Infrared integrated optical evanescent field sensor for gas analysis

The high step in refractive index between silicon core and gas allows very small bending radii so that a sufficiently long waveguide can be realised on small chip area (about 1 m on 1 cm2). The waveguide is patterned as a spiral or a meander in the wafer plane. A suitable freestanding cross section profile is realized by a sequence of anisotropic dry etching, oxidation and isotropic dry etching of crystalline silicon bulk material.