Abstract:
A variable modulator assembly includes an active layer having a first and second surface. A deformable layer is in operational contact to the first surface of the active layer, and an electrode configuration consisting of a plurality of electrodes is in operational contact to the second surface of the active layer. A controller is configured to selectively apply a variable signal to the selected electrodes of the electrode configuration. Application of the variable signal causes the deformable layer to reconfigure to an alternated shape having distinct peaks and valleys. The distance between the peaks and valleys being determined by the value of the applied variable signal.  
     In accordance with another aspect of the present invention, provided is an optical modulating method, including positioning a variable modulator assembly to receive light from a light source. The variable modulator assembly includes a deformable layer in operational contact to a first surface of an active layer of the variable modulator. It is the deformable layer, which is located to receive the light from the light source. Deformation of the deformable layer is controlled by selective activation of an electrode configuration in operational contact to a second surface of the active layer. The activation of the electrode configuration is controlled by a controller. In the process, the controller generates a variable signal and transmits the variable signal to selected electrodes of the electrode configuration, wherein activation of the electrodes causes electrostatic charges which deform the deformable layer into a pattern corresponding to the activated electrodes.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present application relates to optical grating assemblies, and more particularly to an assembly and method for a configurable grating assembly based on a surface relief pattern for use as a variable optical attenuator.  
           [0002]    Fiber networks normally employ point-to-point links, which are static, where most of the intelligence, provisioning and grooming functions are provided by electronics at the ends of each link. As network architectures grow in size and complexity, however, this approach to building and maintaining network infrastructure will not satisfy the requirements of reliability, efficiency and cost-effectiveness required by service providers. Therefore, the industry is moving to optically reconfigurable networks where optical paths, wavelengths and data rates are dynamically changed to satisfy network system requirements, such as provisioning new wavelengths, balancing data loads and restoring after-service malfunctions.  
           [0003]    Variable optical attenuators (VOA) are used to permit dynamic control of optical power levels throughout a network. As an example of their usefulness, if a network is providing a wavelength route that is approximately 60 km in length, at a predetermined power, and the network attempts to change the wavelength route to one which is 30 km, it would be expected that excessive power would be delivered to the end receivers of the 30 km route, potentially resulting in a malfunction in the network. A VOA will lower the power output of the switched wavelength to permit a signal of acceptable strength at the end receiver. Existing VOAs implement mechanical systems to attenuate the light. In one design, attenuation is accomplished by moving two separate optical fibers, and in another by inserting a motor-driven blade or filter in the light path. While these devices have acceptable optical performance, tradeoffs include slow speed, undesirable noise and a potential for mechanical failure.  
           [0004]    It has been appreciated by the inventors, that systems now exist which describe structures incorporating deformed/deformable structures for light modulation.  
           [0005]    Sheridon, in an article entitled, “The Ruticon Family of Erasable Image Recording Devices,”  IEEE Transactions on Electron Devices , ED-19, No. 9, September 1972, pp. 1003-1010, teaches Ruticons are solid-state cyclic image recording devices. They have a layered structure consisting of a conductive transparent substrate, a thin photoconductive layer, a thin deformable elastomer layer, and a deformable electrode such as a conductive liquid, a conductive gas, or a thin flexible metal layer. When an electric field is placed between the conductive substrate and the deformable electrode the elastomer will deform into a surface relief pattern corresponding to the light-intensity distribution of an image focused on the photoconductor. Light modulated by the deformation of the elastomer surface can in turn be converted to an intensity distribution similar to the original image by means of simple optics. Ruticons are expected to find initial applications in image intensification, holographic recording, and optical buffer storage.  
           [0006]    Further, in “The Optical Processing Capabilities of the Ruticon,” SPIE Vol. 128,  Effective Utilization of Optics in Radar Systems  (1977), pp. 244-252, Sheridon, et al. teach the Ruticon is a solid state optical image modulator consisting of a metallized elastomer layer coated on a photoconductor layer. An electrical field is placed between the metal surface and a transparent conductive substrate. An input image, such as from a CRT or a laser, causes a change in the distribution of electrical fields across the device, and the mechanical forces associated with these electrical fields cause the metallized elastomer surface to deform into an image pattern. Laser light reflected from this surface is phase modulated with the input image information and this modulated light may be used as the input to a coherent optical processing system.  
           [0007]    Other examples of such designs include two patents to Glenn, U.S. Pat. Nos. 4,529,620 and 4,626,920. These patents disclose the generation of video imagery through the use of storing a charge pattern representative of a video frame. The system employs a solid state light modulator structure having an array of space charge storage electrodes. An elastomer layer is disposed on the semiconductor device, over the array of charged storage electrodes. At least one conductive layer is disposed over the elastomer layer. The semiconductor device is responsive to the input video signal to selectively apply voltage between the charged storage electrodes and the one conductive layer to cause deformations of the conductive layer and the elastomer layer. A plastic pellicle layer may be disposed between the elastomer layer and the at least one conductive layer. These patents are hereby incorporated by reference in their entirety.  
           [0008]    Laude et al., U.S. Pat. No. 3,942,048, is directed to an optical grating assembly having a piezoelectric substrate, which supports, on two opposite faces thereof, respective metallic layers. One of these faces of the substrate also carries a grating. Application of a variable voltage between the metal layers sets up an electric field of variable strength in the substrate, resulting in the pitch of the grating being variable due to the piezoelectric nature of the substrate. Laude et al. &#39;048 is incorporated by reference in its entirety.  
           [0009]    Bloom et al., U.S. Pat. No. 5,459,610, describes a modulator for modulating incident rays of light. The modulator includes a plurality of equally spaced apart beam elements, each of which includes a light-reflective planar surface. The elements are arranged parallel to each other with their light reflective surfaces parallel to each other. Means are provided for supporting the beam elements in relation to one another. Additional means are provided to the beam elements relative to one another so that the beams move between a first configuration wherein the modulator acts to reflect the incident rays of light as a plane mirror, and a second configuration wherein the modulator diffracts the incident rays of light as they are reflected. Bloom et al. &#39;610 is hereby incorporated by reference in its entirety.  
           [0010]    An article by Kück et al., entitled “Deformable Micromirror Devices as Phase-Modulating High-Resolution Light Valves,”  Sensors and Actuators  A 54 (1996) 536-541, reports on two different technologies for deformable micromirror devices as phase-modulating light valves for high-resolution optical applications. Disclosed is a fabricated light valve with CMOS addressing and viscoelastic layer deformable mirrors. On top of a substrate carrying pixel electrodes is the viscoelastic control layer covered with a mirror electrode. A bias voltage of typically 250 V is applied between the pixel electrodes and the mirror electrode, whereby the reflective viscoelastic layer behaves like a plane mirror. On applying a single voltage of about ±15 V to neighboring pixel electrodes, the viscoelastic mirror is deformed sinusoidally forming a phase grating corresponding to the active pixels. In order to avoid the imprinting of an image pattern into the viscoelastic layer, the polarity of the signal voltage is changed in subsequent image cycles. Kück et al. is hereby incorporated by reference in its entirety.  
           [0011]    The foregoing material does not address the noted shortcomings, and further fails to disclose a VOA, which also permits for analog control and for specific configurations.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0012]    A variable modulator assembly includes an active layer having a first and second surface. A deformable layer is in operational contact to the first surface of the active layer, and an electrode configuration consisting of a plurality of electrodes is in operational contact to the second surface of the active layer. A controller is configured to selectively apply a variable signal to the selected electrodes of the electrode configuration. Application of the variable signal causes the deformable layer to reconfigure to an alternated shape having distinct peaks and valleys. The distance between the peaks and valleys being determined by the value of the applied variable signal.  
           [0013]    In accordance with another aspect of the present invention, provided is an optical modulating method, including positioning a variable modulator assembly to receive light from a light source. The variable modulator assembly includes a deformable layer in operational contact to a first surface of the active layer of the variable modulator. It is the deformable layer, which is located to receive the light from the light source. Deformation of the deformable layer is controlled by selective activation of an electrode configuration in operational contact to a second surface of the active layer. The activation of the electrode configuration is controlled by a controller. In the process, the controller generates a variable signal and transmits the variable signal to selected electrodes of the electrode configuration, wherein activation of the electrodes causes electrostatic charges, which deform the deformable layer into a pattern corresponding to the activated electrodes.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.  
         [0015]    [0015]FIG. 1A is a cross-sectional view of a variable modulator system according to the teachings of the present application;  
         [0016]    [0016]FIG. 1B is a cross-sectional view of an alternative arrangement of the optical modulator of FIG. 1A, with an interdigitated electrode operation;  
         [0017]    [0017]FIG. 1C depicts the optical modulator of the present application showing various deformations of an upper deformable layer;  
         [0018]    [0018]FIG. 1D depicts the optical modulator having a light beam from a light source impinging upon a deformed surface;  
         [0019]    [0019]FIG. 1E shows a block view of the electrode configuration in a line configuration switching arrangement;  
         [0020]    [0020]FIG. 1F shows the electrode configuration in a pixel-by-pixel switching arrangement;  
         [0021]    [0021]FIG. 1G shows the pixel-by-pixel arrangement wherein deformation will be in the x-axis;  
         [0022]    [0022]FIG. 1H illustrates the pixel control mechanism with a selection wherein the deformation is in the y-axis;  
         [0023]    [0023]FIG. 2A is another embodiment of an optical modulator according to the present application wherein the deformable surface is a patterned interdigitated surface layer;  
         [0024]    [0024]FIG. 2B depicts an arrangement similar to  2 A, with the electrodes on a top surface.  
         [0025]    [0025]FIG. 3 illustrates an embodiment wherein the upper deformable layer and electrode configuration are of a transparent material;  
         [0026]    [0026]FIG. 4A depicts an embodiment of a variable modulator wherein the electrode configuration is a multi-layered configuration;  
         [0027]    [0027]FIG. 4B shows a top view of the electrode configuration of FIG. 4A;  
         [0028]    [0028]FIG. 5 depicts another embodiment of an optical modulator or a substrate wherein the substrate is deformable such that it alters the spacing between the electrodes of the electrode configuration;  
         [0029]    [0029]FIG. 6A illustrates yet another embodiment of a variable modulator wherein the active layer is a thermoplastic settable material;  
         [0030]    [0030]FIG. 6B depicts the optical modulator of FIG. 6A in a deformed state wherein the thermoplastic active layer has been reformed and the controller voltage removed; and  
         [0031]    [0031]FIG. 7 shows a two-channel variable modulator, such as a variable optical attenuator. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    Referring to FIG. 1A, illustrated is a simplified schematic diagram of a variable modulator assembly system  10 , which may be a variable optical attenuator, according to the concepts of the present application. Variable modulator  12  is constructed with an active layer  14 , having an upper surface, which is in operational contact with a deformable compliant layer  16  having a reflective surface  18 . A bottom surface of the active layer  14  has, in operational contact, an electrode configuration  20 , comprising a plurality of electrodes  20   a - 20   n . In one embodiment, the reflective surface may be a polished surface of the deformable layer  16 , or may be a separate blanket or patterned layer made of reflective material including but not limited to a variety of metals. In one embodiment, deformable layer  16  is directly attached onto an upper surface of the active layer  14 . In other embodiments an interposed protective layer (not shown) is provided. Deformable layer  16  is conductive as well as reflective.  
         [0033]    The electrode configuration may be patterned using known photolithography techniques to achieve a desired surface relief pattern, which will correspond to the system&#39;s grating structure. Active layer  14  may be elastomer or electrostrictive material, such as Poly-di-methyl-siloxane (PDMS) formed by known spin-coating or other manufacturing techniques. Piezo-electric materials like poly vinylidene fluoride may also be considered, provided the frequency of operation is carefully chosen.  
         [0034]    Reflective surface  18  of deformable layer  16  is designed to be reflective and act as a mirror when no voltage is applied to variable modulator  12 . In this embodiment, the deformable layer  16  is grounded, and electrode configuration  20  will be supplied with a bias and/or variable voltage from a voltage signal generator/controller  22 .  
         [0035]    Voltage generator/controller  22  can be designed to address each electrode individually, or to address groups of electrodes in common. In either arrangement, controller  22  is able to provide application of a variable voltage to the electrodes.  
         [0036]    [0036]FIG. 1B depicts a variable modulator assembly system  10 ′ similar to FIG. 1A. However, in this design, alternating electrodes (e.g.,  20   b ,  20   n ) are set to ground, which operate the electrodes in an interdigitating arrangement.  
         [0037]    As shown in FIG. 1C, application of the variable voltage signal from controller  22  creates an electrostatic (capacitive force) action causing the active layer  14  and the deformable layer  16  to wrinkle in accordance with the electrode configuration geometry—in this embodiment creating a variable sinusoidal grating  28 . The distance from the valley grating  30  to a peak  32  of the grating surface is defined in this example as a value x. Dotted-line  34  illustrates a situation where signal generator/controller  22  has increased the voltage supplied to the patterned electrodes of electrode configuration  20 . In this situation, the valley  36  to peak  38  difference is x+a. Controller  22  may also decrease the voltage applied to electrodes of electrode configuration  20 . In this situation, the valley to peak difference is decreased.  
         [0038]    [0038]FIGS. 1A and 1C illustrate that deformable layer  16  will form into a surface relief pattern dependent upon the patterned electrode configuration  20 , and as a varying signal is applied to the electrode configuration  20 , the height of the peaks formed in the deformable layer will vary.  
         [0039]    When no variable voltage is supplied from controller  22 , reflective surface  18  acts as a mirror, and displacement of an impinging light is at substantially zero displacement. As the voltage to electrode configuration  20  is increased by the controller  22 , displacement or diffraction of the light is increased. When the surface reliefpattern is displaced by a quarter wavelength, the light reflected from the two surfaces is 180° out of phase, and destructive interference occurs. At this point, the light is totally diffracted, and none is reflected. Therefore, by the described design, analog control of the light, e.g., from a zero state of displacement to a quarter wavelength displacement, is achieved by application of the variable voltage from controller  22 .  
         [0040]    This analog control is refined by monitoring of at least one of the diffracted order wavelengths such as a 1 st  order diffracted wavelength. For example, initially, the 0 th  order (zero displacement) and 1 st  order (quarter length displacement) diffraction intensity as a function of voltage is calibrated and this information used to control the intensity of the 0 th  order by monitoring the 1 st  order diffraction. In one implementation, a light source  50  of FIG. 1D emits a light beam  52 . A reflected light portion  54  is transmitted to an element  56 , such as a fiber, receiver, or other mechanism. A diffracted light wave  58 , is sensed by a sensor  62 . The sensor  62  may be substantially transparent to the wavelength of the diffracted light  58  for situations where additional testing or use of the diffracted light wave  58  is to be undertaken. Output from the sensor  62  is provided via a feedback line  64  to controller  22 . Feedback circuitry included in controller  22  uses the signal obtained from the 1 st  order diffracted wavelength to control the voltage applied to electrode configuration  20 . This design permits for a non-destructive monitoring and controlling of the 0 th  order (zero displaced waveform). Hence, in this example the deformation of deformable layer  16 , with reflective surface  18 , is controlled from the 0 th  order (zero displacement) to the 1 st  order (e.g., quarter wavelength displacement) by an analog control mechanism. By use of this analog control, the intensity output value for the 0 th  order is closely controllable. For example, when no variable voltage is applied (so the surface is essentially a mirror) the intensity output of a beam of light to component  56  may be substantially 100 percent of the light beam  52 . If the desired output requirements change wherein only 75 percent intensity in the 0 th  order is needed, the amount of voltage supplied to the electrode configuration  20  is undertaken to increase the deformation such that 25 percent of the intensity goes into higher order diffracted wavelengths (e.g., 58). More generally, the present design permits analog control from a first displacement to a second displacement.  
         [0041]    [0041]FIG. 1E illustrates the variable signal generated by controller  22  does not have to be supplied to all of the electrodes of electrode configuration  20 . Rather, a more refined control is obtainable. In one embodiment, switches  72   a - 72   n  maybe used to control individual lines of electrodes  74   a - 74   n ,  76   a - 76   n ,  78   a - 78   n . Controller  22  will issue a signal, turning on one or more of switches  72   a - 72   n . Switches  72   a - 72   n  may be high voltage TFT, CMOS or other appropriate switching devices.  
         [0042]    A further refinement in the control of electrode configuration  20  is shown in FIG. 1F. Herein, each electrode pixel  80   a - 80   n  of the electrode configuration will include an electrode  82   a - 82   n , and an associated switch mechanism  84   a - 84   n . By this design, each pixel may be individually addressed by controller  22 . In one embodiment, the switch mechanism  84   a - 84   n  may be TFT, CMOS or other appropriate switching devices.  
         [0043]    It is to be understood that when using one switch for each individual line of electrodes, spacing of the active electrodes can be controlled, and this permits the use of the present design to filter different light wavelengths. Further, when a line and individual switching, such as with TFT or CMOS switches are used, the generated grating can be oriented in distinct directions by activating the appropriate pixel combinations. For example, using the design of FIG. 1F, when the grating structure is oriented in the x-axis, the 1 st  order diffraction pattern will be in the x-axis of the diffraction plane (i.e., in FIG. 1G when pixels in groupings  86   a ,  86   b ,  86   c  are selected), and when the grating structure is oriented in the y-axis, the 1 st  order diffraction pattern will be in the y-axis of the diffraction plane (i.e., in FIG. 1H when pixels in groups  88   a ,  88   b ,  88   c  are selected). Operation of the variable optical attenuator, modulator, as a variable optical attenuation of the present application may be used minimize overlap of signals of a 1 st  order diffraction signal with adjacent channels.  
         [0044]    Turning to FIG. 2A, set forth is another embodiment of a variable modulator (variable optical attenuator)  90  according to the present application. Particularly, in this embodiment, blanket deformable layer (i.e., electrode)  16  of FIG. 1A is replaced with a patterned interdigitated deformable electrode layer  92 . The patterning of the deformable electrode  92  may be accomplished by any known method, using any of a number of materials. This deformable electrode pattern may be transferred to active layer  94  by a variety of transfer operations, including a laser liftoff process. A preferred version of accomplishing the laser lift-off process is to use a low power, plasma-treated PDMS layer so that there is a thin layer of surface oxide and quartz/metal/amorphous silicon for the laser liftoff.  
         [0045]    [0045]FIG. 2B depicts an alternative variable modulator  90 ′ according to the present application. In this embodiment, the top electrodes  92  are selectively connected for activation to a voltage signal generator/controller  98 , while others are placed at common. This design provides for operation in an interdigitated mode.  
         [0046]    In the embodiments of FIGS. 2A-2B, and other embodiments disclosed herein, bottom electrode configuration  96  maybe placed at common/grounded, and the voltage applied to the patterned deformable interdigitated electrode layer  92 . The modulator may be built on any of a number of different substrates, such as a glass substrate  97 . A potential benefit of this embodiment is that the device efficiency will not be limited by the stiffness of the blanket top electrode as in FIG. 1A, when voltage signal generator/controller  98  applies a variable voltage to variable modulator  90 .  
         [0047]    Turning to FIG. 3, shown is another embodiment of a variable modulator  100  according to the teachings of the present application. In this embodiment, a lower-patterned electrode  102  is formed from a transparent material substantially transparent at the wavelengths of light which will impinge at the modulator  100 . The active layer  104 , similar to previous embodiments, may be a spin-coated elastomer or other appropriate material. A conductive transparent blanket layer  106  is employed as the deformable electrode layer, and glass or other appropriate material is used as a substrate  109 . It is to be appreciated, however, that layer  106  may also employ a patterned deformable layer. There may be a loss, dependant upon the material and wavelength used in this embodiment.  
         [0048]    An advantage of the device shown in FIG. 3 is that by using the conductive polymer, higher strain levels are possible than those used with a metal layer such as described in FIG. 1. In this embodiment, operation includes grounding the top transparent blanket electrode  106 , and applying a voltage, via a voltage signal generator/controller  108 , to the bottom transparent, interdigitated electrodes  102 . The variable modulator  100  may be designed with its configurable transmissive grating, in one embodiment as a sinusoidal grating. The method of operating variable modulator  100  is similar to that previously described, except that the operation is in transmission mode. An advantage of this embodiment is that the top layer may not be reflective. This helps in achieving a top electrode layer with a higher compliance, which translates into a device with improved efficiency.  
         [0049]    Turning to FIG. 4A, illustrated is a further embodiment of a variable modulator  110  according to the teachings of the present application. Deformable surface layer  112  is shown as a blanket electrode. However, it is to be appreciated this embodiment may also employ an interdigitated patterned electrode as the deformable layer. The deformable electrode layer  112  is carried on the active layer  114  as in previous embodiments.  
         [0050]    The lower electrode configuration  116  may be a multi-layered electrode configuration having a plurality of electrodes  118   a - 188   h  in a layered design where the electrode configuration in a layer may be placed at angles to electrode configuration in an adjacent layer. This is illustrated more clearly in the top cross-sectional view of FIG. 4B. A dielectric or other insulating material  120  is used to separate the electrodes from each other. A voltage is selectively applied to electrodes  118   a - 188   i , via voltage signal generator/controller  122 .  
         [0051]    The multi-layered concept permits the generation of a complex diffraction grating with different electrode fields being used for different patterns.  
         [0052]    Using this configuration, it is possible to switch, diffracted light, such as the 1 st  order diffracted light, to different points in a plane. Thus, when the grating structure is oriented in the x-axis, the 1 st  order diffraction pattern will be in the x-axis of the diffraction plane, and when the grating structure is oriented in the y-axis, the 1 st  order diffraction pattern will be in the y-axis of the diffraction plane. Operation of variable modulator  110  in this embodiment may be used to minimize the overlap of signals in 1 st  order diffracted signals with an adjacent channel. It is particularly noted that electrodes may be located in a stacked relationship to each other, as is shown by electrodes  118   c ,  118   i  and electrodes  118   f ,  118   j . In this design, the same area of the deformable layer  112  may be manipulated in different orientations.  
         [0053]    Turning to FIG. 5, depicted is a further embodiment of a variable modulator  130  according to the concepts of the present application. In this embodiment, active layer  132 , which carries the deformable layer  134 , incorporates electrode configuration  136  (which is intended to include each electrode of the system). This arrangement is fabricated on a flexible, compliant structure substrate  137 , which permits the grating pitch to be varied. In one embodiment, the flexible substrate  137  may be a piezoelectric material. A variable voltage source  138  is connected between electrode configuration  136  and deformable layer  134 , each of which are electrically conductive layers. When energized by an energy source  138 , the piezoelectric substrate  137  will expand, altering the distance  140  between the electrodes of the electrode configuration  136 . Particularly, if the space between two adjacent electrodes is d, then it is possible to change the spacing from d+Δd to d−Δd, as well as 2d+Δd to 2d−Δd, and so on, wherein Ad is the displacement change that can be created due to the flexible compliant material of substrate  137 . Using this technique, it is possible to obtain a higher wavelength resolution. Other advantages include the ability to filter nearby wavelengths, and for scanning and positioning applications. In addition to a material, which requires electrical operation, the flexible substrate  137  may be a silicone elastomer which is able to be mechanically deformed. Controller  142 , which is similar to controller  22 , permits for the analog control of variable modulator  130 . While variable voltage source  138  and controller  142  are shown in this figure as separate components, it is to be understood that they could be provided as a single unit. It is to be understood that previous and following modulators are shown without a substrate, and is done for clarity. However, for actual manufacture, these modulators will be formed on a substrate such as substrate  137  or a substrate formed from glass or other appropriate material.  
         [0054]    Turning to FIG. 6A, set forth is a variable modulator  150  according to still another embodiment of the present application. In this design, active layer  152 , carrying deformable layer  154  and connected to electrode configuration  156 , is formed of a thermoplastic material. This configuration is carried on a substrate  157 , which may be glass or other appropriate material. Use of the thermoplastic material permits for a bistable device. The thermoplastic layer  152  is heated above its setting point, to enter into a formable state. While in the formable state, a relief pattern generated in accordance with the electrode configuration  156  and operation of controller  158  forms, for example as shown in FIG. 6B, deformed upper layer  154 . Thereafter, the temperature of the thermoplastic material  152  is lowered to below its set point, and thereafter the voltage supplied by controller  158  may be removed (e.g., switch  159  is opened). The deformed upper layer  154  maintains its configuration due to the thermoplastic material having set into that structure.  
         [0055]    When it is desired to alter the deformed upper layer structure  154 , the thermoplastic layer  152  is reheated and a new structure form may be created.  
         [0056]    Turning to FIG. 7, depicted is a two-channel variable optical actuator  160 , including a first variable modulator  162 , and a second variable modulator  164  (shown simply in surface relief). Solid lines  166  and  168  show two (i.e., two channels) 0 th  order waveforms, and the dashed lines  170 ,  172  show two higher order diffracted waveforms. It is noted the solid lines  166 ,  168  are shown as being transmitted to fibers  174 ,  176  for further transmission in a system. Previously described embodiments may be used in such two-channel systems to improve system operation.  
         [0057]    It is to be appreciated that features of the foregoing embodiments maybe combined with features of other embodiments described herein, and although components may be numbered differently, they may include characteristics of similar components found in the various embodiments.  
         [0058]    The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.