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Wavelength Division Multiplexing FBG

Wavelength Division Multiplexing FBG

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Wavelength Division Multiplexing (WDM) allows multiple Fiber Bragg Grating (FBG) sensors to operate simultaneously on a single optical fiber by assigning each sensor a unique Bragg wavelength.

Principle of WDM in FBG Systems

In FBG-based sensing, each Fiber Bragg Grating acts as a wavelength-selective mirror, reflecting light at a specific Bragg wavelength while transmitting other wavelengths along the fiber. WDM leverages this property by assigning distinct wavelengths to each FBG sensor, enabling multiple sensors to coexist on the same fiber without interference. A broadband light source illuminates the fiber, and the reflected wavelengths are analyzed using an optical interrogator or spectrum analyzer to determine the sensor readings, such as strain, temperature, or pressure .

Advantages of WDM for FBG Sensors

  • High sensor count: By carefully spacing the Bragg wavelengths, WDM can accommodate dozens of sensors on a single fiber. Typical interrogators with an 80 nm wavelength span can support up to 70 temperature sensors or 40 strain sensors, and networks with multiple channels can exceed 500 sensing points .
  • Cost-effective and scalable: WDM reduces the need for multiple fibers, lowering installation costs and simplifying network design.
  • Distributed sensing over long distances: WDM FBG networks can span several kilometers, making them suitable for structural health monitoring, aerospace, and civil engineering applications .

Operational Considerations

  • Wavelength spacing: FBGs must be designed with non-overlapping Bragg wavelengths to prevent signal interference.
  • Spectral range: Most WDM FBG systems operate in the S, C, and L telecommunication windows (1460–1625 nm), with interrogators typically covering 1510–1590 nm .
  • Multiplexing combinations: WDM can be combined with Time Division Multiplexing (TDM) to further increase the number of sensors by distinguishing reflections both by wavelength and by time delay .

Applications

WDM-based FBG sensing is widely used for quasi-distributed monitoring in large structures, including bridges, aircraft, pipelines, and industrial machinery. Its ability to interrogate multiple sensors simultaneously with high accuracy and low loss makes it the most commonly used FBG multiplexing technique today . In summary, WDM enables efficient, scalable, and high-resolution monitoring using FBG sensors, making it ideal for applications requiring large sensor networks over long distances.

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