Use of weakly tilted fiber Bragg gratings for sensing purposes

Abstract

Weakly tilted fiber Bragg gratings with gratings planes tilted at small angles with respect to the fiber axis couple light to backward going core mode and cladding modes. Their transmitted spectrum is characterized by narrow resonance dips below the Bragg wavelength corresponding to the core mode coupling. The amplitude spectral evolutions of weakly tilted fiber Bragg gratings in response to diverse physical perturbations such as temperature, mechanical strains, bending and surrounding refractive index changes are presented. Different techniques allowing to efficiently correlate the spectral evolution with the information to be measured are reported. We demonstrate that a selective monitoring of one cladding mode shift with respect to the Bragg wavelength gives temperature-insensitive strain measurements whereas a global monitoring of the cladding modes spectrum offers temperature-insensitive surrounding refractive index measurements. We also point out the possibility of using this global monitoring for bending and transverse strain sensing purposes. Finally, we present the effect of coating (the grating is covered by a polymer) on the sensitivity of weakly tilted fiber Bragg grating to surrounding refractive index changes. For every application, the performances of weakly tilted fiber Bragg gratings sensors are discussed.

Tilted fiber Bragg gratings: Principle and sensing applications

“…Based on mode coupling characteristics of TFBG, temperature and strain responses of core mode and cladding modes were firstly investigated, and C. Chen et al later analyzed strain sensing characteristics of cladding modes for different fiber cladding diameters, which was experimentally proved to have no influence on the strain sensitivity [36][37]. Based on the mode coupling analysis, by employing mode recoupling, J. Albert et al proposed a vibration sensor and experimentally studied its basic sensing characteristics [38][39].…”

Optical fibers and sensors for biomedical applications: bend effects

“…Given the space limitations and access difficulties that often characterize in vivo applications, the probability that FBGs used in biomedical applications will be subject to bends cannot be discounted. Despite their widespread use in telecommunications and sensing there have been only limited reports of the effects of bends on the properties of FBGs [15][16] . In order to further understand FBG bend effects we have measured the spectra of FBGs written in several different fiber types when bent to relatively small bend diameters.…”

High temperature multiparameter sensor

“…7 Another published example describes the use of cladding modes from point-by-point written fs-IR gratings. 8 The drawback of these examples is that neither report such cladding mode sensitivities at temperatures beyond 75 °C.…”