Improving the Signal-to-Noise Ratio of Time Domain Fiber Bragg Grating Sensor Based on Hybrid Simplex and Golay Coding Technique

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.

Digital Filtering Techniques for Performance Improvement of Golay Coded TDM-FBG Sensor

“…However, many of the TDM-FBG key performance parameters, such as the signal-to-noise ratio (SNR), measurement sensitivity, and range, are associated with the optical power of the probe light. Conventional methods to mitigate these limitations are impractical, and they can be complex, impair spatial resolution, and be time-consuming [ 3 , 5 , 8 , 9 ].…”

“…Such techniques resolve the trade-off between the optical power, SNR, and spatial resolution by encoding the probe light with unique coding types and then processing the response signal with a specific pulse compression algorithm. The spatial characteristics of the decoded pulses are identical to those of the conventional single-pulse technique, yet with an enhanced parameter as mentioned above [ 5 , 8 , 10 , 11 ]. In this context, the unique autocorrelation properties of GCPs have proven their significant abilities to improve the performance parameters of both semi and fully DOFS.…”

“…In this context, the unique autocorrelation properties of GCPs have proven their significant abilities to improve the performance parameters of both semi and fully DOFS. Besides their considerable abilities, multiple formats of unipolar and bipolar GCPs are easy to construct and feasible to be combined with other codes [ 8 , 9 , 11 , 12 ].…”

“…Furthermore, the sensing information of the TDM-FBG sensor is encoded within the time domain signals reflected from each FBG. Hence, lacking accurate reads due to noisy background, distortion, broadened signals, or drifted baseline led to insensitive, unrepeatable, and inaccurate measurements [ 8 , 9 , 14 , 15 ].…”

“…Over the past few years, there have been several reports on improving the conventional performance of Golay coded TDM-FBG sensors, including the deployment of interferometric noise suppressing Golay coded optical sources, nesting them with SC technique to improve their shapes and SNIR, and employing their differential form to enhance their spatial distribution and multiplexing capacity [ 8 , 9 , 16 ]. However, to the authors’ knowledge, proposals for easier-to-implement techniques, such as the digital filtering technique, to further improve the Golay coded TDM-FBG signals have not yet been reported.…”