Absorption cavity with entrance and exit waveguides for a chemical or biological sensor

An optical device for a chemical or biological sensor, comprising:

• an absorption cavity including reflective inner walls and configured to receive a chemical or biological medium;
• an injection waveguide, extending outside the absorption cavity and laid out for injection of an analysis light beam inside the absorption cavity;
• and
• an extraction waveguide, extending outside the absorption cavity and laid out for extraction of a measurement light beam, coming from inside the absorption cavity and corresponding to the analysis light beam having transited through the absorption cavity;
• wherein the absorption cavity has a right cylinder shape, with an ellipse portion shaped base, one end of the injection waveguide is arranged at a first focus of the ellipse and one end of the extraction waveguide is arranged at a second focus of the ellipse, and the core of the injection waveguide and the core of the extraction waveguide each include a tip shaped end, with a constant height in a plane parallel to the generatrix of the right cylinder and a tip shaped section in planes parallel to the base of the right cylinder.