyocell-based porous carbon fiber cloth (Ly-ACF-F40). By the technical route of thermal stabilization---sonication assisted phosphoric acid activation---hydrogen bonds introduced by interfacial fluorination, the constructed Ly-ACF-F40 acquires a high specific surface area (1870 m2/g) and total pore volume (1.277 cm3/g), and an excellent hydrogen storage capacity of 3.22 wt% under ambient pressure conditions (77 K, 1 bar). The study directly demonstrated in the experiment that dipole induced hydrogen bonding H(I)-H(II)···F can effectively enhance the atmospheric hydrogen storage density on the basis of other eliminating influencing factors of specific surface area. The simple construction strategy of porous carbon-based materials can provide reference for the research of unsaturated adsorption hydrogen storage materials under ambient pressure conditions, also assist in the application and promotion of low-cost solid hydrogen storage materials.

1.94 & 2.04 µm dual-band four-wavelength-switchable single-frequency narrow linewidth fiber laser using a novel fs-laser direct-written polarization-dependent four-channel filter

We present a dual-band four-wavelength-switchable single-frequency thulium-holmium co-doped fiber laser (THDFL) utilizing a novel band-switchable polarization-dependent four-channel filter (BS-PDFCF). The filter incorporates two high-birefringence fiber Bragg gratings (HB-FBGs) and an electrical-controlled optical switch (EC-OS). Specifically designed for operation in the 1.94 μm and 2.04 μm bands, two HB-FBGs are fabricated using femtosecond (fs) laser direct-writing technology in two segments of polarization-maintaining fibers via a point-by-point method. Each HB-FBG features two narrow-band reflection channels with perpendicular polarization directions. The EC-OS switches the operation band of the BS-PDFCF. A 1.2 m long dynamic ultra-narrow-band filter is employed in the THDFL to achieve single-longitudinal-mode oscillation. The THDFL achieves exceptional output performance, including four single-wavelength and two dual-wavelength operations, spectral wavelength and power fluctuations of ≤0.012 nm and ≤0.386 dB, respectively, OSNRs of >76 dB, RINs of ≤−142.48 dB/Hz@≥5 MHz, linewidths of ≤3.59 kHz@1.94 μm band and ≤5.46 kHz@2.04 μm band, and output power fluctuations of ≤0.109 dB in a measurement time span of 30 min.

Self Q-switched single-frequency all-fiber laser

Here, we propose a self Q-switched single-frequency (SF) all-fiber laser. The intra-cavity Er:Yb co-doped fiber serves not only as an active fiber for lasing but also as a fiber-type saturable absorber (SA). The self-Q-switching behavior is induced by the ground-state reabsorption of the unpumped portion of the active fiber. To achieve SF operation, double fiber loops constructed by two 3 dB optical couplers (OCs) form a cascade sub-cavity, which serves as a mode selector with a narrow bandwidth. Taking the advantage of a high damage threshold of the fiber-type SA, microjoule-level self-Q-switched SF pulses are obtained with a narrow linewidth of ∼252kHz. Combed with the measured pulse width of ∼1.766µs, the corresponding time-bandwidth product is ∼0.445, which is very close to the Gaussian transform limit. The maximum output power of the pulsed SF laser can reach ∼100mW. By stretching the fiber Bragg grating (FBG), the wavelength of the pulsed SF laser can be tuned.

Wavelength extension beyond 3 µm in a Ho3+/Pr3+ co-doped AlF3-based fiber laser.

In this Letter, we report continuous-wave (CW) lasers with wavelengths beyond 3 µm in homemade Ho3+/Pr3+ co-doped AlF3-based glass fibers. The laser cavity was established through the integration of a dichroic mirror (DM, HR@3-3.1 µm) positioned at the pump end and a partial reflectivity (PR) fiber Bragg grating (FBG) situated at the laser emission end. The FBGs in AlF3-based glass fibers were fabricated by a fs laser direct-writing method, and the resonant wavelengths were 3.009, 3.036, and 3.064 µm, respectively. Under the pump of 1.15 µm laser, a maximum unsaturated output power of 1.014 W was obtained at 3.009 µm with an overall laser efficiency of 11.8% and FWHM bandwidth of 0.88 nm. Furthermore, in order to enhance the optical-thermal stability, the FBG was heat-treated at 200°C for 30 min, and a higher output power of 1081 mW (348 mW without heat treatment) at 3.036 µm was achieved. To the best of our knowledge, this is the first demonstration of 3-3.1 µm lasers by using FBGs in Ho3+/Pr3+ co-doped AlF3-based fibers.