Abstract:
An electromagnetic coupler comprising: a coupling waveguide adapted for receiving input modes along an input axis, propagating coupling modes along a coupling axis, and transmitting output modes along an output axis, the output axis being not parallel to the coupling axis; and an output waveguide disposed adjacent the coupling waveguide and adapted for receiving the output modes.

Description:
BACKGROUND  
       [0001]     The present invention relates generally to the field of electromagnetic systems and more specifically to the field of coupling electromagnetic energy between waveguides.  
         [0002]     In a wide variety of applications, photonic band gap (PBG) waveguides are used in combination with conventional dielectric waveguides and conventional optical fiber to form integrated optical circuits. However, conventional geometries used for electromagnetically coupling PBG waveguides with these conventional materials produce junctions where, because of optical mode mismatch, reflection and scattering dissipate a significant fraction of the optical power.  
         [0003]     Opportunities exist, therefore, to reduce the power requirements of integrated optical circuits by designing new coupling geometries providing a higher efficiency junction.  
       SUMMARY  
       [0004]     The opportunities described above are addressed, in one embodiment of the present invention, by an electromagnetic coupler comprising: a coupling waveguide adapted for receiving input modes along an input axis, propagating coupling modes along a coupling axis, and transmitting output modes along an output axis, the output axis being not parallel to the coupling axis; and an output waveguide disposed adjacent the coupling waveguide and adapted for receiving the output modes.  
         [0005]     In addition to apparatus embodiments, method embodiments of the present invention include, without limitation, a method of making an electromagnetic coupler, the method comprising the acts of: providing a coupling waveguide adapted for receiving input modes along an input axis, propagating coupling modes along a coupling axis, and transmitting output modes along an output axis, the output axis being not parallel to the coupling axis; and disposing an output waveguide adjacent the coupling waveguide so as to receive the output modes. 
     
    
     DRAWINGS  
       [0006]     These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:  
         [0007]      FIG. 1  is an isometric drawing illustrating an electromagnetic coupler in accordance with one embodiment of the present invention.  
         [0008]      FIG. 2  is an isometric drawing illustrating an electromagnetic coupler in accordance with another embodiment of the present invention.  
         [0009]      FIG. 3  is an isometric drawing illustrating an electromagnetic coupler in accordance with a more detailed embodiment of the embodiment of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0010]     In accordance with an embodiment of the present invention,  FIG. 1  is an isometric drawing illustrating an electromagnetic coupler  100  comprising a coupling waveguide  110  and an output waveguide  150 . In operation, coupling waveguide  110  receives input modes along an input axis  120 , propagates coupling modes along a coupling axis  130 , and transmits output modes along an output axis  140 . In conventional coupling geometries, output axis  140  is parallel to coupling axis  130 . In contrast, in the embodiment of  FIG. 1 , output axis  140  is not parallel to coupling axis  130 . Output waveguide  150  is disposed adjacent coupling waveguide  110  to receive the output modes. In general, coupling waveguide  110  and output waveguide  150  comprise any materials capable of guiding energy at a desired wavelength including, by way of example but not limitation, conventional waveguide materials and PBG materials.  
         [0011]      FIG. 1  illustrates a particular embodiment of the present invention wherein at least one end of coupling waveguide  110  is tapered. This taper provides matching of a variety of modes along the length of coupling waveguide  110  so that efficient coupling occurs where the mode of coupling waveguide  110  best complements the mode of output waveguide  150 . In other words, optical energy from coupling waveguide  110  is tailored and injected into output waveguide  150 .  
         [0012]     In a more particular embodiment in accordance with the embodiment of  FIG. 1 , coupling waveguide  110  has a widthwise taper with a taper angle  155  in a range from about 5 degrees to about 10 degrees. Taper angle  155  is defined as an acute dihedral angle formed between a plane tangent to a tapering portion of coupling waveguide  110  and a plane tangent to a non-tapering portion. As used herein, “widthwise taper” refers to a variation in the dimension of coupling waveguide  110  measured along an axis orthogonal to both coupling axis  130  and output axis  140 .  
         [0013]     In a more particular embodiment in accordance with the embodiment of  FIG. 1 , at least one of coupling waveguide  110  and output waveguide  150  comprises a photonic band gap material.  
         [0014]     In accordance with another embodiment of the present invention,  FIG. 2  is an isometric drawing wherein coupling waveguide  110  further comprises an active layer  160  disposed adjacent output waveguide  150 . Active layer  160  provides a means for using electromagnetic coupler  100  as an active optical modulator. Depending on the properties (also called “effects”) exhibited by the material chosen, various actuation means are available for modulating the optical properties of active layer  160 . Such actuation means include, without limitation, electric fields (electro-optic effect), optical fields (Kerr effect), heat flux (thermo-optic effect), and acoustic waves (acousto-optic effect). Candidate materials for active layer  160  include, without limitation, polymers, liquid crystals, semiconductors, and optical crystals such as, for example, lithium niobate. In other embodiments in accordance with the embodiment of  FIG. 2 , the material of active layer  160  promotes lasing in coupling waveguide  110 .  
         [0015]     In a more particular embodiment in accordance with the embodiment of  FIG. 2 , active layer  160  comprises at least one quantum well  170 . In some embodiments quantum well  170  is a multilayer quantum well. Such a multi-layer quantum well can be utilized as an electro-optical absorber or modulator.  
         [0016]     The taper shown in  FIG. 2  is a heightwise taper. As used herein, “heightwise taper” refers to a variation in the dimension of coupling waveguide  110  measured along output axis  140 . In another more particular embodiment in accordance with the embodiment of  FIG. 2 , coupling waveguide  110  has heightwise taper with a taper angle  155  of about 45 degrees.  
         [0017]     In accordance with a more detailed embodiment of the embodiment of  FIG. 1 ,  FIG. 3  is an isometric drawing wherein electromagnetic coupler  100  further comprises an input waveguide  180  disposed adjacent coupling waveguide  110 . In operation, input waveguide  180  transmits the input modes along input axis  120  where input axis  120  is not parallel to coupling axis  130 . In a more particular embodiment in accordance with the embodiment of  FIG. 3 , at least one of input waveguide  180 , coupling waveguide  110 , and output waveguide  150  comprises a photonic band gap material. Input waveguide  180  can either be a conventional optical waveguide or a PBG waveguide.  
         [0018]     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.