1,720,978 research outputs found
Brightness enhancement limits in pulsed cladding pumped fiber Raman amplifiers
No full textWe analyze theoretically limitations on the brightness enhancement of a multimode pump beam, to be efficiently converted into a diffraction-limited Stokes beam in a cladding-pumped fiber Raman amplifier. For a given minimum Raman pump absorption, parasitic 2nd Stokes generation limits the cladding-to-core area ratio, and thus the brightness enhancement. A W-type fiber acting as a spectral waveguide filter allows for nearly five times larger inner-cladding areas by suppressing the 2nd Stokes. We further analyze limits set by glass damage and indirectly propagation loss, as well as pulse walk-off. A well-designed fiber with 3.5 dB/km propagation loss allows for a pump-to-signal brightness improvement of up to 3600 times both in the pulsed and the cw regime
High power fiber lasers: a review
No full textIn this paper, we summarize the fundamental properties and review the latest developments in high power fiber lasers. The review is focused primarily on the most common fiber laser configurations and the associated cladding pumping issues. Special attention is placed on pump combination techniques and the parameters that affect the brightness enhancement observed in single-mode and multimode high power fiber lasers. The review includes the major limitations imposed by fiber nonlinearities and other parasitic effects, such as optical damage, transversemodal instabilities and photodarkening. Finally, the paper summarizes the power evolution in continuous-wave and pulsed ytterbium-doped fiber lasers and their impact on industrial applications
A fibre optic force sensing method based on the S2 imaging technique
No full textOptical fibres are the ideal sensing platform to measure strain, pressure, temperature, displacement, vibration, torsion, and humidity [1], thanks to their extreme environmental robustness. Since they are made of dielectric material, optical fibres are immune to electromagnetic interference and corrosion, are highly sensitive, and have a very wide operating temperature range. In addition, optical fibre-based sensors can be lightweight while providing easy integration into a wide variety of structures, while being low cost compared to an alternative approach. In particular, fibre Bragg gratings, polarization-maintaining fibres, and multicore fibres [2] are used as force or strain sensors in a broad range of industrial, medical, and military applications
Comparative modelling and design aspects of PANDA PM fiber
No full textIn this study, we investigate the design parameters of a high-birefringence (Hi-Bi) polarization-maintaining (PM) fiber. Our focus is on PANDA-type (Polarization-maintaining AND Absorption-reducing) fiber design that incorporates B2O3-doped silica stress rods. Utilizing the finite-element method (FEM) within the COMSOL Multiphysics software package, we conduct simulations to analyze the fiber's characteristics. We also provide a comprehensive review of common analytical expressions for birefringence and compare our simulation results with theoretical formulas. Our findings reveal a good agreement between simulation and one theoretical expression, while the other two exhibit discrepancies, each of a different nature
High-efficiency multi-spot beam generation with an all-fiber SMF-SCF structure
No full textWe propose an efficient, fully fiber-based method for generating multi-spot beam patterns using single-mode fiber (SMF) and square-core fiber (SCF) structures. This technique leverages multimode interference in the SCF to produce configurable square lattice beam patterns, such as 2×2, 3×3, and 4×4 arrays, by simply adjusting the SCF length. Both simulations and experiments at a wavelength of 1060 nm validate the approach, demonstrating high power uniformity, minimal loss, and excellent stability across beam configurations. Initial testing of multi-spot laser drilling on metal surfaces shows that increased beam spot counts can significantly enhance processing efficiency. This SMF-SCF structure offers substantial potential for scalable, compact, and high-precision applications in photonics, laser manufacturing, and biomedical imaging, where rapid processing and parallel operation are critical
Efficient multibeam generation in square lattices using SMF-SCF structure
No full textWe present a highly efficient method for generating multiple beam spots through the multimode interference within single mode fiber – square core fiber (SMF-SCF) structures. By adjusting the length of SCF, we can achieve diverse beam spot configurations in a square lattice, such as 4×4, 3×3 and 2×2, providing unparalleled flexibility. Through simulations and experimental validations at a wavelength of 1060 nm, our study unveils significant potential for applications in photonics and laser technology
Multispot fiber lasers for material processing applications
No full textWe introduce a new approach for the generation of high-power multi-spot fiber lasers, employing square core fiber segments to enhance the efficiency of material processing. Utilizing an all-fiber strategy with single mode fiber– square core fiber (SMF-SCF) structures, our approach exemplifies notable progress in beam shaping technologies. Through laser drilling experiments on metals, the effectiveness of this technique is demonstrated, promising diverse applications in advanced manufacturing and industrial processes
Dynamic BPM model for transverse modal instability
No full textA new fast dynamic model for TMI investigation is presented and used to study the evolution of the internal powers, inversion and thermal gratings and the impact of relative phase shifts on the amplifier dynamics, showing the prevalence and importance of nonlinearly-induced beat-length variations. The optical field is represented in a modal basis, with overlaps with thermal field components precomputed. This allows optical propagation to be achieved with an efficient Runge-Kutta scheme, with mode coupling represented by a coupling term. This substantially reduces the computational load of the simulation. New features of TMI dynamics are revealed.</p
Tandem cladding-pumping for control of excess gain in ytterbium-doped fiber amplifiers
No full textWe theoretically detail and explain how to control unwanted excess gain for higher order modes in cladding-pumped large-core ytterbium-doped fiber amplifiers operating on the fundamental mode by using a small inner cladding and pumping close to the emission wavelength in a so-called tandem-pump configuration. Such excess gain can otherwise limit the core size. We study this experimentally by comparing the level of amplified spontaneous emission at the edge of the core in a conventional diode-pumped and tandem-pumped large-core ytterbium-doped multimode fiber. We also discuss the potential benefits of tandem pumping in reducing fiber photodarkening
Design, performance, and limitations of fibers for cladding-pumped Raman lasers
Full text linkIn this paper, we present basic design rules for double-clad fibers that enable efficient 1st-Stokes operation of cladding-pumped fiber Raman devices. Limiting factors that we treat include unwanted 2nd-Stokes generation, material damage in the core, pump pulse dispersion, inner-cladding NA, background loss, pulse shape and pump noise. With a well-designed fiber, we calculate that a pump-to-signal brightness enhancement of over 2000 is possible, with certain pump parameters. On experimental work, we report a 100 W cladding-pumped fiber Raman laser at 1120 nm. Furthermore, a double-clad Raman fiber with large-mode area, 40 µm core diameter, pumped by a Q-switched Nd:YAG laser is used to generate Stokes pulses with 1 mJ energy
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