WO1996021876A1

WO1996021876A1 - Surface deformation type phase modulator

Info

Publication number: WO1996021876A1
Application number: PCT/US1995/013720
Authority: WO
Inventors: Craig D. Engle
Original assignee: Engle Craig D
Priority date: 1995-01-09
Filing date: 1995-10-24
Publication date: 1996-07-18
Also published as: AU3967895A

Abstract

A surface deformation type wavefront phase modulator (36) utilizes a transmissive deformable conductor (30) affixed to a transmissive deformable media layer (24). Layer (24) is affixed to an assemblage compromising a substrate (12) and a dielectric reflector (18) affixed to the substrate (12). Conductor (30) is opposite the substrate (12). Electrostatic forces are applied to the conductor (30) to vary the deformation of layer (24) and conductor (30) to phase modulate a wavefront incident on conductor (30) and reflected by reflector (18). Several advantages are inherent in my invention. Advantages include eliminating extraneous components and avoiding compromises involving reflectivity and conductor thickness while providing an inherent capability to enhance efficiency.

Description

SURFACE DEFORMATION TYPE PHASE MODULATOR

HEL OF THE INTENTION

This invention relates to surface deformation type wavefront phase modulators.

BACKGROUND OF THE INVENTION

Prior art surface deformation type wavefront phase modulators have suffered from a multitude of problems. Devices which utilize a reflective deformable surface are plagued by the complications cited in U. S. Patent 4,879,602 to Glenn, Nov. 7, 1989. As identified by Glenn, tradeoffs involving reflectivity and conductor thickness, a compromise inherent with the utilization of deformable reflectors, adversely effects performance. In addition, intrusion of the incident light onto the control mechanism presents additional problems associated with the utilization of deformable reflectors. Previous alternatives to the utilization of a deformable reflector include the device described in the article titled "Deformable Surface Spatial Light Modulator" by K, Hess et al, Optical Engineering May 1987, Vol. 26, No. 5. and the device described in U. S. Patent 3,835,346 to Mast et al, Sept. 10, 1974. Configurations which rely upon a separation gap between the deformable media and a control mechanism suffer from several complications. As identified in the article titled "Viscoelastic Control Layers for Solid-State light Valves" by R. Tepe, et al, SPIE Vol. 684 Liquid Crystals and Spati l Light Modulators Materials, 1986, page 27, such gaps must be very thin and extremely parallel. In addition, as identified in the article titled "Deformation Behavior of Thin Viscoelastic Layers Used in an Active Matrix Addressed Spatial Light Modulator" by W. Blinker et al SPIE Vol. 1018 Electro-Optic and Magnetic Materials 1988, page 82, elastic electrodes affixed to the deformable media layer leads to a faster response time. Such considerations are important for real time operation of phase modulators.

Additional surface deformation type wavefront phase modulators include the device described in U. S. Patent 4,494,826 to Smith, Jan 22, 1985. In patent 4,494,826 the read light is reflected by a deformable reflective conductor. As such, this device is plagued by the compromises identified in U. S. Patent 4,879,602 to Glenn. In addition, by failing to allow the read light to be reflected from within the deformable media, patent 4,494,826 fails to achieve the advantages inherent to applicant's invention. Accordingly, a need exists for a device which overcomes the limitations of prior art.

SUMMARY OF TflE INVENTION

Accordingly, several objects and advantages of my invention are:

1) To identify how to simplify surface deformation wavefront phase modulator construction by eliminating extraneous components which hinder performance while simultaneously providing a means to enhance performance thereby demonstrating the synergism which is present in my invention.

2) To identify surface deformation wavefront phase modulator device configurations which avoids compromises involving reflectivity and/or deformable conductor thickness.

3) To identify addressing schemes and/or applications which are utilizable with and benefit from my invention.

4) To provide evidence of how my invention enhances modulator performance.

5) To identify advantages inherent to my invention such as enhancing the reflectivity of surface deformation wavefront phase modulators.

Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description of it. BHIEF PESCRffπo QF THE DRAWINGS

In the drawings, closely related figures have the same number but different alphabetic suffixes.

Figure 1 shows a surface deformation type wavefront phase modulator target which utilizes a reflective means affixed to a surface of a substrate which opposes the transmissive deformable media layer.

Figure 2 shows an electron beam addressed surface deformation type wavefront phase modulator.

Figure 3 shows an optically addressed surface deformation type wavefront phase modulator target.

Figure 4 shows an optically addressed surface deformation type wavefront phase modulator utilizing schlieren optics.

Figure 5 shows an internal reflection reflective means for use with my invention. Figure 6 shows a target utilizing reflective electrodes affixed to a substrate as a reflective means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a surface deformation type wavefront phase modulator target 10. Certain portions of the figure has been shown cutaway for clarity. Target 10 further includes a substrate 12. Substrate 12 further includes a first surface 14 and a second surface. The second surface is not visible in the figure. Surface 14 and the second surface are essentially parallel surfaces separated by a substrate thickness 16. Thickness 16 is perpendicular to surface 14. Affixed to the second surface of substrate 12 is a multilayer dielectric reflector 18. Multilayer dielectric reflectors are well understood by those knowledgeable in the state of the art and reflector 18 is shown as a single layer in the figure for convenience. Reflector 18 further includes a first surface 20 and a second surface. The second surface of reflector 18 is not visible in the figure. Surface 20 and the second surface of reflector 18 are essentially parallel planes separated by a reflector thickness 22. Thickness 22 is perpendicular to surface 20. Surface 20 is affixed to the second surface of substrate 12. Affixed to surface 14 of substrate 12 is a transmissive deformable media layer 24. Layer 24 further includes a first surface 26 and a second surface. The second surface of media layer 24 is not visible in the figure. The second surface of layer 24 is affixed to surface 14. In an undeformed state, surface 26 and the second surface of layer 24 are essentially parallel planes separated by a media thickness 28. In an undeformed state, thickness 28 is essentially perpendicular to surface 26. Material utilized as layer 24 possess an index of refraction N.

Affixed to surface 26 is a transmissive deformable conductor 30. Conductor 30 further includes a first surface 32 and a second surface. The second surface of conductor 30 is not visible in the figure. In an undeformed state, surface 32 and the second surface of conductor 30 are separated by a conductor thickness 34. In an undeformed state, thickness 34 is perpendicular to surface 32. The second surface of conductor 30 is affixed to surface 26 of layer 24. Target 10 further includes a first lateral dimension 166 and a second lateral dimension 168. Dimension 166 is perpendicular to thickness 16 and dimension 168. Dimension 168 is perpendicular to thickness 16.

As identified in the patent application admitted to Craig D. Engle titled "Enhanced Wavefront Phase Modulator Device", filed 02/17/95, serial number 08/390,690, the target described in figure 1 is capable of being electron beam addressed. As to be shown herein, alternative configurations are utilizable to phase modulate a wavefront which traverses the target configurations of my invention in accordance with an information bearing signal.

Material selection for the various components utilized in target 10 are dependent, in part, on the target configuration and the addressing mechanism utilized. Materials utilizable in the targets of my invention will be identified herein.

By affixing the reflector to the substrate and utilizing a deformable transmissive conductor affixed to a surface of the deformable media layer which opposes the substrate, my invention avoids the compromises involving reflectivity and conductor thickness which have plagued prior art devices.

Figure 2 shows an electron beam addressed phase modulator 36. Modulator 36 further includes target 10. Modulator 36 further includes an electron beam addressing mechanism 38. Mechanism 38 further includes a vacuum envelope 40. Envelope 40 is fabricated from any suitable material, such as glass, and is of any suitable shape. Materials and shape considerations of vacuum envelopes for use in electron beam addressed devices are well understood by those knowledgeable in the state of the art.

Target 10 is sealed to envelope 40 by the use of a seal ring 42. Techniques to seal a target to a vacuum envelope are well understood by those knowledgeable in the state of the art. See for instance information contained in U. S. Patent 3,445,707, to J. P. Gilvey et al, May 20, 1969. Accordingly, seal ring 42 is not shown in detail.

Mechanism 38 further includes an electron beam gun 44. Gun 44 further includes a filament 46 for heating an electron emissive cathode 48, a first control grid 50 for controlling the beam current of an electron beam 52 generated by gun 44, a second control grid 54 for accelerating electrons in beam 52 and a focusing element 56 for focusing electron beam 52. Electron guns are well understood by those knowledgeable in the state of the art and therefore gun 44 is not show in detail in the figure.

Separated from target 10 by a grid separation distance 58 is an electron collector mesh 60. Electron collector meshes are well understood by those knowledgeable in the state of the art and therefore mesh 60 is not shown in detail. Mechanism 38 further includes an electron deflection means 62. Deflection means 62 enables electron beam 52 generated by gun 44 to be positioned to any location on the second surface of dielectric reflector 18 of target 10. Deflection means include electrostatic and electromagnetic deflection techniques. As well understood by those knowledgeable in the state of the art, selection of a particular type of deflection technique influences the nature of focusing element 56.

Deflection techniques for use in electron beam devices are well understood by those knowledgeable in the state of the art and therefor deflection means 62 is not shown in detail.

As well understood by those knowledgeable in the state of the art, several electron beam read/write techniques exist to deposit an electronic charge 64 on target 10. The preferred writing technique for use in my invention is an equilibrium writing technique described in the patent application titled "Enhanced Wavefront Phase Modulator Device". Use of an equilibrium writing technique requires that the secondary electron emission ratio of the surface of the target which is being bombarded by the electron beam exceed unity. Secondary electron emission curves as a function of primary electron beam energy and the requirements for equilibrium electron beam writing are identified in the references provided herein. Requirements for equilibrium writing are well understood by those knowledgeable in the state of the art.

A voltage source 66 applies voltages to filament 46, cathode 48, focusing element 56 and second control grid 54 for operation consistent with equilibrium writing techniques. The voltages required by mechanism 38 to enable equilibrium writing means to be implemented are well understood by those knowledgeable in the state of the art. The potentials applied to mechanism 38 by voltage source 66 are selected so that electrons associated with electron beam 52 are accelerated by an electron energy which exceed the first crossover point of the secondary electron emission ratio curve versus primary electron energy and below the second crossover point of the curve for the surface of the target being bombarded by the electron beam.

The equilibrium writing technique for use in my invention applies input voltage variations to conductor 30 of target 10. An information bearing signal 68 is applied to an electronic processing module 70. Module 70 applies a synchronization signal 72 to a deflection amplifier 74. Amplifier 74 applies a deflection waveform 76 to deflection means 62 enabling electron beam 52 to scan target 10. Scan patterns, scan velocities, deflection waveform etc. are well understood by those knowledgeable in the state of the art. The scan pattern associated with my invention is preferably an interlaced raster scan pattern. The raster scan pattern is not shown in the figure for convenience.

Module 70 applies a second synchronization signal 78 to a control grid amplifier 80. Amplifier 80 applies a beam current control voltage 82 to control grid 50 to control the potential difference between cathode 48 and control grid 50 to control the beam current of electron beam 52. Beam current is maintained at a constant level during active scan times of the raster scan pattern and is blanked during retrace periods. Such considerations are well understood by those knowledgeable in the state of the art and not shown in detail. Mesh 60 is maintained at a ground potential 84. Module 70 applies a voltage signal 86 to conductor 30 to vary the potential difference between mesh 60 and conductor 30 in accordance with signal 68. Electron beam 52 further includes a spot size 88. As well understood by those knowledgeable in the state of the art, the elemental area of target 10 which is bombarded by the instantaneous location of electron beam spot size 88 will acquire net electronic charge 64 which is related to the value of signal 86 applied to conductor 30 at the time the elemental area of target 10 is bombarded by electron beam 52.

Charge 64 deposited on reflector 18 of target 10 will establish an electric field in layer 24 of target 10 in accordance with signal 68. The electric fields are not shown in the figure for convenience. As well understood by those knowledgeable in the state of the art, electric fields in layer 24 establishes electrostatic forces which act on conductor 30 leading to compressional forces which act on layer 24. Electrostatic and compressional forces are not shown in the figure for convenience. Information concerning the nature of such forces are provided in the references cited herein.

Compressional forces influence thickness variations in layer 24. Due to conductor 30 being transmissive, a wavefront containing the wavelength(s) of interest which is incident upon conductor 30 will traverses layer 24 and substrate 12, impinge on and be reflected by reflector 18 to again traverse substrate 12 and layer 24 then exit target 10. Thickness variations in layer 24, due to variations in the electric fields in target 10, will lead to optical path length variations in the wavefront which traverses target 10 which leads to phase modulations of the wavefront in accordance with the information bearing signal. The wavefront is not shown in the figure for convenience. Since the wavefront traverses substrate 12 prior to impinging upon reflector 18, substrate 12 must be transmissive to the wavelengths of the wavefront which are to be phase modulated. In addition, due to charge storage considerations, substrate 12 is preferably insulating. Materials which are utilizable for the substrate of my invention include glass. 11

Considerations involved in designing a dielectric reflector for use in my invention are well understood by those knowledgeable in the state of the art.

Figure 3 shows an optically addressed phase modulator target 90. Certain portions of the figure are shown cutaway for clarity. Target 90 further includes a photoconductive substrate 92. Substrate 92 is given a different designation than the substrate associated with figures 1 and 2 to emphasize the latitude available with substrate material selection with my invention. Substrate 92 further includes a second surface 94 and a first surface. The first surface of substrate 92 is not visible in the figure. Surface 94 and the first surface of substrate 92 are essentially parallel planes separated by a substrate thickness 96.

Affixed to the first surface of photoconductive substrate 92 is a dielectric reflector 98. Reflector 98 is given a different designation than the reflectors associated with figures 1 and 2 to emphasize the latitude available in my invention in regards to which surface of the substrate the reflective means may be affixed to. In addition, as well understood by those knowledgeable in the state of the art, the index of refraction of the medium surrounding the dielectric reflector in my invention is dependent upon which surface of the substrate the dielectric reflector is affixed and/or the addressing mechanism utilized. Such considerations influence the design of the reflector.

Reflector 98 further includes a second surface 100 and a first surface. The first surface of reflector 98 is not visible in the figure. Second surface 100 and the first surface of reflector 98 are essentially parallel planes separated by a reflector thickness 102.

Affixed to the first surface of reflector 98 is transmissive deformable media layer 24. Layer 24 further includes a second surface 104. In an undeformed state, surface 104 is separated from the first surface of layer 24 by thickness 28. The first surface of layer 24 is not visible in the figure. Surface 104 is in contact with the first surface of reflector 98. Surface 104 adheres to the first surface of reflector 98.

Target 90 further includes transmissive deformable conductor 30.

Conductor 30 further includes a second surface 106. Second surface 106 is separated from the first surface of conductor 30 by conductor thickness 34. The first surface of conductor 30 is not visible in the figure. Surface 106 is affixed to the first surface of layer 24.

Affixed to second surface 94 of photoconductive substrate 92 is a grille electrode structure 108. Structure 108 further includes a plurality of first conductive fingers 110. Adjacent fingers 110 are displaced by a first period 112. First period 112 is perpendicular to thickness 96. Fingers 110 are electrically connected by a first buss 114. Structure 108 further includes a plurality of second conductive fingers 116. Adjacent fingers 116 are displaced by period 112. Fingers 116 are electrically connected by a second buss 118. Each first finger 110 and each second finger 116 further includes a finger width 120. Width 120 is parallel to first period 112. Each finger 110 and each finger 116 further includes a finger thickness 122. Thickness 122 is perpendicular to surface 94. Each finger 110 and each finger 116 further includes a finger lateral dimension 124. Dimension 124 is perpendicular to thickness 122 and first period 112. Fingers 110 and fingers 116 are interwoven to create grille electrode structure 108.

First buss 114 is electrically connected to a first voltage source 126. Second buss 118 is electrically connected to a second voltage source 128. Conductor 30 is electrically connected to a third voltage source 130. As well understood by those knowledgeable in the state of the art, electrically connecting first buss 114 and second buss 118 to respective voltage sources and applying a voltage to conductor 30 allows a periodic electric field to be established in target 90. The electric fields are not shown in the target for convenience. Polarity and magnitude of the voltage sources are selected to be compatible with the resolution and speed of response requirements for the application under consideration. Such considerations are well understood by those knowledgeable in the state of the art.

Conductive fingers have high contact resistance with the photoconductor substrate so that space charge can build up. Irradiating the second surface of the photoconductor relaxes periodicity in the electric field due to charge redistribution which shields the fingers of the grille structure. The electric fields are not shown in the figure. As well understood by those knowledgeable in the state of the art, inhomogeneous electric fields leads to deformations of the conductor and media layer. Deformations of the conductor and media layer lead to variations in the thickness of the media layer which leads to optical path length differences in a wavefront which traverses the target. Optical path length variations leads to phase modulations of the wavefront.

A transmissive support plate 170 is affixed to photoconductor substrate 92 to provide mechanical support. Plate 170 is optional. A write-in wavefront containing a desired wavelength(s) is represented by light rays 132. Rays 132 are incident upon second surface 94 of substrate 92. As well understood by those knowledgeable in the state of the art, the write-in wavefront is a two dimensional information bearing signal. The spatial distribution of irradiance associated with the write-in wavefront forms an input image which influences the periodicity of the electric fields in target 90 which effects the deformations of deformable media layer 24. Due to the method of operation associated with target 90 of figure 3, areas of target 90 which overlap irradiated areas of second surface 94 will tend toward relaxed surface deformations, i.e. layer 24 will tend toward a smooth layer in such regions.

A read-out wavefront containing a desired wavelength(s) which is incident on conductor 30 is represented by rays 134. Due to conductor 30 being transmissive, the wavefront is able to traverse layer 24 and impinges on and is reflected by reflector 98 to again traverse layer 24 a second time and issue from target 90. Thickness variations in layer 24 will lead to optical path length variations in the wavefront which traverses layer 24. Optical path length variations and/or differences leads to wavefront phase modulations.

The wavefront which issues from target 90 is represented by diffracted rays 136. i depicting rays 136 in the figure, it is assumed that write light conditions are such that layer 24 is smooth. Optical path length variations are dependent upon the index of refraction of layer 24, the wavelength of the read-out wavefront, and thickness variations of layer 24. Thickness variations are influenced by mechanical properties associated with conductor 30, and physical properties of layer 24 as well as the previously mentioned electric fields and/or electrostatic forces. As previously indicated, the write-in image which is incident upon the photoconductive substrate influences the thickness variations of the media layer. In this manner, the read-out wavefront is phase modulated in accordance with an information bearing signal. Applications for the target of my invention include real time display applications, such as HDTV displays, storage applications, wavelength converters, image amplifiers. Material selection for various components is influenced by the nature of the application involving the targets. Applications involving long term storage preferably utilizes a nonlinear high-resistivity photoconductor.

Figure 4 shows an optically addressed spatial light modulator 138. Modulator 138 further includes optically addressed target 90. Target 90 is shown without the optional support plate in this figure. Conductor 30 is connected to source 130, first conductive fingers 110 are electrically connected to source 126 and second conductive fingers 116 are electrically connected to source 128. The first buss and second buss associated with target 10 are not visible in the figure. Although the electrical connection of conductive finger to voltage sources has been depicted differently in figure 4 than in figure 3 for convenience, the function remains the same. Modulator 138 further includes a write light device 140. Device

140 further includes a write light source 142, a condenser lens 144, a transparency 146, a relay lens 148. As well understood by those knowledgeable in the state of the art, device 140 is utilized irradiate the second surface of photoconductive substrate 92 with an image of transparency 146. The image of transparency 146 is represented by write- in rays 132. The image of transparency 146 provides an information bearing signal to influence the deformations associated with target 90. Spatial transmission variations in transparency 146 leads to variations in the irradiance of the image incident upon the second surface of photoconductor substrate 92. As well understood by those knowledgeable in the state of the art, irradiance variation on photoconductive substrate 92 leads to variations in the electric fields present in layer 24. An electric field component 228 is shown in figure 4 to represent that electric fields are present in my invention. No effort as been made for component 228 to represent the spatial nature of the electric fields in my invention. As previously identified, inhomogeneous electric fields present in my invention will lead to electrostatic forces on conductor 30. The electrostatic forces are not shown in the figure for convenience. Techniques for establishing and controlling electric fields and hence electrostatic forces acting on conductor 30 are electric field control means.

Modulator 138 further includes a schlieren projector 150. Projector 150 further includes a read-out light source 152 to generate a read-out wavefront which is represented by light rays 134. Rays 134 diverge from source 152 and are collected by a coUimating lens 154 which directs collimated rays 134 to target 90. Conductor 30 is transmissive and the wavefront traverses media layer 24 impinges on and is reflected by reflector 98 to again traverse media layer 24 and then issue from target 90. Light rays are not shown traversing layer 24 in the figure for convenience. Light rays 136 which issue from target 90 are focused by a schlieren lens 156 onto a pin hole aperture 158. A second lens 160 collects the rays 136 which pass through aperture 158 and projects a target image 162 of target 90 onto a screen 164. Lens 160 is adjusted to image target 90 onto screen 164. Aperture 158 is designed to pass rays 136 issuing from regions of target 90 which are "smooth" due to overlapping regions of the photoconductor substrate 92 which are irradiated by write light. Such considerations are well understood by those knowledgeable in the state of the art. Schlieren projectors are well understood by those knowledgeable in the state of the art, and consequently projector 50 is shown in a simplified manner. Screen 164 is a reflective lambertian screen utilized to transform irradiance variations associated with image 162 to brightness variations associated with image 162. The device of figure 4 is the preferred embodiment of my invention. Photoconductive materials which are utilizable as the substrate in my invention include CdS, Si, or CdS powder in plastic or gelatin binder.

Materials which are utilizable as a transmissive deformable conductor include indium tin oxide and transmissive conducting polymers. Transmissive conducting polymers are well understood by those knowledgeable in the state of the art.

Several materials are utilizable as the transmissive deformable media layer of my invention. A transmissive gel, similar to what is described in U. S. Patent 3,835,346 to Mast et al, Sept. 10, 1974 is utilizable in my invention. Gels for use in my invention include weakly cross-linked silicone rubbers or methyl siloxane having a modulus of elasticity of about 0.1 kg per square cm.

Polymers, and elastomers similar to what is utilized with the device described in the article titled "The Ruticon Family of Erasable Image Recording Devices" by N. K. Sheridon, IEEE Transactions on Electron Devices, Sept. 1972 are utilizable in my invention.

Transmissive viscoelastic substances are utilizable in my invention. Quoting from the reference titled "Theoretical Analysis of an Electrically Addressed Viscoelastic Spatial Light Modulator" by R. Tepe, Vol. 4, No. 7/July 1987/J. Opt. Soc. Am. A, "It is characteristic of viscoelastic materials to possess the properties of an ideally elastic solid as well as those of a viscous liquid.". Accordingly, viscoelastic layers exhibit rubbery attributes. Values for viscosity and other properties, such as shear modulus, which are representative of viscoelastic layers utilizable in my invention are identified in the references cited herein. As indicated in the references, shear modulus values include the range of values from 5 X (10 **3) N/(M ** 2) to 10**5, where the symbol ** indicates the power to which the base of ten is raised. See for instance, figure 3 of the reference titled "Theoretical Analysis of an Electrically Addressed Viscoelastic Spatial Light Modulator".

Additional criteria for establishing guidelines for identifying transmissive deformable media layer materials for use in my invention includes the information presented in the report titled "Dielectric Membrane Light Valve Study" by Eugene T. Kozol et al, RADC-TR-71, section 3.1.4 "Deformation of the Elastomer According to Plane Theory of Elasticity". An assumption which is often utilized in modeling the deformation characteristics of certain media layer materials involves assuming the media layer is incompressible. As quoted from the cited reference, "Most rubber-like substances have Poisson's ratio's exceeding 0.49 so for such material, the order of magnitude of the deformations in figure 29 seems reasonable.".

As identified in the article titled "The Ruticon Family of Erasable Image Recording Devices" reflecting light from within the elastomer layer causes the greatest modulation of the read-out light. My invention emulates this attribute of the conductive liquid Ruticon and I believe that my invention provides this benefit and that this benefit is inherent in my invention. All target configurations of my invention provide a double pass through the deformable media.

In addition, by utilizing a transmissive deformable conductor affixed to the deformable media layer my invention eliminates gaps and/or extraneous substrates and provides a means to enhance speed of response.

Characteristics associated with utilizing an incompressible media in surface deformation wavefront phase modulators is described in the article titled "The Ruticon Family of Erasable Image Recording Devices" and the article titled "Deformable-Mirτor Spatial light Modulators" by Larry J. Hombeck, SPIE Critical Review Series Vol. 1150. As described in the cited references, side lobes and protrusions of the media accompany the compressions of the media layer. As well understood by those knowledgeable in the state of the art, total internal reflection has been incorporated as a reflective means in surface deformation type wavefront phase modulators. Examples of such configurations are identified in the references cited herein. An internal reflection reflective means is capable of being integrated with my invention. Figure 5 shows a wavefront phase modulating target 172 which utilizes internal reflection as the reflective means. Figure 5 is not scaled to any parameter. Furthermore, target 172 is greatly exaggerated for convenience in discussing the mechanism of internal reflection in my invention. Target 172 further includes substrate 12. Substrate 12 possess an index of refraction Ns. Affixed to substrate 12 is media layer 24. As previously identified, layer 24 possess an index of refraction N. Affixed to layer 24 is transmissive deformable conductor 30. Conductor 30 possess an index of refraction Nc. Conductor 30 is affixed to surface 26 of layer 24. A line segment 174 is normal to first surface 32 of conductor 30. Target 172 is shown in an undeformed state. The medium in contact with first surface 32 of conductor 30 which opposes layer 24 is designated as "AIR" in the figure and is assumed to have an index of refraction designated as Nair, with Nair = 1.0. A wavefront incidence on conductor 30 is represented by ray 134 which is incident upon conductor 30 with an angle of incidence 176. Angle of incidence 176 is measured between ray 134 and segment 174. Conductor 30 is transmissive and the wavefront traverses conductor 30 with the wavefront being represented by ray 178 in the medium of conductor 30 as the wavefront traverses from surface 32 toward layer 24. The direction of propagation of ray 178 as the wavefront traverses conductor 30 is designated by an angle of refraction 180. Angle of refraction 180 is measured between segment 174 and ray 178. Angle of refraction 180 is dependent upon incidence angle 176 and the index of refraction Nair of the incident medium designated as AIR and the index of refraction Nc of the transmitted medium which is conductor 30. As well understood by those knowledgeable in the state of the art, in an undeformed state, Snell's law is conveniently applied to target 172 to establish the value of angle 180.

Snell's law relates the angles of incidence and refraction and the index of refraction of the mediums associated with the incident and refracted (transmitted) rays. Snell's law is presented below:

(ni) sin(0i) = (nt)sin(0t) where ni is defined to be the index of refraction of the incidence medium. nt is defined to be the index of refraction of the transmitted (refracted) medium. sin(Oi) is defined as the sine of the angle of incidence sin(Ot) is defined as the sine of the angle of refraction

At the interface of conductor 30 and layer 24, a situation similar to what was previously described for the air and conductor interface is encountered. A line segment 182 is normal to surface 26 of layer 24. Ray 178 has an angle of incidence 184 measured between segment 182 and ray 178. Relationships involving angle of refraction 180 and angle of incidence 184 are well understood by those knowledgeable in the state of the art.

Layer 24 is transmissive and the wavefront traverses layer 24 from conductor 30 toward substrate 12. The wavefront which is traversing layer 24 from conductor 30 toward substrate 12 is represented by a ray 186. Again, for an undeformed target 172, Snell's law is conveniently applied to establish an angle of refraction 188 measured between segment 182 and ray 186. Angle of refraction 188 establishes the direction of propagation of ray 186 in layer 24 as the wavefront traverses layer 24 in a direction from conductor 30 toward substrate 12. Ray 186 traverses layer 24 and establishes an angle of incidence 190 measured between a line segment 192 which is perpendicular to surface 14 of substrate 12 and ray 186. Relationships involving angle of incidence 190 and angle of refraction 188 are well understood by those knowledgeable in the state of the art.

Substrate 12 is transmissive and the wavefront traverses substrate 12 with the wavefront represented by a ray 194 in the medium of substrate 12 as the wavefront traverses substrate 12 from layer 24 toward the surface of substrate 12 which opposes layer 24. The direction of propagation of ray 194 is designated by an angle of refraction 196. Angle of refraction 196 is measured between segment 192 and ray 194. Angle of refraction 196 is dependent upon incidence angle 190, index of refraction N and index of refraction Ns. Relationships governing angle of refraction 196 are well understood by those knowledgeable in the state of the art.

Ray 194 establishes an angle of incidence 198 between a line segment 200 which is perpendicular to the surface of substrate 12 which opposes layer 24, and ray 194. Relationships involving angle of incidence 198 and angle of refraction 196 are well understood by those knowledgeable in the state of the art.

An internal reflection occurs for angles of incident which exceed a critical angle 202 which is measured between a reference line 204 and segment 200. Critical angle 202 is dependent upon index of refraction Ns of substrate 12 and index of refraction N2 of the medium surrounding the surface of substrate 12 which opposes layer 24. Figure 5 is label with N2 to denote the medium which establishes an interface with the surface of substrate 12 which opposes layer 24. As well understood by those knowledgeable in the state of the art, if Ns is greater than N2 then the value of the critical angle is dependent on the following relation: sin(0c) = N2/Ns where sin(Oc) is defined to be the sine of the critical angle.

Accordingly, by selecting a substrate material so index of refraction Ns of substrate 12 exceeds the index of refraction N2 of the medium surrounding the surface of substrate 12 which is opposite of layer 24, a critical angle is established. Target 172 is capable of providing a total internal reflection to a wavefront if incidence angle 176 and the index of refractions Nc, N, Ns, N2 are properly related. Utilizing the information provided herein, such considerations for establishing a total internal reflection will be obvious to those knowledgeable in the state of the art.

As well understood by those knowledgeable in the state of the art, conditions for establishing a critical angle involves the index of refraction Ns of substrate 12 and the index of refraction N2. The sine of critical angle 194 is equal to the ratio N2/Ns. A table identifying critical angles for various values for index of refraction ratios is provided in the reference titled "Optics" by Eugene Hecht and Alfred Zajac, Addison-Wesley Publishing Company, copyright 1974, page 81.

Accordingly, after undergoing a total internal reflection, the wavefront traverses layer 24 in a direction from the surface of substrate 12 which is opposite layer 24 toward layer 24 with the wavefront being represented by a ray 206 as the wavefront traverses substrate 12 toward layer 24. Ray 206 establishes an angle of reflection 208 which is measured between ray 206 and segment 200. As well understood by those knowledgeable in the state of the art, angle of reflection 208 is equal to angle 198. The total internal reflection mechanism is inherently associated with substrate 12. The wavefront continues to propagate thru target 172 from the surface of substrate 12 which opposes layer 24 toward the medium designated as AIR and emerges from target 172 as ray 136. Refraction occurs at the remaining interfaces in target 172 as the wavefront traverses target 172 after undergoing total internal reflection. The wavefront is designated as a ray 210 in layer 24 as the wavefront traverses layer 24 after total internal reflection. The wavefront is designated as a ray 212 in conductor 30 as the wavefront traverses conductor 30 after undergoing total internal reflection in target 172. Relationships which govern refraction at the remaining interfaces associated with adjacent mediums of target 172 are identified herein for the conditions identified.

As can be readily seen, my invention provides a extremely simple means to establish a reflective surface deformation type wavefront phase modulator which avoids compromises between reflectivity and conductor thickness which have plagued prior art. In addition, my invention has eliminated the requirement for a dielectric reflector in target 172 by utilizing a total internal reflection within target 172.

The surface of substrate 12 which opposes layer 24 in target 172 is capable of being electron beam addressed. Utilizing the information provided herein, requirements for establishing a total internal reflection at the interface of target 172 involving the surface of substrate 12 which opposes layer 24 and the medium surrounding that surface are will be obvious to those knowledgeable in the state of the art. Accordingly, selecting Ns greater than N2 provides an opportunity to establish a total internal reflection reflective means for use with my invention.

Material properties of interest when utilizing an internal reflection mechanism in target 172 includes the range of values of index of refraction Ns conveniently available with glass substrates and the range of values of index of refraction N of deformable media layer materials that are utilizable with my invention. As identified in the book titled "Optics", page 189, values for Ns include the range of values from Ns = 1.49 to Ns = 1.95. As identified in the references cited herein, a value which is characteristic of the index of refraction N of an elastomer deformable media layer is N = 1.5. Techniques for generating and controlling the angle of incidence of wavefront rays which are incidence on the transmissive deformable conductor of my invention are well understood by those knowledgeable in the state of the art and are not shown for convenience.

Due to the range of values available for the substrate index of refraction Ns and the deformable media layer index of refraction N, values for the index of refraction of the deformable media layer may be chosen to be greater than the index of refraction value of the substrate. As identified herein, the critical angle associated with an interface utilized for a total internal reflection influences the propagation of the wavefront thru the target. Figure 6 shows yet another target 214. Target 214 further includes a substrate 216. Substrate 216 further includes a first surface 218 and a second surface. The second surface of substrate 216 is not visible in the figure. Surface 218 and the second surface of substrate 216 are essentially parallel and separated by a substrate thickness 220. Affixed to substrate 216 is a plurality of reflective electrodes 222. Electrodes 222 further includes a first electrode surface 224 and a second electrode surface. The second electrode surfaces of electrodes 222 are not visible in the figure. Surface 224 and the second surface of electrode 222 are separated by an electrode thickness 226. Materials suitable for use as electrodes includes Aluminum. Electrodes 222 are recessed in substrate 12 so that first surface 224 of each electrode 222 is coplanar with first surface 218 of substrate 216. Electrodes 222 are depicted in a two dimensional array. Techniques to recess electrodes in an insulating substrate are provided in the references cited herein. Affixed to surface 218 of substrate 216 is layer 24. Affixed to surface 26 of layer 24 is conductor 30. The second surface of substrate 216 is capable of being electron beam addressed. Considerations involved in selecting substrate materials for use with my invention includes the secondary electron emission ratio of the substrate. Such considerations are well understood by those knowledgeable in the state of the art. Utilization of target 216 provides an alternative for establishing and/or affixing a reflective means to a substrate.

Thus the reader will see that the surface deformation wavefront phase modulator of my invention provides an efficient means for enhancing the performance attainable by surface deformation type wavefront phase modulators. While my above description contains many specificities, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of one preferred embodiment thereof.

By integrally associating a reflective means with the substrate, my invention avoids pitfalls that have plagued prior art devices. Several other addressing mechanisms are utilizable with my invention to establish and vary the electric fields in the target of my invention. As identified in the patent application titled "Electronically Addressed Deformable Media Light Modulator" admitted to Craig D. Engle, serial no. 08/180,029 filed 01//11/94, thin film transistors are utilizable as an addressing mechanism to establish electrostatic forces on the transmissive deformable conductor of my invention.

Although the transmissive deformable conductor of my invention has been depicted as a monolithic conductor, as identified in the patent application titled "Poppet Valve Modulator" admitted to Craig D. Engle, serial no. 08/020,692, filing date 02/22/93, my invention accommodates transmissive deformable column conductors. As identified in the references cited herein, such conductor means facilitates elimination of electrical crossover networks in active matrix arrays. As such, my invention enhances reliability of active matrix addressed surface deformations type wavefront phase modulators. Distinguishing features of my invention includes consolidating a substrate with a reflective means to avoid the complications of prior art which utilized deformable reflectors affixed to deformable media. By incorporating the reflective means with the substrate, my invention avoids pitfalls of prior art.

As identified in the cited patent applications admitted to Craig D.

Engle, an opaque substrate facilitates isolation of addressing components. The substrate of my invention is capable of being made opaque to assist in preventing the incident light from intruding on control elements thereby enhancing it's functionality.

In addition, surface deformation type wavefront phase modulators have utilized discrete electronic control elements, such as field effect transistors, fabricated in semiconductor substrates. As cited in applicant's referenced patent applications, semiconductor substrates are utilizable with my invention. Accordingly, substrate options for use in my invention include semiconductor substrates which contain discrete electronic switching elements. Due to the storage capability inherent to my invention, application of electric fields by the addressing mechanism may be applied prior to a read¬ out wavefront. Such considerations may be important in applications involving my invention, such as holographic applications.

Utilizing the information contained herein, it will become obvious that alternative addressing configurations and/or mechanism may be utilized with my invention. Alternative photosensitive elements, such as photodiodes, are utilizable to establish electric fields in the target of my invention. Considerations such as the spectral responsitivity and semiconductor band gap of a photoconductive substrate, in addition to the wavelength(s) of the read and write light and spectral reflectivity of the dielectric reflector are utilizable as variables to influence the design of the target. Design considerations include items such as the sequence associated with the arrangement of the substrate, dielectric reflector, media layer etc. Although an equilibrium writing method was described with the electron beam addressing mechanism, alternatives are utilizable with my invention. Alternative electron beam addressing mechanism include the technique described in U. S. Patent 3,626,084 to Wohl et al, Dec. 7, 1971. In addition, the electronic processing module associated with the electron beam addressing module of my invention is capable of providing a transformation of the information bearing signal to a sinusoidal type charge distribution for use with my invention. The sinusoidal type charge distribution is capable of being amplitude modulated in a manner related to the information bearing signal. Charge distributions may be established via scan velocity modulations, beam current modulations, cathode potential modulations etc.

As well understood by those knowledgeable in the state of the art, alternatives to schlieren techniques are available to convert phase modulations to irradiance modulations and/or brightness variations. Such techniques include interferometeric techniques.

Due to the multitude of configurations permissible with my invention, several techniques exist for conjoining the deformable media layer to the substrate of my invention. Embodiments have illustrated deformable media layers in direct contact with the substrate, media layer connected to the substrate by means of a dielectric reflector.

Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.

Claims

C ΔIMS

I claim:

1) An enhanced surface deformation type wavefront phase modulator comprising: a substrate, reflective means integrally associated with said substrate, transmissive electrostatically deformable media means exhibiting rubbery attributes, said media means further includes a first surface facing said substrate and a second surface opposite thereof, transmissive deformable conductor means affixed to said second surface of said media means, said media means is integrally associated with said substrate, said second surface of said media means is opposite said reflective means, electric field control means to apply electrostatic forces to said conductor means, means operatively associated with said control means varying said electrostatic forces which vary the deformation of said conductor means and said media means thereby phase modulating a wavefront incident on said conductor means, at least a portion of said wavefront traversing said media means impinging on and reflected by said reflective means to again traverse said media means and issue from said modulator.

2) The device of claim 1 further including a schlieren means to transform said phase modulated wavefront to a wavefront having identifiable irradiance characteristics.

3) The device of claim 2 further including a viewing screen to view said wavefront having said identifiable irradiance characteristics. 4) The device of claim 3 wherein said media means is selected from the group of materials consisting of transmissive elastomers and transmissive viscoelastic substances.

5) The device of claim 4 wherein said reflective means is a reflective element selected from the group consisting of dielectric reflector(s) affixed to said substrate and reflective electrode(s) affixed to said substrate and total internal reflection dependent on the index of refraction of said substrate.

6) The modulator of claim 5 wherein said reflective means is a dielectric reflector affixed to said substrate.

7) The device of claim 6 wherein said first surface of said media means is in contact with said dielectric reflector.

8) The device of claim 7 wherein said electric field control means further includes electron beam addressing means to deposit charge on said substrate.

9) The device of claim 1 wherein said media means comprises a silicone rubber.

10) An enhanced surface deformation type wavefront phase modulator target comprising: a substrate, reflective means integrally associated with said substrate, transmissive electrostatically deformable media means, said media means is a material selected from the group consisting of transmissive elastomers and transmissive viscoelastic substances, said media means further includes a first surface facing said substrate and a second surface opposite thereof, transmissive deformable conductor means affixed to said second surface of said media means, said media means is integrally associated with said substrate, said second surface of said media means is opposite said reflective means.

11) The device of claim 10 further including electric field control means to apply electrostatic forces to said conductor means, means operatively associated with said control means varying said electrostatic forces which vary the deformation of said conductor means and said media means thereby phase modulating a wavefront incident on said conductor means, at least a portion of said wavefront traverses said media means impinging on and reflected by said reflective means to again traverse said media means and issue from said modulator.

12) The device of claim 11 further including a schlieren means to transform said phase modulated wavefront to a wavefront having identifiable irradiance characteristics.

13) The device of claim 12 further including a viewing screen to view said wavefront having said identifiable irradiance characteristics.

14) The device of claim 13 wherein said reflective means is a reflective element selected from the group consisting of dielectric reflector(s) affixed to said substrate and reflective electrode(s) affixed to said substrate and total internal reflection dependent on the index of refraction of said substrate. 15) The device of claim 14 wherein said reflective element is a total internal reflection dependent upon the index of refraction of said substrate.

16) The device of claim 15 wherein said first surface of said media means is in contact with said substrate.

17) The device of claim 16 wherein said electric field control means further includes electron beam addressing means to deposit charge on a surface of said substrate which is opposite said media means.

18) An enhanced surface deformation type wavefront phase modulator comprising: a substrate, reflective means integrally associated with said substrate, transmissive electrostatically deformable media means, said media means is a material selected from the group consisting of transmissive elastomers and transmissive viscoelastic substances, said media means further includes a first surface facing said substrate and a second surface opposite thereof, transmissive deformable conductor means affixed to said second surface of said media means, said media means is integrally associated with said substrate, said second surface of said media means is opposite said reflective means, electric field control means to apply electrostatic forces to said conductor means, means operatively associated with said control means varying said electrostatic forces which vary the deformation of said conductor means and said media means thereby phase modulating a wavefront incident on said conductor means and traversing said media means and impinging on and reflected by said reflective means to again traverse said media means and issue from said modulator.

19) The device of claim 18 wherein said reflective means is a total internal reflection dependent on the index of refraction of said substrate, said first surface of said media means is in contact with said substrate.

20) The device of claim 19 wherein said control means comprises electron beam means to deposit electronic charge on said substrate.