In an intrinsic optical fiber sensor, the optical fiber itself serves as the sensing medium.
Intrinsic fiber optic sensors utilize the inherent properties of the optical fiber to detect changes in the environment. The measurand (the quantity being measured, such as temperature, pressure, or strain) directly affects the characteristics of the light propagating through the fiber. This is in contrast to extrinsic sensors where the fiber merely acts as a conduit to transmit light to and from a separate sensing element.
How Intrinsic Sensors Work
Here's a breakdown of how intrinsic sensors operate:
- Direct Interaction: The physical parameter being measured directly influences the optical properties of the fiber.
- Modulated Light: The light traveling through the fiber is modulated (changed) by the measurand. This modulation can involve changes in:
- Intensity
- Phase
- Wavelength
- Polarization
- Detection and Interpretation: Changes in the light are detected and analyzed to determine the value of the measurand.
Examples of Intrinsic Sensors
Some examples of intrinsic optical fiber sensors include:
- Fiber Bragg Grating (FBG) Sensors: Changes in strain or temperature cause shifts in the Bragg wavelength reflected by the grating.
- Microbend Sensors: Physical deformation of the fiber induces losses in the transmitted light.
- Interferometric Sensors: Changes in the optical path length of the fiber, due to strain or temperature, alter the interference pattern.
Key Differences: Intrinsic vs. Extrinsic Sensors
| Feature | Intrinsic Sensor | Extrinsic Sensor |
|---|---|---|
| Sensing Element | The fiber itself | A separate sensing element |
| Fiber's Role | Active sensing medium | Light guide (transmitting signal to/from sensor) |
| Integration | Integrated directly into the fiber | Connected to the fiber |
In summary, the sensing medium in an intrinsic optical fiber sensor is the optical fiber itself, which is directly affected by the measurand.
