Four layer integrated optical biosensor

Integrated optical biosensors are capable of combining properties of miniaturization, stability and high sensitivity. In this paper a novel integrated optic biosensor for the measurement of glucose concentration in the blood design is proposed and analysed mathematically. The configuration is based on silicon on insulator technology and consists of four layers, the oxide substrate layer, thin silicon nitride layer to enhance the sensitivity, the silicon ridge waveguide optical guiding layer, and the cover layer consisting of bio-analyte to be measured. The main idea in this configuration is the introduction of thin nitride layer in between silicon and silicon dioxide. Then it was observed that in the case of three layer waveguide the mode penetration into the cladding influences the sensitivity. Introduction of silicon nitride layer between the oxide and guiding layer reduces the refractive index contrast between the substrate and the guiding layer resulting in increased penetration depth. We obtain a sensitivity of 1%, in terms of effective refractive index change.