Abstract:
Disclosed is the use of a polymer material in an optical waveguide structure. The polymer material may be used in either the cladding or the core material of an optical waveguide. The use of polymer material as such is advantageous in that the index of refraction of polymer material varies significantly with changing temperature. The polymer material is subjected to a heating mechanism and/or a cooling mechanism to manipulate the index of refraction as desired.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of optical waveguides and, more particularly, to the materials used to construct optical waveguides. 
     BACKGROUND OF THE INVENTION 
     Current communications networks throughout the world have embraced the use of optical fiber waveguide technology to provide a conduit of transmission components for voice, video, and data signals. Optical networks offer far greater bandwidth and reliability than do conventional electronic networks. As a consequence, current research efforts have been directed to expanding the capabilities of optical waveguide technology at reduced cost to aid in the acceleration of the conversion of the present electrical communications networks to optical communications networks. 
     These optical communications networks are comprised of many different components. These include optical fiber cable, switches, attenuators, couplers, and many more such devices. Typically, these devices are comprised of a core surrounded by a cladding material. Both the materials used for the core and the cladding include silica or doped silica as well as many other similar materials. These materials are employed because they have a desirable index of refraction and as well as other properties which facilitate their use. 
     Even though current materials used in constructing the core and the cladding have many beneficial properties, it can be desirable to manipulate the properties of such materials to create an effect on the propagation of laser radiation through the waveguide. Consequently, there is a need for core and cladding materials with properties that can be manipulated effectively to create a desired effect on the propagation of laser radiation. 
     SUMMARY OF THE INVENTION 
     The present invention entails the use of a polymer material in an optical waveguide structure. The use of polymer material as such is advantageous in that the index of refraction of polymer material varies significantly with changing temperature. The polymer material may be used in either the cladding or the core material of an optical waveguide. 
     The present invention may also be viewed as an optical waveguide system in which the cladding or the core of a waveguide includes the polymer material. The polymer material is in close proximity to or adjacent to a thermo-electric heater which, in turn, is electrically coupled to a voltage source. According to the waveguide system, the index of refraction of the polymer material may be manipulated by applying heat to the polymer material from the thermo-electric heater controlled by the voltage source. In addition, the thermo-electric heater may be replaced by a laser source which focuses laser radiation on the polymer material, causing it to heat as desired. Finally, the waveguide system may include a thermo-electric cooler to cool the polymer material to affect the index of refraction in the reverse manner to heating. 
     Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention, as defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. In the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a drawing showing a conventional optical fiber waveguide; 
         FIG. 2A  is a drawing showing a first optical waveguide according to an embodiment of the present invention; 
         FIG. 2B  is a drawing showing a sectional view of the optical waveguide of  FIG. 2A ; 
         FIG. 3  is a chart of the indexes of refraction of example polymers as a function of temperature; 
         FIG. 4A  is a drawing showing a second optical waveguide according to another embodiment of the present invention; 
         FIG. 4B  is a drawing showing a sectional view of the second optical waveguide of  FIG. 4A ; 
         FIG. 5  is a drawing showing an optical waveguide system that employs a thermo-electric heater with the optical waveguide of  FIG. 2A  according to another embodiment of the present invention; and 
         FIG. 6  is a drawing showing an optical waveguide system that employs a laser source with the optical waveguide of  FIG. 2A  according to yet another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning to  FIG. 1 , shown is a waveguide which comprises a conventional optical fiber  50 . The optical fiber  50  comprises a core  55  surrounded by a cladding  60 . The core  55  is comprised of a material such as, for example, doped silica with an index of refraction of n 1 . The cladding  60  is comprised of a material such as, for example, silica with an index of refraction of n 2 . The optical fiber  50  operates as a waveguide for light radiation  65  when n 1  is greater than n 2  as is known by those skilled in the art. When n 1  is less than or equal to n 2 , the light radiation  65  leaves the core and will not propagate along the core  55 . 
     With these concepts is mind, reference is made to  FIGS. 2A and 2B  which show a waveguide structure  100  according to an embodiment of the present invention. In  FIG. 2A , the waveguide structure  100  includes a doped silica core  105  which is formed on a silica substrate  110 . The doped silica core  105  is surrounded by a silica cladding material  115  which encloses the remaining sides of the core  105  not bounded by the silica substrate  110 . In a section of identifiable length L, a polymer cladding material  120  encloses the remaining sides of the core  105  instead of the silica cladding material  115 . The doped silica core  105  has an index of refraction of n 1 , the silica substrate  110  has an index of refraction of n 2 , the silica cladding material  115  has an index of refraction of n C , and the polymer cladding material  120  has an index of refraction of n p . A dashed line  122  indicates a cutting plane through the waveguide structure  100  at the polymer cladding material  120 . In  FIG. 2B , shown is a sectional view  123  of the waveguide structure  100  taken along the dashed line  122  which further illustrates the core  105 , substrate  110 , and the polymer cladding material  120 . The polymer cladding material  120  is taken from the general category of materials classified as polymers which generally are chemical compounds with high molecular weight comprising a number of structural units linked together by covalent bonds. Polymers which qualify for use as the polymer cladding material  120  should generally possess the optical characteristics including an index of refraction that varies with temperature as will be discussed. 
     Although the core  105  comprises doped silica and the substrate  110  comprises silica, it is understood that other materials may be employed as known by those skilled in the art. Consequently, an exhaustive list of possible materials used to create these components is not offered herein. 
     It is understood that the waveguide structure  100  is for illustrative purposes and is not the only structural configuration possible. It may be possible for example, that the polymer cladding material  120  only contact the doped silica core  105  in specified regions such as on the upper surface of the doped silica core  105 , for example. The design of the actual waveguide structure  100  is such that the polymer cladding material  120  comes into contact with the doped silica core  110  so that the propagation of light radiation through the core  110  can be manipulated by controlling the index of refraction of the polymer cladding material  120  relative to the index of refraction of the doped silica core  105  to achieve certain advantages. 
     The polymer cladding material  120  features a relatively high thermo-optic coefficient 
         ∂     n   P         ∂   T         
 
due to the fact that the index of refraction of polymers can vary significantly with changing temperature. For example, the thermo-optic coefficient 
         ∂     n   P         ∂   T         
 
generally may be as high as −0.0001C −1  and even up to −0.0003 C −1 , where n p  is the refractive index of the polymer and T is temperature. In contrast, the thermo-optic coefficient of silica is much lower and of opposite polarity, being on the order of +0.00001 C −1 . Consequently, the index of refraction of fused silica and other similar materials will not change significantly when subjected to heat, while the index of refraction of the polymer will change significantly. The polymer cladding material may have a thermal coefficient that is greater than the thermal coefficient of the core by a factor of at least 5.
 
     Referring to  FIG. 3 , shown is a graph depicting the index of refraction as a function of temperature in degrees Celsius of three example polymers which may be used according to the various embodiments of the present invention. Line  130  depicts the index of refraction of F/CA polymer which has a thermal coefficient of −0.00002C −1 , line  135  depicts the index of refraction of D-PMMA/D-FA polymer which has a thermal coefficient of −0.000C −1 , and line  140  depicts the index of refraction of FA polymer which has a thermal coefficient of −0.0003C −1 . Note that the starting point at n=1.46 and Temperature=−20° C. were chosen arbitrarily. Ultimately, the indexes of refraction of various polymers depend upon their composition and can vary over a relatively wide range as a function of temperature. 
     The change of the index of refraction of a polymer cladding as contemplated herein provides distinct advantages. For example, a change in the propagation constant β of the guided optical wave through the core can be made by changing the temperature of the polymer cladding. Also, the propagation of light radiation through the core may be diminished or stopped by raising the index of refraction of the polymer cladding above that of the core. 
     Turning next to  FIG. 4A , shown is a second waveguide structure  150  according to another embodiment of the present invention. The waveguide structure  150  features a polymer core  155  formed on a substrate material  160  and surrounded on the remaining sides by a cladding material  165 . The cladding material  165  may be another polymer or other material that has an index of refraction that allows the propagation of light through the polymer core  155 . The relative indexes of refraction of the polymer core  155  and the cladding material  165  are manipulated to achieve the desired propagation through the waveguide structure  150 . The wave guide may have a polymer cladding material that has an index of refraction (RI 165 ) that varies between a first value (x 1 ) that is greater than that of the index of refraction of the core (RI 155 ) and a second value (x 2 ) that is less than that of RI 155 .  FIG. 4B  shows is a sectional view of the waveguide structure  150 . 
     Referring to  FIG. 5 , shown is a waveguide system  200  according to another embodiment the present invention. The waveguide system  200  features the waveguide structure  100  ( FIG. 2A ) which includes the polymer cladding material  120  with the doped silica core  105  formed on the silica substrate  110 . The waveguide system  200  further includes a thermo-electric heater  205  and a thermo-electric cooler  210 . The thermo-electric heater  205  is electrically coupled to a voltage source V 1  and may be of the chrome strip type. Other types of thermo-electric heaters  205  may include electrically conducting glass materials. The thermo-electric cooler  210  is electrically coupled to a voltage source V 2 . The waveguide system  200  may be constructed with the thermo-electric heater  205  alone or with the thermo-electric cooler  210  alone depending on the ambient temperature and the desired range for the index of refraction of the polymer material. The waveguide system  200  is formed, for example, on an integrated optical circuit which are well known by those skilled in the art and not discussed here in detail. 
     Referring next, to  FIG. 6 , shown is a second waveguide system  300  according to yet another embodiment of the present invention. The waveguide system  300  also features the waveguide structure  100  ( FIG. 2B ) which includes the polymer cladding material  120  with the doped silica core  105  formed on the silica substrate  110 . In addition, the waveguide system  300  includes a laser source  305  which produces laser radiation  310 . The laser source  305  is directed such that the laser radiation  310  falls onto the polymer cladding material  120 . The laser radiation  310  heats up the polymer cladding material  120  resulting in a corresponding change in the index of refraction of the polymer cladding material  120 . Note that a thermo-electric cooler  210  ( FIG. 5 ) may be included in the waveguide system  300  similar to the waveguide system  200 . 
     Many variations and modifications may be made to the various embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of the present invention, as defined by the following claims.