Directional coupler and optical communication device

Abstract

A directional coupler of the present invention includes a substrate; a first waveguide layer; a second waveguide layer disposed over the first waveguide layer; a separation layer which separates the first waveguide layer and the second waveguide layer at least at one end; and an optical coupling section which is a predetermined region in which the first waveguide layer and the second waveguide layer approach or come in contact with each other. Each of the first waveguide layer and the second waveguide layer is integrally and continuously formed.

What is claimed is:  
     
         1 . A directional coupler comprising: 
 a substrate;    a first waveguide layer;    a second waveguide layer disposed over the first waveguide layer;    a separation layer which separates the first waveguide layer and the second waveguide layer at least at one end; and    an optical coupling section which is a predetermined region in which the first waveguide layer and the second waveguide layer approach or come in contact with each other,    wherein each of the first waveguide layer and the second waveguide layer is integrally and continuously formed.    
     
     
         2 . The directional coupler as defined by  claim 1 , further comprising: 
 a first cladding layer which is disposed over the substrate and has a projecting portion on the substrate; and    a second cladding layer disposed over the second waveguide layer,    wherein part of the first waveguide layer is disposed over the projecting portion of the first cladding layer to form the optical coupling section.    
     
     
         3 . The directional coupler as defined by  claim 1 , 
 wherein the first waveguide layer is disposed linearly.    
     
     
         4 . The directional coupler as defined by  claim 1 , 
 wherein the second waveguide layer has a bent portion.    
     
     
         5 . The directional coupler as defined by  claim 2 , 
 wherein the second waveguide layer is disposed linearly.    
     
     
         6 . The directional coupler as defined by  claim 1 , 
 wherein the separation layer includes: 
 a first separation layer which separates the first waveguide layer and the second waveguide layer at one end; and  
 a second separation layer which separates the first waveguide layer and the second waveguide layer at the other end.  
   
     
     
         7 . The directional coupler as defined by  claim 6 , 
 wherein the first separation layer and the second separation layer are disposed between the first waveguide layer and the second waveguide layer and integrally and continuously formed with each other.    
     
     
         8 . The directional coupler as defined by  claim 7 , 
 wherein refractive indices of the first cladding layer and the second cladding layer are the same, and    wherein refractive indices of the first and second separation layers differ from refractive indices of the first and second cladding layers.    
     
     
         9 . The directional coupler as defined by  claim 1 , further comprising an electrode layer, 
 wherein distribution of light in the optical coupling section is changeable by applying a predetermined voltage to the electrode layer.    
     
     
         10 . The directional coupler as defined by  claim 9 , 
 wherein the electrode layer comprises an electrode pair including a first electrode layer disposed under the first waveguide layer in the optical coupling section and a second electrode layer disposed over the second waveguide layer in the optical coupling section, and    wherein distribution of light in the optical coupling section is changeable by applying different voltages to the first and second electrode layers, respectively.    
     
     
         11 . The directional coupler as defined by  claim 10 , 
 wherein the electrode pair includes: 
 a first electrode pair having the first and second electrode layers; and  
 a second electrode pair having the first and second electrode layers,  
   wherein a voltage applied to the first electrode layer is higher than a voltage applied to the second electrode layer in the first electrode pair, and    wherein a voltage applied to the second electrode layer is higher than a voltage applied to the first electrode layer in the second electrode pair.    
     
     
         12 . The directional coupler as defined by  claim 1 , further comprising a heating section, 
 wherein distribution of light in the optical coupling section is changeable by heating the optical coupling section by a heating section.    
     
     
         13 . A directional coupler in which a plurality of the directional couplers as defined by any one of  claims 1  to  12  is stacked.  
     
     
         14 . An optical communication device comprising the directional coupler as defined by any one of  claims 1  to  13 .