A study showing the relation between the intensity of the reflected light and concentration, refractive index for citric acid and salicylic acid used Bi-layer surface plasmon resonance based on multimode plastic optical fiber

Abstract

During this work, an optical fiber chemical sensor based on surface Plasmon resonance is designed and implemented to sense and measure the refractive index and concentration for citric acid and salicylic acid. Optical grade plastic optical fibers with a diameter of (100µm) were used with a core of (980µm) diameter and cladding of (20µm), where the sensor is made of a small (10mm) optical part. In the middle is embedded in a resin block and then polishing process is done, after it is deposited with about (60nm) of bi-layer metals compound (30nm) of aluminum thickness and (30nm) of gold thickness and the samples are put on the sensing probe. From the results it was noted that the refractive index rises as the magnitude of the dip position increases the wavelength, so concentration increasing and we found sharp dip happens in T because of the energy of incident light transfer to the electrons of the metal and thus, lessens the reflected light intensity.