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FSG® Technology

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.

 

FSG inscription principle

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.  

 

Advantages

 

FSG® inscription offers additional advantages to the arsenal of DTG® sensors. 

 

  • For one, a standard commercially-available telecom optical fiber, such as an SMF-28 (or similar type) or a pure silica core fiber, with different coatings (polyimide, acrylate, etc.) can be used to inscribe the gratings. 
  • System designers can take advantage of new features, such as; enhanced reflectivity, which can exceed 90%, have a narrow spectral bandwidth (FWHM) down to 200pm and more flexibility in configuring FSG® chains, where spectral spacing between consecutive FBGs is less restricted.
  • Additionally, the process offers a capability to fabricate FSG®s with broad FWHM of higher than 5nm with an option to offer low or high reflection values. 
  • Furthermore, FSG®s offer a higher thermal stability across a wide band of temperatures and can be designed to operate at the temperature limit of the optical fibers.