Why is Germanium (Ge) doped into the fiber? What is hydrogen loading (hydrogenation)?
Germanium (Ge) is doped into optical fibers primarily to increase the refractive index of the fiber core, which creates the necessary waveguide structure for light propagation. More critically for Fiber Bragg Grating (FBG) technology, germanium doping significantly enhances the photosensitivity of the fiber. This means the fiber becomes more susceptible to permanent refractive index changes when exposed to ultraviolet (UV) light, a phenomenon essential for inscribing FBGs into the fiber core.
Hydrogen loading (also known as hydrogenation) is a post-processing technique used to further augment the photosensitivity of optical fibers, particularly those doped with germanium. During this process, optical fibers are subjected to a high-pressure hydrogen atmosphere, often at elevated temperatures, for an extended period. Hydrogen molecules diffuse into the silica glass matrix of the fiber. These diffused hydrogen molecules then react with UV light-induced defects in the glass during the FBG inscription process, leading to a much larger and more stable refractive index modulation. This enables the fabrication of stronger gratings or allows for grating inscription in fibers that are otherwise less photosensitive.
Below is an example of an FBG sensor:
You can learn more about our FBG products here:
OFSCN® Polyacrylate Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare)
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