Co-doped Fiber Research Articles

Q-switched Er3+/Dy3+ codoped ZrF4 fiber laser: continuously tunable pulse generation from 3.06 to 3.62 µm

In this Letter, we report on widely tunable pulse generation from a red-diode-clad-pumped mid-infrared (mid-IR) Er3+/Dy3+ codoped ZrF4 fiber laser, for the first time, to the best of our knowledge. Using a Fe2+:ZnSe crystal, continuously tunable Q-switched pulses across the range of 3.06–3.62 µm have been attained, which not only represents the widest range (in wavelength domain) from a pulsed rare-earth-doped fiber laser at any wavelength, but also almost entirely covers the strong absorption band of C-H bonds in the mid-IR, providing a potential way for gas detection and polymer processing. In addition, the commercial InAs quantum-well-based saturable absorbers (SAs) have been employed instead, and the obtained longest Q-switching wavelength of 3.39 µm is slightly shorter than 3.444 µm determined by its nominal direct bandgap of 0.36 eV.

Over 100 nm Bandwidth Orbital Angular Momentum Modes Amplification For MDM and WDM Transmission With a Ring-Core Bi/Er Co-Doped Fiber

We designed and fabricated a ring-core Bi/Er co-doped fiber (RC-BEDF), and thus investigated the broad-spectrum amplification of orbital angular momentum (OAM) modes. The deviation from the average gain of the OAM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and OAM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> modes enabled gains of <1.8 dB and <1.9 dB respectively, and the differential mode gain (DMG) between the two modes was <1.0 dB over 100 nm bandwidth (1525–1626 nm). In particular, the 3 dB bandwidth of the gain spectra exhibited 74 nm (1552–1626 nm) and 69 nm (1557–1626 nm), respectively. Furthermore, four beams of different wavelengths, i.e., 1525, 1560, 1590, and 1626 nm, were separately extracted from the broad spectra to detect the amplified modes, by which the interferograms of first- and second-order OAM modes were obtained. The amplified OAM mode purities of the wavelengths were all above 95%. Moreover, dual-channel combination of the OAM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> mode at 1550 nm and OAM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mode at 1600 nm was amplified, which indicated realization of different-OAM-modes amplification with wavelength-division multiplexing (WDM). Herein, for the first time, we extended the C+L band OAM modes amplification to 1626 nm and achieved OAM multiplexed amplification of WDM signals. This ultra-broad-spectrum and ultra-low-DMG OAM amplification has been widely considered as a promising technology for long-haul mode division multiplexing and WDM fiber-optics communication systems and networks.

Dispersion-Managed Tm-Ho Co-Doped Ultrashort Pulse Fiber Laser Using Single-Walled Carbon Nanotube and Spectral Filter

In this paper, we have demonstrated a dispersion-managed, high-power, Tm-Ho co-doped ultrashort pulse fiber laser using a single walled carbon nanotube (SWNT) dispersed in polyimide film. An in-line type spectral filter was developed to control the output pulse spectra. Two SWNT films with different modulation depths were examined as a mode-locker. Normal dispersion fiber was used in the fiber laser oscillator, and dependence on net cavity dispersion was investigated. Passive mode-locking was achieved in a wide dispersion range, from −0.319 to +0.101 ps2. Stable soliton mode-locking operation and dissipative soliton mode-locking operations were observed. The pumping efficiency was ~3 times higher than that in a Tm-doped fiber laser with a similar configuration. The developed fiber laser showed self-start and stable operations, and this laser is useful for practical applications.

MIL-68(Al) and MIL-68(Fe) as broadband optical modulators for Q-switching fiber lasers operating at 2 and 2.9 μm

We investigated 2 and 2.9 μm mid-infrared fiber lasers passively Q-switched by MIL-68(Al) and MIL-68(Fe), which were fabricated via the hydrothermal method. The modulation depth of MIL-68(Al) was found to be 9.12% at 1.99 μm. And the modulation depths of MIL-68(Fe) were found to be 18.89% and 15.79% at 1.99 μm and 2.87 μm, respectively. We report Q-switching pulse generation in both Tm3+-doped and Ho3+/Pr3+ co-doped fiber lasers by using the as-prepared MIL-68 (M, M = Al3+, Fe3+) as SAs. The center wavelengths were at 1.99 μm and 2.87 μm, respectively. These results indicate that MIL-68(M) has wideband nonlinear optical properties and promising application prospects in the field of optical modulators at 2- and 2.9-μm mid-infrared waveband. Work clearly accessible to a broad readership.

High Power-Efficiency, Low DMG Cladding-Pumped Few-Mode Er/Yb/P Co-Doped Fiber Amplifier for Mode Division Multiplexing

Mode division multiplexing (MDM) is considered to be an efficient solution to alleviate the exponentially increasing “capacity crunch”. Here, we numerically and experimentally demonstrate a high power-efficiency, low differential mode gain (DMG) few-mode amplifier based on an M-type double-cladding Er/Yb co-doped phosphosilicate fiber. With a large-signal power of 4.1 dBm, the average DMG of <1.5 dB and the maximum gain of >28 dB were achieved for the LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> , LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> , LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21,</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode groups over the 1535–1565 nm range. Additionally, the saturation output power was measured in excess of 35 dBm, with a pump conversion efficiency (PCE) of >31%. This cladding-pumped few-mode Er/Yb co-doped fiber amplifier enables combined mode-division and wavelength-division multiplexed over large-capacity long-haul MDM transmission.

Electrochemical Activation Applied to Perovskite Titanate Fibers to Yield Supported Alloy Nanoparticles for Electrocatalytic Application.

Active bi-metallic nanoparticles are of key importance in catalysis and renewable energy. Here, the in situ formation of bi-metallic nanoparticles is investigated by exsolution on 200nm diameter perovskite fibers. The B-site co-doped perovskite fibers display a high degree of exsolution, decorated with NiCo or Ni3 Fe bi-metallic nanoparticles with average diameter about 29 and 35nm, respectively. The perovskite fibers are utilized as cathode materials in pure CO2 electrolysis cells due to their redox stability in the CO/CO2 atmosphere. After in situ electrochemical switching, the nanoparticles exsolved from the perovskite fiber demonstrate an enhanced performance in pure CO2 electrolysis. At 900°C, the current density of solid oxide electrolysis cell (SOEC) with 200µm YSZ electrolyte supported NiFe doped perovskite fiber anode reaches 0.75Acm-2 at 1.6V superior to the NiCo doped perovskite fiber anode (about 1.5 times) in pure CO2 . According to DFT calculations (PBE-D3 level) the superior CO2 conversion on NiFe compared to NiCo bi-metallic species is related to an enhanced driving force for C-O cleavage under formation of CO chemisorbed on the nanoparticle and a reduced binding energy of CO required to release this product.

High-power, 474 fs, 31.12 MHz, all-polarization-maintaining, 1560 nm fiber laser system based on the chirped-pulse amplification

We report on a 13.2 W, 474 fs, 31.12 MHz, all-polarization-maintaining (PM), 1560 nm fiber laser system based on the chirped-pulse amplification (CPA). The home-built seed laser with the nonlinear amplified loop mirror (NALM) can deliver two trains of laser pulses. Two stages of cascaded all-PM Er:Yb co-doped fiber (EYDF) amplifiers were employed in scaling up the average power. The corresponding numerical simulation and experimental investigations were implemented in optimizing the power amplification process. To our knowledge, this is the highest output power ever reported for the 1560 nm femtosecond all-PM fiber laser systems.

A fiber sensor for different curvature measurement based on nano-erbium-ytterbium co-doped fiber cascade structure as both source and sensor

A fiber sensing system based on Nano-Erbium-Ytterbium co-doped fiber (Nano-EYDF) is proposed and demonstrated, where it works as both source and sensor. Especially, a fiber curvature sensor based on Mach-Zehnder interferometer is fabricated in a Nano-EYDF, which is a cascaded structure composed of single-mode fiber (SMF), Nano-EYDF and SMF. Based on the principle of evanescent wave coupling, the light transmitted in the SMF core can be coupled into the Nano-EYDF cladding. Therefore, the Nano-EYDF core mode and cladding mode that satisfy the phase matching conditions can couple evanescent waves to form a double-beam interference. When the external environment changes, the interference spectrum will change, so the curvature sensing can be realized by observing the wavelength shift. The experimental results show when the length of the Nano-EYDF is 20 mm and 25 mm, the transmission spectrum of the sensor appears blue shift in the downforce curvature range of 0–1.76 m−1, and the curvature sensitivity is −9.763 nm/m−1 and −12.787 nm/m−1 respectively. In the propulsion curvature range of 0–0.94 m−1, the transmission spectrum exhibits blue shift, and the curvature sensitivity can be up to −9.261 nm/m−1 and −9.411 nm/m−1, respectively. The sensor is easily fabricated and has high sensitivity, and demonstrates good application prospects in curvature measurement fields such as 3D shape reconstruction and geological monitoring.

Red-diode-clad-pumped Er3+/Dy3+ codoped ZrF4 fiber: A promising mid-infrared laser platform.

We report, for the first time, to the best of our knowledge, mid-infrared (mid-IR) laser generation, from a red-diode-clad-pumped Er3+/Dy3+ codoped ZrF4 fiber laser. A free-running laser at ∼3.4 µm, mainly from the 4F9/2→4I9/2 transition of Er3+, directly excited by a 659-nm laser diodehas been achieved at room temperature with a maximum power of 0.8 W and 8.8% slope efficiency. In this system, the long-lived 4I11/2 and 4I13/2 states are rapidly depopulated by energy transfer to the codoped Dy3+ ions and energy transfer upconversion between the Er3+ ions, resulting in the accelerated recycling of ions. Additionally, the free-running dual-wavelength operation state at ∼3.3 and ∼3.5 µm is also observed, producing a total maximum power of 0.95 W with 10.7% slope efficiency, representing the first watt-class output from a diode-pumped rare-earth-doped fiber laser far beyond 3 µm. By employing a diffraction grating, continuous spectral tuning across the 642-nm range from 3053.9 to 3695.9 nm has been demonstrated. The proposed scheme provides, to the best of our knowledge, a promising new platform for laser generation in the mid-IR region of 3-4 µm.

Design Optimization and Characterization of Cold Neutron Imaging Detector Based on Novel Gadolinium Scintillation Glass Fiber Arrays and Infinity Corrected Optics

The use of scintillation glass fiber array in the reported cold neutron imaging detector can suppress lateral spreading of the scintillation light effectively and achieve a high spatial resolution while maintaining high detection efficiency. Theoretical analysis and experiments were combined to investigate influencing factors on the spatial resolution, the imaging contrast, the signal-to-noise ratio (SNR), and the detection efficiency with a cold neutron imaging detector made of new gadolinium scintillation glass fiber array and an infinity corrected optical readout system. The experiments were carried out on the Cold Neutron Radiography Facility at China Academy of Engineering Physics (CAEP). The cold neutron imaging detector made of 0.3-mm-thick Tb3+/Ce3+ co-doped Gd2O3 scintillation glass fiber array with a fiber diameter of 6 mm achieved a spatial resolution of 28.8 lp/mm (17.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> ), an SNR of 28.6:1, and a cold neutron detection efficiency of 31.6%, i.e., a cold neutron absorption efficiency of 81.0%.

Improved Fluorescence and Gain Characteristics of Er-Doped Optical Fiber with PbS Nanomaterials Co-Doping.

Er-doped optical fiber (EDF) with ultra-broad gain bandwidth is urgently needed given the rapid advancement of optical communication. However, the weak crystal field of the host silica glass severely restricts the bandwidth of traditional EDF at 1.5 μm. In this study, we theoretically explored the introduction of PbS nanomaterials in the silica network assisted with the non-bridging oxygen. This can significantly increase the crystal field strength of Er3+ ions in the local structure, leading to their energy level splitting and expanding the fluorescence bandwidth. Additionally, the PbS/Er co-doped optical fiber (PEDF) with improved fluorescence and gain characteristics was fabricated using modified chemical vapor deposition combined with the atomic layer deposition technique. The presence of PbS nanomaterials in the fiber core region, which had an average size of 4 nm, causes the 4I13/2 energy level of Er3+ ions to divide, increasing the fluorescence bandwidth from 32 to 39 nm. Notably, the gain bandwidth of PEDF greater than 20 dB increased by approximately 12 nm compared to that of EDF. The obtained PEDF would play an important role in the optical fiber amplifier and laser applications.

Harmonic Dissipative Soliton Resonance in an Er/Yb Co-Doped Fiber Laser Based On SESAM

Fundamental and harmonic mode-locking in the dissipative soliton resonance (DSR) regime is experimentally investigated in a net-normal-dispersion Er/Yb co-doped fiber laser based on the semiconductor saturable mirror (SESAM), where an equivalent narrow-band spectral filter is used for triggering multi-pulsing. By monotonically increasing the pump power with the fixed polarization controller (PC), the fundamental mode-locking operation of DSR pulses can be transformed into the harmonic mode-locking (HML) under the specific conditions. The main reason is the peak-power-clamping effect induced by the combined effects of the spectral filtering and saturable absorption of the SESAM at higher pump levels, which is applied to achieve the HML in the DSR regime for the first time. The DSR pulse broadens linearly with the pump power in a certain range, no matter whether it is in the fundamental mode-locking or HML state. By incorporating the dispersion compensation fiber (DCF) with different lengths, the pulse characteristics are discussed and compared in detail. The enhanced nonlinearity caused by increasing DCF length can lead to higher orders of HML pulses and even the generation of noise-like pulses (NLPs) with a long-enough DCF.

Broadband high-gain Tm3+/Ho3+ co-doped germanate glass multimaterial fiber for fiber lasers above 2 µm.

High-gain Tm3+/Ho3+ co-doped optical fibers are urgently desired for high-repetition-rate mode-locked fiber lasers at >2 µm. Here, Tm3+/Ho3+ co-doped germanate glass with low hydroxyl (OH-) content was prepared by the conventional melt-quenching method combined with the reaction atmosphere procedure (RAP) dehydration technique. The doping concentrations of Tm2O3 and Ho2O3 are 2.5 mol.% (7.1 wt.%) and 0.25 mol.% (0.7 wt.%), respectively. Thanks to the high Tm3+ doping (7.1 wt.%) and low energy transfer efficiency (19.8%) between Tm3+ and Ho3+ ions, it enables achieving broadband and high-gain performance in the 2 µm region. Then a silicate-clad Tm3+/Ho3+ co-doped germanate core multimaterial fiber was successfully drawn by using the rod-in-tube method, which has a broadband amplified spontaneous emission (ASE) with a full width at half-maximum (FWHM) of 247.8 nm at 2 µm. What is more, this new fiber has a high gain per unit length of 4.52 dB/cm at 1.95 µm. Finally, an all-fiber-integrated passively mode-locked fiber laser was built by using this broadband high-gain fiber. The mode-locked pulses operate at 2068.05 nm, and the fundamental repetition rate is up to 4.329 GHz. To the best of our knowledge, this is the highest fundamental repetition rate for the all-fiber passively mode-locked fiber laser above 2 µm. These results suggest that the as-drawn multimaterial fibers with broadband high-gain characteristics are promising for high-repetition-rate ultrafast fiber lasers.

Fabrication and optical properties of Tm3+/Ho3+ co-doped lanthanum aluminosilicate photonic crystal fiber for 2 μm fiber lasers

In this study, the Tm3+/Ho3+ co-doped lanthanum aluminosilicate glass was prepared using the melt-quenching method. The absorption and emission properties of glass were studied. A Tm3+/Ho3+ co-doped lanthanum aluminosilicate photonic crystal fiber (PCF) was fabricated using the stacking and drawing method. The PCF structure effectively enhanced the laser performance and generated laser emission centered at 2051 nm. The max output power of the PCF laser was 256 mW under existing conditions and the optical-to-optical efficiency was 6.37%. In addition, the broadband luminescence characteristics strongly influenced by the length of fibers were presented. The results indicated that the Tm3+/Ho3+ co-doped lanthanum aluminosilicate PCF could be potentially used for 2 μm fiber lasers and amplifiers.

Radiation-Resistant Er-Doped Fiber Based on Ge-Ce Co-Doping

We investigated the radiation responses of Ge-Ce co-doped erbium-doped fibers (EDFs) under gamma radiation with a dose up to 1000 Gy and a dose rate of 0.2 Gy/s. Three EDFs with low or high concentrations of Ge or Ce were fabricated by modified chemical vapor deposition (MCVD). The absorption spectra and amplification performance of the three Ge-Ce co-doped EDFs before and after radiation were tested and analyzed in detail. The radiation-induced absorption (RIA) can be dramatically weakened by heavily co-doping Ge and Ce, and 0.8 dB radiation-induced gain degradation at 1550 nm was obtained in the erbium-doped fiber amplifier (EDFA) with heavy Ge and Ce doping at a dose of 1000 Gy. Furthermore, the possible mechanism of Ce and Ge effects on radiation tolerance enhancement is discussed. Relevant results indicate that the Ge-Ce co-doped EDF has significant performance improvements in radiation resistance, making it ideal for applications in harsh radiation environments.

Passively high-power Q-switching in Er- and Er/Yb doped fiber with CdTe

In this work, Cadmium Telluride (CdTe) thin-film was demonstrated as a saturable absorber (SA) to induce Q-switching in the erbium-doped fiber laser (EDFL) and erbium-ytterbium co-doped fiber laser (EYDFL) cavities. CdTe thin film was prepared by the liquid-phase exfoliation method and sandwiched between two fiber ferrules to complete the fiberized SA assembly. Firstly, the CdTe-SA was inserted into the EDFL cavity and stable Q-switched pulses were observed at a threshold pump power of 88mW. The shortest pulse width and the highest repetition rate measured for the EDFL cavity were 6.10 ± 0.02 μs and 42.3 ± 1.3 kHz respectively, at a maximum pump power of 295 mW. At a maximum pump power of 295 mW, the highest average output power produced by the Q-switched pulses in the EDFL cavity was 0.15 mW. Meanwhile, Q-switched pulses in the EYDFL cavity self-start at the threshold pump power of 1.4 W. The maximum repetition rate obtained was 99.5 ± 1.5 kHz and a pulse width of 2 μs at a maximum pump power of 3 W. At this pump power, the highest average output power produced by the Q-switched pulses in the EYDFL cavity was 70.0 ± 0.2 mW. This is the first demonstration of a high average power passively Q-switched fiber laser operating in the C-band employing EDF and EYDF as the gain medium and CdTe thin-film as SA that we are aware of.

Cladding-Pumped Er/Yb-Co-Doped Fiber Amplifier for Multi-Channel Operation

Cladding-pumped erbium (Er3+)/ytterbium (Yb3+)-co-doped fiber amplifiers are more advantageous at high output powers. However, this amplification technique also has potential in telecom-related applications. These types of amplifiers have complex properties, especially when considering gain profile and a pump conversion efficiency. Such metrics depend on the doped fiber profile, absorption/emission spectra, and the input signal power. In this context, we design, build and characterize an inhouse prototype of cladding-pumped Er3+/Yb3+-co-doped fiber amplifier (EYDFA). Our goal is to identify the EYDFA configuration (a co-doped fiber length, pump power, input signal power) suitable for signal amplification in a multichannel fiber-optic transmission system with a dense wavelength allocation across the C-band (1530–1565 nm). Our approach involves experimentally determining the Er3+/Yb3+-co-doped fiber’s parameters to be used in a simulation setup to decide on an initial EYDFA configuration before moving to a laboratory setup. An experimental EYDFA prototype is tested under different conditions using a 48-channel dense wavelength division multiplexing (DWDM, 100 GHz) system to evaluate the absolute gain and gain uniformity. The obtained results allow the cladding pump amplifier’s suitability for wideband signal amplification to be assessed. The developed prototype provides &gt;21 dB of gain with a 12 dB ripple within 1534–1565 nm. Furthermore, we show that the gain profile can be partially flattened out by using longer EYDF spans. This enhances signal amplification in the upper C-band in exchange for a weaker amplification in the lower C-band, which can be marginally improved with higher pump powers.

Sub-Second Joule-Heated RuO2-Decorated Nitrogen- and Sulfur-Doped Graphene Fibers for Flexible Fiber-type Supercapacitors.

Graphene-based fiber-shaped supercapacitors (FSSCs) have received considerable attention as potential wearable energy storage devices owing to their simple operating mechanism, flexibility, and long-term stability. To date, energy storage capacities of supercapacitors have been significantly improved via strategies such as heteroatom doping and the incorporation of pseudocapacitive metal oxides. Herein, we develop a novel and scalable direct-hybridization method that combines heteroatom doping and metal oxide hybridization for the fabrication of high-performance FSSCs. Using porous and highly conductive nitrogen and sulfur co-doped graphene fibers (NS-GFs) as self-heating units, we successfully convert ruthenium hydroxide anchored to the surface into ruthenium oxide nanoparticles after programmed sub-second electrothermal annealing without structural damage of the fibers. The resulting fibers show an increased gravimetric capacitance of 68.88 F g-1 compared to that of the pristine NS-GF (8.32 F g-1), excellent cyclic stability maintaining 96.67% of the initial capacitance after 20 000 continuous charging/discharging cycles, and good mechanical flexibility. The findings of this work advocate a successful Joule heating strategy for preparing high-performance graphene-based metal oxide hybrid FSSCs for use in energy storage applications.

Investigation of radiation induced static mode degradation in Yb-Ce co-doped pulsed fiber amplifiers

We report on an experimental investigation of radiation induced static mode degradation in Yb-Ce co-doped pulsed fiber amplifiers. For investigating the impact of irradiation on beam quality, radiation-darkened fibers were irradiated by gamma rays. The laser properties of three types of fibers were investigated. With the pump power increased, static mode degradation appeared: M2 factor raised significantly and the output beam profile transformed from LP01 into LP11 shape without high-frequency component. The threshold of static mode degradation decreased with irradiation dose, and related to Yb-Ce co-doped fiber compositions. The doping of Ce benefits to the improvement of the static mode degradation threshold: in the case of the Ce concentration increasing by 35.5%, SMD threshold rose by 16% at most.

Extended L-band few-mode Er/Yb Co-doped fiber amplifier with a cladding-pumped pseudo-two-stage configuration.

Spatial division multiplexing (SDM) is one of the most important technologies that may help to solve the future capacity crisis. However, to date, SDM optical amplification is still a challenge for its application. Herein, we numerically and experimentally demonstrated a few-mode Er/Yb co-doped fiber amplifier (FM-EYDFA) for extended L-band operation. A double cladding Er/Yb co-doped fiber was fabricated to expand the L-band bandwidth and a novel, to the best of our knowledge, cladding-pumped pseudo-two-stage amplification configuration was proposed to enhance the L-band gain. With an initial signal power of -16.8 dBm and an injected pump power of 8.8 W at 940 nm, the 20-dB gain range was covered to 1620 nm for two-mode groups of LP01 and LP11. Importantly, the average gain of 25 dB and average differential modal gain (DMG) of <1 dB were obtained in the wavelength range of 1570-1620 nm for all modes. Our results suggest that the cladding-pumped pseudo-two-stage amplifier based on Er/Yb co-doped fiber providing low DMG, and broad bandwidth has a great potential for increasing the future SDM capacity.