Photonic crystal, method of fabricating the same, optical module, and optical system

Abstract

It is an object of this invention to overcome the problems of prior art by a unique arrangement based on a novel idea, and to provide an optical device having desired characteristics and an optical module and optical system incorporating the optical device. Provided is a photonic crystal including a three-dimensional periodic structure formed by using a first material which changes in properties relatively easily and a second material which does not change in properties relatively easily, wherein the first material is preferentially allowed to change in properties to make a refractive index difference between the first and second materials larger than that before the property change. Also provided is an optical device including a photonic waveguide, gain means, and reflecting means, wherein resonance is generated by reversing the propagating direction of light propagating in the photonic waveguide by the reflecting means while a gain is given to the light by the gain means.

What is claimed is:  
     
         1 . A photonic crystal comprising: 
 a three-dimensional periodic structure formed by using a first material which changes in properties relatively easily and a second material which does not change in properties relatively easily,    wherein said first material is preferentially allowed to change in properties to make a refractive index difference between said first and second materials larger than that before the property change.    
     
     
         2 . A crystal according to  claim 1 , wherein the property change is oxidation.  
     
     
         3 . A photonic crystal fabrication method comprising at least the steps of: 
 forming, on a substrate, a first stripe structure layer in which stripes of a first material and stripes of a second material are alternately arrayed periodically in plane along a first direction;    stacking, on said first stripe structure layer, a second stripe structure layer in which stripes of said first material and stripes of said second material are alternately arrayed periodically in plane along a second direction substantially perpendicular to the first direction;    stacking, on said second stripe structure layer, a third stripe structure layer in which stripes of said first material and stripes of said second material are alternately arrayed periodically in plane along the first direction, such that the array is shifted a half period from the in-plane periodic array of said first stripe structure layer;    stacking, on said third stripe structure layer, a fourth stripe structure layer in which stripes of said first material and stripes of said second material are alternately arrayed periodically in plane along the second direction, such that the array is shifted a half period from the in-plane periodic array of said second stripe structure layer; and    preferentially removing the stripes of said first material by etching, or preferentially changing properties of the stripes of said first material, thereby making a refractive index difference between said first and second materials larger than that before the removal, or before the property change.    
     
     
         4 . A method according to  claim 3 , wherein the property change is oxidation.  
     
     
         5 . An optical device comprising: 
 a photonic waveguide which is formed in a photonic crystal having a three-dimensional periodic refractive index distribution, and in which the periodic refractive index distribution is locally disturbed;    gain means for giving a gain to light propagating in said photonic waveguide; and    reflecting means for reflecting light propagating in said photonic waveguide to reverse the propagating direction of the light,    wherein resonance is generated by reversing the propagating direction of light propagating in said photonic waveguide by said reflecting means while a gain is given to the light by said gain means.    
     
     
         6 . A device according to  claim 5 , wherein 
 said photonic waveguide comprises a main waveguide portion substantially parallel to a principal surface of said photonic crystal and a branched waveguide portion connected at a substantially right angle to said main waveguide and extending toward the principal surface of said photonic crystal, and    said reflecting means is formed at the end of said branched waveguide portion.    
     
     
         7 . A device according to  claim 5 , wherein 
 said photonic waveguide comprises a plurality of branched waveguide portions connected to said main waveguide portion, and    said reflecting means formed at the end of at least one of said plurality of branched waveguide portions has reflectivity lower than that of reflecting means formed at the ends of other branched waveguide portions, and functions as a light output portion or as a light input portion.    
     
     
         8 . A device according to  claim 7 , wherein said branched waveguide portion corresponding to said light output portion or light input portion is connected to the vicinity of a portion where the intensity of light propagating in said main waveguide portion is a maximum.  
     
     
         9 . A device according to  claim 8 , wherein said plurality of branched waveguide portions are periodically connected at equal intervals to said main waveguide portion.  
     
     
         10 . A device according to  claim 5 , wherein said gain means comprises a semiconductor having a p-n junction and gives the gain by injecting minority carriers into said p-n junction.  
     
     
         11 . A device according to  claim 5 , further comprising phase control means for controlling the phase of light propagating in said photonic waveguide.  
     
     
         12 . A device according to  claim 5 , further comprising light modulating means for modulating output light from said photonic waveguide.  
     
     
         13 . A device according to  claim 5 , further comprising light receiving means for detecting output light from said photonic waveguide.  
     
     
         14 . An optical module comprising: 
 an optical device according to  claim 5;     a driving circuit for supplying an electric current for driving said optical device; and    optical means for giving an optical action to output light from said optical device or input light to said optical device.    
     
     
         15 . An optical system comprising: 
 an optical module according to  claim 14;     a signal supply circuit for supplying an electrical signal to said optical module; and    guiding means for guiding output light from said optical module.