Technology

In our structure monitoring systems Light Structures use fiber-optic sensors based on Bragg gratings (FBGs). The gratings are short sections of optical fiber that have been sensitized to strain and temperature through a periodic modulation of the refractive index of the fiber core. A grating reflects a narrow range of wavelengths (colors) determined by the period of the modulation. The most strongly reflected wavelength is called the Bragg wavelength, and is a characteristic of the grating. Strain on the fiber or a change in temperature will modify the modulation period, and hence the reflected wavelength.

Gratings with different Bragg wavelengths may be incorporated on the same fiber, forming a wavelength multiplexed system.

The fiber-optic sensors have a number of advantages over the electrical alternatives, especially in harsh environments:

• High sensitivity
• Good resistance toward water and chemicals
• Signal is wavelength coded, and unaffected by the environment along the cable path
• Immunity toward electromagnetic interference
• Does not contribute to the total surrounding electromagnetic field
• EX-safe
• Multiplexing: Many sensors on a single cable

A functional sensor system is a combination of a light source, sensors and an analyzer that receives the optical signals from the sensors and converts them to a format suited for digital signal processing. The Light Structures FBG Analyzers are based on a scanning filter that gates the light from a broadband source. The FBGA determines the Bragg wavelength of each grating with high precision.