Method for fabricating optical devices by assembling multiple wafers containing planar optical waveguides

Abstract

A method for fabricating optical devices comprises the steps of preparing a first substrate wafer with at least one buried optical waveguide on an approximately flat planar surface of the substrate and a second substrate wafer with at least a second buried optical waveguide. The waveguides so formed may be straight or be curved along the surface of the wafer or curved by burying the waveguide at varying depth along its length. The second wafer is turned (flipped) and bonded to the first wafer in such a manner that the waveguides, for example, may form an optical coupler or may crossover one another and be in proximate relationship along a region of each. As a result, three dimensional optical devices are formed avoiding conventional techniques of layering on a single substrate wafer. Optical crossover angles may be reduced, for example, to thirty degrees from ninety degrees saving substrate real estate. Recessed areas may be provided in one or the other substrate surface reducing crosstalk in a completed three dimensional crossover device. Three dimensional optical couplers may comprise waveguides of identical or dissimilar characteristics. Moreover, three dimensional optical switches may be formed using the proposed flip and bond assembly process.

What we claim is:  
     
         1 . A method for fabricating an optical device, in which at least one wafer containing at least one buried optical waveguide is assembled and bonded to at least one other wafer containing at least one buried optical waveguide, the bonded wafers being positioned with respect to one another and forming said optical device such that different regions of each waveguide are formed by the bonding to be in optical relationship to one another.  
     
     
         2 . The method of  claim 1 , in which at least two planes of waveguide are formed in each of two substrates parallel to one another after the wafers are bonded.  
     
     
         3 . The method of  claim 1 , in which at least two waveguide wafers are bonded to each other such that substantially the extent of planar surfaces of the wafers, each having diffused thereon said at least one waveguide, are in intimate contact.  
     
     
         4 . The method of  claim 1 , in which said at least two wafers are composed of different materials.  
     
     
         5 . The method of  claim 4 , in which at least one of the at least two wafers is crystalline and another one of the at least two wafers is non-crystalline.  
     
     
         6 . The method of  claim 1 , in which at least two of the wafers contain waveguides with different composition from each other.  
     
     
         7 . The method of  claim 1 , in which at least two of the wafers contain waveguides with different refractive index profile from each other.  
     
     
         8 . The method of  claim 1 , in which at least one of the wafers contains at least one waveguide capable of providing optical gain.  
     
     
         9 . The method of  claim 8 , in which an optical gain medium is a semiconductor.  
     
     
         10 . The method of  claim 8 , in which an optical gain medium is doped with rare earth ions.  
     
     
         11 . The method of  claim 10 , in which said optical gain medium is doped with erbium.  
     
     
         12 . The method of  claim 1 , in which at least one of the wafers contains at least one waveguide capable of providing saturable optical absorption.  
     
     
         13 . The method of  claim 12 , in which a saturable absorption medium is a semiconductor.  
     
     
         14 . The method of  claim 12 , in which a saturable absorption medium is doped with rare earth ions.  
     
     
         15 . The method of  claim 14 , in which the saturable absorption medium is doped with erbium.  
     
     
         16 . The method of  claim 1 , in which respective segments of said at least two waveguides of said at least two wafers are positioned so that their guided waves interact to form an optical coupler.  
     
     
         17 . The method of  claim 1 , in which respective segments of said at least two waveguides of said at least two wafers are positioned so that their guided waves cross each other without strong interaction forming an optical crossover.  
     
     
         18 . The method of  claim 1 , in which: 
 at least two waveguide segments are positioned so that their guided waves interact to form an optical coupler; and    at least two waveguide segments are positioned so that their guided waves cross each other without strong interaction, so that an optical crossover is formed; and    at least one optical coupler and at least one optical crossover are interconnected to form an optical integrated circuit.    
     
     
         19 . The method of  claim 1 , in which at least one waveguide is fabricated by a process including dopant in-diffusion.  
     
     
         20 . The method of  claim 1 , in which at least one waveguide is fabricated by a process including ion implantation.  
     
     
         21 . The method of  claim 1 , in which at least one waveguide is fabricated by a process including layer deposition and etching.  
     
     
         22 . The method of  claim 1 , in which the depth of burying at least one waveguide is varied along its length so that the waveguide is curved with respect to the flat planar surface of the wafer.  
     
     
         23 . The method of  claim 1 , in which a region of low refractive index is provided between at least two waveguides to control the degree of coupling between them.  
     
     
         24 . The method of  claim 1 , in which a region of high refractive index is provided between at least two waveguides to control the degree of coupling between them.  
     
     
         25 . The method of  claim 1 , in which a metallic region is provided between at least two waveguides to control the degree of coupling between them.  
     
     
         26 . The method of  claim 22 , in which the depth of at least one waveguide is varied along its length to control the degree of coupling between waveguide segments of at least two waveguides.  
     
     
         27 . An optical amplifier apparatus comprising: 
 at least one waveguide capable of optical gain; and    at least one optical coupler capable of introducing light into said amplifying waveguide without interrupting or terminating said amplifying waveguide in which optical pumping light is coupled into said at least one amplifying waveguide gradually, over an extended region of its length.    
     
     
         28 . An optical amplifier apparatus comprising: 
 at least one waveguide capable of optical gain; and    at least one optical coupler capable of introducing light into said amplifying waveguide without interrupting or terminating said amplifying waveguide in which optical pumping light is coupled into at least one amplifying waveguide at at least three regions along its length.    
     
     
         29 . An optical amplifier apparatus comprising: 
 at least two waveguides capable of optical gain; and    at least one optical coupler capable of introducing light into one of said amplifying waveguides without interrupting or terminating said amplifying waveguide in which at least one optical crossover is provided to enable distribution of a single pump source to said at least two amplifying waveguides.    
     
     
         30 . An optical amplifier apparatus comprising: 
 at least one waveguide capable of optical gain; and    at least one optical coupler capable of introducing light into said amplifying waveguide without interrupting or terminating said amplifying waveguide in which at least one optical crossover is provided to enable distribution of at least two pump sources to said single amplifying waveguide.    
     
     
         31 . An optical amplifier apparatus, comprising: 
 at least one waveguide capable of optical gain; and    at least one optical coupler capable of extracting light from said amplifying waveguide without interrupting or terminating said amplifying waveguide.    
     
     
         32 . The apparatus of  claim 31 , in which said at least one optical coupler extracts light at selected wavelengths to achieve an equalized, gain spectrum of predetermined shape for an optical amplifier.  
     
     
         33 . The apparatus of  claim 32  in which said gain spectrum of predetermined shape comprises a wavelength flattened shape.  
     
     
         34 . An optical switch apparatus containing at least one waveguide capable of saturable absorption, coupled to at least one optical coupler fabricated according to the method of  claim 16 .  
     
     
         35 . An optical switch apparatus containing at least one optical coupler fabricated by the method of  claim 16 , in which the refractive index of at least one waveguide segment is controlled to determine routing of at least one optical signal through the switch.  
     
     
         36 . An optical switch apparatus as recited in  claim 35  said control is provided optically.  
     
     
         37 . An optical switch apparatus as recited in  claim 36  wherein said optical control is provided by at least one waveguide.  
     
     
         38 . An optical switch apparatus as recited in  claim 35  wherein said control is provided electrically.  
     
     
         39 . A method of fabricating an optical device comprising the steps of: 
 forming at least one buried optical waveguide in a planar surface of a first wafer substrate;    forming at least one buried optical waveguide on a planar surface of a second wafer substrate;    placing the second wafer substrate on to the planar surface of the first wafer substrate and bonding the first and second wafer substrates together.    
     
     
         40 . A method of fabricating an optical device as recited in  claim 39  further comprising the step of forming a recessed area on the planar surface of one wafer substrate before bonding the first and second wafer substrates together.  
     
     
         41 . A method of fabricating an optical device as recited in  claim 39  wherein said at least one planar waveguide of one or the other wafer substrate is curved.  
     
     
         42 . A method of fabricating an optical device as recited in  claim 39  wherein said at least one planar optical waveguide of said first wafer substrate crosses said at least one planar optical waveguide of said second wafer substrate at an angle of less than fifty degrees after bonding.  
     
     
         43 . A method of fabricating an optical device as recited in  claim 40  further comprising the step of filling said recessed area with a material other than one of a vacuum, air and an inert gas.  
     
     
         44 . A method of fabricating an optical device as recited in  claim 39  wherein one waveguide is buried at varying depth along its length in relation to the planar surface of its corresponding wafer substrate.