A fiber link equipment for the optical rotation measuring based on AC-DC modulation magneto-optical effect

Based on the magnetic-optical effect, an alternating current-direct current (AC-DC) two-stage modulation is applied in the newly developed equipment, which measures the concentration of solution through the optical rotation of optical active substance. A Faraday coil is combined with the AC-DC signal generator controlled by a pulse width modulation controller. To deduct the measuring error caused by the AC modulation or the DC modulation, a two-stage method based on the Superposition of DC component and AC component is demonstrated, which is characterized by removing the interference of the bigger magnetic rotation angle in the AC modulation alone. The tartaric acid, glucose, and sucrose sugar solutions are taken as the standard examples in testifying the equipment. A linear correlation is found between the measured optical rotation angle and the concentration of the solution, with the optical rotation angle being within a 1% margin of error and the maximum relative error smaller than 0.005 g/ml. The results show that the equipment has the advantage of high precision, high integration, and strong anti-interference capacity. The fiber link makes the equipment portable and compact. The AC-DC two-stage modulation equipment can potentially be used in the optical rotation measurement.