Abstract:
A method and system are disclosed for switching at least part of a light signal out of a first waveguide by a Bragg grating formed from an electro-optic effect in the first waveguide. The Bragg grating is created by turning on a series of electrodes on each side of the first waveguide. The electrodes create electric fields in the core of the first waveguide which raise the refractive index in certain regions of the core. When the electric fields are tilted and evenly spaced apart, at least part of a light signal propagating through the waveguide, at a predetermined wavelength, is reflected out of the first waveguide. The reflected light signal can be switched back into a second waveguide by use of another Bragg grating. When the electric fields are off in the first waveguide the light signal, including the part of the light signal having the predetermined wavelength, continues straight on through the Bragg grating area. Thus a light signal of the predetermined wavelength is either switched to the second waveguide or kept in the first waveguide depending on whether the voltages are turned on or off on the electrodes.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates generally to the field of optical communications, and in particular to an optical switch.  
         BACKGROUND OF THE INVENTION  
         [0002]    The strong growth of optical networks for voice and data communication has created a huge demand for high data rate information transfer capabilities. To enable such transfer capabilities, dense wavelength division multiplexing (DWDM) technology has been developed which allows transfer of multiple wavelength light beams over a single optical fiber leading to data transfer rates up to 40-100 Gb/s. High speed switching and routing devices comprise the core elements of the optical networks and allow dynamic control of the data traveling over the optical network. High data transmission rates impose significant demands on the functionality of the switching devices.  
           [0003]    Optical cross-connect space division switches based on electro-optic (EO) deflection of the light beam have great potential for use in high speed optical networks. The basic requirements for such devices are the need for extremely fast switching time and the capability to handle a large number of input and output channels, e.g., up to 4000×4000 by the year 2003. Reliability and cost are also important design factors for optical switching devices. Existing optical switching devices which employ signal conversion from optical into electrical and back into optical do not satisfy the anticipated requirements for such devices.  
           [0004]    Currently, the main optical switching products on the market are based on micro-electromechanical systems or MEMS technology, which employs rotating micro-mirrors to deflect light. However, these optical switching devices are not very reliable due to the large number of moving parts, and are limited by the switching time caused by the mechanics of the mirrors.  
           [0005]    Therefore, there is a need for a high speed optical switching device which allows switching between a large number of input channels and output channels.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention comprises a method and system for switching at least part of a light signal out of a first waveguide by a Bragg grating formed from an electro-optic effect in the first waveguide. The Bragg grating is created by turning on a plurality of electrodes on each side of the first waveguide. The electrodes create electric fields in the core of the first waveguide which raise the refractive index in certain regions of the core. When the electric fields are tilted and evenly spaced apart, at least part of a light signal propagating through the waveguide, at a predetermined wavelength, is reflected out of the first waveguide. The reflected light signal can be switched back into a second waveguide by use of another Bragg grating. When the electric fields are off in the first waveguide the light signal, including the part of the light signal having the predetermined wavelength, continues straight on through the Bragg grating area. Thus a light signal of the predetermined wavelength is either switched to the second waveguide or kept in the first waveguide depending on whether the voltages are turned on or off so that there is an electrical control of an optical signal path.  
           [0007]    One embodiment of the present invention comprises a method for changing the path of at least part of a light signal propagating through a waveguide, where the waveguide has only a first refractive index, when a plurality of electric fields are absent. First, a fiber Bragg grating having regions of a second refractive index in the waveguide is generated. The regions are formed by the plurality of electric fields at an intermediate portion of the waveguide, where the regions are tilted with respect to a normal to a longitudinal axis of the waveguide. Next, at least part of the light signal at the fiber Bragg grating is reflected out of the waveguide.  
           [0008]    Another embodiment of the present invention comprises an optical switching device for changing a path of at least part of a light signal. The optical switching device includes a slab waveguide having a top clad, bottom clad, and core, where the core has a electro-optic material. The core is positioned in between the top and bottom clads and has a first refractive index. The core receives the light signal. The optical switching device further includes: a plurality of top electrodes attached to the top clad; and a plurality of bottom electrodes attached to the bottom clad. Each top electrode has an associated bottom electrode and they cause an electric field to be formed that is tilted with respect to a perpendicular axis of the core, such that at least part of the light signal is reflected out of the slab waveguide. The electric field changes a region in the core to a second refractive index larger than the first refractive index.  
           [0009]    An aspect of the present invention comprises a method for switching at least part of a light signal from a first waveguide to a second waveguide. The light signal is received by the first waveguide. Next a Bragg grating is formed using a plurality of electric fields, where at least part of the light signal is redirected by the Bragg grating to the second waveguide.  
           [0010]    Another aspect of the present invention comprises a method for switching a light signal from a first waveguide to a second waveguide. First, the light signal is received by the first waveguide. A Bragg grating is created in a region of a first refractive index by alternating tilted sub-regions of a second refractive index formed by a plurality of electric fields with subregions of the first refractive index. The light signal in the first waveguide is reflected at the Bragg grating towards the second waveguide and received by the second waveguide.  
           [0011]    A further aspect of the present invention comprises a system for sending at least a part of a light signal, having a predetermined wavelength, out of a waveguide. The system includes: a plurality of top electrodes positioned parallel and adjacent to a first side of a core of the first waveguide, where the spacing between the plurality of top electrodes is a function of the wavelength; and a plurality of bottom electrodes positioned parallel and adjacent to a second side of the core, where the plurality of bottom electrodes are offset in position from the plurality of top electrodes. Each top electrode has a corresponding bottom electrode and are positioned to create an electric field in the first waveguide at an angle from a normal to a longitudinal axis of the core, such that at least part of the light signal is reflected out of the waveguide as the light signal propagates through one or more electric fields in the waveguide.  
           [0012]    Another embodiment of the present invention comprises a system for switching at least part of a light signal having a first predetermined wavelength between a plurality of slab waveguides. The system includes: a first slab waveguide comprising a first Bragg grating, where the first Bragg grating reflects at least part of the light signal out of the first slab waveguide and is formed by electric fields slanted at an angle in the first slab waveguide; a plurality of electrodes attached to the first slab waveguide for producing the electric fields; and a second slab waveguide having a second Bragg grating for receiving the reflected part of the light signal.  
           [0013]    Yet another embodiment of the present invention comprises a three dimensional multi-layered optical switch includes a first stack of first switching planes for switching light signals between planes, where each first switching plane has at least one waveguide and each waveguide includes Bragg gratings. The Bragg gratings are formed in a core of each waveguide by a plurality of electric fields increasing a refractive index of the core at predetermined regions in the core. The 3D multi-layered optical switch further includes a second stack of electro-optic 2D switches for switching light signals within a plane, where the second stack is optically aligned with the first stack; and a third stack of second switching planes for switching light signals between planes, where the third stack is optically aligned with the second stack. Each second switching plane has at least one waveguide, and each waveguide of the third stack includes Bragg gratings.  
           [0014]    These and other embodiments, features, aspects and advantages of the invention will become better understood with regard to the following description, appended claims and accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a schematic of a top view of a cross-connect switching device.  
         [0016]    [0016]FIG. 2 is a layout of a top view of a three-dimensional (3D) multi-channel optical switch having a plurality of EO 2D switches.  
         [0017]    [0017]FIG. 3 shows a cross sectional view of a fiber Bragg grating in a waveguide.  
         [0018]    [0018]FIG. 4 illustrates the Bragg effect on a non-resonant light signal and a resonant light signal.  
         [0019]    [0019]FIG. 5 is a cross sectional view of a waveguide having an electro-optic Bragg grating of a preferred embodiment of the present invention.  
         [0020]    [0020]FIG. 6 shows the electric fields strengths in a cross sectional view of an electro-optic Bragg granting of an alternative embodiment of the present invention.  
         [0021]    [0021]FIG. 7- 1  is an expanded portion of FIG. 5 of an embodiment of the present invention.  
         [0022]    [0022]FIG. 7- 2  is a schematic of a top view of a portion of FIG. 5 of an embodiment of the present invention.  
         [0023]    [0023]FIG. 7- 3  is a schematic of a top view of a portion of FIG. 5 of another embodiment of the present invention.  
         [0024]    [0024]FIG. 8 is an expanded cross-sectional view of a waveguide having a tilted axis of an embodiment of the present invention.  
         [0025]    [0025]FIG. 9 shows a simplified example of constructive interference of a Bragg reflection in a waveguide of one embodiment of the present invention.  
         [0026]    [0026]FIG. 10 shows an example of the bending of a light signal exiting a waveguide surrounded by a material.  
         [0027]    [0027]FIG. 11 shows a cross-sectional example of single wavelength light signals being switched between planes.  
         [0028]    [0028]FIG. 12 shows another cross-sectional example of single wavelength light signals being switched between planes.  
         [0029]    [0029]FIG. 13 is a cross-sectional view of a demultiplexer of an aspect of the present invention.  
         [0030]    [0030]FIG. 14 is substrate having multiple waveguides with Bragg gratings of one embodiment of the present invention.  
         [0031]    [0031]FIG. 15 is a 2D Bragg grating switch of another embodiment of the present invention.  
         [0032]    [0032]FIG. 16 is a 2D Bragg grating switch of yet another embodiment of the present invention.  
         [0033]    [0033]FIG. 17 shows a multi-channel three-dimensional switch of an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    In the following description, numerous specific details are set forth to provide a more thorough description of the specific embodiments of the invention. It is apparent, however, to one skilled in the art, that the invention may be practiced without all the specific details given below. In other instances, well known features have not been described in detail so as not to obscure the invention.  
         [0035]    U.S. patent application titled “An Optical Switching Apparatus with Divergence Correction,” by Glebov, et. al., filed Apr. 24, 2002, (Attorney Docket No. 25916-245 (6136/60636)), which is herein incorporated by reference in its entirety, provides an improved optical switching apparatus, which allows fabrication of a non-blocking optical cross connect switching matrix with a large number of I/O channels. The optical switching device employs EO induced deflection of an incoming optical beam or optical signal to reroute the incoming light signal from an input port to an output port.  
         [0036]    A hybrid integration process, including an EO deflecting element disposed on a silicon substrate, forming a (2×2) cross-connect switching device is described in this application. The 2×2 cross-connect switching device is used for illustration only, and embodiments of the integration process can easily be extended to fabricate switching systems with a larger number of I/O ports. A N×N cross-connect planar switching device, for the purposes of this application is called an EO 2D Switch, since the planar switching device, switches light signals in a plane using an electo-optical effect. “N” is a positive integer.  
         [0037]    [0037]FIG. 1 is a schematic of a top view of a cross-connect switching device  10 . The cross-connect switching device  10  transfers a first light signal from input port  1  to either output port  1  or to output port  2 . A second light signal may also be transferred from input port  2  to the remaining output port not receiving the first light signal. Thus, if output port  2  receives the first light signal from input port  1 , output port  1  would receive the second light signal from input port  2 . When there is no crossing of optical signals, such as where a light signal input into the first input port  1  is transmitted to the output port  1 , and a light signal input into the second input port  2  is transmitted to the output port  2 , a control voltage is not applied to any of the light deflection elements  13   a ,  13   b ,  15   a , and  15   b , and thus, no light signals are deflected at the light deflection elements  13   a ,  13   b ,  15   a , and  15   b . Accordingly, the light signal input into channel waveguide  11   a  is transmitted to light waveguide  17   a , and the light signal input into channel waveguide  11   b  is transmitted to light waveguide  17   b .  
         [0038]    When a light signal input into the input port  1  is to be transmitted to the output port  2  and a light signal input into the input port  2  is to be transmitted to the output port  1 , a positive control voltage +V is applied to the control electrodes of the light deflection elements  13   a  and  15   b  and a negative control voltage −V is applied to the control electrodes of the light deflection elements  13   b  and  15   a . Accordingly, the light signal input into the input port  1  is deflected toward the right hand direction by light deflection element  13   a , and then, upon reaching light deflection element  15   b , the deflected light signal is deflected again into a direction parallel to the longitudinal axis of optical waveguide  17   b  at light deflection element  15   b , and is focused by focusing lens  16   b  into the optical waveguide  17   b , and then transmitted into the output port  2 . Similarly, the light signal input into the input port  2  is deflected by light deflection element  13   b  and into light deflection element  15   a , and then, upon reaching light deflection element  15   a , the deflected light signal is deflected again into a direction parallel to the longitudinal axis of optical waveguide  17   a  at the light defection element  15   a , and is then transmitted to the output port  1  through the focusing lens  16   a  and the optical waveguide  17   a.    
         [0039]    Multiple EO 2D switches can be stacked to increase the total number of input and output ports. While there is switching of light signals in each plane, there is no switching between planes. Thus the number of switching combinations is limited. One way to achieve switching between planes is to rotate by 90° a second stack of EO 2D switches and connect this second stack to the first unrotated stack.  
         [0040]    [0040]FIG. 2 is a layout of a top view of a three-dimensional (3D) multi-channel optical switch  40  having a plurality of EO 2D switches. Two stacks of EO 2D switches, e.g., stacks  50  and  54 , are connected together by a stack of EO 2D rotated  900 , i.e., stack  52 , to form the three stage 3D switch  40 . The stack  50  of EO 2D switches, include EO 2D switches  60 - 1 ,  60 - 2 , and  60 - 3 . Each EO 2D switch, e.g.,  60 - 1 , has a plurality of light deflection elements, e.g.,  72 ,  76 ,  82 , and  86 . The stack  52  of rotated EO 2D switches, include EO 2D switches  62 - 1 ,  62 - 2 , and  62 - 3 . The stack  54  of EO 2D switches include EO 2D switches  64 - 1 ,  64 - 2 , and  64 - 3 . An example showing the switching of a light signal is given by a light signal  70  entering the EO 2D switch  60 - 1 . The input light signal  70  is switched to intermediary light signal  74  via light deflection elements  72 . The intermediary light signal  74  is switched to output light signal  78  via light deflection elements  76 . The output light signal  78  is switched by rotated EO 2D switch  62 - 1  to EO 2D switch  64 - 1  of stack  54  giving light signal  80 . Light signal  80  is then switched in EO 2D switch  64 - 1  to give output light signal  88  via light deflection elements  82  and  86 . Thus the EO 2D switches in stacks  50  and  54  provide the optical switching in a plane and the rotated switch  52  provides the third dimension in switching from one plane to another plane.  
         [0041]    In an exemplary embodiment of the present invention light signals are transferred between planes using controllable fiber Bragg gratings. While conventionally, permanent Bragg gratings are formed in a waveguide by either ultra-violet beams or by etching them in the waveguide, in the present invention, the Bragg gratings are formed by varying the index of refraction in the waveguide using the electro-optic effect and can be turned off and on using an external voltage. When turned off, there are no Bragg gratings and the light passes through. If turned on, one wavelength of a light signal is reflected out of the and any other wavelengths are passed through. These dynamic Bragg gratings allow switching between planes.  
         [0042]    Actually, a narrow band of wavelengths centered around the one wavelength is reflected, however, for ease of explanation and so as not to obscure the invention, we use single wavelengths rather than bands of wavelengths. However, it should be understood that when we use a discrete single wavelength, a narrow band of wavelengths centered around the given wavelength may be included.  
         [0043]    In conventional fiber Bragg gratings used to reflect a single wavelength, there are uniformly spaced regions formed in the fiber with a refractive index that has been raised from that of the rest of the core. These regions scatter light by what is called the Bragg effect. Bragg gratings selectively reflect one wavelength (or a very narrow range around one wavelength) and allow the other wavelengths to pass on through the grating. The reflected wavelength is twice the spacing between the regions of higher refractive index. Reflection occurs due to constructive interference. The spacing between the regions of higher refractive index is called “A” herein, i.e., the grating pitch.  
         [0044]    [0044]FIG. 3 shows cross sectional view of a fiber Bragg grating in a waveguide  110 . The waveguide  110  includes: a top clad  112 , a core  114 , and a bottom clad  116 . The core  114  has a refractive index of n1. Equally space regions, e.g., regions  120 - 1 ,  120 - 2 ,  120 - 3 ,  120 - 4 ,  120 - 5 ,  120 - 6 , etc., of a higher refractive index n2 (n2&gt;n1) are formed in the core  114 . These regions are the Bragg grating  130 . For example, part of one wavelength of a multi-wavelength light signal  125  is reflected at region  120 - 5 , and the rest of the wavelengths pass-through as light signal  129 . While reflection at only one region is shown, reflection occurs for the one wavelength at each region, e.g., regions  120 - 1 ,  120 - 2 ,  120 - 3 ,  120 - 4 ,  120 - 5 ,  120 - 6 , etc.  
         [0045]    [0045]FIG. 4 illustrates the Bragg effect on a non-resonant light signal  212  and a resonant light signal  214 . Light signal  212  has a wavelength that is not a multiple of two times the spacing, i.e., 2Λ, between the regions, e.g., regions  120 - 1 ,  120 - 2 ,  120 - 3 ,  120 - 4 ,  120 - 5 ,  120 - 6 , etc., and passes through the grating substantially unaffected. Light signal  214  has a wavelength equal to a multiple of 2Λ. This wavelength when measured in air rather than the core is called the Bragg wavelength, λ B , and is given by:  
         λ B   =n 1*2*Λ  [Equation 1] 
         [0046]    where Λ is the spacing between regions and n1 is the refractive index of the core  114  (the refractive index enters Equation 1, because the reflected wavelength is normally measured in air). For illustration, part of light signal  214  is shown in FIG. 4 as being reflected  1800  at region  120 - 5  to give reflected light signal  216 . Because the wavelength of signal  214  is twice the distance between regions, at for example, regions  120 - 4  and  120 - 5 , the reflected light signal  216  is in phase with the parts of light signal  214  reflected from, for example, regions  120 - 1  to  120 - 4  (as well as, e.g., regions  120 - 6 ,  120 - 7 , etc.). Thus at the Bragg wavelength, the parts of the light signal reflected from each region constructively interfere.  
         [0047]    The Bragg effect can be used to reflect a wavelength of a multi-wavelength light signal out of the waveguide, when the regions of higher refractive index, e.g.,  120 - 1 ,  120 - 2 , of FIG. 3 are tilted from the longitudinal axis of the core  114 . If tilted in one direction the wavelength can be reflected up, and if tilted the other way the wavelength can be reflected down (FIGS. 6 and 7).  
         [0048]    [0048]FIG. 5 is a waveguide having an electro-optic Bragg grating of a preferred embodiment of the present invention. In FIG. 5 the waveguide has top clad  312 , core  314  and bottom clad  316 . The core is composed of a electro-optic material with refractive index n1. The top and bottom clad layers,  312  and  314 , have a refractive index n3, such that n1&gt;n3 (i.e., the core has a higher refractive index than the clad layers). Top electrodes  320 ,  322 ,  212 ,  214 , and  218  are positioned on the top clad layer  312 . The bottom electrodes  324 ,  326 ,  220 ,  222 ,  224 , and  226  are positioned on the bottom clad layer  316 . The top and bottom electrodes form pairs, e.g., ( 320 ,  324 ), ( 322 ,  326 ), ( 212 ,  220 ), which have an associated axes, e.g.,  330 ,  332 ,  230 , respectively, tilted at an angle θ  349  from the perpendicular  390 . The electrode pairs are spaced a distance Λ apart from each other. In FIG. 5 the number of electrodes shown is for illustration purposes only and there may be more or less electrode pairs.  
         [0049]    [0049]FIG. 6 shows the electric fields strengths of cross section view of an electro-optic Bragg granting of an alternative embodiment of the present invention. In one embodiment of the present invention all the top electrodes have a positive voltage with respect to the bottom electrodes. In the alternative embodiment of FIG. 6 top electrodes, e.g.,  712  and  716 , with a positive voltage, e.g., positive 5 volts, with respect to their corresponding bottom electrodes, e.g.,  722  and  726 , are alternated with top electrodes, e.g.,  710 ,  714 , and  718 , with a negative voltage, e.g., negative 5 volts, with respect to their corresponding bottom electrodes, e.g.,  720 ,  724  and  728 . An example of electric field intensities between positive voltage electrode  712  and corresponding bottom electrode  722  is about 4 volts per micro-meter (v/μm) for region  736 , about 4 to 12 v/μm for region  734 , and about 12 to 20 v/μm for region  733 . An example of electric field intensities between negative voltage electrode  710  and corresponding bottom electrode  720  is about −4 to −8 v/μm for region  732 , about −8 to −12 v/μm for region  730 , and about −12 to −16 v/μm for region  731 . Region  731  is about 0 v/μm.  
         [0050]    [0050]FIG. 7- 1  is an expanded portion of FIG. 5 of an embodiment of the present invention. In FIG. 7- 1  the waveguide has top clad  312 , core  314  and bottom clad  316 . Top electrodes  320  and  322  are positioned on top clad layer  312 . The electrodes  324  and  326  are positioned on bottom clad layer  316 . A voltage difference between top electrode  320  and bottom electrode  324  produces an electric field  325 - 1  in the core  314 . A voltage difference between electrode  322  and bottom electrode  326  produces an electric field  325 - 2  in the core  314 . Electric field  325 - 1  (and  325 - 2 ) raises the refractive index of core  314  from n1 to n2. A part of light signal  340  is reflected near the boundary of the area of increased refractive index associated with electric field  325 - 1  to give light signal  346 . The remainder of light signal  340  passes straight through as light signal  344 . The reference line  336  is normal to the reference line  330 , where reference line  330  is one from one end of top electrode  320  to end of bottom electrode  324 . θ is also the angle  342  between the light signal  340  and the normal reference line  336 . The light ray  346  portion of the light signal at the Bragg wavelength is reflected at angle θ  348 . A potion of the Bragg wavelength of light signal  340 , is reflected near the boundary of the area of increased refractive index associated with each electric field, e.g.,  325 - 1  and  325 - 2  (not shown). These Bragg reflective wavelengths re-enforce each other by constructive interference. The electrodes  320  and electrodes  322  are spaced a distance Λ  334  (i.e., the electrode pitch) apart.  
         [0051]    [0051]FIG. 7- 2  is a schematic of a top view of a portion of FIG. 5 of an embodiment of the present invention. The slab waveguide  740  has parallel rectangular top electrodes, e.g.,  744  and  748 , which correspond to electrodes  320  and  322  in FIG. 5. The bottom electrodes, e.g.,  742  and  746 , are in dotted lines to illustrate that the bottom electrodes are below the waveguide  740 . The bottom electrodes, e.g.,  742  and  746 , correspond to bottom electrodes  324  and  326  in FIG. 5.  
         [0052]    [0052]FIG. 7- 3  is a schematic of a top view of a portion of FIG. 5 of another embodiment of the present invention. The slab waveguide  750  has curved top electrodes, e.g.,  754  and  758 , which correspond to electrodes  320  and  322  in FIG. 5. The curved bottom electrodes, e.g.,  752  and  756 , are in dotted lines to illustrate that the bottom electrodes are below the waveguide  750 . The curved bottom electrodes, e.g.,  752  and  756 , correspond to bottom electrodes  324  and  326  in FIG. 5. The electrodes are curved to reduce the divergence in the reflected light signal.  
         [0053]    [0053]FIG. 8 is an expanded cross-section of a waveguide having an angled Bragg grating of an embodiment of the present invention. FIG. 8 is similar to FIG. 7- 1  except the electrode pairs are arranged to tilt in the opposite direction. The waveguide shown has top clad  312 , core  314  and bottom clad  316 . On top of clad  312  are top electrodes  352  and  356 . Below bottom clad  316  are bottom electrodes  354  and  358 . Electrodes  352  and  354  are aligned as shown by axis  362  which slants at an angle (90−θ) from the longitudinal axis of the core  314 . Similarly electrodes  356  and  358  are aligned along axis  364 . Axis  362  is a distance Λ  334  from the axis  364 . A multi-wavelength light signal  340  enters the core  314  at an angle θ  376  from the normal  366 . Part of light signal  340  is reflected at angle θ  378  from the normal  366  to give light signal  372 . The rest of light signal  340  continues along the longitudinal axis as light signal  344 . Like in FIG.  7 - 1  only the light with the Bragg wavelength, λ B , is reflected. In the case of FIG. 8 the reflection is downward rather than upward as in FIG. 7- 1 .  
         [0054]    [0054]FIG. 9 shows a simplified example of constructive interference of a Bragg reflection in a waveguide of one embodiment of the present invention. The waveguide and the electrodes are similar in arrangement to FIG. 7- 1 . For the purposes of explaining constructive interference, assume the light signal has only one wavelength that proceeds straight down the center of the waveguide. Part of the light signal  340  propagating in core  314  is reflected at axes  330  to produce light signal  346  at angle θ  348  from normal  336 . The remainder of the light signal proceeds as light signal  344  until axis  332  when another part of light signal  344  is reflected as light signal  394 . The remainder of the light signal continues on as light signal  396 . A wavefront for the first reflected light signal  346  is shown by front  382 . A wavefront for the second reflected light signal  394  is shown by front  384 . The distance between fronts  382  and  384  is “h”  386 , where h=Λ*cos 2θ.  
         [0055]    For constructive interference to occur, reflected the light signal  346  must be in phase with the reflected light signal  394 . This means that a part of wavefront parallel to vertical axis  390  of light signal  340  is reflected at axis  330  to give wavefront  382 . The rest of wavefront (parallel to vertical axis  390 ) proceeds for a distance of A  334  to axis  332 , where part of the rest of wavefront (parallel to vertical axis  392 ) is reflected as wavefront  384 . When wavefront  384  travels a distance h, it will interfere with wave front  382 . When the wavelength is to first order about (A+h), then the two wavefronts will be in phase i.e., wave front  384  will constructively interfere with wavefront  382 . In actuality there is the light signal includes a narrow bandwidth of wavelengths and there are reflections and refractions when the light signal propagates from the core to the clad. However, to first order, the formula for the Bragg wavelength for a tilted higher refractive region (e.g., axis  330 ) at angle θ  349  from a vertical axis  390  is approximately:  
         λ B   =n 1*Λ*(1+cos 2θ)  [Equation 2] 
         [0056]    The light signal  346  in FIG. 9 has been simplified and more specifically bends twice before exiting the waveguide, i.e., the first bend is from core  314  to top clad  312  and the second bend is from top clad  312  to the material surrounding the waveguide. In one embodiment the material is air. In another embodiments the material is one which has a refractive index n4, that is greater n3, i.e., n4&gt;n3. In yet another embodiment n4 may be less than or equal to n3.  
         [0057]    [0057]FIG. 10 shows an example of the bending of a light signal exiting a waveguide surrounded by a material. In this example the material  412  and  414  has a refractive index n4, where n4&gt;n3. The light signal  346  (see also FIG. 9) bends away from the normal (e.g., axis  390 ), when it enters the clad  312 . The ray  420  show the straight line path if the refractive indexes n1 and n3 where the same. Light signal  422  is the refracted light signal  346  in clad  312 . If the material  412  and  414  surrounding the waveguide (clads  312  and  316  and core  314 ), is selected to have a higher refractive index than the clads, i.e., n4&gt;n3, then the light signal  422  will be bent toward the normal when it enters material  412 . Light signal  424  shows the refracted light signal  422  in material  412 . Thus the light signal leaving the waveguide, e.g., light signal  424 , in one embodiment can be made to leave at a direction near the normal, (axis  390 ).  
         [0058]    By arranging a multiple number of Bragg gratings, such as FIG. 5, a plane having multiple waveguides, where each waveguide has multiple Bragg gratings, can be formed to produce a two dimensional (2D) switch. In the preferred embodiment, this 2D switch only switches light signals in or out of the plane, not between waveguides. In another embodiment, this 2D switch switches light signals between waveguides in the plane. Several planes may be stacked on each other in the preferred embodiment to create a 3D switch, which switches light signals between planes.  
         [0059]    [0059]FIG. 11 shows a cross-section of a switch of an embodiment of the present invention for switching single wavelength light signals between waveguides in different planes. In FIG. 11 there are parallel waveguides  512 ,  514 , and  516 , one in each of three parallel planes. A single wavelength light signal  530 , i.e., λ1, is reflected at Bragg grating  520 , which is turned on, in waveguide  512  to give light signal  532 . Single wavelength light signal  532  is then reflected in Bragg grating  524  to produce single wavelength light signal  534 , i.e., λ1, in waveguide  514 . Similarly, single wavelength light signal  540 , i.e., λ2, entering waveguide  514  is reflected at Bragg grating  526  to produce reflected light signal  542 . Light signal  542  is reflected at Bragg grating  528  to produce single wavelength light signal  544 , i.e., λ2, in waveguide  516 .  
         [0060]    [0060]FIG. 12 shows another cross-sectional example of single wavelength light signals being switched between planes. In FIG. 12 there are parallel waveguides  550 ,  552 , and  554 , one in each of three parallel planes. A single wavelength light signal  560 , i.e., λ1, is reflected at Bragg grating  562 , which is turned on, in waveguide  554  to give light signal  564 . Single wavelength light signal  564  is then reflected in Bragg grating  566  to produce single wavelength light signal  570 , i.e., λ1, in waveguide  552 . Similarly, single wavelength light signal  580 , i.e., λ2, entering waveguide  550  is reflected at Bragg grating  582  to produce reflected light signal  584 . Light signal  584  is transmitted straight through Bragg grating  568  in waveguide  552 , because Bragg grating  568  is turned off (i.e., no voltage applied at the electrodes). Light signal  584  is reflected at Bragg grating  586 , which is turned on, to produce single wavelength light signal  588 , i.e., λ2, in waveguide  554 .  
         [0061]    [0061]FIG. 13 is a cross sectional view of a demultiplexer of an aspect of the present invention. There are three parallel waveguides  612 ,  614  and  616 , each with a plurality of Bragg gratings. A multi-wavelength light signal  640 , i.e., λ1, λ2, and λ3, enters waveguide  612 . At Bragg grating  620  a first wavelength  644 , i.e., λ1, is reflected and the other two wavelengths  642 , i.e., λ2 and λ3, are passed through. At Bragg grating  622  the multi wavelength light signal  642 , i.e., λ2 and λ3, is divided into a reflected single wavelength signal  648 , i.e., λ2, and light signal  646 , i.e., λ3, is passed through. The single wavelength light signal  648 , i.e., λ2, is reflected in at Bragg grating  624  in waveguide  614  to produce single wavelength signal  650 , i.e., λ2. Single wavelength signal  644 , i.e., λ1, propagates through Bragg grating  626 , which is turned off and is reflected at Bragg grating  628 , which is turned on, in waveguide  616  to produce single wavelength signal  652 , i.e., λ1. Hence the multi-wavelength signal  640  having three different wavelengths, i.e., λ1, λ2, and λ3, is demultiplexed into single wavelength  646 , i.e., λ3, in waveguide  612 , single wavelength  650 , i.e., λ2, in waveguide  614 , and signal wavelength  652 , i.e., λ1, in waveguide  616 .  
         [0062]    [0062]FIG. 14 is a substrate having multiple waveguides with Bragg gratings of one embodiment of the present invention. The 2D switching plane  810  has multiple parallel waveguides, e.g.,  806  and  808 , each waveguide having a Bragg grating element with vertical cross-sectional view  812 . The cross-sectional view  812  shows a plurality of top transparent electrodes  820 , and a plurality of bottom transparent electrodes  822 , an optical waveguide including a top core  816 , a core  814 , and a bottom clad  818 , and a transparent substrate  824  below the bottom clad  818 . Multiple 2D switching planes like 2D switching plane  810 , can be stacked on top of each other to form a 3D Bragg grating switch that can switch light signals between parallel waveguides on different planes. A transparent substrate  824  can be used to fill the areas between the switching planes, and the refractive index of the substrate  824  may be selected to be greater than the clad of the waveguides to have the reflected light signal bend similarly to FIG. 10.  
         [0063]    [0063]FIG. 15 is a 2D Bragg grating switch  910  of another embodiment of the present invention, where the switching occurs within the plane rather than between planes. Region  912  is an expanded top view a portion of switch  910 . Region  912  shows a plurality of top transparent electrodes  918  and bottom transparent electrodes  920 , for core  914  and top transparent electrodes  922  and bottom transparent electrodes  924  for core  916 . The cores and the electrodes are embedded in a clad material  917 .  
         [0064]    [0064]FIG. 16 is a 2D Bragg grating switch  1010  of yet another embodiment of the present invention. The switching occurs again within the plane rather than between planes. Region  1012  is a top view of an expanded cross-section of a portion of 2D switch  1010 . Region  1012  shows cores  1014  and  1016  embedded in a clad later  1018 . The top Bragg grating electrodes are slanted, e.g., top electrodes  1020  and  1022 . The slanted bottom electrodes (not shown) are on the bottom of the cores  1014  and  1016 , respectively.  
         [0065]    [0065]FIG. 17 shows a multi-channel three-dimensional switch of an embodiment of the present invention. There are two stacks  1202  and  1206  of Bragg grating switching planes separated by a stack  1204  of EO 2D switches. The first stack  1202  has Bragg grating switching plane  1212 - 1 ,  1212 - 2 ,  1212 - 3  and  1212 - 4 . Each switching plane, e.g., plane  1212 - 1 , has a plurality of waveguides, e.g., waveguides  1214 - 1 ,  1214 - 2 , and  1214 - 3 . And each waveguide, for example, waveguide  1214 - 1  has a plurality of Bragg gratings, e.g.  1216 - 1  and  1216 - 2 . FIG. 14 shows an example of a switching plane, e.g., plane  1212 - 1 . A second stack of Bragg gratings  1206  has a plurality of Bragg grating switching planes  1226 - 1 ,  1226 - 2 ,  1226 - 3 , and  1226 - 4 . Like stack  1202 , each Bragg grating switching planes has a plurality of waveguides, e.g.,  1228 . The Bragg grating switching planes stacks  1202  and  1206  are separated by an EO 2D switch stack  1204  which has four 2D EO switching planes  1220 - 1 ,  1220 - 2 ,  1220 - 3 , and  1220 - 4 . Thus the two Bragg grating switching stacks  1202  and  1206  provide the switching between the planes and 2D EO stack  1204  provides the switching in a plane.  
         [0066]    An example of how the 3D optical switching array of FIG. 17 works is given for an input light signal  1240 . Light signal  1240  enters a waveguide (not shown) in Bragg grating switch  1212 - 2  and is reflected by a Bragg grating (not shown) in the waveguide to give reflected light signal  1244 . Reflected light signal  1244  is transmitted to switch  1212 - 1  from switch  1212 - 2  and is reflected in Bragg grating  1216 - 3  to produce light signal  1246 . The light signal  1246  enters 2D EO switch  1220 - 1  from switch  1212 - 1  and is switched via prism elements  1248  to give light signal  1250 , i.e., light signal  1250  is switched within the plane. Light signal  1250  is switched by prism elements  1251  to produce light signal  1252 . Light signal  1252  goes from EO 2D switch  1220 - 1  to waveguide  1228  on Bragg grating switch  1226 - 1 . At Bragg grating  1230  light signal  1252  is reflected to give light signal  1254  which goes to a waveguide (not shown) on card  1226 - 3  Light signal  1254  is then reflected in a Bragg grating (not shown) on card  1226 - 3  to produce light signal  1256 , which propagates through the waveguide (not shown) in Bragg grating card  1226 - 3  to produce light signal  1258  as the output light signal. Thus input light signal  1240  on a bottom waveguide in switch  1212 - 2  (the second switch) has been switched to a middle waveguide on switch  1226 - 3  (the third switch) to output light signal  1258 .  
         [0067]    The specification and drawings are provided for illustrative purposes. It will be evident that additions, subtractions, deletions, and other modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims.