Estimation of LiBr-H2O Using Multimode Interference (MMI)

E.E. Antúnez-Cerón, M.A. Basurto-Pensado, A.R. Mejía-Aranda, R.J. Romero, J.J. Sánchez-Mondragón, H.H. Cerecedo-Núñez, A. Ochoa-Zezzati


We use multimode interference (MMI) as an alternative optical technique to estimate lithium bromide (LiBr)concentration, of the work pair LiBr-H2O, in absorption heat pumps (AHP). The sensing element is a singlemodemultimode-singlemode (SMS) fiber optic structure. This is fabricated by splicing a precisely dimensioned multimodefiber (MMF) section between two singlemode fibers (SMFs). The operation principle is based on the multimodeinterference (MMI) effect occurring in the MMF section. For that purpose, different concentrations of the mixture wereprepared (from 44.30% to 60.69%) to study their optical response. The input field profile entering the sensing element,which is the naked (no cladding) MMF section of the SMS fiber structure, produced different transmitted intensityresponses for each of these concentrations. Thus the optical characterization of the mixture was used to establish amathematical relation to estimate the LiBr concentration. A linear fit for solutions with concentrations ranging from43.30% to 50.87% and refractive indices between 1.421 and 1.439 is demonstrated.


multimode interference, fiber optic, refractive index.

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