The Optical Sensing Theory And Application Study Of The U-shaped Wave-guide Coupled Single Micro-ring Structure

The concept and structure of optical micro-ring resonator was proposed by Marcatili in 1969. And it has attracted more and more different attention in optical communications, information processing, sensing and so on. After thirty years of in-depth study on theory and experiment, the micro-ring resonator has made rapid development in its special application areas, variety materials and performance-improving.The traditional sensor has a larger volume, lower integration, complex structure, limited measurement rang, lower sensitivity, resulting in some limitations in many applications. In recent years, the sensor is experiencing a changing from the traditional to the new sensor. Micro-ring sensor is the representative of many new types of sensors. Therefore, the micro-ring sensor basing on different structures, materials and application fields has been extensively studied and discussed. This paper presents the theory and application study of optical sensing based on the U-shaped wave-guide coupled single micro ring structure. A higher sensitivity and larger measurement range is obtained through theoretical simulations, and the main work of this paper is:Firstly, the significance of micro-ring sensors is explained. With the new reported micro-ring acceleration sensors, temperature sensors, and biochemical sensors as examples, the paper explains the researching status of micro-ring sensor in details, and analyzes the characteristics of its compact structure, high integration, miniaturization, high sensitivity and so on.Secondly, based on optical wave-guide and coupled mode theory, the transfer matrix method is introduced. The basic principles of micro-ring, key performance parameters, mathematical models and manufacturing process are discussed in details lately, and making a U-shaped wave-guide coupled single micro-ring structure as a mathematical model of the optical sensor, the paper analyzes its transmission characteristics through the transfer matrix method and discusses the impacts of coupling coefficient, loss, the effective refractive index of the wave-guide, micro ring radius and the distance of two U-shaped wave-guide coupling points to the output spectrum. Therefore, it provides a theoretical basis for applying study and designing in optical sensing.Finally, the paper analysis the sensing properties of the micro-ring humidity sensors and the temperature sensors based on this structure. The humidity sensor uses polyimide as a wet-sensing material, and its basic principle can be explained as this: the changing of the relative humidity makes the drift of the output spectrum. After discussing the the best sensing position of the whole structure, the paper finds its sensitivity is larger than traditional humidity sensor and analysis the measures to suppressing the interference of temperature; the material of the temperature sensor is SOI, and its basic principle can be explained as this: the changing of the temperature makes the drift of the output spectrum. Simulation results show that the measurement range is approximately twice of the traditional single temperature sensor, but it’s still small, then the bending loss is increased through reducing the radius in order to broaden the measurement range farther, so the paper analysis of the methods to reduce the bending loss.