Intensity based optical fiber sensors for calcium detection

Two optical fiber sensors are proposed and demonstrated for monitoring calcium concentration in a liquid solution. The first sensor utilizes a bundle plastic optical fiber (POF) as a probe. The system comprises fiber optic transmitter, fiber optic probe which consists of 1000 cores as a receiver, mirror reflection, photodiode detector, lock-in amplifier and computer.The measurementis based on the peak voltage of the output which increases with the calcium concentration of the solution varying from 0 to 2.5%. It is found that the peak voltage of the detector increases with the calcium concentration due to the scattering effects which allow more photons to be collected by the receiver. The sensitivity of the bundled POF based sensor is obtained at 4.321mW% with a resolution of 0.05%. The second sensor employs a silica microfiber as a probe. The system consists of an amplified spontaneous emission (ASE) light source, microfiber probe and optical spectrum analyzer (OSA). The transmitted light intensity is observed to decrease with the increase in calcium concentration due to the change in the refractive index of the solution. The sensitivity of the second sensor is obtained at 2.4dB/% with a resolution of 0.8%. Both sensors show a good stability and high sensitivity. They are simple in design and low in fabrication cost, which are appropriate for chemical, biomedical, pharmaceutical and process control applications.