FBGS’s FemtoSecond Grating (FSG®) technology complements the existing DTG® technology by adding new manufacturing capabilities due to special demands for Fiber Bragg Gratings (FBGs). The fabrication processes of both techniques maintain the pristine high mechanical-strength of the optical fiber. In addition, FSG®s can provide sensor configurations and features needed for special applications.
FSG® exploits the through-coating FBG inscription process, which utilizes ultrafast laser pulses launched via special optics to the fiber core without damaging the fiber coating. See below the schematic for FSG® inscription.
The focused high-power laser pulses change the index of refraction of the glass material in the core of the optical fiber due to nonlinear absorption processes. These effects are nearly independent of the doping level of the optical fiber or the type of glass, which uniquely sets this process to offer an advantage in its ability to modify any type of optical fiber. The laser pulses are guided via special optics to form a unique interference pattern, which is geometrically co-aligned with the longitudinal axis of a stationary standard optical fiber. The impinging pattern creates the desired modulated index of refraction onto a selected local length along the core of the optical fiber. This inscription defines the required reflected Bragg wavelength. In addition, an array of desired FBGs can be inscribed by translating the optical fiber along its longitudinal axis.
FSG® inscription offers additional advantages to the arsenal of DTG® sensors.