How much attenuation do hydrogen molecules cause in the 1383nm and 1550nm bands after entering the core?
Hydrogen molecules diffusing into the fiber core lead to increased optical attenuation, a phenomenon known as hydrogen darkening. This occurs as hydrogen reacts with the silica glass to form Si-OH and Ge-OH bonds, which have distinct absorption peaks in the near-infrared spectrum.
Specifically:
- 1383nm band: This is a fundamental absorption peak for the first overtone of these OH bonds. Therefore, optical fibers exposed to hydrogen environments experience significant attenuation in this wavelength band, making it highly susceptible to hydrogen darkening.
- 1550nm band: While less affected than the 1383nm band, the 1550nm region can still experience increased attenuation due to combination overtones and higher-order harmonics of the OH absorption. The exact attenuation depends on the hydrogen concentration, temperature, exposure duration, and the specific fiber composition, but it is generally lower than at 1383nm.
To mitigate the impact of hydrogen darkening, OFSCN offers solutions leveraging its robust packaging technology. For environments where hydrogen ingress is a concern, we recommend sensors with OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensor design. The product images are as follows:
This packaging utilizes seamless metallic materials, which serve as a physical barrier and significantly reduce the permeability of hydrogen molecules into the optical fiber, thereby delaying and minimizing hydrogen darkening effects.
You can find more technical details on our packaging and its shielding effects here:
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