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What is a Double-Clad Fiber?
Double-clad fiber is an optical fiber designed to efficiently combine signal transmission with high-power optical pumping. It features a central core surrounded by two concentric cladding layers, allowing the signal to propagate through the core while pump light is guided through the inner cladding.
This architecture increases the amount of pump power that can be coupled into the fiber while maintaining good signal confinement. Double-clad fibers are therefore widely used as gain fibers in high-power fiber lasers and amplifiers, where efficient pump absorption and power scaling are essential.
HOW a Double-Clad Fiber Works
The operation of a double-clad fiber can be understood through three main elements:
Signal guidance
The central core guides the laser signal, typically in a single-mode or large-mode-area regime depending on the fiber design.
Pump guidance
The inner cladding surrounds the core and provides a larger optical area for guiding high-power pump light from laser diodes. This allows significantly more pump power to be injected than would be practical through the core alone.
Energy conversion
In an active double-clad fiber, the core is doped with rare-earth ions such as ytterbium, erbium, or thulium. The pump light is absorbed by these ions, generating optical gain and amplifying the signal. The double-clad architecture therefore supports efficient power scaling while preserving beam quality.
