Abstract:
One embodiment relates to a method of independently controlling amplitude and phase modulation by a spatial light modulator. Light is illuminated onto upper layer deflectable planar areas and lower layer deflectable planar areas over a substrate of the spatial light modulator. First active circuitry on the substrate is used to provide amplitude modulation by controlling a relative displacement between upper layer deflectable planar areas and adjacent lower layer deflectable planar areas. Second active circuitry on the substrate is used to provide phase modulation by controlling a displacement between the (upper and lower layer) deflectable planar areas and the substrate. Other embodiments and features are also disclosed.

Description:
GOVERNMENT LICENSE RIGHTS 
   The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract No. N66001-04-C-8029 awarded by The Department of the Navy, Space and Naval Warfare Systems Command (SPAWAR) Division, in cooperation with the Defense Advanced Research Projects Agency (DARPA). 

   CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is related to U.S. patent application Ser. No. 11/165,399, entitled “Complex Spatial Light Modulator,” filed Jun. 22, 2005 by inventors Jahja I. Trisnadi et al. 
   TECHNICAL FIELD 
   The present disclosure relates generally to spatial light modulators. 
   BACKGROUND 
   A spatial light modulator (SLM) includes of an array of optical elements (or pixels) in which each element acts independently to modulate incident light. The incident light beam may be modulated in intensity, phase, polarization or direction. The majority of spatial light modulators are intensity modulators. In such devices, often the intensity modulation causes some phase modulation, but the phase modulation is not typically done independently of the intensity modulation. 
   An example of an intensity modulation type of SLM is a Grating Light Valve™ (GLV™) device from Silicon Light Machines Corporation of Sunnyvale, Calif. The GLV™ device switches and modulates light intensities via diffraction. The GLV™ device is comprised of many parallel highly-reflective micro-ribbons that are suspended over an air gap above a silicon substrate. When the ribbons of a GLV™ pixel are co-planar, incident light becomes specularly reflected (like a mirror) from the GLV™ pixel. By deflecting alternate ribbons of a GLV™ pixel, the incident light may be controllably diffracted from the GLV™ pixel. 
   It is highly desirable to improve spatial light modulators for use in a variety of applications. 
   SUMMARY 
   One embodiment relates to a multi-layer spatial light modulator device for amplitude and phase control. The device includes a substrate, lower layer deflectable planar areas positioned above the substrate, a lower layer support structure, upper layer deflectable planar areas positioned above the lower layer, and an upper layer support structure. A first portion of incident light impinges on the upper layer of deflectable planar areas, and a second portion of the incident light impinges on the lower layer of deflectable planar areas. 
   Another embodiment relates to a method of independently controlling amplitude and phase modulation by a spatial light modulator. Light is illuminated onto upper layer deflectable planar areas and lower layer deflectable planar areas over a substrate of the spatial light modulator. First active circuitry on the substrate is used to provide amplitude modulation by controlling a relative displacement between upper layer deflectable planar areas and adjacent lower layer deflectable planar areas. Second active circuitry on the substrate is used to provide phase modulation by controlling a displacement between the (upper and lower layer) deflectable planar areas and the substrate. 
   Other embodiments and features are also disclosed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and various other features and advantages of the present invention may be apparent upon reading of the following detailed description in conjunction with the accompanying drawings and the appended claims provided below. 
       FIG. 1  is a cross-sectional diagram of a multi-layer light valve device for amplitude and phase control of incident light in accordance with an embodiment of the invention. 
       FIG. 2  is a top-down view of a first configuration of a multi-layer light valve device in accordance with an embodiment of the invention. 
       FIG. 3A  is a top-down view of a lower layer of the first configuration of a multi-layer light valve device in accordance with an embodiment of the invention. 
       FIG. 3B  is a top-down view of an upper layer of the first configuration of a multi-layer fight valve device in accordance with an embodiment of the invention. 
       FIG. 3C  is a cross-sectional view of the first configuration of a multi-layer light valve device in accordance with an embodiment of the invention. 
       FIG. 4  is a top-down view of a second configuration of a multi-layer light valve device in accordance with an embodiment of the invention. 
       FIG. 5A  is a top-down view of a lower layer of the second configuration of a multi-layer light valve device in accordance with an embodiment of the invention. 
       FIG. 5B  is a top-down view of an upper layer of the second configuration of a multi-layer light valve device in accordance with an embodiment of the invention. 
       FIG. 5C  is a cross-sectional view of the second configuration of a multi-layer light valve device in accordance with an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   The present disclosure describes the design, construction and method of use of a multi-level diffractive optical micro-electro-mechanical system (MEMS) device. The multi-level diffractive optical MEMS device is capable of controllably modulating both the amplitude and phase of incident illumination. The device includes at least two deformable layers, preferably located in different planes with respect to the incident illumination. 
   In accordance with an embodiment of the invention, the structure of the device includes at least one lower layer planar light valve or deformable membrane and at least one upper layer planar light valve or deformable membrane. Both the lower and upper layer planar light valves or deformable membranes are structurally supported by support structures. The support structures for a lower planar light valve or deformable membrane may be attached to or built on an underlying substrate. The support structures for an upper planar light valve or deformable membrane may be attached to or built on 1) the movable portion of the lower layer membrane or light valve, 2) the support structures of the lower layer, and/or 3) the substrate material directly. 
     FIG. 1  is a cross-sectional diagram of a multi-layer light valve device for amplitude and phase control of incident light in accordance with an embodiment of the invention. As shown in  FIG. 1 , the multi-layer light valve includes a substrate  106 , an arrangement or array of lower deformable membranes  102 , and an arrangement or array of upper deformable membranes  104 . A portion (preferably half) of the incident optical illumination  108  impinges upon the lower deformable membrane array  102 , and a portion (preferably half) of the incident illumination  108  impinges upon the upper deformable membrane array  104 . For purposes of ease of illustration and understanding, the support structures are not shown in  FIG. 1 . 
   The multi-layer light valve device modulates the amplitude of reflected light by changing the deflection of one or a group of the lower deformable membranes  102  with respect to (in relation to) an adjacent one or a group of adjacent upper deformable membranes  104 . By doing so, the optical path length difference between the pertinent lower and upper deformable membranes provides for a range of constructive or destructive interference in the reflected illumination so as to controllably modulate the amplitude of reflected light. 
   The multi-layer light valve device modulates the phase of reflected light by modulating the deflection of one or a group of the lower deformable membranes  102  to the same extent as an adjacent one or a group of adjacent upper deformable membranes  104  while keeping the optical path length difference between the upper and lower membranes constant. In other words, the deflections of the lower membranes  102  and adjacent upper membranes  104  are deflected in parallel to perform the phase modulation. In this way, the multi-layer light valve device may be operated to modulate the phase of reflected illumination in one area of the device with respect to adjacent or other areas of the device (while, if desired, keeping the optical path length difference between upper and lower membranes constant). 
   The multi-layer light valve device disclosed herein thus provides a means of independently modulating the phase or the amplitude, or a combination of both. 
   In accordance with a first example implementation, in order to allow for independent modulation of phase and amplitude, the device may be configured to provide for deformation at least three-quarters of the wavelength of incident illumination the upper layer membranes and to provide for deformation at least one-half of the wavelength of incident illumination the lower layer membranes. For the phase modulation, a one-half wavelength range of both the upper and lower layer membranes may be used to create an optical path length variation of up to one full wavelength. For the amplitude modulation, a one-quarter wavelength range of the upper layer membranes may be used to create an optical path length difference of one-half wavelength for modulation between constructive and destructive interference. 
   In accordance with a second example implementation, the device may be configured to provide for deformation at least one-half of the wavelength of incident illumination the upper layer membranes and to provide for deformation at least three-quarters of the wavelength of incident illumination the lower layer membranes. For the phase modulation, a one-half wavelength range of both the upper and lower layer membranes may be used to create an optical path length variation of up to one full wavelength. For the amplitude modulation, a one-quarter wavelength range of the lower layer membranes may be used to create an optical path length difference of one-half wavelength for modulation between constructive and destructive interference. 
   Regarding the above two example implementations, there may be process-related reasons why one implementation is preferable over the other. 
   In one application, by modulating both the phase and amplitude of incident illumination independently, the multi-layer light valve device may be utilized to render holographic displays or for recording in holographic media. The multi-layer light valve device may also be used in other applications. 
     FIG. 2  is a top-down view of a first configuration of a multi-layer light valve device in accordance with an embodiment of the invention. The surface areas of the lower layer membranes (darker shaded areas)  102  and of the upper layer membranes (white circular areas)  104  are depicted. Support structures are shown super-imposed on the diagram of  FIG. 2  for purposes of explanation. 
   In this embodiment, both the lower layer membranes  102  and the upper layer membranes  104  include circularly-symmetric or circularly-shaped diffracting edges to reduce the polarization dependence of diffraction and efficiency. As shown in  FIG. 2 , portions of the circularly-shaped lower layer membranes  102  are covered or blocked by the circularly-shaped upper layer membranes  104 . 
   The support structures for the lower layer membranes  102  include lower layer posts/vias  202 . In this embodiment, the lower layer posts/vias  202  are positioned underneath centers of the upper layer membranes  104 . With this covering of the lower layer support structures by the upper layer membranes, greater optical efficiency is advantageously achieved. The lower layer posts/vias  202  may be attached to or built on the substrate of the device. Hence, the lower layer posts/vias  202  may also advantageously provide an interconnect path or via for the electrical activation (deflection) of the upper layer membranes  104 . The lower layer is depicted with further clarity in  FIG. 3A . 
   The support structures for the upper layer membranes  104  include upper layer posts/vias  204 . The upper layer is depicted with further clarity in  FIG. 3B . 
     FIG. 3A  is a top-down view of a lower layer of the first configuration of a multi-layer light valve device in accordance with an embodiment of the invention. The circular areas of the lower layer membranes  102  and the triangular-shaped lower layer posts/vias  202  are shown. In addition, further lower layer support structure  302  is shown (in white) which connects the lower layer membranes  102  to the lower layer posts/vias  202 . 
     FIG. 3B  is a top-down view of an upper layer of the first configuration of a multi-layer light valve device in accordance with an embodiment of the invention. The circular areas of the upper layer membranes  104  and the triangular-shaped upper layer posts/vias  204  are shown. In addition, further upper layer support structure  304  is shown (in white) which connects the upper layer membranes  104  to the upper layer posts/vias  204 . Also, the openings (darker areas)  306  to the lower layer membranes are depicted. 
     FIG. 3C  is a cross-sectional view of the first configuration of a multi-layer light valve device in accordance with an embodiment of the invention. The cross-sectional view depicted is along a vertical cut on  FIG. 2 . In  FIG. 3C , the insulating membrane material (see  102  and  104 ) is indicated in white, and the conducting metals (see  322  and  324 ) are indicated in gray. Open gaps are shown under the insulating membranes. In this embodiment, both the lower layer posts/vias  202  and the upper layer posts/vias  204  are built or fabricated on top of the substrate  321 . 
   In this embodiment, a lower layer membrane  102  may be activated by controlling the voltage difference between the potential applied by the active circuitry  326  to the lower layer conductor  324  on that membrane and the potential applied by the active circuitry  327  underlying that membrane. An upper layer membrane  104  may be activated by controlling the voltage difference between the potential applied by the active circuitry  328  to the upper layer conductor  322  on that membrane and the potential applied by the active circuitry  326  to the lower layer conductor  324  underneath that membrane. 
     FIG. 4  is a top-down view of a second configuration of a multi-layer light valve device in accordance with an embodiment of the invention. Here, the lower layer membranes  102  are the medium-shaded circularly-shaped areas, and the upper layer membranes  104  are the darker-shaded nearly-diamond-shaped areas (with curved edges). Support structures are shown super-imposed in the diagram of  FIG. 4  for purposes of explanation. 
   The support structures for the lower layer membranes  402  include lower layer posts/vias  406 . In this embodiment, the lower layer posts/vias  406  are positioned underneath centers of the upper layer membranes  404 . With this covering of the lower layer support structures by the upper layer membranes, greater optical efficiency is advantageously achieved. The lower layer posts/vias  406  may be attached to or built on the substrate of the device. Hence, the lower layer posts/vias  406  may also advantageously provide an interconnect path or via for the electrical activation (deflection) of the upper layer membranes  404 . 
   The support structures for the upper layer membranes  404  include upper layer posts/vias  408 . In this embodiment, these posts  408  may be built or fabricated at or near the centers of the underlying lower membranes  402 . 
     FIG. 5A  is a top-down view of a lower layer of the second configuration of a multi-layer light valve device in accordance with an embodiment of the invention. The circular areas of the lower layer membranes  402  and the square-shaped lower layer posts/vias  406  are shown. In addition, further lower layer support structure  503  is shown (in white) which connects the lower layer membranes  402  to the lower layer posts/vias  406 . 
     FIG. 5B  is a top-down view of an upper layer of the second configuration of a multi-layer light valve device in accordance with an embodiment of the invention. The areas of the upper layer membranes  404  and the square-shaped upper layer posts/vias  408  are shown. In addition, further upper layer support structure  507  is shown (in white) which connects the upper layer membranes  404  to the upper layer posts/vias  408 . Also, the openings (darker areas)  505  to the lower layer membranes are depicted. 
     FIG. 5C  is a cross-sectional view of the second configuration of a multi-layer light valve device in accordance with an embodiment of the invention. The cross-sectional view depicted is along a 45 degree diagonal of  FIG. 4 . In  FIG. 5C , the insulating membrane material (see  402  and  404 ) is indicated in white, and the conducting metals (see  522  and  524 ) are indicated in gray. Open gaps are shown under the insulating membranes. 
   In this embodiment, the upper layer support structures  408  are built or fabricated on top of the centers of the lower layer membranes  402 . The lower layer support structures  406  are built or fabricated on top of the substrate  521 . 
   In this embodiment, conductive vias  524  through the lower layer support structures  406  may be utilized to contact active circuitry  526  below on the substrate  521  and to so enable activation (i.e. electrostatic deflection) of the upper layer membranes  404 . The lower level membranes  402  may be activated by controlling the voltage difference between the active circuitry  528  underlying the lower membranes on the substrate  521  and the upper layer conductor/vias  522 . 
   In one implementation, the activation of the lower membranes  402  may be global for the device or for an area of the device. In this case, the overall phase of reflected illumination for the device (or area of the device) may be controlled by the active circuitry  528  underlying the lower membranes, while the amplitude of the reflected illumination may be independently controlled per pixel separately from the phase modulation by the active circuitry  526  underlying the upper layer membranes. 
   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.