What is a Fiber Optic Circulator?

International Zone (English) General Knowledge
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How does it enable unidirectional light transmission and the extraction of reflected signals?

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A fiber optic circulator is a non-reciprocal optical device that directs light sequentially from port to port in only one direction. It is a fundamental component in many fiber optic systems, especially in Fiber Bragg Grating (FBG) sensing, for its ability to isolate reflected signals.

Here’s how it enables unidirectional light transmission and the extraction of reflected signals:

  1. Unidirectional Light Transmission: A typical 3-port circulator has a specific input and output path. Light entering Port 1 will exit only through Port 2, not reflecting back to Port 1 or going to Port 3. Similarly, light entering Port 2 will exit only through Port 3. This sequential, one-way flow is achieved using Faraday rotators and birefringent crystals that manipulate the polarization of light in a magnetic field, ensuring that light travels in the intended direction.

  2. Extraction of Reflected Signals: In FBG sensing, the interrogator sends broadband light into Port 1 of a circulator. This light exits Port 2 and travels along the optical fiber to the FBG sensor. When the light encounters the FBG, a specific wavelength (Bragg wavelength) is reflected back towards the circulator’s Port 2. Because of the non-reciprocal nature of the circulator, this reflected light entering Port 2 is then directed to Port 3, where it can be analyzed by the FBG interrogator. This prevents the reflected light from going back into the light source (Port 1), thus efficiently isolating and extracting the sensor’s reflected signal.

This functionality is crucial for accurately measuring the Bragg wavelength shifts, which correspond to changes in strain or temperature detected by the FBG.

Our OFSCN® Fiber Bragg Grating Interrogators are designed to work seamlessly with such optical setups to acquire and process FBG sensor data.

Here is a standard image of our FBG Interrogator:

FBG-Analyzer-02
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You can find more details about our interrogators here:
OFSCN® Fiber Bragg Grating Interrogator