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Overlap-Proof Fiber Bragg Grating Sensing System Using Spectral Encoding

In this letter, a spectral encoding of fiber Bragg grating (FBG) sensors is proposed in order to solve their wavelength under overlapping conditions. Our technique uses optical orthogonal codes (OOCs) to define the spectral shape of the FBG sensors. In this way, we design encoded FBG sensors composed of more than one reflection band; the spectral location of the reflection bands is determined by the OOC, providing each encoded FBG sensor with a unique spectral signature. The demodulation technique for the proposed sensors makes use of their orthogonal nature: it obtains the wavelength position for each sensor by obtaining the autocorrelation product between the reflection spectrum and each sensor's spectral code. These FBG sensors have been manufactured and experimentally validated. The results demonstrate the overlap-proof nature of the encoded sensors. Furthermore, the very simple demodulation technique provides highly accurate wavelength detection and can be implemented in real-time detection systems.