Optical retro-reflective apparatus with modulation capability

An optical MEMS retro-reflective apparatus with modulation capability having a retro-reflecting structure including a pair of reflective surfaces; and a MEMS device for moving at least one of the reflective surfaces of said pair of reflective surfaces relative to another one of the reflective surfaces of said pair of reflective surfaces a distance which causes the pair of reflective surfaces to switch between a reflective mode of operation and a transmissive mode of operation. A substrate and a moveable grating structure may be substituted for the reflective surfaces.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Provisional Patent Application No. 60/420,177, filed Oct. 21, 2002, and entitled “Conformal Retro-Modulator or Optical Devices,” the disclosure of which is hereby incorporated herein by reference. The subject matter of the present application may also be related to the following U.S. Patent Application: “Conformal Retro-Modulator Optical Devices” Ser. No. 10/690,486, filed Oct. 20, 2003.

TECHNICAL FIELD

This invention relates to an optical retro-reflector device with modulation capability preferably in the kHz to MHz range (or even greater). This device is compact and rugged and can be used in a variety of communication, interconnect, and remote sensing applications. Clusters of several retro devices on a common platform can be used to address a large field of view. A similar cluster can also be used to provide for additional wavefront correction beyond tilt-error compensation (i.e., wavefront errors of odd order in phase), forming a so-called “pseudo-conjugator.” The retro-modulator can be functional in visible, IR, or mid-IR portions of the spectrum, depending on the materials and coatings employed. The disclosed devices preferably utilize MEMS-based technology to alter the retro-reflective nature of the disclosed devices.

BACKGROUND OF THE INVENTION

A retro-modulation device with modulation capability, as disclosed herein, includes a compact, monolithic optical MEMS structure, which uses mechanical motion, induced electrostatically or thermally, to displace various components of the structure for the modulation encoding. In general, retroreflectors have the property of taking an incident optical (or RF) beam received from a source and redirecting the beam back to the source via a sequence of reflections within the retro-device As such, retro-reflective devices, in essence, “track” the source location and thus provide auto-compensation for beam wander, relative platform motion and wobble. In addition, by encoding a modulation signal at (or within) the retro-reflective device, the return beam can be encoded with the information from the modulation signal. In this manner, information can be directed from a remote site back to the location of an interrogation or source beacon without the need for an optical (or RF) source or transmitter at the remote site. Retro-reflection and modulation devices have myriad applications to free-space links, optical interconnects, remote sensors, IFF/ID battlefield scenarios, guidance control for free-space or underwater platforms, etc.

The retro-reflecting structures can be in the form of a corner cube or cat's eye configuration as well as an array of such devices (the latter is referred to as a pseudo-conjugator). In either case, in accordance with the present invention, a modulation signal is used to displace the element(s) of the structure to, in essence, reversibly “defeat” the retro-directive capability of the device. The result is that the return beam returns back to the transceiver location as an amplitude-modulated beam or as an on-off digitally or binary modulated beam, bearing the desired encoded temporal information. Since the mechanical displacement is cyclical (billions of cycles have been demonstrated using optical MEMS devices in general), modulation information can be relayed using such a device with high reliability over a very long period of time. Modulation bandwidth in the range of kHz to many MHz are possible using this scheme.

Large arrays of retro-reflecting structures can be utilized as disclosed in U.S. provisional patent application Ser. No. 60/420,177 noted above.

Both types of retro-reflection devices (cat's eye and corner cube structures) are known, per se, in the prior art. Additionally, the four variations of optical switches subsequently discussed herein have also been discussed in the prior art. The present invention merges the two notions (retro-reflection devices with optical switching methods) to form a retro-modulator. This concept is not apparent to persons skilled in the art, since the primary applications of the four classes of switches have been presented by experts in the field in the context of high-definition display-mode devices (spatial light modulators, SLMs), high-density optical interconnection elements for telecommunications networks, wavelength divisional multiplexing (WDM) optical devices of high-density communication traffic networks and optical spectrometers. The notion of combining any of these switching approaches for use as modulated retro-devices is not known in the prior art. Therefore, the present invention is novel and, as discussed above and below, has myriad uses and applications in a variety of fields and scenarios. The disclosed retro-modulator should find itself very useful in many applications. For example, the disclosed retro-modulators can be used for combat ID/IFF, remote sensor optical links, interconnects, free-space links to communicate with missiles, high-speed smart projectiles, underwater devices, UAVs, and micro-UAVs, etc., and for communication links in general (telecommunication, wireless, interconnects, etc.). The disclosed retro-modulators can be used in connection with inter vehicle communication and accident avoidance tagging.

One object of this invention is to make it possible to realize a compact remote communication device, with modulation capability. The advantages of this invention include:1. The disclosed retro-modulation devices are preferably passive; therefore the optical interrogation source needs only to be located at the interrogation/beacon site, and not necessarily at the retro-device location.2. The disclosed retro-modulations device can be of rugged, lightweight, compact, low-power consuming, and low cost construction, yet it can operate at elevated temperatures.3. MEMS devices, if used, can function at high-g values owing to their small sizes and mass and their favorable mass to size ratio.4. The retro nature of the device provides for automatic tilt error correction as well as automatic beam wander compensation (e.g., wobbling, relative platform motion).5. The disclosed retro-modulation devices may be made very compactly using MEMS devices, for example, in combination with a variety of photonics components, such as detectors, optical elements, modulators, fibers and other integrated optical components, etc., with which the MEMS devices may be integrated and interfaced.6. The disclosed retro-modulation devices can be fabricated using a variety of well known materials, such as Si, poly-Si, GaAs, InP, etc., and can be manufactured in high volume using commercially available technology.

Prior art includes conventional retro-reflectors with upstream external modulators (e.g., liquid crystals, MQWs, E-O crystals). In addition, the prior art includes phase-conjugate mirrors with modulation capability (via applied electric fields or modulated pump beams). The prior art also describes optical MEMS with a modulation capability.

It has been known in the prior art that a MEMS device can be associated with a retro-reflecting corner cube. By tilting one of the mirrors of the corner cube with desired modulation information, the retro-return property of the device can be controlled in a time-wise fashion. That is, the retro-aspect of the device can be defeated temporally (i.e., the reflected light no longer returns along the reverse direction from which the corner cube was illuminated). This results in apparent modulation of the light received back at the source location, since the light either returns back to its source location or is diverted over another path, according to the tilt of one of the mirrors in the corner cube device. A drawback is that a relatively large angular displacement of the corner cube mirror is necessary to divert the backward-propagating light beyond the diffraction spread of the small MEMS device. Assuming a 50 μm scale size, a 2° tilt is required to divert the reflected light away from its diffraction-limited return path to the sender. This implies a 2 μm displacement of the mirror edge, which is relatively large, and places demands on the device geometry, the drive voltage, its slew rate, etc., of the MEMS device controlling the mirror.

The present invention improves upon this existing art by imposing the modulation via a diffractive effect (or a displacement of a very small cantilever) or via an optical Fabry-Perot effect. Each effect can be utilized in either a cat's eye or a corner cube arrangement. In the disclosed embodiments, the required mechanical displacement can be as small as 100 nm, or only 5% of what the prior art requires. This implies that the required drive voltage or electrical drive current for the present invention would be only 5% of that required for the prior art devices, thereby reducing the drive power by the square of this ratio, potentially increasing the bandwidth of the modulation from the KHz to MHz. The required mechanical displacement is a small fraction of the wavelength of the light modulated by the disclosed devices.

Also, the present invention can lead to a larger depth-of-modulation for a given drive voltage. This follows since the beam in the “off-state” is deflected over a much greater angle for a given MEMS displacement (using, e.g., the diffraction-based embodiments of this invention). The same argument also applies to the Fabry-Perot embodiments. In both cases, this reduced MEMS displacement also enables the required drive voltage to be even less for the same depth-of-modulation performance, relative to the mirror-tilt-based corner cube (the prior art). In yet a third embodiment of this invention, a small MEMS cantilever is employed at the focal plane of a lens to encode the modulation information. In this case, the MEMS device can be much smaller than the tilt device in the corner cube geometry (e.g., 10 μm versus about 50 to 100 μm), resulting in a lower voltage and torque required for the modulation encoding. The prior art also includes O-MEMS for displays (TI's DMD SLMs using MEMS cantilevers; Silicon Light Machine's diffractive-based structures), and tunable MEMS optical filters for WDM. These devices pertain to large-screen, high-definition TV multi-pixel display systems or to add/drop devices, but not to retro-communication or remote sensing devices. The prior art does not discuss or imply the possibility of using these structures as elements for retro-devices or as retro-modulation devices, nor does the prior art imply this application or even imply how they can be designed or used for the devices disclosed herein.

Examples of prior art devices are shown inFIGS. 1,2aand2b.FIG. 1shows a passive retro-reflector device24with an external modulator22. The construction of the retro-device can be in the form of an embossed mold with a reflective coating (in the mid-IR range), a corner cube, a three-mirror structure, lens/mirror combination, or an array of the same. A corner cube is depicted inFIG. 1for ease of illustration. The external modulator22can be in the form of an electro-optic amplitude or phase modulator (e.g., a liquid crystal) or a multi-quantum well electro-absorptive modulator.

A laser10forms a laser beam12which is directed to a communications retro-reflector20. Reflector20houses the aforementioned passive retro-reflector device24and its associated external modulator22. Beam12usually will have to transit a propagation path14, as will a beam12rreflected by retro-reflector20. The reflected beam12ris modulated with data by means of modulator22. The modulated data is detected by a detector18and a beam splitter18may be conveniently used to separate the reflected beam12rfrom the incident beam12.

FIGS. 2aand2bshow additional prior art devices. InFIG. 2a, the retro-reflector device24is a monolithically fabricated optical MEMS structure using reflective elements to form the required device. In this case, the mirrors of a corner cube can be deflected (by tilting them on an axis27) to defeat the retro-directive property of the corner cube24(effectively resulting in a modulated return beam). InFIG. 2a, a MEMS device26is used to move at least one of the mirrors (or other reflector element)24aof a corner cube reflector24. The MEMS device is responsive to a signal on line20sfor controlling the actuation of the MEMS device26. By putting data on line20s, the reflected signal is, in effect, modulated since a detector18would only “see” the reflected beam12rwhen mirror24ais in its “normal” position. InFIG. 2adashed lines are used to illustrate movement of mirror24afrom is “normal” (solid line) portion to its actuated (dashed line) position. When mirror24ais in its actuated position, the beam is deflected in a direction12dwhich does not permit detection by detector18. As discussed above, the relatively large size of this MEMS-activated mirror24a, coupled with the constraint of having to deflect the beam over an angle d in excess of the diffraction-limited spread of the retro-directed beam, limits the modulation bandwidth for a given drive voltage and slew rate. This constraint is greatly relaxed using the embodiments of the present invention.

Another example of the prior art is shown inFIG. 2b, where a phase-conjugate mirror25is shown with an applied modulation capability (the modulation can be externally applied as in the case ofFIG. 1). The conjugator wavefront reverses the incident beam12and produces a reflected beam12r, while, at the same time, the modulator encodes temporal information onto this beam.

DETAILED DESCRIPTION

Various embodiments of the present invention are shown inFIGS. 3,4,5,6,7,8,9,10,10a,10b,10b-1and10c. In these figures, retro-modulators using cat's eye as well as corner cube structures as the basic retroreflective configurations are shown. The (binary) modulation can be encoded using four different methods, which can be integrated into these two (cat's eye and corner cube) basic retroreflective structures: (1) deflection of the optical beam using compact MEMS cantilevers; (2) diffraction of the beam using switchable grating structures; (3) reflection of the beam using binary switchable Fabry-Perot elements; (4) switching of an optical beam using a moveable bubble in a TIR (total internal reflection) binary set of states.

FIGS. 3,4,5and8show examples of embodiments using cat's eye devices.FIG. 3shows an embodiment using a cat's eye retro-device with a small MEMS cantilever device26placed at the backplane34of a lens or diffractive element32. The cantilever device26can be driven (electrostatically, optically or thermally) to deflect the beam into one of two different angular states by moving the back plane34to location34d, so that the return beam can be effectively modulated. Typically, the MEMS device26is driven by an electrical or an optical signal on line20s. Without a signal, a “normal” retro-direction is realized (as indicated by the presence of reflected beam12r) and in the presence of the drive voltage (in the case of a non-optical MEMS device embodiment), the retro-direction12ris defeated and the non-retro direction12dis instead realized. Of course, the sense of the two states can be inverted, if desired. Such cantilevers26can be relatively small (10 μm scale size) so that operation at high modulation rates (kHz and above) can be realized and low modulation powers need be applied. Large arrays of these basic cantilevers (all in a plane, and without a retro-device) have been employed for spatial light modulators for display mode applications.

FIG. 4shows an alternate embodiment using a cat's eye retroreflector, but, now with a binary, switchable grating structure44shown in greater detail inFIGS. 4aand4b. With the signal or voltage off (on line20s), the grating44bis in the plane of the substrate44a, so that a specular reflection is realized in direction12r(inFIGS. 4aand4blens32is omitted for ease of illustration); but with an applied signal or voltage on line20s, the grating44bnow is above (in a direction towards the source of the incident beam12as shown byFIG. 4b) the surface and diffracts the incident beam12over an angle beyond the retro-direction to the non-retro direction12d. Note that the required displacement of the grating44bfrom the substrate44aneed only be in the range of λ/4 (where λ is a wavelength of the incident beam12), so that small drive signals and drive powers are required for the MEMS device26to effect the needed movement and thereby allow modulation to be applied to beam12(on beam12r) by device20. Large arrays of these basic gratings (all in a plane, and without a retro-device) have been employed for spatial light modulators for display mode applications.

FIG. 5shows a cat's eye device with a switchable MEMS-based optical filter54to provide the modulation. A two-mirror Fabry-Perot filter54is configured using a pair of compact reflecting elements54a,54bso that in one state, it reflects the desired beam12r, whereas in the other state, the beam is transmitted through the optical cavity as beam12d. One or both of the compact reflecting elements54a,54bis positioned by at least one MEMS device26. The two-mirror Fabry-Perot filter54, which is known per se in the prior art, is shown in greater detail byFIGS. 5aand5b. By displacing the pair of MEMS reflecting elements from a spacing L1(seeFIG. 5a) to a spacing L2(seeFIG. 5b) between reflecting elements54a,54b, the beam can be switched. Displacements as small as 100 nm (0.1 micron) have been demonstrated for WDM applications, resulting in a very small drive voltage relative to typical (microns) MEMS-based displacement devices. The system20is configured so that the reflected beam12rcompletes the retro-mode, whereas the transmitted beam12ddoes not. This device20may not have a limited field of view, dictated by the angular dependence of the Fabry-Perot cavity spectral response.

FIG. 8depicts a TIR device74arranged as a cat's eye retro reflector. The TIR device74includes a moveable bubble74fplaced between a pair of glass or Si substrates74a&74b, forming a three-element structure, as is shown byFIG. 8. This bubble74f, when positioned (thermally, electrostatically, etc.) along the path of the optical beam12, enables transmission of the beam through the three-element structure74a,74f,74bsince it preferably has an index of refraction the same as that of the substrates74a,74b. When the bubble is positioned out of the path of beam12, the incident beam12experiences total internal reflection (TIR), and is scattered onto many different directions. Substrate74bhas a conductive and reflective surface74con its rear surface for reflecting beam12after it passes through bubble74f.

The bubble can be controlled (moved) by imparting electrical signals between transparent electrodes74don the surface of substrate74aand the conductive surface74c. An electric field between one of the electrodes74dand surface74cwill attract bubble74f.

The internally facing surfaces74eof substrates74aand74bare preferably etched to cause the total internal reflection (TIR) to occur when the bubble74fis not in way of the beam12. However, when bubble74fhas been urged to fall within the path of beam12, it effectively wets those portions of the etched surfaces74ein way of the beam12allowing the beam to pass easily through the bubble74fand reflect off surface74c.

This binary switching device74can be incorporated into either the cat's eye device, as shown inFIG. 8, or, as will be seen, into the corner cube retro-reflector as shown byFIG. 9.

FIGS. 6,7,9and10show embodiments using corner cubes as the basic retro-reflecting device.FIG. 6depicts an embodiment employing a corner cube retro-reflector24awhich has one mirror28of a normal corner cube reflector replaced with a switchable grating structure44(seeFIGS. 4aand4b). The device24ais configured so that with the grating44in an off state, a specular return is realized on path12rvia mirror28, thereby providing the corner cube's retro capability. With an applied signal voltage on line20s, the grating now diffracts the incident beam12preferably beyond the diffraction-limited retro-angle in a direction12d. The grating structure44is used as a diffractive element (i.e., effectively a reflector), which can be raised or lowered (in-plane or out-of-plane) to deflect or not deflect the incident beam in the retro-direction12r, resulting in an effective binary modulation of the retro-reflected beam12r. Note that a very small displacement (λ/4) is required, as compared with a conventional mirror element for a MEMS controlled corner cube, whose required deflection may be a factor of 5 or more times greater than that necessary by the embodiments using MEMS devices disclosed herein.

FIG. 7shows a corner cube embodiment using a switchable Fabry-Perot filter54as the binary-encoded modulation element (seeFIGS. 5aand5b). The Fabry-Perot filter54has MEMS26controlled mirrors54a,54b. Here, the reflected state of the filter54is used to realize a retro-return beam12rvia mirror28, whereas the transmitted state provides for the off state by passing the incident beam12as beam12d.

A detector60(seeFIGS. 5 and 7) can be provided to easily detect the presence of incident beam12, which is useful in a communications application of the present invention such as that shown by U.S. provisional patent application Ser. No. 60/420,177 mentioned above. In such an embodiment, the Fabry-Perot devices ofFIG. 5or7could be substituted for the Fabry-Perot Multiple Quantum Well devices of U.S. provisional patent application Ser. No. 60/420,177 mentioned above, for example.

The detector60can also detect information encoded on the incident beam12. The encoded information, in addition to data, can include a high frequency jitter on the data. When detector60is in a detection mode, then the Fabry-Perot device54is passing incident signal12as opposed to absorbing incident signal12. The jitter can be used to test how well the Fabry-Perot device is passing the incident signal since the high frequency jitter can be detected and decoded to determine whether the Fabry-Perot device54is optimally tuned or whether it is slightly off frequency. For example, the plates54aand54bcould be 1) properly spaced, 2) too close or 3) too far apart. The analog signal output by detector60can be analyzed by a control system62to determine whether the plates are properly spaced. If not, then a DC control voltage output by the control system62can be applied via an operational amplifier64to the MEMS device26to adjust (increase or decrease) the spacing of plates54a,54bappropriately. The data signal on line20sbecomes active whenever the device is used to transmit data on the return beam12r. The received data is passed via a low pass filter68to a computer72for decoding the incident data and for generating the transmitted data on20s.

The light12dpassing through to the detector70can be utilized to adjust (fine tune) the Fabry-Perot device54to compensate for:(1) wavelength changes in beam12;(2) thermal effects (expansion, etc of the system);(3) light arriving off the axis of beam12(see the off-axis beam12oa). The Fabry-Perot device54has a wide field of view, so it can “see” beam12oa, but its plates54a,54bmight then be improperly spaced for beam12oasince the light of beam12oawill travel farther within device54than would the light of beam12.

The control system62can be used to help compensate for such issues by detecting the high frequency jitter. If control system is not used, then the Fabry-Perot device may be slightly mistuned, thereby decreasing its sensitivity somewhat.

In the case of the embodiments ofFIGS. 3-9, the reflected beam12ris generally co-incident with the incident beam12and would normally be separated therefrom, for detection purposes, at a location remote from apparatus20using a beam splitter16(previously discussed with reference toFIG. 1) and the split-off beam would then be detected using a detector18(also previously discussed with reference toFIG. 1).

The aforementioned corner cube embodiments ofFIGS. 6,7and9have all been depicted with preferably two planar surfaces, namely a mirrored surface28and a surface44,54or74whose reflection abilities can be altered in response to an electrical signal20s. Surface44,54or74will hereinafter be referred to generically as an electrically controllable reflective surface. Additionally, corner cube devices can have two or three nominally reflective surfaces and, moreover, one, two or all such surfaces can be implemented as an electrically controllable reflective surface whose reflection abilities can be altered in response to an electrical signal20s.

FIG. 10depicts a corner cube with three mirrored surfaces each disposed orthogonally with respect to each of the other two mirrored surfaces. In this embodiment, two surfaces28are preferably simple mirrors while one surface is an electrically controllable reflective surface84. The electrically controllable reflective surface84is depicted with parallel lines to reflect the fact that this surface may well have gratings associated therewith, as shown inFIGS. 4a,4b, and8.

FIG. 10ais similar toFIG. 10, but in this embodiment all three mirrored surfaces are implemented as electrically controllable reflective surfaces84. In this embodiment the electrically controllable reflective surfaces are labeled84a,84band84c. Of course, surfaces84a,84band84care each disposed orthogonally with respect to each of the other two surfaces. The spacings of the parallel lines differ for each of the surfaces84a,84band84cto reflect the fact that the spacings or intervals of their gratings44, if used, need not be the same for each surface84a,84band84c. Indeed, it is preferable that such spacings or intervals be different as that should help break up a deflected beam12dand help make it even less detectable.

FIG. 10bis again similar toFIG. 10, but in this case one of the mirrored surfaces is implemented by an electrically controllable reflective surface84which is pixelated, as is represented by the grid pattern shown on surface84ofFIG. 10b. A pixelated electrically controllable reflective surface84can be implemented as a grid or array of pixelated electrically controllable reflective elements94. Each element94can be implemented as a MEMS controlled device of the type, for example, previously discussed with reference toFIGS. 2a,4or5or by a MEMS element whose moveable arm is coupled to a small mirrored surface96(seeFIG. 10c-1). If the individual elements94are implemented as moveable gratings as shown inFIGS. 4,4aand4b, then the gratings44of neighboring elements94in pixelated surface84are preferably disposed at angles relative to each other as shown in the more detailed view ofFIG. 10b-1and are preferably implemented with different grating periods.

If the individual elements94are implemented with small mirrors that can be tilted as shown inFIG. 2a, the tilt axes27for neighboring elements94are preferably disposed at angles and adjacent different edges of the neighboring elements94, again as represented inFIGS. 10b-1.

Alternatively, a pixelated electrically controllable reflective surface84can be implemented by a spatial light modulator (SLM), which functions as a spatial phase modulator in a monolithic package.

FIG. 10cis similar toFIG. 10b, but in this embodiment the remaining two mirror surfaces of the embodiment ofFIG. 10bare here depicted as electrically controllable reflective surfaces84which have associated gratings or may also be pixelated (as represented by the dashed lines on one of the three surfaces84). The incident beam12, the return beam12rand the deflected beam(s)12dare also depicted in this Figure.

The spacings (periods) of the gratings preferably fall in the range of about 1-100 μm. Due to the Bragg condition, the smaller the grating period, the larger the angle by which a reflected beam is reflected away from its usual (for a planar surface) angle of reflection. However, the corner reflector will also have some dispersion associated with its reflected beams, including beams12rand12d, due to aperture effects. The deflected beam(s)12dshould preferably be deflected by a greater angle from beam12rthan that which would be attributable to normal aperture effects so that an interrogating beam12sees little or no reflection(s) during a portion of the time the beam is being modulated (for example when the amplitude of the modulating signal is at its maximum (or minimum)) to increase the contrast ratio between beams12rand12das the incoming light is modulated by the corner cube device.

FIG. 10c-1depicts mirrors96which are moved in a piston-like fashion relative to neighboring mirrors96(keeping the associated mirrors in parallel planes as opposed to tilted as done when the embodiment ofFIG. 2ais used with the embodiment of10b). The individual mirrors96are moved by MEMS devices26and when the MEMS devices26are unactuated, the mirrors preferably align in a planar configuration98. The size of the piston-like mirrors96are also preferably in the range of 1-100 μm on a side for the same reasons as given above. If tilting mirrors are used, then they can each fill or occupy one of the elements84in the array.

InFIG. 10c-1only four mirrors96are shown for ease of illustration, it being understood that the mirrors96would preferably be arranged in a large two dimensional array of mirrors96.

Generally speaking, the larger the number of elements84in an array, the better the array is in causing a greater number of deflected beams12dto be generated during modulation, but with a downside of increasing the cost of the corner cube device due to the fact that the number of MEMS devices will similarly increase (assuming that there is one MEMS device, for example, associated with each pixel84). In a military application, for example, it may well be that one does not want some undesirable third party trying to read the deflected beam12d. By throwing the deflected beams12din thousands (for example) of different directions, the amount of light headed in any particular direction that is off the normal retro-reflection axis of the return beam12ris reduced considerably, thereby making it more difficult for an undesirable third party to try to eavesdrop on the deflected beam(s)12d.

The MEMS devices discussed above are described as being electrically controlled, which is the conventional manner for controlling MEMS devices. However, optically controlled MEMS devices are known in the art and the MEMS devices used in the disclosed embodiment could be either electrically or optically controlled. When array(s) of pixelated electrically controllable reflective elements are utilized, then the individual reflective elements in the array can be controlled either by a common control signal or by individual control signals.

Having described this invention in connection with a number of embodiments, modification will now certainly suggest itself to those skilled in the art. As such, the invention is not to be limited to the disclosed embodiments except as required by the appended claims.