Complex spatial light modulator

One embodiment relates to a spatial light modulator (SLM) for modulating light incident thereon. The SLM includes a plurality of pixels, each pixel including a plurality of phase shift elements. The SLM also includes a transform filter adapted to control the imaging system to resolve each pixel but not each phase shift element in each pixel. The plurality of pixels are controlled to independently modulate phase and magnitude of light reflected therefrom. Other embodiments are also disclosed.

TECHNICAL FIELD

The present disclosure relates generally to spatial light modulators, and more particularly to spatial light modulators and to methods of operating the same.

BACKGROUND OF THE INVENTION

Spatial light modulators are arrays of one or more devices that can control or modulate an incident beam of light in a spatial pattern that corresponds to an electrical input to the devices. The incident light beam can be modulated in intensity, phase, polarization or direction. The majority of spatial light modulators are intensity modulators (often intensity modulation causes some phase modulation, but the phase modulation cannot be done independently to the intensity modulation). Some modulation can be accomplished through the use of Micro-ElectroMechanical System devices (or MEMS) that use electrical signals to move micromechanical structures to modulate light incident thereon.

SUMMARY OF THE INVENTION

One embodiment relates to a spatial light modulator (SLM) for modulating light incident thereon. The SLM includes a plurality of pixels, each pixel including a plurality of phase shift elements. The SLM also includes a transform filter adapted to control the imaging system to resolve light reflected from each pixel but not light reflected from each phase shift element in each pixel. The plurality of pixels are controlled to independently modulate phase and magnitude of light reflected therefrom.

Another embodiment relates to a method of modulating light incident on a spatial light modulator (SLM) having a substrate with an upper surface and a plurality of pixels, each pixel including a plurality of phase shift elements disposed above the upper surface of the substrate. Light is caused to impinge upon the plurality of phase shift elements, and the plurality of phase shift elements are moved relative to the upper surface of the substrate. Reflected light is filtered using a transform filter adapted to resolve each pixel but not individual phase shift elements in each pixel. The phase shift elements are controlled in such a way as to modulate phase independently from amplitude.

Another embodiment relates to

Other embodiments are also disclosed.

DETAILED DESCRIPTION

Spatial light modulators are increasingly being developed for use in various applications, including display systems, holographic display systems, optical information processing and data storage, printing, and maskless lithography. However, for these and many other applications requiring high or very high resolution, such as leading edge semiconductor processing, spatial light modulators having both magnitude and phase modulation would be preferred. In the semiconductor industry, phase-shift mask (PSM), and its extension such as alternating PSM and attenuated PSM, has been known as a powerful resolution enhancement technique. Here the conventional (magnitude) mask is superimposed with phase-shift elements, usually a transparent material with thickness that provides a π (180 degree) phase retardation at designated locations. Unintended constructive interference between adjoining light and dark pixels, or lighter and darker pixels, can cause blurring of boundaries between pixels and a loss of detail in the resultant image. While this may be acceptable or unnoticeable for certain applications, such as displays, it is not acceptable for other applications, such as photolithography for manufacturing semiconductor devices, in which images having features of microns or less must be produced with great precision. Accordingly, there is a need for a spatial light modulator capable of independently modulating both magnitude and phase of light incident thereon.

There is a further need for a spatial light modulator that modulates the light intensity in an analog gray scale and independently also the phase in an analog gray scale manner. These features may be used for further resolution enhancement and other purposes, but they are only applied in a very limited manner in conventional lithography; for example only two values of phase shifts (0 and π) are practically implemented.

In addition, it is desirable for the spatial light modulator to have the following characteristics: a large étendue, a high number of pixel count, high modulation speed, high power handling capability in a wide spectral range of the light, and high dynamic range.

The present disclosure is directed to a novel spatial light modulator (SLM) which may be referred to as a Complex Spatial Light Modulator (Complex SLM or CSLM) and a method of continuously and independently modulating both the phase and magnitude of light incident thereon.

A Complex SLM comprises a SLM that is configured to simultaneously modulating both the magnitude and phase of light incident thereon, i.e. to modulate the complex amplitude of the light field. Applications for which a Complex SLM according to the present invention is particularly useful include high speed, high resolution applications such as: maskless lithography for fabricating semiconductor devices and Integrated Circuits (ICs), holographic display modulators, and similar applications.

A Complex SLM and operation thereof will now be described with reference to the figures of the present application. For purposes of clarity, many of the details of SLMs in general and diffractive SLMs in particular that are widely known and are not particularly relevant to the present invention have been omitted from the following description.

In general, a Complex SLM according to an embodiment of the present invention comprises an array of a number of pixels, each pixel with multiple phase shift elements. The Complex SLM may also be preferably equipped with imaging optics including a Fourier filter adapted to resolve each pixel, but not the individual phase shift elements and other sub-pixel features. In accordance with an embodiment of the invention, the Complex SLM may be configured and controlled so as to be functionally equivalent to a spatial light modulator that simultaneously modulates the magnitude and phase of light, i.e. that modulates the complex amplitude of the light field.

In one embodiment, shown inFIG. 1, each of the phase shift elements include an electrostatically movable mirror104supported above and oriented to reflect light away from a negligible area or substantially non-reflective background106. In one example, the movable mirror104comprises a piston mirror, and the background106may comprise a substantially non-reflective surface of a substrate110. An arbitrary shape of the mirror104is shown inFIG. 1, as the mirror104may be implemented in various shapes (square, circular, etc.). Preferably, each pixel108consists of an m×n unit cell, where m≧2 and/or n≧2. In the example illustrated inFIG. 1, the pixel108comprises a 2×2 unit cell.

Applicants have determined that a Complex SLM having an array of piston mirrors, such as shown inFIG. 1, can simultaneously and continuously modulate both the magnitude and phase of the light field. The principals of operation and performance of Complex SLMs according to certain preferred embodiments of the present invention will now be described in detail.

Concept

Starting with a simple case in which there are 2×2 cells per pixel, and three output states: 0, 1, and −1. Note that −1=1eiπ. As shown inFIG. 2, in accordance with an embodiment of the invention, the 0th-order normalized electric field contribution from the piston mirrors in a pixel is 0.5<γ≦1, while by controlling the areas and/or electric field reflectivity that from the background is 1−γ.

FIG. 2are phasor diagrams of the 0th-order light field contributed by the background and each of the four phase shifting elements or mirrors according to an embodiment of the present. Of course, other implementations may have a different number of phase shifting elements per pixel. As shown, the 0th-order light field202from the background has a magnitude of 1−γ. The four phase shifting elements each contribute a 0th-order light field having a magnitude of γ/4 (206,208,210and212). As shown inFIG. 2, when the light field contributions from each of the four elements have a same phase, then the combined light field contribution204from the four elements together has a magnitude of γ.

FIG. 3shows three example 0th-order output states which can be created by appropriate deflection of the mirrors in a pixel according to an embodiment of the invention. The three phasor diagrams inFIG. 3each show the light field contributed by the background, the phase shifting elements or mirrors, and the resultant light field for one output state. The three output states include two reflecting (1, −1) states and one non-reflecting (0) state. The background contribution202is the same in each of the three states, and is shown inFIG. 3as having a phase shift of +π/2.

The phasor diagram on the left corresponds to the “1” reflecting state. In this state, the contributions from the four phase shifting elements (302,304,306, and308) are such that the resultant light field310(after combining with the background contribution202) has a zero phase shift. Note that, in this case, each of the reflective elements is positioned (by way of a piston or other means) so as to provide a contribution with a same phase (so that the four contributions line up as shown).

The phasor diagram in the middle corresponds to the “−1” reflecting state. In this state, the contributions from the four phase shifting elements (312,314,316, and318) are such that the resultant light field320(after combining with the background contribution202) has a phase shift of π. Again, in this case, each of the reflective elements is positioned (by way of a piston or other means) so as to provide a contribution with a same phase (so that the four contributions line up as shown).

The phasor diagram on the right corresponds to the “0” non-reflecting state. In this state, the contributions from the four phase shifting elements (322,324,326, and328) combine to a complex vector329of equal magnitude and opposite phase as the background contribution202. Hence, the resultant light field330has a zero magnitude.

Generalization

A Complex SLM having m×n individual phase shift elements (for example, electrostatically displaceable mirrors, such as piston mirrors) per pixel, m≧2 and/or n≧2 will now be considered. However, for simplicity of the illustration, without loss of generality, the special case of m=n=2 will be discussed.

In some embodiments, circuitry is configured to independently control the deflection of each individual phase shift element. In other embodiments, circuitry may be configured to drive two or more of the individual phase shift elements together with a same voltage drive signal (in effect, electrically “ganging” or grouping the elements together). For example, to drive the displacements corresponding to the phasor diagram on the right side ofFIG. 3, the mirrors associated with the phasors322and324may be electrically “ganged” together, and the mirrors associated with the phasors326and328may be electrically “ganged” together.

Referring toFIG. 4, one specific solution for a single pixel with each of the mirrors positioned or operated in a specified way so as to produce a gray level magnitude with 0 or π phase shift is shown inFIG. 4. Other specific solutions are possible by using a Complex SLM in accordance with an embodiment of the invention.

In the state shown on the left side ofFIG. 4, the contributions from the four phase shifting elements (402,404,406, and408) add together to create a combined complex vector409. Each of the reflective elements is positioned (by way of a piston or other means) so as to provide a contribution with a different phase. The combined vector409is such that the resultant light field410(after adding together with the background contribution202) has a zero phase shift. Note, however, that the magnitude of the resultant light field410in this phasor diagram is smaller than in the phasor diagram on the left side ofFIG. 3. In this way, a gray level with zero phase shift is achieved.

In the state shown on the right side ofFIG. 4, the contributions from the four phase shifting elements (412,414,416, and418) add together to create a combined vector419. Each of the reflective elements is positioned (by way of a piston or other means) so as to provide a contribution with a different phase. The combined vector419is such that the resultant light field420(after adding together with the background contribution202) has a phase shift of π. Note, however, that the magnitude of the resultant light field420is smaller than in the phasor diagram in the middle ofFIG. 3. In this way, a gray level with phase shift of π is achieved.

Referring toFIG. 5, another gray level state is illustrated. In the state shown inFIG. 5, the contributions from the four phase shifting elements (502,504,506, and508) add together to create a combined vector509. Each of the reflective elements is positioned (by way of a piston or other means) so as to provide a contribution with a different phase. The combined vector509is such that the resultant light field510(after adding together with the background contribution202) has a magnitude and a phase shift with gray levels, but of limited range.

Note that the realizations of the states shown inFIGS. 4 and 5are not unique—many piston mirror configurations corresponds to the same output state. This degree of freedom may be advantageously exploited in accordance with an embodiment of the invention.

A general complex amplitude modulator, that is a Complex SLM operated to produce a gray level but with arbitrary phase, will now be considered with reference toFIGS. 6 and 7.

Referring to the phasor diagrams ofFIG. 6, if all the stationary parts are made totally non-reflecting or if the piston-mirrors are adapted to have a 100% fill-factor (described below), then the array becomes a truly complex amplitude modulator. In other words, the background contribution has zero magnitude. In this case, all magnitudes from “0” to a “maximum” and all phases (modulo 2π) are then reachable.

The state shown on the left side ofFIG. 6corresponds to a “0” non-reflecting state. In this state, the contributions from the four phase shifting elements (602,604,606, and608) cancel each other out so that the resultant light field610has a zero magnitude.

The state shown in the middle ofFIG. 6corresponds to a reflecting state with an intermediate magnitude (between zero and the maximum) and an intermediate phase (between zero and 2π). In this state, the four phase shifting elements are positioned such that their contributions (612,614,616, and618) add together to provide the resultant light field620. The resultant light field620has a specific (controllable) intermediate magnitude and a specific (controllable) phase.

The state shown on the right side ofFIG. 6corresponds to a reflecting state with a maximum magnitude. In this state, the four phase shifting elements are positioned so as to reflect light with a same (controllable) phase such that their contributions (622,624,626, and628) add together maximally. The resultant light field630has a maximum magnitude. By controlling the position of the elements, the phase of the resultant light field630may be controlled.

An arbitrarily normalized complex amplitude can be expressed as A=|A| exp(iφ), where 0≦|A|≦1 and 0≦φ≦2π. The phasor configuration for this complex amplitude is not unique, but can be advantageously standardized.FIG. 7shows one possible standard phasor configuration for the case where there is an even number of piston mirrors per pixel. In this example, half of the piston mirrors may be deflected equally by αλ/4π (where λ is the wavelength of the light) to produce a phase-shift α, and the other half by βλ/4π to give a phase-shift β. The magnitudes of both halves may be considered to be ½. As shown inFIG. 7, the complex amplitudes of the two halves (702and704) combine together to produce a resultant light field706as follows.
A∠φ=1/2∠α+1/2∠β
Hence, the two piston mirror phase deflections that produce magnitude 0≦|A|≦1 and phase-shift 0≦φ≦2π can be calculated to be
α=φ+cos−|A|
β=φ−cos−1|A|

As can be seen from the above equations, two address lines per pixel are sufficient to produce an arbitrary magnitude and phase (i.e. two degrees of freedom per pixel).

Efficiency

The optical efficiency of a Complex SLM made and operated in accordance with an embodiment of the present invention will now be discussed with reference toFIG. 8.FIG. 8is a phasor diagram of the light field contributed by the background, the mirrors, and the resultant light field for a pixel in a 0thorder output state for a Complex SLM. In this “1” state, like the state shown in the left side ofFIG. 3, the contributions from the four phase shifting elements (302,304,306, and308) are such that, after combining with the background contribution202, the resultant light field310has a zero phase shift.

The efficiency of a Complex SLM in the “1” state, shown for example inFIG. 8, is 2γ−1≦1. Note that 0.5<γ≦1. Therefore, it is desirable to have γ as large as possible so as to advantageously increase the efficiency.

A phasor diagram for an embodiment with no contribution from the background is shown inFIG. 9. In this state, the four phase shifting elements are positioned such that their contributions (902,904,906, and908) add together maximally with zero phase shift. The resultant light field910has a magnitude of γ.

Referring toFIG. 9, because the stationary part (i.e. the background) is totally non-reflecting, the efficiency of the “1” state becomes γ2, which is higher than or equal to the above 2γ−1 (again, note that 0.5<γ≦1).

A device with 100% fill piston mirror and 100% reflectivity will be the most efficient.

Contrast

Because n≧2 (and m≧2) in accordance with an embodiment of the invention, the pixel spatial frequency is lower than the unit cell spatial frequency and may be advantageously discriminated by Fourier filtering to produce a high contrast image, as demonstrated in simulations shown and described in more detail below. To achieve high contrast, it is preferred to have the phase shift elements diffract the light with the highest possible grating frequency (that is, the most alternating arrangement possible). In a preferred embodiment, the Fourier filter is adapted to resolve each pixel but not the individual phase shift element in each pixel. The Fourier filter may include, for example, an aperture. More preferably, the Fourier filter includes an apodized aperture to substantially reduce, if not eliminate, the occurrence of ripples in the resultant image.

Exemplary Embodiments

Certain exemplary embodiments of a Complex SLM according to the present invention will now be described in greater detail with reference toFIGS. 10A and 10B.FIG. 10Adepicts a planar view top of a complex SLM having a 100% (or nearly 100%) fill-factor mirror array and also depicts a detailed perspective view of a single phase shift element or cell thereof.

Referring toFIG. 10A, the Complex SLM generally includes a film or membrane disposed above an upper surface of a substrate (the substrate is not shown in these figures) with a number of displaceable or movable portions or actuators1008formed therein. Supported above and affixed to each actuator by a mirror support structure1006is a mirror1004having a light reflective surface that is positioned generally parallel to the upper surface of the substrate and oriented to reflect light incident on a top surface of the Complex SLM. Each of the actuators1008and its associated mirror1004may form an individual phase shift element.

Individual actuators1008or groups of actuators are moved up or down over a very small distance (typically only a fraction of the wavelength of light) relative to the substrate by electrostatic forces controlled by drive electrodes in the substrate underlying the actuator membrane. Preferably, the actuators1008can be displaced by n×λ/2 wavelength, where λ is a particular wavelength of light incident on the complex SLM, and n is an integer equal to or greater than 0. Moving the actuators1008brings reflected light from the planar light reflective surface1004of one phase shift element into constructive or destructive interference with light reflected by adjoining phase shift elements in a pixel1002, thereby modulating light incident on the Complex SLM.

The complex SLM can include any number of phase shift elements arranged and operated to form pixels1002of any configuration or size. As noted above, a pixel1002is made up of one or several actuators.

In general, each actuator in a pixel1002is connected to an electrode and is independently displaceable. In practice, the actuators may be grouped into several groups, and each group may be operating under the same (ganged) electrode.

Generally, the complex SLM can include two or more pixels each having two or more phase shift elements per pixel. Thus, both a maximum size of the complex SLM and the pixels therein are constrained only by the size of a substrate on which it is fabricated. In certain preferred embodiments, shown inFIGS. 1 and 10, each individual pixel includes a square 2×2 array of phase shift elements. However it will be apparent to those skilled in the art that the complex SLM can include any number of pixels having any number of phase shift elements arranged in any configuration including square, triangular, hexagonal and circular.

The underlying structures of the complex SLM, such as the actuator membrane, will now be described in greater detail with reference to the perspective view of the single phase shift element in the bottom portion ofFIG. 10Aand with reference to the top view of a single actuator1008as shown inFIG. 10B. It is to be understood that the embodiment shown inFIGS. 10A and 10B, and the specific dimensions given therein, are exemplary only, and the complex SLM of the present invention is not limited to this particular embodiment and dimension shown. In this embodiment, the actuator membrane (see membrane1010) is anchored or posted (see flexure1012and anchor posts1014) to the underlying substrate at the corner of each actuator1008. The tent membrane is sparsely or lightly posted to the substrate at the extremities of the illustrated array.

Referring toFIG. 10B, the actuator membrane, and the actuators1008formed therein, include a taut silicon-nitride (SiN) layer, and an electrically conductive film or layer (i.e., titanium-nitride TiN). The conductive layer is electrically coupled to electrical ground in the substrate through one or more of the posts1014, such that a voltage applied to the drive electrode (not shown in this figure) through an integrated drive cell or channel in the substrate deflects actuators toward or away from the substrate. Generally, a single conductor from the drive channel branches into mini-electrodes or drive-electrodes underneath each individual actuator in a single pixel.

In order to provide stable operating condition, the distance, h, between the actuator and substrate is larger than 3× the maximum displacement, i.e., h>3λ/2, for example preferably h is 2λ.

Preferably, the design of the actuator membrane is carefully engineered such that the mirrors remain parallel to one another and to the surface of the substrate as they are displaced. The following design features facilitate this:

(1) The actuator disks are suspended by narrow flexures1012, which sustain most of the deformation as they assume a parabolic shape under electrostatic deflection.

(2) The actuator disks1010are connected to the flexure1012only at their centers, and as far away from the anchor posts1014as possible. As the actuators deflect, the centers of the flexures, and therefore the mirrors supported thereon, remain parallel to the substrate.

(3) The actuator disk1010is minimally connected to the flexure1012only at the attachment points. Thus, little deformation is mechanically transmitted from the flexure1012to the actuator disk1010or the mirror supported thereon.

(4) Optionally, if additional stiffness is required, other high modulus films, such as oxides, could be patterned onto the actuator disk1010and not on the flexures1012.

Generally, the mirrors comprise a TiN layer with a surface coated with reflective material, such as aluminum. More preferably, the design of the mirror is also carefully engineered such that the mirrors remain substantially flat and co-planar with the substrate, especially as they are deflected. Design features that facilitate this include proper selection of film thickness and use stress engineering techniques and/or layer(s) of stiffener oxides, in addition to an Aluminized TiN layer. Optionally, the mirror can further be stiffened by use of topography or features, such as corrugations or dimples. Preferably, the corrugations or dimples are formed in the mirror away from the reflective surface.

In the embodiment shown inFIG. 10Athe Complex SLM includes a 100% or nearly 100% fill-factor mirror array in which the peripheral edges of each mirror abuts peripheral edges of adjoining mirrors such that substantially none of the light incident on the complex SLM passes between the mirrors to impinge on the underlying actuators, flexures or posts. It will be appreciated that this embodiment provides the highest optical efficiency.

Specifications for an exemplary High Fill Factor complex SLM according to this embodiment are as follows:

FIG. 16depicts a Fourier transform (FT) filter configuration in accordance with an embodiment of the invention. The FT filter configuration may be used to control the imaging system to resolve light reflected from each pixel but not light reflected from each phase shift element in each pixel in a spatial light modulator (SLM)1602. The configuration may include the SLM1602in an object plane1604, a Fourier transform (FT) lens1606, a Fourier transform (FT) filter1608in a Fourier transform (FT) plane, an inverse Fourier transform (IFT) lens1610, and an image plane1612.

The FT lens1606maps light from the SLM1602to its transform, and the IFT lens1610maps the light from the transform to an image (which is a filtered image of the light from the SLM1602, but upside-down) in the image plane1612. The spatial frequency spectrum of the light from the SLM1602is formed at the FT plane1609.

FT or spatial filtering may be done by placing an amplitude and/or phase filter1608at the FT plane1609. In one embodiment, the FT filter1608may comprise an aperture with suitable apodization that transmits the 0th-order of light and blocks the ±1 and all higher orders of light.

To create a bright pixel on the image, the corresponding SLM pixel is set in the mirror state. The incoming illumination will be passed undiffracted, i.e. as the 0th-order, through the central aperture of the FT filter1608and transmitted maximally to the image plane1612. To create a dark pixel on the image, the corresponding SLM pixel is set in the maximally diffracting state. The incoming illumination will be diffracted maximally as ±1 and higher orders, which are blocked by the non-transmitting portion of the FT filter1608. Intermediate diffraction can be used to create gray levels.

Simulated Performance

Imaging performance of the Complex SLM according an embodiment of the present invention will now be described with reference toFIGS. 11–15.

FIG. 11illustrates a simple binary phase pattern generated using a complex SLM according to an embodiment of the present invention. The pattern shown inFIG. 11is generated by a 100% (or nearly 100%) fill-factor piston-mirror array (2×2 mirrors/pixel). An Apodized Fourier filter is used.FIG. 11demonstrates that a complex SLM according to an embodiment of the invention configured in a pure phase modulation mode may operate as an intensity spatial light modulator. This mode has some similarities with chromeless phase mask lithography in the lithography art.

FIG. 12illustrates the performance of the Complex SLM with “phase-shift mask” (PSM) in generating a line grating. Intensity and phase modulation may be performed simultaneously with a complex SLM operating in accordance with an embodiment of the invention. The bright/dark lines inFIG. 12(a) are produced by pixels that have the same phase (i.e. this is a simple binary line grating), while the bright/dark lines inFIG. 12(b) have alternating 0 and π phases (analogous to an alternating PSM). The advantageous higher contrast of the latter is evident.

An example of improved resolution is shown inFIG. 13in accordance with an embodiment of the invention. Here, the pattern being resolved has a “compatible phase-shift requirement.” The interior and the exterior of the closed-loop patterns have the same phase inFIG. 13(a). In contrast, in accordance with an embodiment of the invention, the interior of the closed-loop patterns inFIG. 13(b) are π phase-shifted with respect to the exterior. Clearly, the interior lines inFIG. 13(b) are better resolved.

Another example of improved resolution is shown inFIG. 14in accordance with an embodiment of the invention. Here, the pattern being resolved has a “conflicting phase-shift requirement.”FIG. 14(a) illustrates the problem, andFIG. 14(b) the solution. Referring toFIGS. 14(a) and14(b), alternating 0 and π phase-shift may be applied to the interior of the center feature. However, this poses a conflicting phase-shift requirement to the exterior area1402—the question marks inFIG. 14(a) indicate the problem of what phase to assign to the exterior area1402. Applicants have determined that simply assigning π to the left half and 0 to the right half of the exterior area will cause undesirable diffraction at the 0−π boundary. To prevent diffraction, applicants have found that softening the transition by employing a phase ramp1404in the exterior area1402, as shown inFIG. 14(b) will reduce the diffraction effect. This analog phase transition1404cannot be practically done in conventional PSM (which employs 0 and π only), but it may be readily achieved by a complex SLM in accordance with an embodiment of the invention.

FIG. 15depicts a “conflicting phase-shift requirement” pattern as generated by a Complex SLM in various operating modes. Specifically,FIG. 15(a) is the pattern without PSM.FIG. 15(b) is the pattern with alternating PSM in interior (0 phase in the left interior and π phase in the right interior), but with 0 phase in the exterior. Notice that the left interior is only marginally resolved.FIG. 15(c) is the pattern with π phase in the left exterior and 0 phase in the right exterior. Strong diffraction is seen as occurring at the 0−π boundary. In accordance with an embodiment of the invention, the best result is shown inFIG. 15(d), obtained with smooth phase transition (in eight equal steps of π/8) as explained above in relation toFIG. 14(b).

The above discussed results demonstrate advantages of the Complex SLM over conventional PSM.

One aspect of the present invention relates to a Complex SLM for modulating light incident thereon. Generally, the SLM has a number of pixels, each pixel including a plurality of phase shift elements disposed above a substrate, and a Fourier transform filter adapted to control the imaging system to resolve each pixel but not the individual phase shift element in each pixel. The pixels and the phase shift elements are adapted such that although not all light incident on the SLM is reflected, substantially all light reflected from the SLM comes from the phase shift elements.

Preferably, the phase shift elements are electrostatically displaceable mirrors, and the SLM further includes means for applying an electrostatic force between the substrate and the electrostatically displaceable mirrors to independently deflect each mirror relative to the substrate. More preferably, the means for applying an electrostatic force and the mirrors are adapted to enable each mirror to be deflected by a distance of about n·λ/2, where λ is a particular wavelength of light incident on the SLM, and n is an integer equal to or greater than 1. It should be noted, that in reflective operation, every λ/2 deflection corresponds to a 2π phase shift. The mirrors are adapted such that the interference of the light fields from the displaceable mirrors in a pixel create a net light field that has a magnitude anywhere between a minimum (usually near zero) and a maximum values, and has a phase anywhere between 0 and n·2π. For example, assuming there are even number of mirrors in a pixel, a maximum magnitude at 0 phase corresponds to all mirrors in a pixel undeflected, a minimum magnitude is obtained from deflecting half of the mirrors in a pixel by π/4 and the other half undeflected, an intermediate magnitude and phase by deflecting half of the mirrors in a pixel by one value and the other half by another value.

In one embodiment, each of the phase shift elements include a movable actuator flexibly supported above an upper surface of a substrate by a number of posts extending from the upper surface of the substrate and by a number of flexures extending from a peripheral edge of the movable actuator to at least one of the number of posts. Each of the electrostatically displaceable mirrors further include a support affixed to the top surface of the actuators, and a mirror surface supported by the support above the actuators, flexures and posts. The mirror surfaces are sized and shaped such that peripheral edges of each mirror surface abuts peripheral edges of adjoining mirror surfaces, whereby substantially none of the light incident on the SLM passes between the mirror surfaces to impinge on and/or be reflected by the actuators, flexures or posts.

Another aspect of the present invention relates to a method of modulating both phase and magnitude of light incident on the SLM described above. Generally, the method includes the steps of: (i) causing the light to impinge upon the plurality of phase shift elements such that substantially all of the light reflected from the SLM is reflected by the phase shift elements; and (ii) filtering the reflected light using a Fourier transform filter adapted to resolve each pixel but not the individual phase shift element in each pixel.

The foregoing description of specific embodiments and examples of the invention have been presented for the purpose of illustration and description, and although the invention has been described and illustrated by certain of the preceding examples, it is not to be construed as being limited thereby. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications, improvements and variations within the scope of the invention are possible in light of the above teaching. It is intended that the scope of the invention encompass the generic area as herein disclosed, and by the claims appended hereto and their equivalents.