Optical waveguide structure

Abstract

A waveguide structure according to the invention comprises a core layer (10), having a refractive index n core , and an array of rods (11) in the core layer having a refractive index n rods The refractive indices satisfy the inequality n rods >n core In a planar waveguide structure buffer (12) and cladding (13) layers are included, having a refractive index n buffer and n cladding respectively The refractive indices then satisfy the inequality n rods >n core >n cladding and n buffer This condition provides greater vertical confinement of the E-field of an optical signal passing through the waveguide. Furthermore, it allows waveguides to be formed of a glassy material having a similar refractive index and core dimensions to that of a fibre A high refractive index contrast within the photonic crystal region is used while totally eliminating the need for mode conversion to launch light in and out of the waveguide

1  An optical waveguide structure comprising a core layer having a first refractive index n core , and an array of sub-regions within the core layer having a second refractive index n rods , the array of sub-regions giving rise to a photonic band structure within the core layer, wherein  
       n rods >n core    
     
     
         2  An optical waveguide structure according to  claim 1 , wherein the waveguide structure is a planar waveguide structure, the core layer being formed between a cladding layer and a buffer layer, the cladding layer having a third refractive index n cladding , and the buffer layer having a fourth refractive index n buffer , wherein  
       n rods >n core >n cladding  and n buffer    
     
     
         3  An optical waveguide structure according to  claim 1 , wherein the waveguide structure is an optical fibre, further comprising a cladding layer having a third refractive index n cladding , surrounding the core layer, wherein  
       n rods >n core >n cladding    
     
     
         4  An optical fibre according to  claim 3 , wherein the cladding layer is planarised in the vicinity of the array of sub-regions, the array of sub-regions extending through the planarised cladding layer and into the core layer  
     
     
         5  An optical waveguide structure according to  claim 1 , wherein the array of sub-regions gives rise to a photonic bandgap.  
     
     
         6  An optical waveguide structure according to  claim 1  wherein the sub-regions are formed from silicon  
     
     
         7  An optical waveguide structure according to  claim 1 , wherein the core layer is formed from silicon nitride, silicon oxynitride doped silica, tantalum pentoxide or doped tantalum pentoxide  
     
     
         8  An optical waveguide structure according to  claim 2  or  3 , wherein the cladding is formed from silicon dioxide.  
     
     
         9  A planar optical waveguide structure according to  claim 2 , wherein the sub-regions extend through the cladding layer as well as the core layer  
     
     
         10  A planar optical waveguide structure according to  claim 2 , wherein the sub-regions extend partially into the buffer layer.  
     
     
         11  An optical waveguide structure according to  claim 2  or  3 , wherein the cladding layer includes sub-regions corresponding to the sub-regions in the core layer, having a refractive index which is greater than or equal to the refractive index of the cladding layer but which is less than or equal to the refractive index of the core  
     
     
         12 . An optical waveguide structure according to  claim 1 , wherein the array of sub-regions are arranged in a square lattice  
     
     
         13 . An optical waveguide structure according to  claim 1 , wherein the core layer includes a waveguiding region having no sub-regions  
     
     
         14  An optical waveguide structure according to  claim 10 , wherein the waveguiding region includes a bend  
     
     
         15  An optical device incorporating an optical waveguide structure according to  claim 1   
     
     
         16  A method of manufacturing a optical waveguide structure comprising the steps of 
 providing a core layer having a first refractive index n core ,  
 forming an array of holes in the core layer,  
 filling the holes with a material having a second refractive index n rods , wherein  
 n rods >n core .  
 
     
     
         17  A method according to  claim 16 , wherein the optical waveguide is a planar waveguide, the method further including the steps of 
 providing a buffer layer having a refractive index n buffer  on one side of the core layer, and  
 providing a cladding layer having a refractive index n cladding  on the other side of the core layer, wherein  
 n rods >n core >n cladding  and n buffer    
 
     
     
         18 . A method according to  claim 16  wherein the optical waveguide is an optical fibre, the method further including the steps of 
 providing a cladding layer having a refractive index n cladding  surrounding the core layer wherein  
 n rods >n core >n cladding    
 
     
     
         19 . A method of guiding an optical signal comprising the step of passing an optical signal through a waveguiding region of an optical waveguide structure comprising a core layer having a first refractive index n core , and an array of sub-regions within the core layer having a second refractive index, n rods , the array of sub-regions giving rise to a photonic band structure within the core layer, wherein  
       n rods >n core    
     
     
         20  A method according to  claim 19  wherein the waveguide is a planar waveguide, wherein the core layer is formed between a cladding layer and a buffer layer, the cladding layer having a third refractive index n cladding , and the buffer layer having a fourth refractive index n buffer , and wherein  
       n rods >n core >n cladding  and n buffer    
     
     
         21  A method according to  claim 19 , wherein the optical waveguide is an optical fibre, wherein a cladding layer has a third refractive index n cladding , and surrounds the core layer, and wherein  
       n rods >n core >n cladding