A novel optical fiber biochemical sensor based on long period grating

In this paper, our present work, which aimed at investigating a novel optical fiber biochemical sensor based on long period grating (LPG), is introduced. Biochemical sensor is one of the most attractive fields of sensor research, especially with the development and occurrence of all kinds of novel theory and technology such as LPG. When there is a refraction index periodic perturbation, the guiding mode and cladding mode in LPG couple with each other. This make the LPG is sensitive to the ambient refractive index. This means it can be a novel bio-chemical sensor when it is applied in the fields of biochemistry. After investigating the principle of coupling in LPG, where the formulas of resonance wave length and band width are induced by 3-layer step index model, we developed an optical fiber biochemical sensor. The structure of its probe is designed by coating some function films whose thickness is between several tens and several hundreds nanometers on the cladding of optical fiber. Experiments of monitoring the saline separateness process of Bovine Serum Albumin (BSA) and Mice-Immunoglobulin G (M-IgG) by using the developed LPG sensor have been done. The monitoring indicated that for the BSA, the saline separateness occurs when the saturation is between 50% and 60%, for the M-IgG, the percentage is between 30%-40%. Besides the monitoring, the experiments could also analyze the effects of protein type (different molecule structure), protein consistency and saline saturation to saline separateness. The experimental results show that the optical fiber biochemical sensor based on LPG has many advantages such as simple structure, high sensitivity and miniature. It has a promising future in many research fields and application fields.