Novel chemical sensor/biosensor platform based on optical multimode interference (MMI) couplers

We present a novel platform for chemical sensing and biosensing. The working principle is based on the interference properties of an optical multimode interference coupler. A humidity sensor has been implemented as a proof of principle. It has been realised using hybrid sol–gel planar technology to allow integration on a silicon substrate. y, we describe the theory of multimode interference and we model the sensor response to the change of the sensing layer refractive index. Then, the sensing material is described and characterised regarding optical and sensing properties. Finally, the prototype device is characterised. A linear response to relative humidity is obtained and it is shown that sensitivity can be tuned using the MMI design technique.