Fiber Amplifier Applications Research Articles

Broadband 27 μm amplified spontaneous emission of Er^3+ doped tellurite fibers for mid-infrared laser applications

Er3+ doped tellurite fibers have been fabricated using a convenient suction technique. Different scanning calorimetry (DSC), Electro-probe micro-analyzer (EPMA), Raman, steady and dynamic luminescence spectra were performed to investigate their thermal, structure, and luminescent properties. Broadband 2.7 μm amplified spontaneous emission (ASE) emission with concurrent 1.5 μm and visible up-conversion emissions have been achieved in fibers with various lengths upon the excitation of 980 nm laser diode (LD). A quantitative study of the spectroscopic properties has been further analyzed in detail according to the Jude-Ofelt model, rate equation, and Dexter’s theory to evaluate the competitive relationship among them. The desirable spectroscopic characteristics associated with excellent thermal stability and mechanical properties indicate that the Er3+ doped tellurite fibers are excellent host matrices for 2.7 μm lasing and may provide applications in mid-infrared fiber lasers and amplifiers.

Preparation of Yb2O3 submicron- and nano-materials via electrospinning

Yb2O3 nano- and submicron-materials were prepared via electrospinning an homogeneous solution obtained by mixing ytterbium acetylacetonate with cellulose acetate in 1:1 acetyl acetone (2,4-pentanodione) and glacial acetic acid, followed by heat treatments for 2h in air atmosphere at temperatures from 550°C to 850°C. The electrospinning procedure was carried out at 15kV, with a tip to collector distance of 10cm. Thermogravimetric analysis of the electrospun materials indicates their complete decomposition and oxidation below 425°C, with a total weight loss of ~92%. The Williamson–Hall and the Brunauer−Emmett−Teller methods, and scanning and transmission electron microscopy observations were used to characterize the grain size and morphology of the samples. An initial very small grain size (<100nm) and high porosity were observed in the samples treated at 550°C, which is related to the important total weight loss. Further heat treatments at higher temperatures lead to the grain growth and agglomeration, increasing the average size to submicron dimensions. Due to their easy grain size tuning, these materials are particularly suitable for applications in fiber amplifiers, fiber optic technologies and lasers.

Enhanced 1.8 µm emission in Cr3+/Tm3+ co-doped fluorogermanate glasses for a multi-wavelength pumped near-infrared lasers

Cr3+/Tm3+ co-doped fluorogermanate glasses were prepared by melt-quenching technique, and their luminescent properties were investigated under excitation of Xenon lamp and 808 nm laser diode, respectively. Through strong sensitization of Cr3+, an enhanced 1.8 µm emission band of Tm3+: 3F4→3H6 can be achieved in an extremely extended excitation band of 380-900 nm. The possible energy transfer mechanism between Cr3+ and Tm3+ is rationally discussed. On the basis of experimental data, the highest energy transfer efficiency is up to 91.70%. Our results suggest this efficient Cr3+/Tm3+ co-doping system provides a selective pump mechanism for obtaining 1.8 µm laser and thus shows attractive applications in near-infrared fiber lasers and amplifiers.

Femtosecond-Pulse Fiber Based Amplification Techniques and Their Applications

Three kinds of pulse amplification techniques including chirped-pulse amplification (CPA), parabolic pulse amplification, and divided-pulse amplification (DPA) based on rare-earth doped fiber gain medium are reviewed. Large core area fiber and cladding-pumping technique compose the foundation of high average power, high pulse energy fiber CPA technology. Femtosecond pulses have been demonstrated at average powers of up to 830 W, pulse energies of up to 2.2 mJ and compressed pulse duration of 23 fs from different fiber CPA systems. The state-of-the-art performance of fiber CPA system to date is the simultaneous generation of 530 W, 1.3 mJ compressed femtosecond pulses at 400 kHz repetition rate. The balance between fiber gain, dispersion and nonlinearity is required for the self-similar propagation and thus the formation of pulses with parabolic intensity profile. Sub-33 fs pulses were demonstrated from a gain-cascaded parabolic amplification system. A newly emerging DPA technique is also reviewed. In addition, the applications of pulsed fiber amplifiers in the areas of supercontinuum generation and material micromachining system are also introduced.

Enhanced thermal stability of oleic-acid-capped PbS quantum dot optical fiber amplifier

Poor thermal stability has remained a severe obstacle for practical applications of optical fiber amplifiers based on quantum dots (QDs). We demonstrate that thermal stability at elevated temperatures can be achieved by using oleic-acid-capped QDs. Optical fiber amplifiers using oleic-acid-capped QDs for the gain medium exhibited stable gain of more than 5 dB at 1550 nm between 25 °C and 50 °C that did not degrade upon cooling. In contrast, fiber amplifiers employing oleylamine-capped QDs exhibited reduced gain when heated and subsequently cooled.

Large mode area modified clad leakage channel fibers with low bending and higher differential losses

In this work, a simple design for all-solid large mode area leakage channel fibers with asymmetric cladding has been proposed to achieve effectively single mode operation through low index doped rods of two different diameters for high power fiber lasers and amplifier applications. Through numerical simulations, carried out by a full-vectorial finite-element method based solver, the modal properties of the proposed design have been investigated and the results have confirmed that the proposed fiber exhibits low fundamental mode bending loss and a very high differential ratio between the fundamental and higher order modes at practically allowable bending radii of 5–15 cm. The effective mode area of the fundamental mode at 1064 nm is 1974.2 μm2 for the straight fiber and shrinks when the fiber is bent at different radii. We have also numerically investigated the mode area enhancement under bent conditions by introducing a microsized center doped capillary in the fiber core.

Effect of alkali metal oxides R2O (R=Na, K) on 1.53 μm luminescence of Er3+-doped Ga2O3-GeO2 glasses for optical amplification

This paper reported the thermal stability and spectroscopic properties of Ga2O3-GeO2-Na2O-K2O (GGNK) glasses doped with Er3+. The GGNK glasses were characterized by differential scanning calorimetry (DSC), Raman spectra, absorption and infrared-visible fluorescence spectra. Measured DSC result showed that these glasses possessed an excellent stability (ΔT=188.6 °C). The relationship between glass composition and Judd-Ofelt intensity parameters and other optical properties of Er3+, such as the absorption and stimulated emission cross-sections, were clarified. Meanwhile an intense broadband 1.53-μm emission with a full width at half- maximum of 51 nm and peak emission cross-section of 9.32×10−21 cm2 of Er3+-doped GGNK glass was obtained upon 980 nm diode-laser excitation. Effects of K2O replacing Na2O on the thermal stability and spectroscopic properties were investigated. It was found that the incorporation of K2O into Er3+-doped Ga2O3-GeO2-Na2O glass could effectively improve the 1.53 μm emission luminescence. The results showed that GGNK glass might be more attractive host material for their application in C-band optical fiber amplifiers.

Synthesis and Characterization of Yttrium Titanate and Er doped Yttrium Titanate Nanofibers

ABSTRACTYttrium titanate belongs to a family of compounds called pyrochlores with significant properties such as ionic conduction, optical non-linearity and radiation tolerance that have resulted in applications thermal barrier coatings, high-permittivity dielectrics, and materials for safe disposal of actinide-containing nuclear waste, and hydrogen storage material. The application of these materials in ODS ferritic steels, photocatalytic water splitting and a more efficient host material than TiO2 for Er3+ luminescence have been evaluated. ErxY2-xTi2O7 has tremendous applications in fiber amplifiers, integrated optical devices and selective emitters for thermophotovoltaic applications. Since 1-D nanostructures are deemed to be important building blocks for future optical and optoelectronic nanodevices, we have used electrospinning methods to synthesize nanofibers and freestanding, non-woven nanofibers membranes of single phase yttrium titanate and ErxY2-xTi2O7 (Er/(Ti+Er) at. ratio= 0 -15 %) with diameters less than 150 nm and have characterized the physical, thermal and optical properties of these nanofibers.

Luminescence Properties of Er&lt;sup&gt;3+&lt;/sup&gt;-Doped Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-GeO&lt;sub&gt;2&lt;/sub&gt;-Bi&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-R&lt;sub&gt;2&lt;/sub&gt;O (R=Na and K) for 1.53 μm Fiber Amplifier

An intense broadband 1.53-μm emission with a full width at half-maximum of 51.2 nm and peak emission cross-section of 8.58×10-21 cm2 of Er3+-doped Ga2O3-GeO2-Bi2O3-R2O (R= Na+, K+) glass have been obtained upon 980 nm diode-laser excitation. Effects of alkali metal ions on the thermal stability and spectroscopic properties of Er3+-doped Ga2O3-GeO2-Bi2O3 glass have been investigated. It is found that the incorporation of Na+ replacing K+ into Er3+-doped Ga2O3-GeO2-Bi2O3 glass can effectively improve the 1.53-μm emission and deduce upconversion luminescence .The results show that Ga2O3-GeO2-Bi2O3-Na2O glass might be an attractive host material for their application in C-band optical fiber amplifiers.

Design and analysis of dual-shape-core large-mode-area optical fiber

We present a large effective area fiber design using dual-shape core (DSC) fiber. The fiber is essentially a depressed-index clad fiber with a dual-shape-core consisting of a large central core and a small slightly lower-index side core. The refractive indices of the two cores are so chosen as to perfectly guide the fundamental mode. All the higher-order modes of the fiber are leaky. The fiber shows large-mode-area single-mode operation by higher-order modes discrimination. We have analyzed the structure by using the transfer matrix method. Our numerical simulation results suggest that the DSC fiber can have single-mode operation with effective mode area as large as 580 μm2 and low bending loss. The bending loss of the fiber could be brought down by more than 2 orders of magnitude compared to the corresponding step-index fiber. We also show that the mode field area is relatively insensitive to design parameters in comparison to the leakage loss of the mode. The fiber is amenable to fabrication by modified chemical vapor deposition technology and is expected to find applications in high power fiber lasers and amplifiers.

Detailed investigation of self-imaging in largecore multimode optical fibers for application in fiber lasers and amplifiers

Properties of the self-imaging effect based on multimode interference (MMI) in large-core passive optical fibers are investigated and analyzed in detail, with the purpose of using multimode active fibers for high power single-transverse-mode emission. Although perfect self-imaging of the input field from a standard single-mode fiber (SMF-28) in a multimode fiber becomes practically impossible as its core diameter is larger than 50 microm, a quasi-reproduction of the input field occurs when the phase difference between the excited modes and the peak mode inside the multimode fiber is very small. Our simulation and experimental results indicate that, if the length of the multimode fiber segment can be controlled accurately, reproduction of the input field with a self-imaging quality factor larger than 0.9 can be obtained. In this case, a low-loss hybrid fiber cavity composed of a SMF-28 segment and a very-large-core active multimode fiber segment can be built. It is also found that for the hybrid fiber cavity, increasing the mode-field diameter of the single-mode fiber improves both the self-imaging quality and the tolerance on the required length accuracy of the multimode fiber segment. Moreover, in this paper key parameters for the design of MMI-based fiber devices are defined and their corresponding values are provided for multimode fibers with core diameters of 50 microm and 105 microm.

Novel Bi-doped glasses for broadband optical amplification

Broadband infrared luminescence is observed in various Bi-doped oxide glasses prepared by conventional melting-quenching technique. The absorption spectrum of the Bi-doped germanium oxide glass consists of five broad peaks at below 370, 500, 700, 800 and 1000 nm. The fluorescence spectrum exhibits a broad peak at about 1300 nm with full width at half maximum (FWHM) of more than 300 nm when excited by an 808 nm laser diode. The fluorescence lifetime at room temperature decreases with increasing Bi2O3 concentration. Influence of the glass composition and melting atmosphere on the fluorescence lifetime and luminescent intensity is investigated. The mechanism of the broadband infrared luminescence is suggested. The product of stimulated emission cross-section and lifetime of the Bi-doped aluminophosphate glass is about 5.0 X 10(-24) cm(2) s. The glasses might be promising for applications in broadband optical fiber amplifiers and tunable lasers. (c) 2007 Elsevier B.V. All rights reserved.

Spectroscopic Properties of Er3+/Yb3+-codoped PbO–Bi2O3–Ga2O3–GeO2 Glasses

We investigate the spectroscopic properties of the 1.5-microm emission from the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions in PbO-Bi(2)O(3)-Ga(2)O(3)-GeO(2) glasses for applications in broadband fiber amplifiers. The measured emission peak locates at 1,532 nm with a full width at half-maximum of approximately 45 nm. The glasses exhibit a large stimulated emission cross-section of 0.89 x 10(-20) cm(2) and a large FWHM x sigma(e)(peak) product of 40.0. Infrared-to-green upconversion occurs simultaneously upon excitation of the 1.5-microm emission with a commercially available 980 nm laser diode. The green-upconversion intensity has a quadratic dependence on incident pump laser power, indicating a two-photon process. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of the (2)H(11/2) of Er(3+). The results indicate the possibility towards the development of lead-bismuth-gallate-germanate based glasses as photonics devices.

Novel alkaline-free Er 3+-doped fluorophosphate glasses for broadband optical fiber lasers and amplifiers

Two sets of Er 3+-doped alkaline-free glass systems, MgF 2–BaF 2–Ba(PO 3) 2–Al(PO 3) 3 (MBBA) and Bi(PO 3) 3–Ba(PO 3) 2–BaF 2–MgF 2 (BBBM), have been prepared and investigated with the aim of using them as active media. Radiative lifetimes ( τ rad) and branching ratios ( β) have been obtained for the excited states of Er 3+. The absorption spectra were recorded to obtain the intensity parameters ( Ω t ) which are found to be Ω 2 = 4.47 × 10 −20 cm 2, Ω 4 = 1.31 × 10 −20 cm 2, Ω 6 = 0.81 × 10 −20 cm 2 for the MBBA system and Ω 2 = 4.03 × 10 −20 cm 2, Ω 4 = 1.34 × 10 −20 cm 2, Ω 6 = 0.53 × 10 −20 for the BBBM system, respectively. The emission cross-section for the 4I 13/2 → 4I 15/2 transition is determined by the Fuchtbauer–Ladenburg method and found to be 2.35 × 10 −20 cm 2 and 3.54 × 10 −20 cm 2 for the MBBA and BBBM system, respectively. Comparison of the measured values to those of Er 3+ transitions in other glass hosts suggests that our new glass systems are good candidates for broadband compact optical fiber and waveguide amplifier applications.

Laser-diode-excited intense luminescence and green-upconversion in erbium-doped bismuth–germanate–lead glasses

We investigate the spectroscopic properties of the 1.5-μm emission from the 4I 13/2 → 4I 15/2 transition of Er 3+ ions in bismuth–germanate–lead glasses for applications in broadband fiber amplifiers. The emission peak locates at 1532 nm with a full width at half-maximum (FWHM) of ∼65 nm. The measured lifetime and the calculated emission cross-section of this transition are 3.3 ms and 8.66 × 10 −21 cm 2, respectively. IR-to-green-upconversion occurs simultaneously upon excitation of the 1.5-μm emission with a commercially available 980 nm laser diode. Effects of PbF 2 content on the thermal stability, structure and spectroscopic properties of Er 3+-doped bismuth–germanate–lead glasses have been examined. We find that the substitution with PbF 2 provides a couple of potentials: shortening the UV cutoff band and decreasing the phonon energy of host glasses. Codoping of Yb 3+ significantly enhances both the green-upconversion and 1.5-μm emission intensity by means of a nonradiative Yb 3+ → Er 3+ energy transfer. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of the 2H 11/2 level, which is an emitting level of the green-upconversion of Er 3+. The results indicate the possibility towards the development of bismuth–germanate–lead based glasses as photonics devices.

High Quantum Efficiency and High Concentration Erbium-Doped Silica Glasses Fabricated by Sintering Nanoporous Glasses

A new method was used to prepare erbium-doped high silica (SiO 2 > 96%) glasses by sintering nanoporous glasses. The concentration of erbium ions in high silica glasses can be considerably more than that in silica glasses prepared by using conventional methods. The fluorescence of 1532 nm has an FWHM (Full Wave at Half Maximum) of 50 nm, wider than 35 nm of EDSFA (erbium-doped silica fiber amplifer), and hence the glass possesses potential application in broadband fiber amplifiers. The Judd-Ofelt theoretical analysis reflects that the quantum efficiency of this erbium-doped glass is about 0.78, although the erbium concentration in this glass (6 × 10 3) is about twenty times higher than that in silica glass. These excellent characteristics of Er-doped high silica glass will be conducive to its usage in optical amplifiers and microchip lasers.

Experimental demonstration of novel end-pumping method for double-clad fiber devices

We present experimental demonstration of an end-pumping scheme based on splicing the multimode pump and single-mode signal fibers directly to a double-clad fiber with a tailored cross section. The method is used to pump a double-clad, erbium- and ytterbium-doped, fiber ring laser. The efficiency of the end-pumping method is tested by determining the slope efficiencies of the fiber ring laser and the fiber laser in a Fabry-Perot configuration. Comparable slope efficiencies are found when both laser configurations have similar output coupler ratios. The developed pumping scheme and double-clad fiber can find applications in cost-effective power fiber amplifiers and lasers.

Preparation and spectroscopic properties of Er3+-doped high silica glass fabricated by sintering nanoporous glass

A compact nonporous high silica (SiO2%>96%) glass containing 3400 ppm Er3+ ions, which was about ten times higher than that in Er-doped silica fiber amplifier (EDSFA), was synthesized by sintering porous glass immersed into erbium nitrate solution. The 1532 nm fluorescence has a FWHM (Full Width at Half Maximum) of 45 nm wider than that of EDSFA and possesses the glass with potential application in broadband fiber amplifiers. The Judd–Ofelt theoretical analysis reflects that Er3+ ions are located in a higher covalent environment which are comparable to those of aluminosilicate glass.

Grating stabilization design for high-power 980-nm semiconductor pump lasers

Wavelength stabilization of high-power pump lasers for fiber amplifier applications involves complex interactions between the laser chip and the fiber Bragg grating (FBG). We present a comprehensive theoretical model for the window of operation in the coherence collapse (CC) regime while maintaining wavelength locking in 980-nm FBG-stabilized pumps. Experimental data from the development of a 500-mW grating stabilized pump verifies the theory. We also provide the first evidence that the critical feedback distance for CC operation of longer laser diode chips is sensitive to detuning.

Refinement of Er3+-doped hole-assisted optical fiber amplifier

This paper deals with design and refinement criteria of erbium doped hole-assisted optical fiber amplifiers for applications in the third band of fiber optical communication. The amplifier performance is simulated via a model which takes into account the ion population rate equations and the optical power propagation. The electromagnetic field profile of the propagating modes is carried out by a finite element method solver. The effects of the number of cladding air holes on the amplifier performance are investigated. To this aim, four different erbium doped hole-assisted lightguide fiber amplifiers having a different number of cladding air holes are designed and compared. The simulated optimal gain, optimal length, and optimal noise fig. are discussed. The numerical results highlight that, by increasing the number of air holes, the gain can be improved, thus obtaining a shorter amplifier length. For the erbium concentration NEr=1.8x1024 ions/m3, the optimal gain G(Lopt) increases up to ~2dB by increasing the number of the air holes from M=4 to M=10.