Just like the spacing of a physical fence, what does this microscopic distance actually determine?
In Fiber Bragg Grating (FBG) technology, the grating pitch (denoted as \Lambda) is the physical distance between the periodic perturbations in the refractive index within the fiber core.
1. Technical Principle
The grating pitch is the fundamental geometric parameter that determines the Bragg wavelength (\lambda_B), which is the specific wavelength of light reflected by the sensor. This relationship is governed by the Bragg condition:
\lambda_B = 2 \cdot n_{eff} \cdot \Lambda
Where:
- \lambda_B: The reflected Bragg wavelength.
- n_{eff}: The effective refractive index of the fiber core.
- \Lambda: The grating pitch.
2. What does this distance actually determine?
- Wavelength Selection: By precisely controlling the pitch during the manufacturing process (using phase masks or femtosecond lasers), we can define the specific “color” (wavelength) each sensor reflects. This allows for Wavelength Division Multiplexing (WDM), where multiple sensors with different pitches can be placed on a single optical fiber.
- Sensing Sensitivity: When the fiber is subjected to temperature changes or mechanical strain, the physical distance of the pitch (\Lambda) changes due to thermal expansion or physical stretching. This change in pitch causes a shift in the reflected wavelength, which is exactly how an FBG sensor measures physical parameters.
3. Related Products
At OFSCN®, we utilize advanced laser processing to precisely control the grating pitch for various sensing applications. For instance, our bare fiber gratings are the foundation for all our specialized sensors:
- OFSCN® Polyimide Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare)
- OFSCN® Standard Femtosecond Fiber Bragg Gratings / Fiber Bragg Grating Strings (Bare)
Product Illustrations:
By adjusting the grating pitch, we can customize sensors to operate within the standard C-band (1525 nm to 1565 nm) or extended ranges (1510 nm to 1605 nm) depending on your project requirements.