Graded-Index Ytterbium-Doped Optical Fiber Fabricated through Vapor Phase Chelate Delivery Technique

Herein, the fabrication of ytterbium-doped graded refractive-index few-mode fiber (GRIN-FMF) is described for the first time following a vapor phase chelate delivery technique. Investigation is carried out to find out the best possible approach to fabricate the preform. The optimization of the process steps along with composition and associated process parameters leads to a parabolic refractive-index profile with a profile parameter of 2 in the developed fiber. A large core of 30 mu m diameter and a low numerical aperture (NA) of 0.08 with graded distribution of dopant ions is achieved with a good repeatability. Amplification gain of more than 20 dB with good beam quality for pulses with kW peak power without any distortion in temporal, spectral, and spatial profile proves the potential of the fiber for many promising applications

Synthesis and characterization of Tm2O3-doped Lu2O3 nanoparticle suitable for fabrication of thulium-doped laser fiber

Synthesis of Tm2O3-doped Lu2O3 nanoparticle using homogeneous co-precipitation method along with its material/optical characterization is reported. Four different compositions with variation of Tm: Lu ratios are synthesized followed by calcination at different temperatures (800, 1000 and 1200 degrees C) was performed to optimize the synthesis process as well as composition. The XRD analysis indicates steady growth of particle size with increasing calcination temperature and an average particle size of 100 nm was achieved at 1200 degrees C. Pure bixbyite structure was observed for every sample independent of Tm: Lu ratio. The FESEM and HRTEM analysis associated with EDX indicates formation of pure crystalline particles and results are in good agreement with XRD analysis. The photoluminescence spectra observed under 808 nm excitation exhibit characteristic Tm emission peak that extended beyond 2 micron region the intensity of which is strongly depends on Lu: Tm ratio as well as calcination temperature. The overall result reveals that the synthesized material which indicates good thermal stability is a potential doping material for the development of Thulium-doped fiber suitable for eye-safe laser application

Investigation on porous aluminosilicate soot layer for fabrication of specialty optical fiber using VPCD technique

The basic investigation of aluminosilicate porous core layer deposited using Vapour Phase Chelate Delivery (VPCD) technique is presented to optimize soot deposition parameters for subsequent processing to develop specialty optical fiber. Different soot deposition parameters namely vapour phase composition and porous core layer deposition temperature were studied in order to evaluate the change of porous soot layer morphology in terms of average pore size, pore size distribution, and chemical composition with the objective of selecting the optimized aluminosilicate soot structure. The field emission scanning electron microscope (FESEM) investigation reveals that the average pore size of the aluminosilicate soot strongly depends on the selected deposition tem-perature and its value increases from 0.7 mu m to 1.8 mu m for increasing deposition temperature from 1150 degrees C to 1250 degrees C. This average pore size of aluminosilicate soot however, increases significantly with addition of dopants like GeO2 and P2O5 and reaches the value of 3.9 mu m and 5.8 mu m respectively. It is also observed that the aluminium deposition efficiency in porous aluminosilicate soot layer depends on selected deposition temperature and for an increase of 20 degrees C, the deposition efficiency of Aluminium in the soot layer increases by-2.7%. It is also observed that aluminium incorporation efficiency using direct VPCD technique reaches a value of-90% compared to 72% if the process carried out by following deposition of porous soot layer. The observed result could help to achieve better control over the VPCD technique and could be extended to fabricate rare earth doped specialty optical fiber of specific design

Bend Insensitive YB-Doped Fiber Fabricated Through Vapour Phase Doping Process

Bend insensitive newly designed Yb doped silica fiber fabricated using vapor phase doping technique is presented. It exhibits improved transmission characteristics compared to step-index and depressed clad fiber with similar Yb-concentration, besides showing excellent lasing amplification characteristics

Multimode Mamyshev oscillator

We present a spatiotemporally mode-locked Mamyshev oscillator. A wide variety of multimode mode-locked states, with varying degrees of spatiotemporal coupling, are observed. We find that some control of the modal content of the output beam is possible through the cavity design. Comparison of simulations with experiments indicates that spatiotemporal mode locking (STML) is enabled by nonlin- ear intermodal interactions and spatial filtering, along with the Mamyshev mechanism. This work represents a first, to the best of our knowledge, exploration of STML in an oscil- lator with a Mamyshev saturable absorber

Synthesis and characterization of Yb3+activated Lu2O3 nanoparticles doped optical fiber preform for high power laser application

Yb3+-activated Lu2O3 is known to exhibit excellent thermal conductance, which can be a potential candidate to develop high-power laser fiber. Here we report the synthesis of Yb3+-activated Lu2O3 nanoparticles following the homogeneous coprecipitation method along with their material and optical characterization. Five different samples were synthesized using different concentrations of Cetyl Trimethyl Ammonium Bromide (CTAB) as a cationic surfactant, Yb-Lu ratio in the presence/absence of aluminium (Al) as an additional dopant, followed by calcination at different temperatures. Differential thermal analysis (DTA) and thermogravimetry (TG) analysis were performed to optimize the thermal annealing condition while the X-ray diffraction (XRD) analysis shows the formation of a pure bixbyite structure with an average particle size of -15 nm at 800 degrees C that reaches up to -120 nm with increasing calcination temperature to 1400 degrees C. The field emission scanning electron microscope (FESEM) analysis shows nearly cubic morphology while high-resolution Transmission Electron Microscope (HRTEM) analysis confirms the crystalline nature and the average particle size corroborates with the XRD analysis result. The developed nanoparticle was found to exhibit characteristics of Yb-absorption and emission peaks showing no interference with Lu2O3. The emission intensity and fluorescence lifetime of the Yb3+-activated Lu2O3 nanoparticles were found to depend on the Yb concentration, average particle size, and presence of aluminium as a co-dopant. To evaluate the practical application of the developed nanoparticles, an optical preform is developed using synthesized nanoparticles as Yb-source through modified chemical vapor deposition (MCVD) coupled with solution doping (SD) technique and the initial performance of the preform is also reported

Novel Dopant Tailored Fibers Using Vapor Phase Chelate Delivery Technique

The vapor phase chelate delivery (VPCD) technique in conjunction with the modified chemical vapor deposition (MCVD) process is adopted to fabricate fibers with customized doping profiles. The three large-mode area (LMA) step-index fibers with different rare-earth doping profiles in the core region, such as uniform doping, centralized doping, and circumferential doping, are fabricated by optimizing the fabrication parameters. The fibers are tested in a cladding-pumped amplifier configuration and their output beam qualities and signal-to-noise ratio (SNR) are characterized. The investigation reveals that the fiber with centralized doping in the core region exhibits lower M 2 compared with the fibers with uniform and circumferential doping, as it has a lower overlap of the higher-order modes with the doped region. The experimental result is further affirmed through theoretically simulated results. The developed fabrication technique shows potential to fabricate specialty fibers of varied designs, where customized doping profiles are required

Gain-induced Kerr beam cleaning in a femtosecond fiber amplifier

Kerr beam cleaning is a nonlinear phenomenon in graded-index multimode fiber where power flows toward the fundamental mode, generating bell-shaped output beams. Here we study beam cleaning of femtosecond pulses accompanied by gain in a multimode fiber amplifier. Mode-resolved energy measurements and numerical simulations showed that the amplifier generates beams with high fundamental mode content (greater than 30% of the overall pulse energy) for a wide range of amplification levels. Control experiments using stretched pulses that evolve without strong Kerr nonlinear effects showed a degrading beam profile, in contrast to nonlinear beam cleaning. Temporal measurements showed that seed pulse parameters have a strong effect on the amplified pulse quality. These results may influence the design of future high-performance fiber lasers and amplifiers. (c) 2023 Optica Publishing Grou

Recognition-Mediated Light-Up of Thiazole Orange with Cucurbit[8]uril: Exchange and Release by Chemical Stimuli

This article reports a convenient supramolecular strategy to construct fluorescent photoswitchable molecular assemblies between a macrocyclic host, cucurbit[8]uril (CB8), and a fluorogenic dye, thiazole orange (TO). The interaction mechanism and the stable stoichiometric host–guest arrangements have been claimed on the basis of the optical absorption, steady-state and time-resolved fluorescence lifetime and anisotropy measurements, and also the geometry optimization studies. The CB8 recognized TO in its 2:2 stoichiometry exhibited spectacular fluorescence enhancement of the order of 1700 fold, which is the largest directly determined value so far reported for a dye in an organic macrocyclic system. This prospective 2CB8:2TO assembly responded to selected chemical stimuli such as metal ions, adamantylamine, and tryptophan, providing different dissociation mechanisms and demonstrating a controlled exchange and release action desired with such noncovalently linked assemblies. Positively, considering the aqueous solubility and biocompatibility of the host–guest constituents, this methodology can evolve into a general approach to deliver and operate intracellularly functional molecular components under chemical/thermal/optical trigger control, especially for therapeutic applications