Why must the coating be stripped before grating inscription? How is the fiber protected after stripping?
The coating must be stripped before grating inscription primarily because the standard UV laser inscription process requires the UV light to directly reach the core of the optical fiber to induce the refractive index modulation that forms the Fiber Bragg Grating (FBG). The fiber coating, typically made of acrylate or polyimide, is designed to absorb or block UV light, which would prevent the grating from being successfully written.
After stripping, the optical fiber’s mechanical strength is significantly reduced, making it susceptible to damage. To protect the fiber, it is typically immediately recoated with a new polymer layer, such as polyacrylate or polyimide, in a process called recoating. This restores the fiber’s mechanical integrity and protects it from environmental factors like moisture and abrasion. For specialized applications requiring high temperature resistance or robust packaging, the recoated FBG might then be further protected by metal or other resistant materials, as seen in OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensors.
Here are examples of OFSCN® bare FBGs that undergo this process, offering different temperature capabilities based on their recoating material:
- OFSCN® Polyacrylate Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare) (up to 100°C)
- OFSCN® Polyimide Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare) (up to 300°C)
An alternative inscription method, femtosecond laser inscription, can directly write gratings through the fiber’s original coating, eliminating the need for stripping and recoating in some cases. You can find more information on this technology here: OFSCN® Standard Femtosecond Fiber Bragg Gratings / Fiber Bragg Grating Strings (Bare).
Below are images of our bare FBGs:
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