A multiplexing technique for fibre Bragg grating sensors with the same reflection wavelength by the synthesis of optical coherence function

Abstract

We propose a technique for multiplexing fibre Bragg grating (FBG) sensors with the same Bragg wavelength. We have already developed a technique for the synthesis of an optical coherence function, in which we can select one signal among various reflections along an optical path in an interferometer. By applying the technique, the reflection spectrum of each FBG in arrayed FBGs can selectively be obtained, even if the array is composed of FBGs with the same Bragg wavelength. In this paper, we first describe the principle of the proposed system, and then show the experimental results.

Simplified optical correlation-domain reflectometry using polymer fiber

“…The laser output frequency was sinusoidally modulated by direct modulation of the driving current [11,12,13,14,15,16,17,18,19,20]. The modulation frequency f m was swept from 5.52 MHz to 11.05 MHz with a repetition rate of 10 Hz.…”

“…One promising technique for mitigating these problems is optical correlation (or coherence)-domain reflectometry (OCDR) [11,12,13,14,15,16,17,18,19,20] using synthesized optical coherence function (SOCF) [18], which operates based on optical correlation control through modulated optical frequency of the laser output. Two methods have been reported to implement the frequency modulation: sinusoidal modulation [13,14,15] and stepwise modulation [16,17,18]. The latter includes the use of an optical frequency comb [19,20], which improves the measurement stability.…”

“…In a standard OCDR-SOCF system [13,14,15,16,17,18,19,20], the Fresnel spectrum is shifted by several tens of megahertz by optical heterodyne detection using an acousto-optic modulator (AOM) to avoid the overlap of low-frequency noise of the electrical devices. To perform electrical signal processing in the frequency range near direct current (DC), and thus to reduce the cost of the relevant devices, we have recently succeeded in excluding the optical heterodyne detection (i.e.…”

Multiplexing technique using amplitude-modulated chirped fibre Bragg gratings with applications in two-parameter sensing

“…There have been many methods proposed previously that utilise the spectral-overlap multiplexing, such as carrier modulation [12,13], intensity modulation [14], optical coherence function [15], minimum variance shift using genetic algorithm [16,17], and the use of chirped FBG based Fabry-Perot cavity sensors [18]. In the present multiplexing technique, an important criterion is to have some mechanisms to uniquely identify each spectrally overlapped AMCFBG; otherwise, they will not be able to distinguish one from another.…”

Fiber optic nerve systems for smart materials and smart structures

“…Setup for multi-point strain measurement by fiber gratings with the same Bragg wavelength by synthesis of optical coherence function[22,23].…”