Optical characterization of LiBr-H_2O using MMI in optical fiber

摘要

Heat pumps work with a refrigerant mixture of lithium bromide-water (LiBr-H_2O) and the efficiency of the heat pump may be adjusted depending on the concentration of this mixture. On the basis of the last, in this work an analysis of LiBr concentration by multimode interference (MMI) effects occurring in a single-mode-multimode-single-mode (SMS) fiber structure is presented. In the SMS structure the sensitive element consists in a multimode fiber (MMF) section spliced between two single-mode fibers (SMF) in order to launch light into and recover light from that multimode waveguide. The multimode fiber (MMF) has no cladding so that its exposed core interacts with different concentrations of LiBr-H_2O which refraction indices are between 1.423 and 1.472. The different refraction indices of the solution covering the exposed core generate variations in the modes coupling inside the multimode section of the SMS fiber, and therefore, a different response for each case. SMS fiber structure was designed to generate a first self-image of the input profile at a 1555 nm wavelength. The experimental set up consists of a laser diode operating at 1550 nm as the source of the system, a photodetector as the transducer of the transmitted intensity and a digital multimeter.