Abstract
We report on the experimental results of the combination of unique auto-correlation properties of Golay complementary code and Hadamard matrix properties of standard simplex code. The combination of the two coding techniques results in improvement of the signal-to-noise ratio (SNR) of time domain multiplexed fiber Bragg grating (TDM-FBG) sensor for temperature measurement. Previously, we have analyzed the properties of both coding techniques when deployed separately in the TDM-FBG sensor. In this case, both coding techniques result in the same amount of SNR improvement for code length longer than 31 bits. In this paper, we demonstrate the combination and simultaneous deployment of the two techniques to measure multiple FBGs under room condition (25 °C) and 50 °C temperature. The two schemes combination results in remarkable improvement of SNR and still retains the original spatial property of the decoded FBG signals, confirming the successful deployment of the hybrid codes. From the measurement of two FBG sensors located after 16 km of fiber, the combination of 31 bits of simplex- and 64 bits of Golay codes has resulted in a total of 10.5 dB improvement of SNR.
Highlights
Strain and temperature measurements in fiber optic cable based on fiber Bragg grating (FBG) are an advanced optical fiber sensing technique, thanks to the remarkable features of FBG sensor such as small size, light weight, measurement accuracy, immunity to electromagnetic interferences and high sensitivity [1], [2]
One can observe that both FBG signals are not flat especially for 3 bits simplex ×64 bits Golay combination case; this might be contributed by the accumulation of side lobe noise near the falling edge of the FBG during the autocorrelation process
Pattern B was the continuation of Pattern A with fixed length of Golay codes of 64 bits, while the simplex code length was set to 3, 7, 15 and 31 bits
Summary
Strain and temperature measurements in fiber optic cable based on fiber Bragg grating (FBG) are an advanced optical fiber sensing technique, thanks to the remarkable features of FBG sensor such as small size, light weight, measurement accuracy, immunity to electromagnetic interferences and high sensitivity [1], [2]. Compared to other optical sensing techniques, FBG sensors are self-referenced sensing devices that can be produced in bulk at low cost. Wavelength division multiplexing (WDM) technique has been applied in the FBG sensing technique for the purpose of improving the sensing distribution, which is limited by the bandwidth of the light source [8], [9]. Interrogating a series of FBG sensors by employing the technique of optical frequency domain reflectometry (OFDR) is
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