In a spectral plot, what quality of the grating does a high or low SMSR represent?
In a spectral plot, the Side Mode Suppression Ratio (SMSR) is a critical parameter that quantifies the quality of a Fiber Bragg Grating (FBG) by comparing the power of the main reflection peak to the power of the strongest side lobe.
- High SMSR: A high SMSR (e.g., ≥ 15 dB) indicates that the main reflection peak is very dominant and clean, with minimal spurious side lobes. This is desirable for most sensing applications because it means the reflected signal is clearly defined, making it easier for the interrogator to accurately determine the Bragg wavelength. A high SMSR reduces the likelihood of wavelength ambiguity and improves the signal-to-noise ratio, which is crucial for precise measurements, especially when multiple gratings are multiplexed or when signals are weak.
- Low SMSR: A low SMSR implies that there are significant side lobes present in the reflection spectrum, relatively close in power to the main peak. This can lead to inaccuracies in wavelength detection, as the interrogator might struggle to differentiate between the true Bragg wavelength and the side lobe peaks. Low SMSR can also cause crosstalk between adjacent gratings in a sensor array and degrade the overall performance of the sensing system.
For OFSCN® Fiber Bragg Gratings, the default Side Mode Suppression Ratio is typically ≥ 15 dB. It is important to note that SMSR is related to the grating length and can be customized within a certain range to meet specific application requirements.
Our OFSCN® Polyacrylate Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare), for example, exhibit a typical SMSR of ≥ 15 dB, ensuring high spectral purity for accurate sensing.
Here is an image of a bare FBG:
You can find more detailed technical parameters on our product page:
OFSCN® Polyacrylate Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare)
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