There are still very strong interests for power scaling in high power fiber lasers for a wide range of applications in medical, industry, defense and science. In many of these lasers, fiber nonlinearities are the main limits to further scaling. Although numerous specific techniques have studied for the suppression of a wide range of nonlinearities, the fundamental solution is to scale mode areas in fibers while maintaining sufficient single mode operation. Here the key problem is that more modes are supported once physical dimensions of waveguides are increased. The key to solve this problem is to look for fiber designs with significant higher order mode suppression. In conventional waveguides, all modes are increasingly guided in the center of the waveguides when waveguide dimensions are increased. It is hard to couple a mode out in order to suppress its propagation, which severely limits their scalability. In an allsolid photonic bandgap fiber, modes are only guided due to anti-resonance of cladding photonic crystal lattice. This provides strongly mode-dependent guidance, leading to very high differential mode losses. In addition, the all-solid nature of the fiber makes it easily spliced to other fibers. In this paper, we will show for the first time that all-solid photonic bandgap fibers with effective mode area of ~920μm2 can be made with excellent higher order mode suppression.
KEYWORDS: Optical fibers, Fermium, Frequency modulation, Waveguides, Cladding, Fiber lasers, Birefringence, High power lasers, Defense technologies, Defense and security
There are still very strong interests for power scaling in high power fiber lasers for a wide range of applications in
medical, industry, defense and science. In many of these lasers, fiber nonlinearities are the main limits to further scaling. Although numerous specific techniques have studied for the suppression of a wide range of nonlinearities, the fundamental solution is to scale mode areas in fibers while maintaining sufficient single mode operation. Here the key problem is that more modes are supported once physical dimensions of waveguides are increased. The key to solve this problem is to look for fiber designs with significant higher order mode suppression. In conventional waveguides, all modes are increasingly guided in the center of the waveguides when waveguide dimensions are increased. It is hard to couple a mode out in order to suppress its propagation, which severely limits their scalability. In an all-solid photonic bandgap fiber, modes are guided due to anti-resonance of cladding photonic crystal lattice. This provides strongly modedependent guidance, leading to very high differential mode losses. In addition, the all-solid nature of the fiber makes it easily spliced to other fibers. In this paper, we will show for the first time that all-solid photonic bandgap fibers with effective mode area of ~800m2 can be made with excellent higher order mode suppression.
There are very strong interests for power scaling in high power fiber lasers for a wide range of applications in medical,
industry, defense and science. In many of these lasers, fiber nonlinearities are the main limits to further scaling.
Although numerous specific techniques have studied for the suppression of the wide range of nonlinearities, the
fundamental solution is scaling mode areas in fibers while maintaining sufficient single mode operation. Here the key
problem is that more modes are supported once physical dimensions of waveguides are increased. There are two basic
approaches, lower refractive index contrast to counter the increase of waveguide dimension or/and introduction of
additional losses to suppress higher order modes. Lower index contrast leads to weak waveguides, resulting in fibers no
longer being coil-able. Our research has been focused on designs for significant higher mode suppression. In
conventional waveguides, modes are increasingly guided in the center of the waveguides when waveguide dimensions
are increased. It is hard to couple the modes out to suppress them. This severely limits the scalability of all designs based
conventional fibers. In an all-solid photonic bandgap fiber, modes are guided due to anti-resonance of cladding photonic
crystal lattice. This leads strongly mode-dependent guidance. Our theoretical study has shown that it can have some of
the highest differential mode losses among all designs with equivalent mode areas. Our design and experimental works
have shown the potential of this approach for all-glass fibers with >50μm core which can be coiled for high power
applications.
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