PRINCIPLE OF FIBER BRAGG GRATING MEASUREMENTS

The SENSFIB Hull Stress Monitoring system is based on Fiber Bragg Grating (FBG) sensors. The FBGs are an internal stripe pattern in the core of the optical fiber that strongly reflects one wavelength (or color) of light.

The wavelength is determined by the period of the stripe pattern, which means that a strain or temperature that changes the period of the FBG can be characterized by monitoring the wavelength reflected from that FBG.

In a measurement system a broadband light source illuminates the FBGs. A single peak wavelength is reflected from each FBG. The reflections are measured using a wavelength selection device that scans the spectrum. The temperatures and strains are then determined from the measured wavelengths.

More than one FBG can be coupled in series. This means that we can package sensors to measure more than one parameter. This is how Light Structures’s strain sensors also measure the temperature at the sensor location.

The technique does not require much light to work well so the optical power level can be kept very low, less than 1 mW. As many of our systems are operating in explosion hazardous environments we have ATEX certified our sensors and interrogators.