Optical waveguide and method of fabricating the same

Abstract

An optical waveguide comprises a silica substrate, a buffer layer formed on the silica substrate, cores formed on the buffer layer, and upper cladding layer formed on the buffer layer, covering the cores. The thermal expansion coefficients of the buffer layer and upper cladding layer are set to be substantially equal. As a result, the stresses in the cores are isotropic, effectively suppressing birefringence.

1 . An optical waveguide, comprising: 
 a silica substrate;    a buffer layer provided on the silica substrate;    at least one core provided on the buffer layer; and    an upper cladding layer provided on the buffer layer and covering the core,    in which a thermal expansion coefficient of the buffer layer and a thermal expansion coefficient of the upper cladding layer are substantially equal.    
   
   
       2 . The optical waveguide as claimed in  claim 1 , wherein a refractive index of the buffer layer is higher than a refractive index of the silica substrate.  
   
   
       3 . The optical waveguide as claimed in  claim 1 , wherein a softening temperature of the upper cladding layer is lower than a softening temperature of the buffer layer.  
   
   
       4 . The optical waveguide as claimed in  claim 2 , wherein a softening temperature of the upper cladding layer is lower than a softening temperature of the buffer layer.  
   
   
       5 . The optical waveguide as claimed in  claim 3 , wherein at least boron (B) and phosphorus (P) are added to the upper cladding layer.  
   
   
       6 . The optical waveguide as claimed in  claim 4 , wherein at least boron (B) and phosphorus (P) are added to the upper cladding layer.  
   
   
       7 . The optical waveguide as claimed in  claim 5 , wherein at least germanium (Ge) is added to the buffer layer.  
   
   
       8 . The optical waveguide as claimed in  claim 6 , wherein at least germanium (Ge) is added to the buffer layer.  
   
   
       9 . (canceled)  
   
   
       10 . The optical waveguide as claimed in  claim 1 , further comprising another buffer layer interposed between the silica substrate and the above buffer layer, a thermal expansion coefficient of the another buffer layer is between a thermal expansion coefficients of the silica substrate and the above buffer layer.  
   
   
       11 - 12 . (canceled)