What Is a Fiber Bragg Grating?
A fiber Bragg grating (FBG) is a type of diffraction grating created by exposing the core of an optical fiber to a laser beam. It selectively reflects specific wavelengths of light that correspond to the grating’s periodic refractive index variations, allowing it to act as a sensor for measuring physical parameters such as pressure, strain, and temperature.
Uses of Fiber Bragg Gratings
FBGs are exceptionally suited for use in environments where traditional sensors fail, such as in extreme temperatures, radiation levels, and vacuums. They find applications in monitoring the structural health of wind turbine blades, measuring loads in aircraft fuel tanks, strain in nuclear reactors, and conditions in spacecraft. Their capability to cover long distances and support a large number of sensors makes them invaluable in such scenarios.
Principle of Fiber Bragg Gratings
FBG sensors work by measuring the changes in the wavelength of light that is reflected from the grating. These changes occur due to variations in strain and temperature affecting the grating’s period. An interrogator device is used to analyze the intensity of the returned light, from which the physical changes can be deduced using predefined coefficients.
Other Information on Fiber Bragg Gratings
1. Bragg Wavelength and Wavelength Shift
The Bragg wavelength, the specific wavelength that an FBG reflects, shifts in response to changes in temperature, strain, and pressure. This shift, resulting from the physical deformation of the optical fiber, is used to measure the relevant physical parameters accurately.
2. Fiber Bragg Grating Method
Creating an FBG involves irradiating the core of a germanium-doped optical fiber with ultraviolet light. This process induces a lasting change in the refractive index within the core, forming stable diffraction gratings. Such gratings enable the multiplexing of multiple sensor sections within a single fiber.
3. Acquisition of Reflected Light
An interrogator introduces light into the optical fiber, which travels to the FBG and is partly reflected. This reflected light is then captured by the interrogator, providing the data necessary to determine the monitored conditions based on the characteristics of the reflected light.