In strain measurement, how does the elasto-optic coefficient influence the wavelength shift?
In strain measurement, the elasto-optic coefficient is a crucial parameter that describes how the refractive index of an optical fiber changes when subjected to mechanical strain. When an FBG is strained, two primary effects contribute to the shift in its Bragg wavelength:
- Physical Elongation: The grating period of the FBG changes due to the applied strain, directly altering the Bragg wavelength.
- Photoelastic Effect: The strain induces a change in the refractive index of the fiber core, governed by the elasto-optic coefficient. This change in refractive index also shifts the Bragg wavelength.
The elasto-optic coefficient (often denoted as P_e or p_e) quantifies this photoelastic effect. A larger elasto-optic coefficient means a greater change in refractive index for a given strain, leading to a more significant wavelength shift. The overall wavelength shift (ΔλB) due to strain (ε) in an FBG is typically described by the equation:
ΔλB / λB = (1 - P_e) ε
Where λB is the initial Bragg wavelength and P_e is the effective photoelastic constant, which combines different elasto-optic coefficients of the fiber material. For standard silica optical fibers, the value of (1 - P_e) is approximately 0.78, indicating that for every unit of strain, the wavelength shifts by about 78% of the strain value multiplied by the original Bragg wavelength.
This fundamental relationship ensures that FBGs can accurately measure strain by detecting the corresponding wavelength shift.
OFSCN offers a range of Fiber Bragg Grating strain sensors designed for various applications and environments. These include:
- OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensor
- OFSCN® Polymer-encapsulated Fiber Bragg Grating Strain Sensor (1.5mm/2.3mm diameter)
- OFSCN® Polymer-encapsulated Fiber Bragg Grating Strain Sensor (0.7mm/1.2mm diameter)
Here are some standard product images:
