A Fiber Bragg Grating (FBG) sensor consists of a core with an inscribed grating, cladding, and protective jacket, each serving a specific optical and mechanical function.

Core

The core is the central part of the optical fiber where light propagates. It is typically made of doped silica, which allows precise control of the refractive index. The Bragg grating—a periodic modulation of the refractive index—is inscribed along the core, enabling the reflection of specific wavelengths of light, known as the Bragg wavelength, in response to environmental changes such as strain or temperature .

Cladding

Surrounding the core is the cladding, which has a lower refractive index than the core. This difference confines light within the core through total internal reflection, ensuring efficient light transmission and minimal loss. The cladding also contributes to the mechanical stability of the fiber .

Protective Jacket

The outer jacket encases the cladding and core, providing mechanical protection against physical damage, environmental factors, and chemical exposure. It enhances the durability of the sensor, especially in harsh or long-term monitoring applications .

Bragg Grating

The Bragg grating itself is a periodic variation in the refractive index along the fiber core. It is typically created using ultraviolet laser irradiation or holographic techniques. The grating reflects a specific wavelength of light while transmitting others, and shifts in this reflected wavelength correspond to changes in strain or temperature, which are measured by an interrogation system .

Optional Components

• Packaging materials: For harsh environments, FBG sensors may include additional packaging to protect against moisture, vibration, or extreme temperatures.
• Multiplexing arrangements: Multiple FBGs can be inscribed along a single fiber to allow distributed sensing at different points . In summary, an FBG sensor is composed of a core with an inscribed Bragg grating, cladding, and protective jacket, with optional packaging and multiplexing features for enhanced durability and functionality. These components work together to provide precise, reliable measurements of strain, temperature, and other physical parameters.