Optical waveguide having a varying index gradient

Abstract

A photoacoustic detection device including a nanophotonic circuit including a first chip on which is formed at least one optical waveguide and in which is formed a set of cavities defining a Helmholtz resonator; at least one optical source capable of emitting an optical signal in a given wavelength range, capable of being modulated at an acoustic modulation frequency, this source being attached to the first chip; a second chip forming a cap for said cavities and including acoustic sensors; and electronic circuits for processing the output of the acoustic sensors formed in the first or the second chip. Further, an optical waveguide comprising, on a silicon substrate, a silicon germanium core with a variable germanium concentration along a direction perpendicular to the substrate, said core being covered with a cladding silicon layer.

What is claimed is: 
     
         1 . An optical waveguide comprising, on a silicon substrate, a silicon germanium core with a variable germanium concentration along a direction perpendicular to the substrate, said core being covered with a cladding silicon layer. 
     
     
         2 . The optical waveguide of  claim 1 , wherein the proportion of germanium in the silicon germanium varies to obtain an index gradient with a triangular shape. 
     
     
         3 . The optical waveguide of  claim 1 , wherein the proportion of germanium in the silicon germanium varies to obtain an index gradient with a trapezoidal shape. 
     
     
         4 . The optical waveguide of  claim 1 , wherein the cladding layer is a layer of monocristaline silicon. 
     
     
         5 . The optical waveguide of  claim 1 , wherein the cladding layer is a layer of amorphous silicon. 
     
     
         6 . Waveguide of  claim 1  adapted to operate in a wavelength range comprised between 3 and 10 μm.