Optical Amplifier Applications Research Articles

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.

Optical properties and crystallization behavior of 45GeS2·30Ga2S3·25Sb2S3 chalcogenide glass

Glass-ceramics containing Ga2S3 nano-crystals were reproducibly fabricated from the 45GeS2·30Ga2S3·25Sb2S3 chalcogenide glass by heat treatment at 335°C (Tg+30°C) for different durations. The obtained glass-ceramics are still transparent in the IR region and show improved thermal stability. Crystallization mechanism was investigated using the non-isothermal method. The results show that the crystallization rate constant K at 335°C for the Ga2S3 phase is about 2 orders of magnitude larger than that of the second crystallization peak in the DSC curve. So it is easy to control the crystallization process with only Ga2S3 crystallites precipitated. With the above advantages, it has a great potential for drawing infrared transmitting glass-ceramic fibers with improved mechanical properties and enhanced luminescence for application in optical amplifiers.

Engineering lattice matching, doping level, and optical properties of KY(WO4)2:Gd, Lu, Yb layers for a cladding-side-pumped channel waveguide laser

Single-crystalline KY1-x-y-zGdxLuyYbz(WO4)2 layers are grown onto undoped KY(WO4)2 substrates by liquid-phase epitaxy. The purpose of co-doping the KY(WO4)2 layer with suitable fractions of Gd3+ and Lu3+ is to achieve lattice-matched layers that allow us to engineer a high refractive-index contrast between waveguiding layer and substrate for obtaining tight optical mode confinement and simultaneously accommodate a large range of Yb3+ doping concentrations by replacing Lu3+ ions of similar ionic radius for a variety of optical amplifier or laser applications. Crack-free layers, up to a maximum lattice mismatch of ~0.08 %, are grown with systematic variations of Y3+, Gd3+, Lu3+, and Yb3+ concentrations, their refractive indices are measured at several wavelengths, and Sellmeier dispersion curves are derived. The influence of co-doping on the spectroscopy of Yb3+ is investigated. As evidenced by the experimental results, the lattice constants, refractive indices, and transition cross-sections of Yb3+ in these co-doped layers can be approximated with good accuracy by weighted averages of data from the pure compounds. The obtained information is exploited to fabricate a twofold refractive-index-engineered sample consisting of a highly Yb3+-doped tapered channel waveguide embedded in a passive planar waveguide, and a cladding-side-pumped channel waveguide laser is demonstrated.

Synthesis and strong near-infrared fluorescence of LiLa1−xNdx(PO3)4 nanocrystals with high doping concentrations

A series of LiLa(1-x)Nd(x)(PO(3))(4) (LLNP) nanocrystals are synthesized by a combustion method for the first time. With irregular short-rod shapes and an average size of about 70 nm, the LiLa(1-x)Nd(x)(PO(3))(4) nanocrystals exhibit stronger fluorescence emission of 1.8-6.5 times in the doping concentration range of 1 mol% to 100 mol% than Nd(3+) (2.5 wt%) doped phosphate glass, and have a long lifetime of 122 μs for the fully doped nanocrystals. Moreover, the LiLa(1-x)Nd(x)(PO(3))(4) nanocrystals show the lowest lifetime decay rate of 5.09 μs per mol% and a quenching ratio of 10.81%. Considering the above outstanding performances, LiLa(1-x)Nd(x)(PO(3))(4) nanocrystals may have promising applications in optical amplifiers and lasers.

Broadband near-infrared luminescence from transparent glass–ceramics containing Ni2+-doped SrTiO3 nanocrystals

Transparent strontium titanium silicate glass–ceramics (GCs) containing Ni2+-doped SrTiO3 nanocrystals were synthesized by heat treatment method. Absorption spectra confirmed that the coordination environment of Ni2+ ions was changed from the trigonal bipyramid fivefold sites in as-cast glasses to the octahedral sites in the GCs. Upon 980nm laser excitation, the GCs exhibited broadband near-infrared emissions covering 1.1–1.7μm wavelength region with the full width at half maximum (FWHM) of more than 290nm and fluorescent lifetime of up to 735μs, which originated from the 3T2g (3F)→3A2g (3F) transition of octahedral Ni2+ ions in the SrTiO3 nanocrystals. This kind of Ni2+-doped transparent GCs have potential applications in super-broadband optical amplifiers and tunable lasers.

Luminescent character of mesoporous silica with Er2O3 composite materials

Erbium oxide has been successfully incorporated into SBA-15 and different types MCM-41 mesoporous materials via thermal diffusion methods. A series of characterizations were used to characterize the prepared materials. In the prepared host–guest materials, the frameworks of the host materials were kept intact, and the guest erbium oxide mainly located inside the pores of the host materials. The host–guest composite materials showed the luminescent properties, and the luminescent intensities were excellent. Luminescence studies also revealed that the different particle size of the host materials have biggish influence to the luminescence characters. Moreover, the luminescence intensity and luminescence lifetime could be increased by the modification of the mesoporous materials surface. The better luminescent performances made these prepared materials show potential applications in optical amplification, laser systems, or medical diagnostics.

Preparation and Physical Properties of Erbium-Doped Polymer Patterns by Micromolding in Capillaries for Optical Waveguide Amplifiers

Er3+-doped precursor solutions were first prepared using 2,2,3,3,4,4,5,5-octafluoropentyl acrylate as a fluoromonomer, tetrahydrofurfuryl acrylate as a solubility enhancer, Ebecryl 220 as a cross-linking agent, Darocur 4265 as a radical photoinitiator and erbium(III) trifluoromethane sulfonate as an erbium source with various weight ratios. The crosslinked, patterned and erbium-doped fluoropolymer films were fabricated by micromolding in capillaries on glass substrates for planar optical amplifier applications. The fluoropolymer films acting as host materials for the Er3+ ions had excellent transmission properties (more than 90% over the visible and near-infrared regions), high thermal decomposition temperatures (greater than 300°C) and the ability to support high erbium complex concentrations (up to 10 wt% based on the polymer matrix). These results are sufficient for the films to be used in planar optical amplifier applications.

Er3+-doped phosphate glasses with improved gain characteristics for broadband optical amplifiers

Optical properties of Erbium-doped sodium aluminum telluro–phosphate glasses with compositions of 48P2O5–21Na2O–23Al2O3–(8−x)TeO2–(x)Er2O3 (where x=2–7) were investigated. From the measured optical absorption spectra, Judd–Ofelt (JO) analysis has been carried out to predict radiative properties of doped Er3+ ion luminescent levels. The estimated emission cross sections were found to be more than other commonly available short-length optical amplifier (aluminosilicate) glasses. Relative emission intensity enhancement with the increase of Er3+ ion concentration is observed for the laser transition, 4I13/2→4I15/2 (at 1.53μm). Higher emission lifetimes (4.2–6.23ms), higher quantum efficiencies (44–65%) relative at higher Er3+ ion concentrations, high gain bandwidth and gain per unit length at 1.5μm are the most notable features of these glasses for future optical amplifier applications.

Strategies to increase the modal gain in heterogeneously integrated III–V amplifiers on silicon-on-insulator

A novel waveguide shape is proposed to take advantage of the high index contrast in adhesively bonded III–V on silicon-on-insulator (SOI) waveguides for application in on-chip semiconductor optical amplifiers. By decreasing the effective index of the top contact layer, the confinement in the active region can be increased by 70%, boosting the achievable modal gain and reducing the required device length to achieve a certain gain. This technique could reduce the footprint of amplifiers, lasers and other active devices integrated on the SOI platform.

Luminescence Properties of Er<sup>3+</sup>-Doped Ga<sub>2</sub>O<sub>3</sub>-GeO<sub>2</sub>-Bi<sub>2</sub>O<sub>3</sub>-R<sub>2</sub>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.

Enhanced 1.5 μm luminescence lifetime of vacuum deposited erbium-doped organic thin films for optical amplification applications

ABSTRACTInorganic erbium-doped glasses are widely used in telecommunications due to the sharp intra-atomic 4I13/2 → 4I15/2 transition in the 4f orbital of erbium resulting in an emission at ∼ 1.5 μm, which is the low loss window of silica optical fibres. The limited erbium concentration of about 1020 ions/cm3 in inorganic erbium-doped glasses and the low absorption coefficient of the Er3+ ions, imply that relatively long lengths of fibre are required. Organic erbium complexes present higher absorption cross sections due to the photosensitization of erbium by the organic conjugated ligands and broader emission bands than those of the free Er3+ ions. Such properties open the possibility to develop compact, low power and broadband infrared emitting devices. We present the study of an organic fluorinated erbium complex exhibiting 1.5 μm luminescence lifetime of several hundreds of microseconds measured on thin film. The organic complex has been deposited by vacuum sublimation technique. This deposition method allows the realization of an erbium-doped thin film without the help of an organic polymer matrix, which is a potential source of vibrationnal luminescence quenching. We report the synthesis, the sublimation process, and the characterization of the thin films. The chemical structure of the complex is assessed by FTIR, NMR and MALDI-TOF. Chemical integrity of the thin film after vacuum deposition is determined by FTIR. The morphology of the thin film is characterized by X-ray diffraction experiments. The optical properties of the thin film are determined by spectroscopic ellipsometry, UV-Vis-NIR absorption spectroscopy and time resolved NIR photoluminescence spectroscopy.

Fluorescence properties of polyaryletherketone rare earth-coordinated complexes in near-infrared region

Novel rare earth-coordinated polymers were prepared using carboxyl-containing polyaryletherketone (PEK) as the macromolecular ligand and 8-hydroxyquinoline (HQ) as the co-ligand to coordinate with erbium (Er3+), neodymium (Nd3+) and ytterbium (Yb3+), respectively. The FTIR, elemental analysis, inductively coupled plasma, and UV-vis results confirm that the rare earth ions have been attached to the polymer backbone via a coordination bond. The complexes can emit the characteristic near-infrared fluorescence of the corresponding rare earth ions. Moreover, it is found that the synergistic effect of PEK and HQ can significantly enhance the emission intensities. In particular, for PEK-Er3+-HQ, the full width at half maximum (FWHM) of the 4I13/2→4I15/2 transition is up to 78 nm. The combination of strong fluorescence emission in the near-infrared range, high glass transition temperature and wide gain bandwidth provides promising potential for optical amplification applications.

Fabrication and Characterization of Erbium-Doped Fluoropolymer Patterns via UV-Nanoimprint Lithography for Use in Planar Optical Amplifiers

The Er-doped precursor solutions were first prepared using 2,2,3,3,4,4,5,5-octafluoropentyl acrylate as a fluoromonomer, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol diacrylate as a cross-linking agent, poly(2,2,3,3,4,4,4-heptafluorobutyl acrylate) as a binding polymer, Darocure 4265 as radical photoinitiator and erbium(III) trifluoromethane sulfonate as an erbium source with various weight ratios. The crosslinked, patterned and erbium-doped fluoropolymer films were fabricated by UV-nanoimprint lithography on glass substrates for application as planar optical amplifiers. The fluoropolymer films acting as a host material for the Er ions showed excellent transmission properties—more than 80% over the visible and near-infrared regions—a high thermal decomposition temperature greater than 350°C and the ability to support a high Er concentration—up to 10 wt% based on the polymer matrix. These results were good enough for the films to be used in planar optical amplifier applications.

NIR-luminescence from ternary lanthanide [Ho III, Pr III and Tm III] complexes with 1-(2-naphthyl)-4,4,4-trifluoro-1,3-butanedionate

The ligand 1-(2-naphthyl)-4,4,4-trifluoro-1,3-butanedionate (Htfnd) has been employed to synthesize six novel ternary–lanthanide complexes in which the synergic ligands were 1,10-phenanthroline-5,6-dione (dione) and 4,5-diazafluoren-9-one (dafone), respectively. Two series of complexes Ln(tfnd) 3dione and Ln(tfnd) 3dafone (Ln=Ho, Pr, Tm) were obtained. These complexes were characterized by elemental analysis, Fourier Transform Infrared spectra and diffused reflectance. After ligand-mediated excitation, Ln(tfnd) 3dione and Ln(tfnd) 3dafone all show the characteristic NIR luminescence of the corresponding Ln 3+ ions (Ln=Ho, Pr, Tm). This can be attributed to the efficient energy transfer from ligands to central Ln 3+ ions, via an antenna effect. The indirect energy transfer in the complexes has been investigated and the differences in the luminescence intensity between Ln(tfnd) 3dione and Ln(tfnd) 3dafone were discussed in detail. The excellent luminescent performances enable these NIR-luminescent complexes to have potential applications in optical amplification operating at 1300 or 1500 nm.

Vacuum Deposited Erbium-Doped NIR Luminescent Organic Thin Films For 1.5 μm Optical Amplification Applications

AbstractInorganic erbium-doped glasses are widely used in telecommunications due to the sharp intra-atomic 4I13/2 → 4I15/2 transition in the 4f orbital of erbium resulting in an emission at ∼ 1.5 μm, which is the low loss window of silica optical fibres. The limited erbium concentration of about 1020 ions.cm−3 in inorganic erbium-doped glasses and the low absorption coefficient of the Er3+ ions, imply that relatively long lengths of fibre are required. The organic erbium complexes present higher absorption cross sections due to the photosensitization of erbium by organic conjugated ligands and broader emission bands than those of the free Er3+ ion. Such properties open the possibility to develop compact, low power and broadband infrared emitting devices. We present the study of a highly doped organic thin film obtained from organic erbium complexes deposited by a vacuum sublimation technique. This deposition method allows the realization of an erbium-doped thin film without the help of an organic polymer matrix, which is a potential source of vibrationnal luminescence quenching. The ligands used in the present study are fluorinated in order to limit the vibrationnal quenching of the ligand itself, and to increase the volatility of the complexes. In this paper, we report the synthesis, the sublimation process and the characterization of the thin films.

Site Selective Spectroscopy on Erbium Ions in Stoichiometric Lithium Tantalate

Ferroelectric materials such as lithium niobate (LiNbO3) and the isostructural lithium tantalate (LiTaO3) play an important role in integrated optics since they allow the possibility to combine their favourable electro-optical, acousto-optical, and nonlinear properties with the ability to add additional functional groups by doping. Examples are rare earth ions that act as active centres for laser and optical amplifier applications. We present our sites-selective spectroscopic studies on Er3+ doped nearly stoichiometric LiTaO3 that include results about the assignment of excitation and emission peaks to different sites, symmetry properties of these sites, energy transfer among major sites, and up-conversion efficiencies. We compare the results in LiTiO3 with the corresponding ones in the much better studied LiNbO3 host and find that the type of centres and their spectral feature are very similar.

High-energy, kHz-repetition-rate, ps cryogenic Yb:YAG chirped-pulse amplifier

We demonstrate amplification of picosecond laser pulses to 40?mJ at a 2?kHz pulse repetition frequency (PRF) from a two-stage cryogenic chirped-pulse Yb:YAG amplifier, composed of a regenerative amplifier (RGA) and a two-pass booster amplifier. The RGA produces 8.2mJ of energy at 2kHz PRF and 13.2mJ at 1kHz PRF with excellent energy stability (approximately 0.3% rms) and beam quality (M(2)<1.1). Pulse stretching and compression are achieved by using a chirped fiber Bragg grating and a multilayer dielectric grating pair, respectively. Compressed 15?ps pulses from the RGA are obtained with a throughput efficiency of approximately 80% (approximately 6.5 mJ for 2kHz). The booster amplifier further amplifies the pulses to 40mJ at 2kHz PRF, and approximately 32 mJ, approximately 15 ps pulses are expected after compression. The amplifier chain seeded from a femtosecond Yb-fiber laser enables the optical self-synchronization between signal and pump in optical parametric chirped-pulse amplifier applications.

Electrospinning preparation and photophysical properties of one-dimensional (1D) composite nanofibers doped with erbium(III) complexes

1D composite nanofibers of poly(vinylpyrrolidone) (PVP, M W≈60,000) doped with three Er(III) complexes were prepared by electrospinning. They demonstrated strong near-infrared (NIR) photoluminescence (PL) at 1535 nm and ternary Er(TTA) 3Phen (denoted as Er2, where TTA=2-thenoyltrifluoroacetonate; Phen=1,10-phenanthroline) fibers (Er2/PVP) exhibited maximum PL intensity. The crystal structure of Er2 complex has been determined by X-ray diffraction measurements. Er2 doped in fibers exhibited better thermal stability of NIR PL than the pure Er2 complex. These luminescent composite fibers have potential application in optical amplifiers.

Broad gain spectra of single and multiple InGaAsN quantum well systems

AbstractThe optical gain of single and multiple quantum well systems fabricated from InGaAsN/GaAs was investigated. We performed a numerical analysis to find structures which would increase the gain bandwidth for application in semiconductor optical amplifiers and broadband tunable lasers. A 10‐band k · p Hamiltonian was used to calculate TE modal gain spectra. First, we calculated the gain spectra of a single quantum well for varying nitrogen compositions and well widths at fixed carrier density. Next, we calculated the gain spectra for two‐ and three‐quantum‐well systems which used the compositions and sizes of the previously analyzed single wells. The three‐quantum‐well system had an approximate 100% increase of gain bandwidth in comparison with a single quantum well. This increase is due to carefully selected different values of nitrogen compositions in various quantum wells. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Enhanced broadband near-infrared luminescence from Ni in Bi/Ni-doped transparent glass ceramics

Spectral properties of Bi/Ni-doped transparent MgO–Al2O3–Ga2O3–SiO2–TiO2 glass ceramics (GCs) containing spinel solution nanocrystals were investigated. The emission intensity of Ni in Bi/Ni-doped GCs was about 4 times stronger than that of Ni-doped GCs due to energy transfer from Bi to Ni. The Bi/Ni-doped GCs with 0.75 mol% Bi2O3 concentration exhibited a near-infrared emission with full width at half maximum of about 270 nm and a fluorescent lifetime of about 350 µs, making them very promising for applications in broadband optical amplifiers and tunable lasers.