Vernier effect using in-line highly coupled multicore fibers

Abstract

We demonstrate optical fiber sensors based on highly coupled multicore fibers operating with the optical Vernier effect. The sensors are constructed using a simple device incorporating single-mode fibers (SMFs) and a segment of a multicore fiber. In particular, we evaluated the performance of a sensor based on a seven-core fiber (SCF) spliced at both ends to conventional SMFs, yielding a versatile arrangement for realizing Vernier-based fiber sensors. The SMF–SCF–SMF device can be fabricated using standard splicing procedures and serve as a “building block” for both, reflection and transmission sensing configurations. As demonstrated with our experimental results, the Vernier arrangements can yield a ten-fold increase in sensitivity for temperature measurements compared to a conventional single SMF–SCF–SMF device, thereby confirming the enhanced sensitivity that can be attained with this optical effect. Furthermore, through theoretical analysis, we obtain the relevant parameters that must be optimized in order to achieve an optimal sensitivity for a specific application. Our findings thus provide the necessary guidelines for constructing Vernier-based sensors with all-fiber devices based on highly coupled multicore optical fibers, which constitutes an ideal framework to develop highly sensitive fiber sensors for different applications.

Ratiometric Temperature Sensing Using Highly Coupled Seven-Core Fibers

“…We can also assume that the light transmitted to the outlet SMF corresponds to the light present in the central core of the SCF at the outlet SCF-SMF interface. Previous works have demonstrated a good correlation between this approach and experimental results [ 12 , 21 ]. Among the advantages of using SCF as a sensing element are the ease of integration with fiber optics technology, reduced size and mass, and an interferometric-like behavior characterized by a periodic spectral response.…”

“…The transmission of an SMF-MCF-SMF structure can be modeled within the coupled-mode theory [ 21 ]. In a centrosymmetric MCF such as a seven-core fiber (SCF), one can assume that the light from the inlet SMF couples to the central core of the SCF.…”

“…Briefly, each core can be seen as an individual waveguide and according to coupled-mode theory, the energy from the central core couples to the external cores as a function of wavelength and transmitted length. More precisely, the normalized transmitted intensity I in an SMF-SCF-SMF is a function of the length L of the SCF and the coupling coefficient κ as follows [ 21 ]: …”

“…Transmission measurements in cascade configuration do not require metallic coatings or fiber couplers to acquire the corresponding signal. Moreover, it has been demonstrated that the envelope of transmitted/reflected and cascaded/parallel signals from two SMF-SCF-SMF devices contain similar frequency components [ 21 ].…”

“…In recent years, an increasing interest has been demonstrated in implementing multicore fibers (MCFs) in fiber sensing systems [ 1 , 2 , 3 ]. Measurements and detection in deformation [ 4 , 5 , 6 , 7 , 8 ], refractive index [ 9 , 10 , 11 , 12 ], temperature [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ], curvature [ 22 , 23 , 24 ], vibration [ 25 ], and polarization state [ 26 ] have been reported using MCF devices. MCFs have been described as revolutionary waveguides, as these fibers have allowed new alternatives for developing sensing systems whose performances cannot be easily achieved using conventional fiber optics [ 22 ].…”