Method of thermally drawings structured sheets

Abstract

A method of drawing a material into sheet form includes forming a preform comprising at least one material as a large aspect ratio block wherein a first transverse dimension of the preform is much greater than a second transverse dimension substantially perpendicular to the first transverse dimension. A furnace having substantially linearly opposed heating elements one spaced from the other is provided and the heating elements are energized to apply heat to the preform to create a negative thermal gradient from an exterior surface along the first transverse dimension of the preform inward toward a central plane of the preform. The preform is drawn in such a manner that the material substantially maintains its first transverse dimension and deforms across its second transverse dimension.

What is claimed is: 
     
         1 . An interference-based thin film for selective reflection and selective transmission of waves manufactured by a method comprising the steps of:
 providing a preform comprising at least one material as a large aspect ratio block wherein a first transverse dimension of the preform is greater than a second transverse dimension that is approximately perpendicular to the first transverse dimension;   providing a furnace having at least one heating element on at least one side of the furnace;   energizing the at least one heating element to apply heat to the preform to create a thermal gradient from an exterior surface along the first transverse dimension of the preform inward toward a plane of the preform, wherein the at least one heating element creates approximately uniform temperature distribution along the second transverse direction;   feeding the preform into the furnace; and   drawing the preform in such a manner that the material does not substantially deform across its first transverse dimension and deforms across its second transverse dimension.   
     
     
         2 . The method of  claim 1 , further comprising preheating the at least one material before the at least one material enters a hottest zone of the furnace and further heating the at least one material after it leaves said hottest zone to gradually bring said at least one material to a lower temperature. 
     
     
         3 . The method of  claim 1 , wherein the step of providing a preform comprises providing a cylindrical preform and the step of drawing the preform further comprises drawing said preform to an elliptical fiber. 
     
     
         4 . The method of  claim 1 , wherein the step of providing a preform comprises providing a preform with a square cross-section and the step of drawing the preform further comprises drawing said preform to a rectangular fiber. 
     
     
         5 . The method of  claim 1 , wherein heating is applied approximately symmetrically. 
     
     
         6 . The method of  claim 1 , wherein the at least one material comprises at least one of a thermoplastic polymer, any type of glass, amorphous materials that can be stretched when heated, and metals. 
     
     
         7 . The method of  claim 1 , wherein the preform comprises two or more materials with similar thermal and mechanical properties. 
     
     
         8 . The method of  claim 1 , wherein the step of providing a preform comprises providing a first block comprising a first material and embedding in the first block a second block of a second material; wherein, upon completion of the drawing step, the sheet form comprises layers corresponding to said first and second materials. 
     
     
         9 . The method of  claim 1 , wherein the step of providing a preform comprises providing a first block comprising a first material and embedding in the first block parallel layers of different materials or identical materials with different dopants; wherein, upon completion of the drawing step, the sheet form comprises layers corresponding to said first material and said different materials or identical materials with different dopants. 
     
     
         10 . The method of  claim 1 , wherein the step of providing a preform comprises providing a first block comprising a first material and embedding in the first block a plurality of vertically aligned secondary material elements centered on a vertical axis of the preform; wherein, upon completion of the drawing step, the sheet form comprises layers corresponding to said first material and said plurality of vertically aligned secondary material elements. 
     
     
         11 . The method of  claim 1 , wherein the step of providing a preform comprises providing a first block comprising a first material and embedding in the first block a plurality of parallel aligned secondary material elements; wherein, upon completion of the drawing step, the sheet form comprises layers corresponding to said first material and said plurality of parallel aligned secondary material elements. 
     
     
         12 . The method of  claim 1 , wherein the first transverse dimension of the preform is at least 1.5 times greater than the second transverse dimension. 
     
     
         13 . The method of  claim 1 , wherein the first transverse dimension of the preform is at least five times greater than the second transverse dimension. 
     
     
         14 . The method of  claim 1 , wherein the first transverse dimension of the preform is at least ten times greater than the second transverse dimension. 
     
     
         15 . The method of  claim 1 , wherein the step of providing a furnace comprises providing a plurality of heating elements to create a temperature gradient in one direction that is larger than a temperature gradient in another direction to cause asymmetric drawing. 
     
     
         16 . The method of  claim 1 , wherein the first transverse dimension of the preform is at least one thousand times greater than the second transverse dimension. 
     
     
         17 . An optical waveguide manufactured by a method comprising the steps of:
 providing a preform comprising at least one material as a large aspect ratio block wherein a first transverse dimension of the preform is greater than a second transverse dimension that is approximately perpendicular to the first transverse dimension;   providing a furnace having at least one heating element on at least one side of the furnace;   energizing the at least one heating element to apply heat to the preform to create a thermal gradient from an exterior surface along the first transverse dimension of the preform inward toward a plane of the preform, wherein the at least one heating element creates approximately uniform temperature distribution along the second transverse direction;   feeding the preform into the furnace; and   drawing the preform in such a manner that the material does not substantially deform across its first transverse dimension and deforms across its second transverse dimension.   
     
     
         18 . The method of  claim 17 , further comprising preheating the at least one material before the at least one material enters a hottest zone of the furnace and further heating the at least one material after it leaves said hottest zone to gradually bring said at least one material to a lower temperature. 
     
     
         19 . An array of optical waveguides manufactured by a method comprising the steps of:
 providing a preform comprising at least one material as a large aspect ratio block wherein a first transverse dimension of the preform is greater than a second transverse dimension that is approximately perpendicular to the first transverse dimension;   providing a furnace having at least one heating element on at least one side of the furnace;   energizing the at least one heating element to apply heat to the preform to create a thermal gradient from an exterior surface along the first transverse dimension of the preform inward toward a plane of the preform, wherein the at least one heating element creates approximately uniform temperature distribution along the second transverse direction;   feeding the preform into the furnace; and   drawing the preform in such a manner that the material does not substantially deform across its first transverse dimension and deforms across its second transverse dimension.   
     
     
         20 . The method of  claim 19 , further comprising preheating the at least one material before the at least one material enters a hottest zone of the furnace and further heating the at least one material after it leaves said hottest zone to gradually bring said at least one material to a lower temperature.