Optical code division multiplexing in the design of encoded fiber Bragg grating sensors

Abstract

ABSTRACT:The design of spectrally encoded fiber Bragg grating (FBG) sensors is proposed in order to incorporate more information in the optical measurement system. This information can provide full distinction between sensors operating at the same wavelength range. The encoded sensors are inspired by Optical Code Division Multiplexing (OCDM) techniques, specifically, we used Optical Orthogonal Codes (OOC) in order to define the spectral shape of the FBG sensors, providing them with a unique spectral signature. As a result we demonstrated the detection and tracking of the proposed sensors which allows effective measurement of temperature or strain even under overlapping conditions. The interrogation of the proposed encoded sensors could be performed easily and in real time through the autocorrelation product between the reflected spectrum and each sensor codeword. A simple addition to this identification method is implemented in order to remove any error in the interrogation process. Furthermore, a simulation of the proposed sensors under overlapping conditions is performed in order to test the distinction capability of the system. Finally the manufacturing and measurement of the sensors is described.Key words: Fiber Bragg gratings, FBG, Optical sensing, Encoded sensors. REFERENCES AND LINKS

Code Division Multiplexing Applied to FBG Sensing Networks: FBG Sensors Designed as Discrete Prolate Spheroidal Sequences (DPSS-FBG Sensors)

“…In this paper, we propose the use of code division multiplexing in order to resolve optical FBG sensors. The main difference with our previous work relies in the fact that here we use magnitude and phase patterns to encode the FBG sensors while in our previous approaches [12]- [14] we were shaping the sensors only in amplitude. Still, the fundamental idea is to add another multiplexing dimension, compatible with traditional WDM schemes, increasing the number of sensors that can be deployed in the system.…”

“…Note that since such structures will be manufactured as a compound of individual FBGs, they will preserve the sensing properties of any standard FBG sensor. Indeed, we have demonstrated in previous works [12]- [14] that providing the sensors with a distinctive amplitude shape makes it possible to achieve orthogonality between them, in such a way that each sensor in the network can be unequivocally distinguished even in overlapping scenarios. It is worth noting that other sensing systems have included CDMA concepts before [15], nevertheless the encoding of this kind of systems occurs in the source, not in the shape of the sensors, so they are more likely to be classified as a variation of a TDM.…”

Algorithm of FBG Spectrum Distortion Correction for Optical Spectra Analyzers with CCD Elements

“…The complexity of multiplexing technologies is also related to the fact that any spectrum overlaps of FBG spectra leads to significant errors in measurements of their central wavelengths [ 6 , 7 , 8 ]. The multiplexing technologies and microwave-photon interrogation methods of spectrally-encoded and addressed Bragg gratings have been developed; they allow separating, spectrally, the responses of sensors in the same frequency range [ 9 , 10 , 11 , 12 ]. Some researchers worked on sensor detection and tracking using Slepyan codes [ 13 , 14 , 15 , 16 ]; thus, a measurement of temperature and deformation in the case of sensors spectra overlapping became possible.…”

Algorithm of FBG Spectrum Distortion Correction for Optical Spectra Analyzers with CCD Elements

“…The complexity of multiplexing technologies is also related to the fact that any spectrums overlap of FBG spectra leads to significant errors in measurements of their central wavelengths [6,7,8]. The multiplexing technologies and microwave-photon interrogation methods of spectrally-encoded and address Bragg gratings have been developed, it allows separating spectrally the responses of sensors in the same frequency range [9,10,11,12]. Some researchers worked on sensor detection and tracking using Slepyan codes [13,14,15,16], thus a measurement of temperature and deformation in case of sensors spectra overlapping became possible.…”