Ultraweak Waveguide Modification With Intact Buffer Coating Using Femtosecond Laser Pulses

This letter reports a new fabrication technique to inscribe in-line, ultraweak waveguide structures. To the best of our knowledge, this is the first time that an in-line grating structure has been fabricated within the core of an optical fiber with an intact buffer coating, allowing the fiber to retain optimal mechanical properties, an important consideration for strain and temperature sensing applications. Low energy pulses from a femtosecond laser were adjusted to avoid buffer absorption while inscribing a terahertz fiber Bragg grating (THz FBG) within the optical fiber core. Strain and temperature tests were conducted using both a THz FBG sensor fabricated using the reported method and a second THz FBG fabricated using a previously reported method requiring buffer removal. Highly similar results from both Thz FBGs were observed, indicating that the new intact buffer fabrication technique holds substantial potential as a method of fabricating optical fiber grating structures for distributed sensing applications.