Patent Publication Number: US-6983087-B1

Title: Cascading optical switch multi-plane system and method

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of optical signal beam manipulation and propagation. More particularly, the present invention relates to a system and method to facilitate multi-plane cascaded switching of optical signal beams with viable incidence angle correction and beam spread correction. 
   BACKGROUND OF THE INVENTION 
   Systems utilizing various types of signals to represent information have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems facilitate increased productivity and cost reduction in analyzing and communicating information in most areas of business, science, education and entertainment. Advanced optical signal based technologies offer the potential for rapid processing and communication of large amounts of data associated with a variety of activities. The optical based systems typically involve signal manipulation by signal switching operations. However, a number of optical signal beam manipulation problems associated with achieving optimal incidence angles and/or minimal optical signal beam spreading often make traditional control of the signals difficult or impractical. 
   To obtain maximized performance from information systems it is usually critical for the information to be processed and communicated rapidly and reliably. Encoding information in optical signals offers the potential for manipulation and conveyance of significant amounts of information very quickly. For example, most optical systems have significant potential bandwidth capacity for processing and communicating a large quantity of data per unit of time. While some types of optical signal beam controls are relatively simple and easy to accomplish such as transmission of an optical signal beam along a confined single waveguide path (e.g., formed by a fiber optic cable strand), other types of optical signal beam control such as dynamically directing an optical signal beam along various paths are relatively difficult. 
   The ability to control the manipulation and propagation of optical signal beams through a variety of paths usually involves the implementation of switching elements. Switching elements provide a mechanism for directing the optical signal beam to a particular destination, often redirecting the signals along particular designated paths. However, the resources involved in manufacturing attempts at a single switch capable of redirecting optical signals goes up as the number of potential paths increase. Manufacturing attempts at three dimensional or multi-plane switching is typically very complex and resource intensive. Some traditional switching network system configurations attempt to forward a signal to multiple potential destinations by utilizing a network of discrete limited switches connected with external cabling. These traditional attempts typically consume significant resources to manufacture each discrete switch of limited capability and additional resources to “wire” them together (e.g., connect cables between each individual limited switch). Another traditional approaches to switching operations involves converting an optical signal into an electrical signal and vise versa. These approaches are usually slow and require significant resources to implement. 
   Switching optical signal beams typically involves significant challenges for single switches capable of directing optical signal beams along a variety of paths. The nature of light propagation gives rise to a number of complications that can potentially limit or impede the ability to direct an optical signal beam to a particular destination. Cumulative detrimental effects associated with repeated redirection of optical signals tend to limit the practical utilization of traditional optical switches for applications involving significant control flexibility. The relationship of incidence angles and output angles can give rise to detrimental effects in situations where angles become cumulatively deeper each time an optical switch redirects an optical signal beam. Large incidence angles often prevent the propagation of an optical signal beam to a nearby device at an optimal incidence angle. Another potential detrimental impact of repeated redirection of an optical signal beam is deteriorating divergence or spread of the optical signal beam. Each time an optical beam is switched it spreads and a portion of the signal energy is lost. Theses energy losses are typically cumulative and have adverse impacts on interpreting the weakened signals. 
   SUMMARY 
   The present invention is a system and method that facilitates efficient optical signal beam switching. A present invention cascaded optical switching system includes architectures that provide three dimensional multi-plane optical signal beam steering utilizing two dimension optical signal beam steering devices (e.g., two dimensional optical switches). The architectures facilitate redirection of an optical signal beam along paths in different planes. In one embodiment of the present invention, the propagation of optical signal beams along different planes permits greater switching flexibility along shorter multi-plane cascading switch fabrics. The present invention multi-plane cascaded optical switching system and method facilitates flexible high density switching configurations by permitting numerous switches to be arranged in close proximity to one another in multiple planes with each plane providing a variety of different switching routes. 
   In one embodiment, a cascaded optical switch fabric includes a plurality of cascaded optical switches arranged in multiple planes or stages and are coupled to optical switch support members separated by a bracing member. The plurality of cascaded optical switches form a cascaded optical switch fabric and a multi-plane directional device directs an optical signal beam from one of the plurality of optical switches to another of the plurality of optical switches in a different stage or plane. The optical switch support members support the plurality of cascaded optical switches in a cascaded configuration across multiple stages in different planes. The bracing member holds the optical switch support members in a position relative to one another and forms a cascaded optical switch fabric. In one embodiment of the present invention, a multi-plane directional device is included in a cascaded optical switch fabric stage and directs a signal to another optical switch fabric stage in a different plane(e.g., a multi-plane directional device directs an optical signal beam from a first optical switch stage to a second optical switch stage oriented in a different plane). 
   In one exemplary implementation, the optical signal beam is directed through “free-space” (e.g., air or glass not confined by a waveguide) by cascaded switching elements. The present invention cascaded optical switching system and method facilitates minimization of cumulative detrimental impacts associated with cascaded switching of optical signal beam. For example, a present invention cascaded optical switching system can “regenerate” an optical signal beam path with a realigned or corrected incidence angle. A corrected incidence angle permits an optical signal beam to be forwarded at a relatively shallow output angle to an optical switch located in a relatively close proximity on the cascading optical switch fabric. In one embodiment of the present invention, the corrected incidence angle facilitates shortening the cascaded switch fabric length. In one exemplary implementation, a present invention cascaded optical switching system refocuses optical signal beams mitigating adverse impacts (e.g., energy loss) associated with diverging or spreading beams. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a block diagram of a invention cascaded optical switching system in accordance with one embodiment of the present invention. 
       FIG. 1B  is a block diagram of an alternate embodiment in which optical switches are mounted on the surface of a single substrate. 
       FIG. 1C  is a different block diagram view of cascaded optical switching system in accordance with one embodiment of the present invention. 
       FIG. 1D  is a block diagram view of one exemplary cascaded optical switching system from another axis perspective. 
       FIG. 1E  is a three dimensional view of one embodiment of a cascaded optical switching system. 
       FIG. 2  is a block diagram section of cascaded optical switching system in which an optical signal beam is forwarded in two different spatial planes. 
       FIG. 3A  is a block diagram illustration of cascaded optical switching system, one embodiment of the present invention in which multiple optical signal channels are switched simultaneously. 
       FIG. 3B  is a block diagram of one embodiment of an optical cross connect system including a present invention cascaded optical switching system. 
       FIG. 4A  is a three dimensional block diagram of a dynamically variable grating based optical switch included in one embodiment of the present invention. 
       FIG. 4B  shows a cross section side view block diagram of grating from an optical switch. 
       FIG. 4C  illustrates a three dimensional cut-away view of the optical switch where the grating is shown with alternating ribbons in a deflected position relative to undeflected ribbons in accordance with one two level grating embodiment of the invention. 
       FIG. 4D  is a block diagram illustration of a variety of two level configurations for a dynamically variable grating based optical switch. 
       FIG. 4E  is a block diagram illustration of a variety of blaze patterns for a dynamically variable grating based optical switch. 
       FIG. 4F  is a three dimensional block diagram of one embodiment of the present invention in which dynamically variable grating based optical switches are included in cascading topical switch fabric. 
       FIG. 5  is a block diagram illustration of cascaded optical switching system, one embodiment of the present invention with a fixed incidence angle regeneration device. 
       FIG. 6  is a three dimensional representation of a cascaded optical switching system with a fixed incidence angle regeneration device. 
       FIG. 7A  is a block diagram illustration of cascaded optical switching system, one embodiment of the present invention with a dynamically variable incidence angle regeneration device. 
       FIG. 7B  is a three dimensional block diagram illustration of cascaded optical switching system, one embodiment of the present invention with a dynamically variable incidence angle regeneration device. 
       FIG. 8A  is a three dimensional block diagram of a fixed angle incidence corrective device that also provides optical signal spread beam correction, one embodiment of the present invention. 
       FIG. 8B  is a three dimensional block diagram of a dynamically variable and incidence corrective device that also provides optical signal beam spread correction, one embodiment of the present invention. 
       FIG. 9  is a flow chart of a cascaded optical switching method, one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Reference will now be made in detail to the preferred embodiments of the invention, a multi-plane cascading ribbon system and method, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one ordinarily skilled in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the current invention. 
     FIG. 1A  is a side view block diagram of cascaded optical switching system  100 , one embodiment of the present invention. Cascaded optical switching system  100  includes optical switches  10 ,  42  and  52 , multi-plane directional devices  11 ,  12 ,  13 ,  14 ,  21 ,  31 ,  41 , and  51  and optical switch support members  111  and  112 . Optical switch support member  111  is coupled to optical switches  22  (not shown),  32  (not shown),  42  and  52 , and multi-plane directional devices  11 ,  12 ,  13 , and  14 . Optical switches  22  and  32  are not shown in this view because they are on different planes on the Y axis and located “behind” multi-plane directional devices  13  and  14 . Thus, the present invention permits the overall length of the switch fabric to be shortened because these switches are located “behind” the multi-plane directional devices. Optical switch support member  112  is coupled to optical switch  10  and multi-directional devices  21 ,  31 ,  41 ,  51 . In one embodiment of the present invention, the optical switches and multi-plane directional devices are coupled to support members  111  and  112  in a cascaded multi-plane pattern. In one embodiment of the present invention, the optical switch support members are reflective optical switch fabric boundary planes coupled to each other by position bracing members (not shown) that hold the optical switch support members in a position relative to one another. 
   The designation of a component as an optical switch or a multi-plane directional device is based upon the primary function the component provides. For example, an optical switch primarily directs the light in a single plane (e.g., a plane formed by the Z and X axis) and a multi-plane device primarily directs light between planes (e.g., directs the light from a first plane formed by the Z and X axis to a second plane formed by the Z and X axis at a different location on the y axis). 
   It is appreciated that embodiments of the present invention are well suited for use with a variety of different types of components. In one embodiment of the present invention, optical switches and multi-plane directional devices include a reflective component and in another they include a diffractive component. For example, the diffractive components facilitate easier semiconductor manufacturing processes and the reflective components facilitate easier optical manufacturing processes. The reflective components and diffractive components may be fixed (e.g., direct an optical signal beam at a particular output angle for a given input angle) or dynamically variable (e.g., direct an optical signal beam at variable output angles for a given input angle). In an alternative embodiment, one exemplary implementation the multi-directional devices are fixed reflective devices or fixed diffractive devices (e.g., a fixed grating). In one implementation, a multi-plane directional device comprises a fixed reflective surface oriented at a particular angle to guide said optical signal beam to said different plane. For example, a pair of fixed mirrors or fixed gratings oriented to direct the optical signal beam between planes. In one exemplary implementation, the angled mirrors (e.g., angled at less than 45 degrees) are fabricated on silicon using KOH etch yielding 33 degree angle to the mirrors. In yet another embodiment of the present invention, the optical switches and multi-plane directional devices include a variable diffraction component (e.g. a dynamically variable grating based switch). In one exemplary implementation, the optical switches are grated light valve (GLV) switches. In some exemplary implementations, a combination of different types of components are included in the switch fabric. 
     FIG. 1C  is a different block diagram view of cascaded optical switching system  100 , one embodiment of the present invention.  FIG. 1B  illustrates one example of the cascaded optical switch stages formed in different planes. For example, optical switch  10  and multi-plane directional devices  11 ,  12   13 , and  14  form a first plane, multi-plane device  21  and optical switch  22  form a second plane, multi-plane device  31  and optical switch  32  form a third plane, etc. Multi-plane directional devices  11 ,  12 ,  13 , and  14  redirect an optical signal beam from the first plane to another plane and multi-dimensional directional devices  21 ,  31 ,  41  and  51  redirect the signal from the first plane along their respect optical switch fabric planes or stages. Optical switches  22  and  32  are shown in this view and are located “parallel” to multi-plane directional devices  13  and  14 .  FIG. 1D  is a block diagram view of cascaded optical switching system  100  from another axis perspective.  FIG. 1E  is a three dimensional view of one embodiment of cascaded optical switching system  100 . 
   The components of cascaded optical switching system  100  cooperatively operate to direct the propagation of an optical signal beam though cascaded optical switching system  100 . In one embodiment, cascaded optical switching system  100  is configured in an architectures that enables three dimensional multi-plane optical signal beam steering utilizing two dimension optical signal beam steering devices. For example, two dimensional optical switches and two dimensional multi-plane devices that individually direct the optical signal beam in two directions within a single plane but when combined in a present invention architecture facilitate multi-plane three dimensional optical signal beam steering. In one exemplary implementation, the optical signal beam is directed through “free-space” (e.g., air or glass not confined by a waveguide) by cascaded switching elements. In one exemplary implementation of the present invention, an optical signal beam enters a present invention cascading optical switch fabric and is directed along the cascaded optical switches to another receiver or path (e.g., to a waveguide such as an optical cable or other optical device). 
   In embodiment of the present invention, the optical switches are arranged in cascaded switching stages in which each stage includes a plurality of optical devices. For example, a first stage comprising SW 10 , M 11 , M 12 , M 13 , M 14  in a first plane, a second stage comprising M 21  and SW 22  in a second plane, and a third stage comprising M 31  and SW 32  in a third plane. In one embodiment of the present invention, the optical switch support members  111  and  112  are cascade “boundary” planes coupled to each other by position bracing members (not shown) that hold the optical switch support members in a position relative to one another. In one embodiment of the present invention, optical switch support members  111  and  112  are surfaces of a single substrate  188  (e.g., a free space such as glass) and the optical switches are mounted in the substrate  188 .  FIG. 1B  is a block diagram of an alternate embodiment in which the optical switches (e.g., dynamically variable optical switches  181 ,  182  and  183 ) are mounted on the surface of a single substrate  189 . 
   There are a variety of cascading configuration implementations of the present invention cascaded optical switching system  100 . In one embodiment of the present invention, cascaded optical switching system  100  directs optical signal beams to a variety of receivers or paths with different spatial orientation. For example, cascaded optical switching system  100  directs optical signal beams to optical switches in the same spatial planes or stage or in different spatial planes (See  FIG. 1E ).  FIG. 2  is a block diagram section of cascaded optical switching system  200  in which an optical signal beam is forwarded in two different spatial planes. Cascaded optical switching system  200  comprises optical switches  220  and  230 , optical switch support members  241  and  245 , position bracing member  245  and optical waveguide receiver  250 . Optical switch support member  241  is coupled to optical switch  220  and optical switch support member  242  is coupled to optical switch  230 . In one embodiment of the present invention, cascaded optical switching system  200  comprises additional optical switches (not shown) upstream and downstream from optical switches  210  and  230  and position bracing member  245  forms a reflective optical switch fabric boundary plane coupled to the optical switch support members  241  and  242 . 
   The components of cascaded optical switching system  200  cooperatively operate to direct the propagation of an optical signal beam though cascaded optical switching system  200 .  FIG. 2  shows optical waveguide receiver  250  coupled to optical waveguide  251  (e.g., a fiber optical cable) which is in a different spatial plane than the cascaded optical switches of cascaded optical switching system  200 . Optical signal beam  210  is received by cascaded optical switching system  200  and directed in a cascaded fashion to optical switch  220  which directs it to optical switch  230 . Optical switch  230  directs optical signal beam  210  to optical waveguide receiver  250  which forwards the optical signal beam  210  to optical waveguide  251  (e.g., fiber optical cable). Optical waveguide  251  directs the optical signal beam  210  along a path in a spatial plane different from the cascading plane of cascaded optical switching system  200 . 
   A present invention cascaded optical switching system is adaptable to manipulate and convey a variety of different optical signals in numerous different cascaded configurations. For example, a present invention cascaded optical switching system is capable of handling a plurality of optical signals simultaneously.  FIG. 3  is a block diagram illustration of cascaded optical switching system  300 , one embodiment of the present invention. In one exemplary implementation of the present invention, a plurality of optical signals are communicated in one optical signal beam  390  simultaneously to optical switch  310 . In one exemplary implementation, optical signal beam  390  comprises a plurality of optical signals oscillating at different frequencies (e.g., different colors). Optical switch  310  directs the resulting different color optical signal beams to different receivers or paths. For example, optical signal beam  393  oscillating at a first frequency is directed along a first path (e.g., to optical switch  320 ) and optical signal beam  395  oscillating at a second frequency is directed along a second path (e.g., to optical switch  330 ). Directing the two optical signal beams along different paths facilitates different manipulation and conveyance of the signals simultaneously. For example, optical signal beam  393  could be directed by optical switch  320  to optical waveguide  375  and optical signal beam  395  could be directed by optical switch  330  along the optical switch fabric to other downstream optical switches (not shown). 
   In one exemplary implementation of the present invention, a reflective switch is included in the cascaded optical switch fabric. In one embodiment of the present invention, the reflective switch has a reflective mirror surface and the direction it is pointing is adjustable to reflect the optical signal light beam in a different direction. For example, an optical signal beam hits the reflective surface at a particular incidence angle and is reflected to a second destination (e.g., a second reflective switch included in the cascaded optical switch fabric). The direction the reflective surface is pointing is altered (e.g., a mirror rotating on an axis) and the optical switch light beam is reflected to a second destination (e.g., a third reflective switch included in the cascaded optical switch fabric). 
   A present invention cascaded optical switching system is readily adaptable to provide a variety of functions. For example, a one by four (1×4) optical switch fabric that includes 4 pairs multi-plane directional devices (e.g., angled mirrors) and steer a light beam to any one of four discrete spatial locations.  FIG. 3B  is a block diagram of one embodiment of an optical cross connect system  390  comprising a present invention cascaded optical switching system. In one exemplary implementation, an optical signal beam is directed into optical cross connect system  390  on a fiber cable (e.g., fiber 1, fiber 2, . . . fiber N) and is directed out on another one of the fiber cables (e.g., fiber 1, fiber 2, . . . fiber N). 
     FIG. 4A  is a three dimensional block diagram of dynamically variable grating based optical switch  10 , one example of a dynamically variable grating based optical switch. Dynamically variable grating based optical switch  10  is included in one embodiment of the present invention and includes ribbon micro electromechanical machines (MEMs). In one exemplary implementation of the present invention, dynamically variable grating based optical switch  10  is a grating light valve switch. Dynamically variable grating based optical switch  10  utilizes diffraction to control the direction of an optical signal. The diffraction grating of dynamically variable grating based optical switch  10  comprises multiple ribbons  30  supported in a position relative to one another. In one exemplary implementation multiple ribbons  30  are supported by an integrally attached support base  20 . 
     FIG. 4B  shows a cross section side view block diagram of an exemplary grating included in one embodiment of dynamically variable grating based optical switch  10 . In one exemplary implementation of the present invention, each ribbon  30  includes a reflective planar surface  35 . The ribbons of the grating are easily arranged in a variety of configurations. For example, the ribbons can be arranged in a two level pattern, a blaze pattern, a sinusoidal pattern, a triangular pattern, a combination of patterns, etc. The ribbons of grating are arranged in a single planar configuration in  FIG. 4A  and  FIG. 4B .  FIG. 4C  illustrates a three dimensional cut-away view of the optical switch where the grating is shown with alternating ribbons in a deflected position relative to undeflected ribbons in accordance with one two level embodiment of the invention (e.g., forming a square well pattern switch). A two level ribbon arrangement is one in which each ribbon is located in one of two plans.  FIG. 4D  is a block diagram illustration of a variety of two level configurations  471 ,  472 ,  473 , and  474 .  FIG. 4E  is a block diagram illustration of blaze patterns  491  and  492 . 
   In one embodiment of the present invention, the ribbons are dynamically varied. In one exemplary implementation of the present invention, the ribbons are dynamically varied by selectively introducing electromagnetic fields that deflect the ribbons. For example, a mechanism for applying an electrostatic force between each ribbon and support base  20  is included. The position of the deflected ribbon is controlled by varying the strength of the applied electric field. Other ways or mechanisms for moving the ribbons relative to one another could be employed. In one exemplary implementation, the ribbons are supported on their ends by slide supports which allow the ribbons to move as rigid bodies with minimal ribbon end deformation. 
   The configuration style and arrangement of the ribbons govern the diffraction angle of an optical signal beam. In one exemplary implementation of the present invention, mathematical formulas utilized to express the behavior of a diffracted signal beam define the different results that are achievable with different configuration styles and arrangements. For example, the diffraction of an optical signal beam by one configuration of a two level optical switch (e.g., forming a square well pattern) is governed by the equations:
 
 P=n ( W+S ), where  P  is the period or pitch,  n  is the number of ribbons utilized in forming a single grating period,  W  is the ribbon width, and  S  is the space between the ribbons; and
 
 B=Arc sin(( m*Y*N )±Sin  A ), where  N= 1 /P  or 1/( n ( W+S )),  B  is the diffraction angle, A is an optical signal impingement or incidence angle,  m  is the order of the diffraction beam and  Y  is the wavelength of the optical signal.
 
One example of an optical signal beam diffraction by a blaze ribbon configuration pattern is defined by the equation:
 
 B=Arc sin(( m*Y*N )±sin  A ), where  N =1 /P.  
 
For any given A and Y, the value of B can be altered for a given order by controlling N which is done by deflecting the ribbons and manipulating the grating period or pitch (e.g., the number of ribbons in a period). Different ribbon deflection configurations result in different optical signal beam diffractions.
 
     FIG. 4F  is a three dimensional block diagram of one embodiment of the present invention in which dynamically variable grating based optical switches are included in cascading optical switch fabric. Cascaded optical switching system  400  comprises dynamically variable grating based optical switches  420 ,  430  and  435 , and optical switch support members  441  and  445 . Optical switch support member  441  is coupled to optical switch  420  and optical switch support member  442  is coupled to optical switch  430  and  435 . In one embodiment of the present invention, cascaded optical switching system  400  comprises additional optical switches (not shown) upstream and downstream from optical switches  410  and  435 . 
   Some embodiments of a present invention cascaded optical switching system facilitate optical signal beam incidence angle “correction” or realignment. The corrected incidence angle enables a plurality of optical switches to be cascaded in a relatively short configuration. For example, the corrected incidence angle is a normal (zero) incidence angle or near normal incidence angle in some implementations of the present invention. The present invention cascaded optical switching system utilizes an incidence corrective device to realign the incidence angle to produce a relatively shallow output angle. The shallow output angle directs the optical signal beam on a path to a close optical switch included in the cascaded optical switch fabric. 
     FIG. 5  is a block diagram illustration of cascaded optical switching system  500 , one embodiment of the present invention with a fixed incidence angle regeneration device. Cascaded optical switching system  500  includes optical switches  521 ,  531 ,  532 ,  541 ,  542 ,  551 ,  552 ,  571 ,  572 ,  581  and  582 , optical switch support members  511  and  512 , and incidence corrective device  585 . Optical switch support member  511  is coupled to optical switches  531 ,  532 ,  551 ,  552 ,  581  and  582  and optical switch support member  512  is coupled to incidence corrective device  585  and optical switches  521 ,  541 ,  542 ,  571 , and  572 . The optical switches and optical switch support members of cascaded optical switching system  500  are similar to those in cascaded optical switching system  100 . The incidence corrective device  585  receives an optical signal beam from an optical switch (e.g., optical switch  551 ) at a first incidence angle and directs it at a second output angle that is shallower than the first incidence angle. 
   In one embodiment of the present invention, the incidence corrective device  585  directs the optical signal beam at an angle that leads it on a path normal to the base of corrective device  585  coupled to optical switch support member  512 . In one exemplary implementation of the present invention, the incidence corrective device  585  directs the optical signal beam at an angle that leads it on a path normal to an optical switch (e.g., optical switch  581 ) and thereby regenerates a zero angle of incidence at the optical switch. This enables downstream optical switches (e.g., optical switches  571  and  582 ) to be placed in closer proximity to one another in the cascaded optical switch fabric. 
   A present invention incidence corrective device has a number of configurations and is flexibly adaptable to a number of different implementations. In one embodiment of the present invention, an incidence corrective device includes a fixed reflective component oriented at a particular angle. In one exemplary implementation of the present invention, an incidence corrective device includes a fixed reflective component (e.g., a mirrored surface) oriented at an angle defined by one half the output angle an optical signal beam is forwarded from. For example, the reflective component orientation angle of corrective device  585  is a half of a first output angle (e.g., theta minus one) of an optical signal beam from optical switch  551 . 
   The “regenerated” or corrected incidence angle (e.g., alpha) at which the optical signal beam strikes the next optical switch (e.g., optical switch  581 ) is close to zero. The optical signal beam is forwarded at a second output angle (e.g., theta) that is relatively shallow and permits the optical signal beam to travel on a path directed to an optical switch (e.g., optical switch  571 ) located in a relatively close proximity on the cascading optical switch path.  FIG. 6  is a three dimensional representation of a cascaded optical switching system  500  with a fixed incidence angle regeneration device. In another embodiment, a fixed incidence angle regeneration device is a fresnel mirror device configured with concentric fresnel grooves. 
     FIG. 7A  is a block diagram illustration of cascaded optical switching system  700 , one embodiment of the present invention with an incidence corrective device capable of providing dynamically variable incidence angle regeneration. Cascaded optical switching system  700  includes optical switches  721 ,  731 ,  732 ,  741 ,  742 ,  751 ,  752 ,  771 ,  772 ,  781  and  782 , optical switch support members  711  and  712 , and incidence corrective device  787 . Optical switch support member  711  is coupled to switches  731 ,  732 ,  751 ,  752 ,  781  and  782  and optical switch support member  712  is coupled to incidence corrective device  787  and switches  721 ,  741 ,  742 ,  771 , and  772 . The optical switches and optical switch support members of cascaded optical switching system  700  are similar to those in cascaded optical switching system  100 . The incidence corrective device  787  receives an optical signal beam from an optical switch (e.g., optical switch  751 ) at a first incidence angle and directs it at a second angle that is shallower than the output angle from a previous optical switch. The output angle of an optical signal beam directed from incidence corrective device  787  is dynamically variable which permits flexible control of optical signal propagation and can direct the optical signal beam so that it strikes a downstream optical switch at a corrected or “regenerated” incidence angle. A corrected or regenerated incidence angle is one that assists the reduction of cumulative detrimental effects associated with a deteriorating or deepening incidence and output angle. 
   As indicated above, a present invention incidence corrective device has a number of configurations and is flexibly adaptable to a number of different implementations. In one of the present invention, an incidence corrective device is a dynamically variable incidence corrective device. In one exemplary implementation of the present invention, a dynamically variable incidence corrective device includes a variable reflective component (e.g., a mirrored surface or a reflective optical switch) capable of being oriented or adjusted to point in a variety of directions. The corrected or “regenerated” incidence angle (e.g., alpha) at which the optical signal beam strikes the next optical switch is close to zero.  FIG. 7B  is a three dimensional block diagram illustration of cascaded optical switching system  700 , one embodiment of the present invention with a dynamically variable incidence corrective device. In one exemplary implementation, the incidence corrective device is a dynamically variable grating based optical switch similar to dynamically variable grating based optical switch  10 . 
   In one embodiment, the present invention includes an optical signal beam spread mitigation device in an optical switch fabric. A present invention optical signal beam spread correction device corrects beam spreading by refocusing the optical signal beam. Refocusing the optical signal beam mitigates signal loss and facilitates efficient interpretation of signal content. 
     FIG. 8A  is a three dimensional block diagram of a fixed optical signal beam spread corrective device  810 , one embodiment of the present invention. Fixed spread corrective device  810  has a concave reflective face  811  that reflects the optical signal beam in a focusing pattern. In one embodiment of the present invention, fixed optical signal beam spread corrective device  810  also reflects the optical signal beam at a corrected incidence angle. For example, an optical signal beam made up of components  821 ,  822  and  823  are reflected by dual spread and incidence corrective device  810  to a focal point on optical switch  830 . By redirecting the components of the optical signal beam towards a single focal point the optical signal beam is concentrated in a tighter area. Present invention fixed spread corrective devices have a variety of reflective face configurations for converging the beam to a tighter focus (e.g., a concave shaped reflective face, a fresnel mirror, etc.). 
     FIG. 8B  is a three dimensional block diagram of a spread corrective device  870 , one embodiment of the present invention with dynamically variable spread corrective capabilities that also performs spread correction. Dynamically variable spread corrective device  870  forms a chirped reflective face that reflects the optical signal beam in a converging pattern. In one exemplary implementation, the dynamically variable spread is a dynamically variable grating based optical switch (similar to dynamically variable grating based optical switch  10 ) and the ribbons are deflected so that a chirped grating pattern is formed in which the periodicity gradually decreases towards the periphery. The deflection of the ribbons is dynamically variable and facilitates flexible control of an optical signal. In one embodiment of the present invention, spread corrective device  870  performs dual spread and incidence angle correction functions. 
   In one embodiment of the present invention, incidence angle correction and beam spread correction are provided by a single optical device. In one exemplary implementation, a dual purpose spread and incidence corrective device corrects incidence degeneration problems by redirecting the focused optical signal beam along a vector that is normal to the switching stage. For example, spread corrective devices  810  and  870  are capable of performing dual spread and incidence angle correction functions. In one embodiment of the present invention, a dual purpose corrective device is included in a cascading optical switch fabric in place of an incidence corrective device (e.g., incidence corrective device  585  or  787 ). 
     FIG. 9  is a flow chart of cascaded optical switching method  900 , one embodiment of the present invention. In one embodiment of the present invention, cascaded optical switching method  900  includes an optical signal beam incidence angle regeneration process. In one embodiment of the present invention, cascaded optical switching method  900  includes an optical signal beam spread corrective process. 
   In step  910 , an optical signal beam is received by a cascaded optical switch fabric. In one exemplary implementation of the present invention the optical signal beam is introduced to a cascading optical switch fabric from a waveguide (e.g., a fiber optic cable). 
   In step  920 , the optical signal beam is propagated along the optical switch fabric. In one embodiment of the present invention, the optical signal beam is received by a number of optical switching points and the continued path direction of the optical signal beam is controlled. In one embodiment of the present invention, the optical switching points are arranged in a cascaded order or configuration. In one exemplary implementation, optical signals are received by optical switching points, including a dynamically variable grating based optical switch. In one embodiment of the present invention, the optical signal beam is forwarded along the switch fabric in a different plane (e.g., forwarded to an optical switch stage in a different plane). 
   In one embodiment, cascaded optical switching method  900  includes reflecting an optical signal beam in a particular direction to another switching point. In one exemplary implementation, the direction of the reflection is dynamically varied, which in turn varies the direction of the optical signal beam. In one embodiment, cascaded optical switching method  900  includes dynamically varying the grating pitch within a light diffraction grating of a dynamically variable grating based optical switch, which in turn varies the diffraction angle of an optical signal beam switched by the dynamically variable grating based optical switch. In one exemplary implementation of the present invention, step  920  includes independently moving each ribbon of the dynamically variable grating based optical switch in coordination with other ribbons to provide a dynamically varying grating pitch. For example, cascaded optical switching method  900  includes applying an electromagnetic field in the proximity of the ribbons which causes the ribbons to move (e.g., deflect). 
   In step  930 , the optical signal beam is forwarded away from the optical switch fabric. In one embodiment of the present invention, the optical signal beam is forwarded to an external waveguide (e.g., a fiber optic cable). 
   In one embodiment of the present invention, the optical signal beams are forwarded (“regenerated”) at a desired incidence angle to the destination (e.g., a corrected incidence angle). In one embodiment, an incidence angle is dynamically corrected so that said optical signal beam is forwarded at a relatively shallow output angle. In one exemplary implementation, the desired incidence angle is one that results in a shallow output angle. For example, the “regenerated” incidence angle (e.g., alpha) of the optical signal beam strikes the next cascaded optical switch at an angle that is close to zero. The optical signal beam is forwarded at a second output angle (e.g., theta) that is relatively shallow and permits the optical signal beam to travel on a path directed to an optical switch located in a relatively close proximity on the cascading optical switch fabric path. 
   In one exemplary implementation of the present invention, the optical signal beam is forwarded by an incidence corrective device that includes a fixed reflective component (e.g., a mirrored surface) oriented at a set angle (e.g., an angle defined by one half the output angle an optical signal beam is forwarded from). In one exemplary implementation of the present invention, the optical signal beam is forwarded by an incidence corrective device that includes dynamically variable grating based optical switch ribbons deflected in a manner that propagates an optical signal beam on a path that is normal to a cascaded second optical switch. In one embodiment of step  930 , an optical signal beam is directed away in a manner that corrects spread problems by refocusing the optical signal beam in a tighter pattern. 
   Thus, the present invention facilitates the inclusion of a number of switches in a cascaded device in a manner that facilitates efficient optical signal switching. Architectures of the present invention enable three dimensional multi-plane optical signal beam steering to be performed with two dimensional steering devices. For example, two dimensional steering devices which are easier to manufacture than individual three dimensional steering switches. The ability to direct optical signal beams to optical switched in multiple planes facilitates flexible high density switching configurations. The flexible high density switching configurations permit numerous switches to be arranged in close proximity to one another in multiple planes with each plane providing compact flexible switching routes to numerous different spatial locations. The present invention cascaded optical switching system and method also facilitate minimization of cumulative detrimental impacts associated with cumulatively increasing incidence/output angles and spreading of an optical signal beam. A present invention cascaded optical switching system “regenerates” an optical signal beam path with a realigned or corrected incidence angle. In one embodiment of the present invention, the corrected incidence angle facilitates shortening the cascading optical switch fabric length. Correcting the incidence angle also facilitates utilization of optical switches that are economical to manufacture, however, have limited switching range (e.g., switch with limited reflection or diffraction movement). In one exemplary implementation, a present invention cascaded optical switching system refocuses spreading optical signal beams and mitigates signal loss. 
   The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.