Spectral Filtering
Periodic variations in the refractive index of an optical fiber core create a wavelength-specific dielectric mirror. A fiber bragg grating reflects a narrow band of light while transmitting all other wavelengths through the waveguide. The reflected wavelength depends on the grating period and the effective refractive index of the core material.
Sensing Mechanism
External physical influences like temperature or mechanical tension alter the physical spacing of the grating segments. When the fiber stretches, the bragg wavelength shifts toward longer values in a predictable, linear fashion. Precision interrogators measure these shifts to determine strain with resolutions often exceeding one microstrain.
Thermal sensitivity requires compensation techniques or specialized packaging to isolate strain measurements from ambient temperature fluctuations.
Fabrication Quality
Ultraviolet laser interference patterns typically define the grating structure during the manufacturing process. Long term stability depends on the thermal aging of the index change and the mechanical durability of the glass. High quality units undergo annealing to ensure the spectral response does not drift over years of service.
Hydrogen loading sometimes enhances the photosensitivity of the fiber before exposure to the laser source.
Metrological Reference
National standards for length and temperature provide the basis for calibrating these optical sensors. Repeatability across multiple cycles defines the reliability of the sensor in structural health monitoring. Calibration certificates specify the gauge factor and temperature coefficient for each individual unit.
