Investigation of fiber Bragg grating based mode-splitting resonant sensors

Abstract

In this paper, we report on theoretical investigation of split mode resonant sensors based on fiber Bragg grating (FBG) ring resonators and π-shifted fiber Bragg grating (π-FBG) ring resonators. By using a π-shifted Bragg grating ring resonator (π-FBGRR) instead of a conventional fiber Bragg grating ring resonator (FBGRR), the symmetric and antisymmetric resonance branches (i.e., the eigen-modes of the perturbed system) show peculiar and very important features that can be exploited to improve the performance of the fiber optic spectroscopic sensors. In particular, the π-FBGRR symmetric resonance branch can be taylored to have a maximum splitting sensitivity to small environmental perturbations. This optimal condition has been found around the crossing points of the two asymmetric resonance branches, by properly choosing the physical parameters of the system. Then, high sensitivity splitting mode sensors are theoretically demonstrated showing, as an example, a strain sensitivity improvement of at least one order of magnitude over the state-of-the-art.

Fiber Bragg grating ring resonators under rotation for angular velocity sensing

“…The possibility of replacing typical Bragg gratings with BGRR is reported in [21], while the guidelines for a band edge slow light magnification together with a Q-factor enhancement are given in [22]. In the frame of strain sensors, the fiber BGRRs (i.e., FBGRRs) have been proposed and experimentally investigated as splitting mode resonant sensors, due to their enhanced performance [23][24][25]. For this purpose, in this paper we investigate, for the first time to the best of our knowledge, the effect of the rotation Ω on FBGRRs and π-shifted FBGRRs (i.e., defective FBGRRs), whose schemes are sketched in Figs.…”

Enhanced spectral response of π-phase shifted fiber Bragg gratings in closed-loop configuration

“…The π-FBGRR is injected from port P1 (field E 1 ). Analytical expressions for the fields E 3 and E 4 transmitted at ports P3 and P4, respectively, can be obtained with the formalism introduced in [11]. In the simplified case of a lossless resonator,…”

“…2, jE 3 λj 2 and jE 4 λj 2 are plotted in the vicinity of the central resonance of the π-FBG, along with the corresponding open-loop transmission of the grating (red line). The FBG parameters are the same as in [11].…”

Split-mode fiber Bragg grating sensor for high-resolution static strain measurements

“…While a full theoretical description of the spectral properties of FBGRRs can be found in [12,13], the general behavior of these devices is recalled in the following. At wavelengths where the FBG reflectivity R ∼ 0, the loop behaves like a conventional ring resonator, with the optical power circulating only in the direction of excitation and an output spectrum formed by equally-spaced resonances.…”

“…The two counterpropagating modes are coupled by their continuous exchange of energy via the FBG element, resulting in a frequency splitting, S, of the cavity resonances. For a resonance at wavelength λ, in the small coupling approximation, the splitting is given by [12,13]:…”