A highly asymmetric hybrid directional coupler sensor

Abstract

The advances in the microelectronics industry and microfabrication techniques in the past few decades have lead to an increase in the capabilities and features of all kinds of sensors. From pressure sensors to chemical sensors, all kinds of devices have gone through fundamental improvements, giving rise to a generation of sensors with better quailty, higher precision and lower cost and power consumption. In this work, a new optical chemical sensor was designed. The structure is based on a highly asymmetric directional coupler, where the asymmetry implies a high refractive index difference between the core layers of the waveguides in the coupler, rather than an asymmetry in geometry. The device designed presents a very high sensitivity to both the operating wavelength, and the index of refraction of the target matirial. Therefore, monitoring can be performed in two alternative ways, namely, by monitoring the output power at a specified wavelength of operation, or by monitoring the whole multi-wavelength spectrum for a changing refractive index. The coupler is composed of a polymer ridge waveguide and a semiconductor slab waveguide. Fabricating the sensor employs conventional microelectronic fabrication techniques and can easily be integrated with various microelectronic components. The complete top-down fabrication scheme for the devices is presented, giving specific recipes and techniques. The materials to be used for the fabrication are selected to yield the best results in he device performance. Also, the fabrication process for each individual layer are optimized in order to obtain the desired device structure.