Abstract:
There is provided a method of manufacturing an optical waveguide, the method including: allowing a beam to be incident in an optical waveguide direction of an optical waveguide material; generating an optical solution in the optical waveguide material by adjusting intensity of the incident beam according to the optical waveguide material; allowing the incident beam to be re-incident at an intensity higher than an intensity of the incident beam after checking generation of the optical solution in the optical waveguide material; and increasing a refractive index of an optical solution-generating area of the optical waveguide material by the re-incident beam to thereby form an optical waveguide.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 2007-33361 filed on Apr. 4, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method of manufacturing an optical waveguide, and more particularly, to a method of manufacturing an optical waveguide using an optical solution generated in an optical waveguide material. 
         [0004]    2. Description of the Related Art 
         [0005]    An optical waveguide or optical fiber is an optical member transmitting a beam in one direction without being diffracted when the beam propagates through a material. The most common example for the optical waveguide is an optical fiber used in optical communication. This optical waveguide is one of essential parts in the modern information society. Particularly, in the optical telecommunication area, the optical waveguide technology is considered to determine capability of an overall system, thereby gaining increasing importance. 
         [0006]    The optical waveguide utilizes total reflection characteristics in which a beam, when propagating from a high-refractivity material to a low-refractivity material, is not transmitted but totally reflected at a critical angle or more. In a conventional method of manufacturing the optical waveguide, ions such as Ge and Ti are diffracted in a waveguide material such as glass and LiNbO 3  to locally increase refractivity and guide the beam. 
         [0007]    However, in this method, the Ge or Ti ions added are not diffracted deeply, thereby forming an optical waveguide only on a surface of the optical waveguide material and complicating a manufacturing process. 
       SUMMARY OF THE INVENTION 
       [0008]    An aspect of the present invention provides a method of manufacturing an optical waveguide, capable of forming an optical waveguide easily using an optical solution generated in a non-linear material. 
         [0009]    According to an aspect of the present invention, there is provided a method of manufacturing an optical waveguide, the method including: allowing a beam to be incident in an optical waveguide direction of an optical waveguide material; generating an optical solution in the optical waveguide material by adjusting intensity of the incident beam according to the optical waveguide material; allowing the incident beam to be re-incident at an intensity higher than an intensity of the incident beam after checking generation of the optical solution in the optical waveguide material; and increasing a refractive index of an optical solution-generating area of the optical waveguide material by the re-incident beam to thereby form an optical waveguide. 
         [0010]    The allowing a beam to be incident on an optical waveguide material in an optical waveguide direction may include: focusing the beam of a femto-second laser by a lens and allowing the beam to be incident in an optical waveguide direction of an optical waveguide material, the femto-second laser spaced apart from the optical waveguide material and the lens disposed between the optical waveguide material and the femto-second laser. 
         [0011]    The optical waveguide material may be formed of a glass material selected from a group consisting of LiNbO 3 , LiTaO 3 , KTP, AlGaAs, ZnSe, Al 2 O 3 and SiO 2 . 
         [0012]    The generating optical solution in the optical waveguide material may include adjusting intensity of the incident beam according to non-linear characteristics (optical kerr effects) of the optical waveguide material. 
         [0013]    The optical waveguide material may be formed of the SiO 2  glass material and the incident beam for generating the optical solution has an intensity of 10 11  to 10 12  W/cm 2 . 
         [0014]    The allowing a beam to be incident in an optical waveguide direction, the generating optical solution in the optical waveguide material, the increasing intensity of the incident beam for generating the optical solution, and the increasing a refractive index of an optical solution-generating area of the optical waveguide material by the re-incident beam may be performed repeatedly, whereby the plurality of optical waveguides are formed in the optical waveguide material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0016]      FIG. 1  is a configuration view for explaining a method of manufacturing an optical waveguide using an optical solution according to an exemplary embodiment of the invention; 
           [0017]      FIGS. 2A and 2B  are configuration views for explaining a method of manufacturing an optical waveguide according to an exemplary embodiment of the invention; and 
           [0018]      FIG. 3  is a flow chart illustrating a method of manufacturing an optical waveguide using an optical solution according to an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0020]      FIG. 1  is a configuration view for explaining a method of manufacturing an optical waveguide using an optical solution according to an exemplary embodiment of the invention. 
         [0021]    As shown in  FIG. 1 , in manufacturing the optical waveguide using the optical solution according to the present embodiment, the optical solution is generated in an optical waveguide material  30  using, for example, a femto-second laser  10  and a lens  20 . Then, the generated optical solution is utilized to a manufacture optical waveguide  50 . 
         [0022]    In the method of manufacturing the optical waveguide using the optical solution according to the present embodiment, the plurality of optical waveguides  50  may be manufactured in the optical waveguide material via the femto-second laser  10  and the lens  20 . Here, the femto-second laser  10  allows a beam to be incident in an optical waveguide direction of the optical waveguide material  30  prepared for manufacturing the optical waveguide and made of a glass material, for example, LiNbO 3 , LiTaO3, KTP, AlGaAs, ZnSe, Al 2 O 3 , and SiO 2 . Also, the lens  20  is disposed at one side of an incident surface of the optical waveguide material  30  to focus the beam generated by the femto-second laser  10 . 
         [0023]    First, a description will be given of the optical solution employed in manufacturing the optical waveguide according to the present embodiment. 
         [0024]    In general, a beam is diffracted when propagating through a vacuum or a material. Even a laser beam is necessarily diffracted when traveling a long distance or focused by a lens. As shown in  FIG. 2A , when the beam generated from the femto-second laser  10  is focused by the lens  20  and made incident on the optical waveguide material  30 , the beam is naturally re-diffracted in the optical waveguide material  30 , which is a non-linear material. 
         [0025]    However, the beam may maintain its original optical size without being diffracted when traveling through a material, which is referred to as an optical spatial solution. Specifically, as shown in  FIG. 2B , the beam focused by the lens  20  propagates through the material  30 , with the focused size maintained, without being diffracted any more in the non-linear optical waveguide material  30 , under following mechanism. 
         [0026]    The beam generated from the femto-second laser  10  shown in  FIG. 1  generally has a Gaussian distribution. That is, the beam has a strong intensity in a central portion and a weaker intensity toward an outer periphery. This beam, when incident on the non-linear optical wave guide material  30 , is greatly changed in refractive index in the central portion with a strong intensity and less changed in refractive index toward the outer periphery due to optical kerr effects caused by tertiary non-linearity of the material  30 . 
         [0027]    Therefore, the beam experiences an effect as in the lens, i.e. a self-focusing phenomenon. This self-focusing phenomenon, and diffraction, which is the unique characteristic of a beam, may be balanced, thereby generating the solution  40  in which the beam no longer is diffracted or focused, as shown in  FIG. 2B . 
         [0028]    As a method to manufacture the optical waveguide using such an optical solution, first, to generate the optical solution  40 , a beam of the femto-second laser  10  is focused by the lens  20  in an optical waveguide direction of the optical waveguide material  30 , i.e., in a length direction of the optical waveguide material  30  and made incident on the optical waveguide material  30  in S 31 . 
         [0029]    Then the incident beam of the femto-second laser  10  is adjusted in intensity to be made re-incident so that a spatial solution is generated in the optical waveguide material  30  by the incident beam of the femto-second laser  10  as in S 32 . 
         [0030]    Conditions for generating the optical solution in the optical waveguide material  30  are determined by non-linear characteristics of the optical waveguide material  30  and intensity of a beam of the femto-second laser  10 . For example, in a case where the optical waveguide material  30  is a SiO 2  glass material, a beam having an intensity of 10 11  to 10 12  W/cm 2  should be incident from the femto-second laser  10  to generate the solution in the optical waveguide material  30 . 
         [0031]    Specifically, conditions for generating the spatial solution are determined as follows. To begin with, E(r,t) pertaining to the incident beam and PNL representing non-linear characteristics in the following relations are inputted to Maxwell&#39;s wave Equation 1 and then nonlinear schrodinger equation is derived as in Equation 2. 
         [0000]    
       
         
           
             
               E 
                
               
                 ( 
                 
                   r 
                   , 
                   t 
                 
                 ) 
               
             
             = 
             
               
                 1 
                 2 
               
                
               
                 U 
                  
                 
                   ( 
                   
                     r 
                     , 
                     z 
                   
                   ) 
                 
               
                
               
                  
                 
                    
                    
                   
                     ( 
                     
                       kz 
                       - 
                       
                         ω 
                          
                         
                             
                         
                          
                         t 
                       
                     
                     ) 
                   
                 
               
             
           
         
       
       
         
           
             
               P 
               NL 
             
             = 
             
               
                 
                   P 
                   
                     ( 
                     3 
                     ) 
                   
                 
                  
                 
                   ( 
                   
                     r 
                     , 
                     t 
                   
                   ) 
                 
               
               = 
               
                 
                   3 
                   4 
                 
                  
                 
                   ɛ 
                   0 
                 
                  
                 
                   χ 
                   
                     ( 
                     3 
                     ) 
                   
                 
                  
                 
                   
                      
                     U 
                      
                   
                   2 
                 
                  
                 U 
                  
                 
                     
                 
                  
                 
                    
                   
                      
                      
                     
                         
                     
                      
                     kz 
                   
                 
               
             
           
         
       
     
         [0032]    where E is an electric field, U is an electric field amplitude, r is a location, t is a time, m 0  is a permeability of the vacuum, e is a dielectric constant of material, e 0  is a permittivity of a vacuum, P NL  is a function of non-linear polarization, X (3)  is a third order susceptibility, and k is a wave vector. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         ∇ 
                         2 
                       
                        
                       
                         E 
                          
                         
                           ( 
                           
                             r 
                             , 
                             t 
                           
                           ) 
                         
                       
                     
                     - 
                     
                       
                         μ 
                         0 
                       
                        
                       ɛ 
                        
                       
                         
                           ∂ 
                           2 
                         
                         
                           ∂ 
                           
                             t 
                             2 
                           
                         
                       
                        
                       
                         E 
                          
                         
                           ( 
                           
                             r 
                             , 
                             t 
                           
                           ) 
                         
                       
                     
                   
                   = 
                   
                     
                       μ 
                       0 
                     
                      
                     
                       
                         
                           ∂ 
                           2 
                         
                          
                         
                           
                             P 
                             NL 
                           
                            
                           
                             ( 
                             
                               r 
                               , 
                               t 
                             
                             ) 
                           
                         
                       
                       
                         ∂ 
                         
                           t 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   1 
                 
               
             
             
               
                 
                   
                     
                       
                         ∂ 
                         U 
                       
                       
                         ∂ 
                         z 
                       
                     
                     = 
                     
                       
                         
                           i 
                           4 
                         
                          
                         
                           
                             
                               ∂ 
                               2 
                             
                              
                             U 
                           
                           
                             ∂ 
                             
                               x 
                               2 
                             
                           
                         
                       
                       + 
                       
                         i 
                          
                         
                             
                         
                          
                         
                           
                             z 
                             0 
                           
                           
                             z 
                             NL 
                           
                         
                          
                         
                           
                              
                             U 
                              
                           
                           2 
                         
                          
                         U 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       z 
                       0 
                     
                     = 
                     
                       
                         π 
                          
                         
                             
                         
                          
                         
                           nw 
                           0 
                           2 
                         
                       
                       
                         λ 
                         0 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       z 
                       NL 
                     
                     = 
                     
                       
                         8 
                          
                         n 
                       
                       
                         3 
                          
                         
                           χ 
                           
                             ( 
                             3 
                             ) 
                           
                         
                          
                         
                           
                              
                             U 
                              
                           
                           2 
                         
                          
                         
                           k 
                           0 
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                         3 
                         
                           8 
                            
                           n 
                         
                       
                        
                       
                         χ 
                         
                           ( 
                           3 
                           ) 
                         
                       
                        
                       
                         
                            
                           U 
                            
                         
                         2 
                       
                     
                     = 
                     
                       
                         n 
                         2 
                       
                        
                       I 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
         [0033]    Equation 2 satisfies above relations and thus can be derived into Equation 3 as follows. 
         [0000]    
       
         
           
             
               
                 
                   
                     U 
                     = 
                     
                       
                         sech 
                          
                         
                           ( 
                           
                             
                               
                                 2 
                                  
                                 a 
                               
                             
                              
                             x 
                           
                           ) 
                         
                       
                        
                       
                          
                         
                           
                              
                              
                             
                               σ 
                               2 
                             
                              
                             z 
                           
                            
                           
                               
                           
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     a 
                     = 
                     
                       
                         z 
                         0 
                       
                       
                         z 
                         NL 
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
     
         [0034]    That is, the solution travels in the form of a Sech function in the optical waveguide material  30 . 
         [0035]    Also, in a case where the optical waveguide material  30  is formed of, for example, a non-linear material such as a fused silica satisfying n 2 =2.6×10 −16  cm 2 /W, the incident beam for generating the optical solution has an intensity ranging from 10 11  to 10 12  W/cm 2 . 
         [0036]    As described above, with the optical solution generated in the optical waveguide material  30 , the beam of the femto-second laser  10  has an intensity increased over the beam for generating the solution as in S 33  to be made re-incident. 
         [0037]    Specifically, with the solution generated in the optical waveguide material  30 , the beam from the femto-second laser  10  has an intensity increased over the beam for generating the optical solution, which has an intensity ranging from 10 11  to 10 12  W/cm 2 . For example, the beam from the femto-second laser  10  is made incident at an intensity of 10 13  to 10 15  W/cm 2 , and particularly, 10 14  W/cm 2 . Then multi-photon of the incident beam is absorbed non-linearly along an area where the solution is generated and diffracted in the optical waveguide material  30  to cause optical breakdown, thereby forming microplasma. 
         [0038]    This microplasma formed leads to change in a grating structure of the optical waveguide material  30  and thus the area where the solution is generated and diffracted has a refractive index increased, for example, by 0.003 over a refractive index of a surrounding area. Accordingly this allows the optical waveguide  50  to be formed along the area where the solution is generated and diffracted as in S 34 . 
         [0039]    According to the present embodiment, the aforesaid processes are repeated to easily form the plurality of optical waveguides  50  in the optical waveguide material  30 . Also, the incident beam can be adjusted in intensity and size using the femto-second laser  10  and the lens  20  to uniformly form the optical waveguides  50  having various refractive indices and sizes 
         [0040]    As set forth above, according to exemplary embodiments of the invention, a solution is generated in an optical waveguide and with the solution generated, an incident beam is increased in intensity to be made re-incident, thereby forming an optical waveguide. This allows a plurality of optical waveguides with uniform refractive indices to be formed easily. 
         [0041]    While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.