Racetrack micro-resonators based on ridge waveguides made of porous silica

The fabrication of micro-resonators, made from porous silica ridge waveguides by using an electrochemical etching method of silicon substrate followed by thermal oxidation and then by a standard photolithography process, is reported. The design and fabrication process are described including a study of waveguide dimensions that provide single mode propagation and calculation of the coupling ratio between a straight access waveguide and the racetrack resonator. Scanning electronic microscopy observations and optical characterizations clearly show that the microresonator based on porous silica ridge waveguides has been well implemented. This porous microresonator is destined to be used as an optical sensor. The porous nature of the ridge waveguide constitutes the detection medium which will enhance the sensor sensitivity compared to usual micro-resonators based on the evanescent wave detection. A theoretical sensitivity of 1170 nm per refractive index unit has been calculated, taking into consideration experimental data obtained from the optical characterizations.