What is the impact on measurement accuracy when comparing a reflectivity of 70% versus 20%?
Reflectivity is a key parameter of a Fiber Bragg Grating (FBG) that indicates the ratio of the reflected light intensity to the incident light intensity at the Bragg wavelength.
In the context of OFSCN® FBG sensors, the typical reflectivity value is 70%, and we generally guarantee a minimum value of greater than 20%.
Impact on Measurement Accuracy: 70% vs. 20%
Technically, reflectivity itself does not directly change the physical sensitivity (e.g., pm/°C or pm/με) of the sensor. However, it significantly impacts the Signal-to-Noise Ratio (SNR), which indirectly affects measurement accuracy in the following ways:
-
Signal-to-Noise Ratio (SNR):
- 70% Reflectivity: Provides a much stronger reflected signal. This leads to a higher SNR, making it easier for the FBG interrogator to accurately identify the peak wavelength, even in environments with higher optical loss or background noise. Higher SNR generally results in better resolution and stability.
- 20% Reflectivity: The signal is weaker. While still measurable, the system becomes more sensitive to noise. If the fiber line has significant attenuation (e.g., long distances or multiple connectors), a 20% signal might approach the noise floor, increasing the jitter in wavelength detection and reducing accuracy.
-
System Capacity (Multiplexing):
- Higher reflectivity (70%) is excellent for single-point or low-count sensors.
- Lower reflectivity (20% or even lower) is often intentionally used in FBG Strings with a high number of sensors (e.g., dozens of sensors on a single fiber) to prevent excessive cumulative loss and “shadowing” effects, ensuring that light can reach and return from the end of the string.
OFSCN® Product Reference
All OFSCN® sensors are built upon our high-quality gratings. For instance, our OFSCN® Polyimide Fiber Bragg Gratings are designed to maintain stable performance even at low reflectivity when used in large-scale multiplexing.
Summary:
While 20% reflectivity is sufficient for many standard interrogators to achieve precise measurements, 70% reflectivity offers a “safety margin” for signal integrity, leading to more robust data in complex or high-loss industrial environments.
For more technical details, you can refer to:
OFSCN® Polyacrylate Fiber Bragg Gratings
OFSCN® High-Strength Fiber Bragg Gratings