Abstract:
An apparatus including: a first conductive layer extending between opposed ends and at a reference potential; a second conductive layer extending widthwise between first and second ends and apart from the first conductive layer and including a resistive layer, substantially uniform between the first and second ends, such that a voltage potential applied across the second conductive layer ranges uniformly across the width of the second conductive layer from a first voltage potential at the first end to a second voltage potential at the second end; a liquid crystal layer between the first and second conductive layers to variably shift a phase of light incident thereto linearly based upon a voltage potential across the first and second conductive layers; and a diffraction grating extending between first and second ends and adjacent to one of the first and second conductive layers, the diffraction grating receiving and diffracting the phase shifted light.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 62/132,434 filed on Mar. 12, 2015, the contents of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates generally to methods and devices for projecting scanning patterns over objects, and more particularly to methods and devices to generate diffraction based structured light scanner using liquid crystal phase modulation. 
         [0004]    2. Prior Art 
         [0005]    Projection of diffraction based structured light onto a target is a widely employed method in 3D imaging devices. One main advantage of such scanning systems is that they do not require optical reflection lens systems and that they can provide sharp patterns regardless of the projecting distance. However, to spatially move the projected pattern over the object, such as in a scanning type of motion, actuated mirror motion systems of different types have generally been employed to change the direction of light direction. Such mirror systems require moving parts and generally suffer from relatively slow response time, large size, and high actuation energy requirement. 
         [0006]    For example, U.S. Pat. No. 8,662,707, titled “Laser Beam Pattern Projector” discloses a device which projects structured light that is generated using a diffractive element, while scanning of the projected pattern is achieved using mechanically driven mirrors. 
         [0007]    In general, for high precision 3D imaging, it is highly desirable to project various scanning patterns onto the object. It is also highly desirable that the scanning is not mechanical, so that it can be done at high speeds and issues such as wear and component breakage and the like are eliminated. The devices can also be made to withstand accidental drops and vibration significantly better. 
       SUMMARY 
       [0008]    A need therefore exists for methods and devices for projecting scanning patterns over objects in which mechanical means are not used to generate the scanning motion of the projected patterns. 
         [0009]    An objective is to provide new methods and related devices for projecting scanning patterns over objects. The developed methods and devices are optical and use a diffraction technique and use novel techniques to achieve pattern scanning using liquid crystal layers with specifically designed electrode layers. 
         [0010]    Accordingly, a scanning apparatus is provided. The scanning apparatus comprising: a first conductive layer extending between opposed ends and being at a reference potential; a second conductive layer extending widthwise between opposed first and second ends and situated apart from the first conductive layer, the second conductive layer comprising a resistive layer having a resistivity which is substantially uniform between the first and second ends of the second conductive layer such that a voltage potential applied (V) across the second conductive layer will range uniformly across the width of the second conductive layer from a first voltage potential (V 1 ) at the first end to a second voltage potential (V 2 ) at the second end; a liquid crystal layer situated between the first and second conductive layers and configured to variably shift a phase of light incident thereto linearly based upon a voltage potential across the first and second conductive layers; and a diffraction grating extending between first and second ends and situated adjacent to one of the first and second conductive layers, the diffraction grating configured to receive the phase shifted light from the liquid crystal layer and diffract the phase shifted light. 
         [0011]    The apparatus can further comprise a voltage source which generates the voltage potential (V) as a time varying voltage so as to generate a continuously varying phase shift across the liquid crystal layer. 
         [0012]    The apparatus phase shifted diffracted light can project a pattern on an object. The voltage potential (V) cam be varied as a function of time so as to scan the surface of the object with the pattern. 
         [0013]    The diffraction grating can comprise a reflective diffraction grating. The diffraction grating can reflect the phase shifted light back through the liquid crystal layer. 
         [0014]    The diffraction grating can comprise a reflective diffraction grating that is coupled to receive the phase shifted light and reflect the phase shifted light back through the liquid crystal layer for a second phase shifting. 
         [0015]    The apparatus first and second conductive layers can be transparent to pass light incident thereto. 
         [0016]    The first and second conductive layers can have at least one of an inductivity and a capacitance. 
         [0017]    Also provided is a scanning pattern projection apparatus, comprising: a first conductive layer extending between opposed ends defining a width and opposed edges defining a length, the first conductive layer being at a reference potential; a second conductive layer extending between opposed ends defining a width and opposed edges defining a length, the second conductive layer comprising a resistive layer having first through fourth electrodes each separate from each other and configured to receive first through fourth respective voltage potentials (V 1 , V 2 , V 3 , V 4 , respectively), the second conductive layer having a resistivity which is substantially uniform across the length and width thereof such that voltage potentials range uniformly across the width and across the length of the second conductive layer; a liquid crystal layer situated between the first and second conductive layers and configured to variably shift a phase of light incident thereto linearly based upon distributed voltage potentials across the first and second conductive layers; and a diffraction grating extending between first and second ends and situated adjacent to one of the first and second conductive layers, the diffraction grating configured to receive the phase shifted light from the liquid crystal layer and diffract the phase shifted light. 
         [0018]    The first through fourth voltage potentials (V 1 , V 2 , V 3 , V 4 , respectively) can be varied over time in accordance with a voltage profile. The first through fourth voltage potentials (V 1 , V 2 , V 3 , V 4 , respectively) can be varied over time to scan an object using the projected pattern. The projected pattern can be shifted based upon relative magnitudes of the first through fourth voltage potentials (V 1 , V 2 , V 3 , V 4 , respectively). The first through fourth voltage potentials (V 1 , V 2 , V 3 , V 4 , respectively) can be varied over time to spatially shift the projected pattern over time. The first through fourth voltage potentials (V 1 , V 2 , V 3 , V 4 , respectively) can be varied over time to generate a two-dimensional scanning pattern projected onto an object. 
         [0019]    The first through fourth voltage potentials (V 1 , V 2 , V 3 , V 4 , respectively) can be varied such that V 2 −V 1 =V 4 −V 3 . 
         [0020]    The diffraction grating can have a diffraction grating pattern configured so that the diffracted phase shifted light is projected to form a circular or grid pattern on an object. 
         [0021]    The first through fourth electrodes can be located at first through fourth corners, respectively, of the second conductive layer. 
         [0022]    The phase shifted diffracted light can project a pattern on an object. The at least one of the first through fourth voltage potentials (V 1 , V 2 , V 3 , V 4 , respectively) can be varied as a function of time so as to scan a surface of an object with the diffracted phase shifted light projected as a pattern. 
         [0023]    Still further provided is an apparatus, comprising: a plurality of scanning projection devices, each scanning projection device situated adjacent to another of the plurality of scanning projection devices and comprising: a first conductive layer extending between opposed ends and being at a reference potential; a second conductive layer extending widthwise between opposed first and second ends and situated apart from the first conductive layer, the second conductive comprising a resistive layer having a resistivity which is substantially uniform between the first and second ends of the second conductive layer such that a voltage potential (V) applied across the second conductive layer will range uniformly across the width of the second conductive layer from a first voltage potential (V 1 ) at the first end to a second voltage potential (V 2 ) at the second end; a liquid crystal layer situated between the first and second conductive layers and configured to variably shift a phase of light incident thereto linearly based upon a voltage potential across the first and second conductive layers; and a diffraction grating extending between first and second ends and situated adjacent to one of the first and second conductive layers, the diffraction grating configured to receive the phase shifted light from the liquid crystal layer and diffract the phase shifted light. 
         [0024]    The plurality of scanning projection devices can be arranged in a linearly pattern. The voltage potential (V) applied across each scanning projection devices can phase shift the phase shifted light by a phase offset (Δφ 1 ). 
         [0025]    The voltage potential (V) applied across the second conductive layer of at least two of the scanning projection devices can be equal so as to obtain the same slope of a wave front. 
         [0026]    The voltage potential (V) applied across the second conductive layer of at least two of the scanning projection devices can be varied to obtain a desired phase shift profile. 
         [0027]    The phase shifted diffracted light can project a pattern on an object. The at least one voltage potential (V) of at least one of the plurality of scanning projection devices can be varied as a function of time so as to scan a surface of an object with a pattern formed by a projection of the diffracted phase shifted light. 
         [0028]    The first and second conductive layers can have at least one of an inductivity and a capacitance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    These and other features, aspects, and advantages of the apparatus of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0030]      FIG. 1A  illustrates the schematic of the first embodiment of a scanning pattern projection device. 
           [0031]      FIG. 1B  illustrates the voltage profile along the width of the resistive conductive layer of the first embodiment of  FIG. 1A  of the scanning pattern projection device. 
           [0032]      FIG. 1C  illustrates projected scanning pattern obtained with the first embodiment of  FIG. 1A  of the scanning pattern projection device. 
           [0033]      FIGS. 2A and 2B  show first and second examples of possible diffraction gratings that can be used in the diffractive layer of the embodiment of  FIG. 1A . 
           [0034]      FIG. 3  illustrates the process of diffraction of a coherent light source by a diffraction grating element and the line (strip) patterns formed over an object. 
           [0035]      FIG. 4  illustrated the schematic of another embodiment of the scanning pattern projection device that uses a diffractive element in reflection configuration. 
           [0036]      FIG. 5  illustrates an isometric view of the schematic of the first embodiment of the scanning pattern projection device of the present invention shown in  FIG. 1A . 
           [0037]      FIG. 6  illustrates the voltage profile along the width and length of the electrically resistive conductive layer of the embodiment of  FIG. 5  of the scanning pattern projection device. 
           [0038]      FIG. 7  illustrates an example of scanning projected patterns, in this case concentric circular strips, using appropriately provided diffraction grating patterns with the embodiment of  FIG. 5 . 
           [0039]      FIG. 8  illustrates another example of scanning projected pattern, in this case a grid pattern, using appropriately provided diffraction grating patterns with the embodiment of  FIG. 5 . 
           [0040]      FIG. 9  illustrates the cross-sectional view of two scanning pattern projection device sections for achieving larger angle between the incident wave front and the phase shifted wave front. 
           [0041]      FIG. 10  illustrates the cross-sectional view of a single device section of the scanning pattern projection device of  FIG. 9 , constructed as the diffractive element in reflection configuration as illustrated in  FIG. 4 . 
           [0042]      FIG. 11  illustrates the method of achieving a continuous phase shifting across multiple sections of scanning pattern projection device by providing an appropriate amount of phase offset between each two section of the device. 
           [0043]      FIG. 12  illustrates an alternative method of achieving a continuous phase shifting across multiple sections of scanning pattern projection device by providing two top and bottom electrically resistive electrode layers for each section of the scanning pattern projection device an applying an appropriate varying voltages to both electrode layers. 
           [0044]      FIG. 13  shows an example of the possible phase shifting profile along the width of a section of a scanning pattern projection device obtained by varying the electrical resistivity of the conductive layer over different sections of the device. 
           [0045]      FIG. 14  shows an example of the possible phase shifting profile along the width of a section of a scanning pattern projection device obtained by varying the thickness of the liquid crystal layer along the width of a section of the device. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0046]    A schematic of the first embodiment  10  of the scanning pattern projection device is shown in the schematic of  FIG. 1A . In  FIG. 1A  a cross-sectional view of the embodiment  10  is shown. The embodiment  10  is considered to be planar and extend a certain length perpendicular to the cross-sectional view of  FIG. 1A . 
         [0047]    As can be seen in  FIG. 1A , the embodiment  10  consists of a liquid crystal layer  14 , which is sandwiched between a highly conductive electrode layer  12  and the electrode layer  11 , which is considered to have a relatively high electrical resistivity. Both electrode layers  11  and  12  are considered to be transparent to the passing incident light  15 . Hereinafter, the incident light is considered to be coherent, monochromic and parallel. The highly conductive electrode layer  12  is grounded, such as at ground  13 , as shown in  FIG. 1A . A diffractive element layer  23 , which can have diffraction grating  63 , which can be made of identical, parallel, and equidistant grooves, such as those in  FIG. 2A , or multi-slit diffraction grating  64  such as those shown in  FIG. 2B , or any other grating types known in the art, which are considered to have infinite length, positioned over the surface of the electrode layer  11 . For the gratings, the only parameter to be defined is the periodicity α, which is the separation of two neighboring grooves,  FIG. 2A  (or multi-slit diffraction grating,  FIG. 2B ). The optics of diffraction process with diffraction gratings is well known in the art. In  FIG. 3 , the relationship between angles θ diff  of the diffracted strips (line patterns projected on an object positioned in front of the diffraction grating element such as  23  in  FIG. 1A ) and the incident wave (light) front angle θ inc  are defined as 
         [0000]    
       
         
           
             
               
                 sin 
                  
                 
                     
                 
                  
                 
                   θ 
                   diff 
                 
               
               + 
               
                 sin 
                  
                 
                     
                 
                  
                 
                   θ 
                   inc 
                 
               
             
             = 
             
               p 
                
               
                 λ 
                 a 
               
             
           
         
       
     
         [0000]    where λ is the wavelength of the incident light and p is an integer. 
         [0048]    The ends  18  and  19  of the electrode layer  11  are connected to an electronic circuit to be described below such that a current can be induced to flow from one of the ends  18  of the electrode layer  11  to the other end  19 . As a result, for example when the voltage at the end  18  is V 1  and the current is flowing from end  18  to end  19 , then due to the electrically resistivity of the electrode layer  11 , the voltage will be reduced proportionally to a lower level V 2  at the end  19 . It will be appreciated by those skilled in the art that if the electrode layer  11  has a uniform electrical resistivity along the width of the layer from end  18  to end  19 , then the voltage will linearly drop from the level of V 1  to the level of V 2  along the width of the electrode layer  11  from one end  18  to the other end  19  as shown in the plot of  FIG. 1B . In which case, the electric field in the liquid crystal layer  14  between the electrode layer  11  and the highly conductive and grounded (or any reference voltage) layer  12  will be linearly varied from its end  16  to its other end  17 . As a result, the liquid crystal layer  14  will shift the phase of the incident light  15  decreasingly and in a linear manner from the one end  16  to the other end  17  as shown schematically by the dotted line  20 . The magnitude of the phase shift at the one end  16  of the liquid crystal layer  14  is dependent on the level of the voltage V 1 , while the slope of the phase shift drop line  20  and the magnitude of phase shift at the other end  17  (corresponding to the voltage V 2 ) of the liquid crystal layer  14  is dependent on the electrical resistance of the electrode layer  11 . 
         [0049]    As a result, the phase of the incident light  15  is changed continuously along the diffraction grating element  23  from the one end  16  to the other end  17  of the device embodiment  10  of  FIG. 1A . Now if the voltage V 1 =V 2 =0, i.e., if the phase shift of the incident light  15  along the width of the device  10  from the one end  16  to the other end  17  is the same (in this case zero). The diffraction grating element  23  will then cause line patterns  21  to be projected onto the surface of the object positioned certain distance in front of the device  10  as shown in  FIG. 1C . Now if the voltages V 1  and V 2  are applied to the ends  18  and  19 , respectively, of the electrically resistive electrode layer  11 , thereby causing a uniformly decreasing voltage along the width of the electrode layer  11  from the voltage V 1  at the end  18  to the voltage V 2  at the other end  19  of the said electrode layer  11 , as shown in  FIG. 1B , then the phase of the incident light  15  is changed most at the end  16  of the device  10 , dropping linearly to its lowest shifting magnitude at the end  17  of the device  10 . As a result, the projected line patterns  21 ,  FIG. 1C , will be shifted a certain distance either to the right or to the left, such as shown as being shifted to the right in  FIG. 1C . It will be appreciated by those skilled in the art that the amount of shifting of the line patterns  21  to the right or left is dependent on the magnitude of the applied voltage V 1  and its drop to the voltage V 2 , which is made possible due to the electrical resistance of the electrode layer  11  along the width of the device  10  from its end  18  to its other end  19 , and the characteristics of the liquid crystal layer and the diffraction grating. 
         [0050]    It will be appreciated by those skilled in the art that the projected line patterns  21  will shift to the right if the applied voltage V 1  (to the end  18  of the electrode layer  11 ) is higher than the voltage V 2  applied to the end  19  of the electrode layer  11  as shown in  FIG. 1C . This is the case since the phase shifting is proportional to the applied voltage across the liquid crystal layer  14 ,  FIG. 1A , which would cause the wave front angle θ inc ,  FIG. 3 , to change accordingly. 
         [0051]    Hereinafter and for the sake of simplicity, the object over which the line patterns  21 ,  FIG. 1C , are projected is considered to be flat and parallel with the surface of the device  10 ,  FIG. 1A , i.e., parallel with the frontal surface of the diffraction grating layer  23  as shown in the schematics of  FIGS. 2A and 2B . 
         [0052]    As was described above, by applying the voltages V 1  and V 2  to the one end  18  and the other end  19 , respectively, of the electrically resistive electrode layer  11 , the projected line patterns  21 ,  FIG. 1C , are shifted to the right or left depending on the sign of the applied voltage V 1 , such as shown to be shifted to the right by the dashed lines  22  in  FIG. 1C  when the voltage V 1  is greater than the voltage V 2 . 
         [0053]    Similarly, by applying time varying voltage patterns V 1  and V 2  to the one end  18  and to the other end  19 , respectively, of the electrically resistive electrode layer  11 , the projected line patterns  21 ,  FIG. 1C , would shift to the right or left following the pattern of the applied voltages V 1  and V 2 . For example, by holding the voltage V 2  constant and applying a voltage level V 1  that varies as a sinusoidal function of time, then the projected line patterns  21  will similarly scan the object surface to the right and left (without any rotation) within a range determined by the amplitude of the sinusoidal voltage V 1 . It will be appreciated by those skilled in the art that the voltage V 1  may be varied over time using any arbitrary profile, and that the projected line patterns  21  would then similarly scan (i.e., shift to the right and left) over the object. It is also appreciated that one may choose to vary both voltages V 1  and V 2  as a function of time to obtain a desired scanning (shifting) of the light patterns  21  over the object. 
         [0054]    Using the schematic of  FIGS. 1A, 1B, 1C and 3 , one method for the design and operation of a device for projecting scanning line patterns over the surface of an object was described. In this method at least one coherent, monochromic and parallel incident light source is used. Then by generating a continuously varying electric filed across a liquid crystal layer through which the incident light is passed, a continuous phase shift is generated in the incident light before passing through a provided diffraction grating. Scanning of the projected line patterns over the object is then achieved by varying the electric field across the liquid crystal layer as a function of time as was previously described, thereby causing the projected line patterns to similarly shift (scan) over the projected object. 
         [0055]    The same method of generating a continuously varying electric field across a liquid crystal layer and thereby generating a continuously varying phase shift in the incident coherent, monochromic and parallel light along the width of the liquid crystal layer described above may be similarly used to generate a continuously varying phase shift on a diffractive grating element in reflection configuration. In such a device and as it is described below, a liquid crystal layer is similarly sandwiched between the phase control electrodes (similar to the electrode layers  11  and  12  in the embodiment  10  of  FIG. 1A ). The incoming coherent, monochromic and parallel incident light is then passed through the sandwiched layers, thereby achieving a first phase shift depending on the electric field generated between the electrode layers by the applied voltage as was previously described. The phase shifted incident light is then reflected by a reflective diffractive grating element that is positioned behind the sandwiched layers. The reflected incident light undergoes a second phase shift as it passes a second time thought the phase shifting liquid crystal layer and exits the device. By similarly applying a time varying voltage to one end of the electrically resistive electrode layer of the device, a continuously and linearly changing electric field is applied to the liquid crystal layer. The output light phases are thereby similarly modulated. Scanning line patterns are then similarly projected over the surface of an object as was previously described. The schematic of one such embodiment  30  of the scanning pattern projection device is shown in the schematic of  FIG. 4 . 
         [0056]    In  FIG. 4 , a cross-sectional view of the embodiment  30  is shown. The embodiment  30  is also considered to be planar and extend a certain length perpendicular to the cross-sectional view of  FIG. 4 . 
         [0057]    As can be seen in the schematic of  FIG. 4 , similar to the embodiment  10  of  FIG. 1A , the embodiment  30  also consists of a liquid crystal layer  31 , which is similarly sandwiched between a highly conductive electrode layer  32  and the electrically resistive electrode layer  33 . Similar to the electrode layer  11  of the embodiment of  FIG. 1A , the electrode layer  33  is considered to have a relatively high electrical resistivity, which for the sake of simplicity is considered to be uniform along the width of the device  30 . Both electrode layers  32  and  33  are considered to be transparent to the passing coherent, monochromic and parallel incident light  34 . The highly conductive electrode layer  32  is grounded at a certain point, such as at point  35 , as shown in  FIG. 4 . A reflective diffraction grating layer  36  is positioned behind the electrode layer  32 . The reflective diffraction grating layer  36  can be of a blazed grating type, however, other types of reflective gratings may also be employed. 
         [0058]    The one end  37  and other end  38  of the electrically resistive electrode layer  33  are connected to an electronic circuit to be described below such that a current can be induced to flow from the one of the ends  37 ,  38  of the electrode layer  33  to the other end  37 ,  38 . As a result, for example, when the voltage at the end  37  is V 1  and the current is flowing from the end  37  to the end  38 , then due to the electrically resistivity of the electrode layer  33 , the voltage will be reduced proportionally to a lower level V 2  at the end  38 . It will be appreciated by those skilled in the art that if the electrode layer  33  has a uniform electrical resistivity along the width of the layer from the end  37  to the end  38 , then the voltage will linearly drop from the level of V 1  to the level of V 2 ,  FIG. 4 , along the width of the electrode layer  33  from its end  37  to the end  38  similar to the plot shown in  FIG. 1B . In which case, the electric field in the liquid crystal layer  31  between the electrode layer  33  and the highly conductive and grounded (or any reference voltage) layer  32  will be linearly varied from its one end  39  to its other end  40 . As a result, the liquid crystal layer  31  will shift the phase of the incoming incident light  34  as well as the reflected incident light  41  decreasingly and in a linear manner from the one end  39  to the other end  40  of the device  30 . The magnitude of the phase shift along the length of the liquid crystal layer  31  during the passing of the incident light is dependent on the level of the voltages V 1  and V 2  as was previously described for the embodiment  10  of  FIG. 1A . It will, however, be appreciated that since the incident light is passed twice through the liquid crystal layer  31 , the device of the embodiment  30  of  FIG. 4  achieves twice as much phase shift and thereby twice as much shift in the projected line patterns as the device of the embodiment  10  of  FIG. 1C . 
         [0059]    If the voltage V 1 =V 2 =0, i.e., if the phase shift of the incoming incident light  34  as well as the phase shift of the reflected incident light  41  are the same (in this case zero) along the width of the device  30  from the one end  39  to the other end  40 , then the first set of line patterns similar to lines  21  shown in  FIG. 1C  will be projected onto the object positioned a certain distance in front of the device  30 . 
         [0060]    Then if voltage V 1  and a lower voltage V 2  are applied to the one end  37  and to the other end  38 , respectively, of the electrically resistive electrode layer  33 , thereby causing a uniformly decreasing voltage along the width of the electrode layer  33  from the voltage V 1  at the end  37  to the voltage V 2  at the other end  38  of the electrically resistive electrode layer  33  as shown in the plot of  FIG. 1B , then the phase of the incoming incident light  34  as well as the phase of the reflected incident light  41  are shifted most at the end  39  of the device  30 , dropping linearly to its lowest shifting magnitude at the end  40  of the device. As a result, the projected line patterns will be similarly shifted a certain distance either to the right or to the left, such as shown in  FIG. 1C , where the line patterns  21  are shifted to the right, as shown in  FIG. 1C . It will be appreciated by those skilled in the art that the amount of the shifting of the line patterns to the right is dependent on the magnitude of the applied voltages V 1  and V 2  and the characteristics of the liquid crystal layer and the diffraction grating and is twice as much as similar voltages V 1  and V 2  would achieve in the embodiment  10  of  FIG. 1A  since in the latter device, the incident light has passed twice through the phase shifting liquid crystal layer  31 . 
         [0061]    It will be appreciated that as was previously described for the embodiment  10  of  FIG. 1A , the line patterns  21  will be shifted to the right if the applied voltage V 1  is higher than the voltage V 2  and to the left if it is lower. 
         [0062]    By still considering the case in which the object over which the line patterns  21  are projected is flat and held parallel with the device  30 ,  FIG. 3 , i.e., parallel with the frontal surface of the electrode layer  33 , the projected line patterns  21  would similarly shift in parallel to the right or left depending on the applied voltages V 1  and V 2  as was described for the embodiment  10  of  FIG. 1C . 
         [0063]    Then as was described above for the embodiment  10  of  FIG. 1A , by applying time varying voltage patterns V 1  and V 2  to the ends  37  and  38 , respectively, of the electrically resistive electrode layer  33 , the projected line patterns  21 ,  FIG. 1C , would shift to the right or left following the pattern of the applied voltages V 1  and V 2 . For example, by holding the voltage V 2  constant and applying a voltage level V 1  that varies as a sinusoidal function of time, then the projected line patterns  21  will similarly scan the object surface to the right and left (without any rotation) within a range determined by the amplitude of the sinusoidal voltage V 1 . It will also be appreciated by those skilled in the art that the voltage V 1  may be varied over time using any arbitrary profile, and that the projected line patterns  21  would then similarly scan (i.e., shift to the right and left) over the object. It will also be appreciated that one may choose to vary both voltages V 1  and V 2  as a function of time to obtain a desired scanning (shifting) of the light patterns  21  over the said object. 
         [0064]    In the embodiments  10  of  FIG. 1A and 30  of  FIG. 4 , a time varying voltage level was generated along the length and over the surface of the electrically resistive electrode layer  11  ( 33 ) by applying the voltages V 1  and V 2  to one end (edges)  18  ( 37 ) and  19 ( 38 ), respectively, of the electrically resistive electrode layers. It will be, however, appreciated by those skilled in the art that varying voltage levels may be similarly generated along the widths as well as lengths of the electrically resistive electrode layers  11  and  33 . Such a method of applying a linearly varying voltage levels over the surface of an electrically resistive electrode layer such as the layer  11  ( 33 ) of  FIG. 1A  ( FIG. 3 ) is described below using a perspective view of the embodiment  10  of  FIG. 1A  is shown in the schematic of  FIG. 5 . 
         [0065]    In  FIG. 5 , an isometric view of the embodiment  10  of  FIG. 1A  is used to illustrate the embodiment  50  of the scanning pattern device. In the schematic of  FIG. 5 , the scanning pattern projection device  10  is shown to be configured to achieve phase shifting of the incident coherent, monochromic and parallel light over the two-dimensional plane of the liquid crystal layer  42  ( 14  in the embodiment  10  of  FIG. 1A ). As can be seen in  FIG. 5 , in the embodiment  50 , the (top) electrically resistive electrode  43  ( 11  in the embodiment  10  of  FIG. 1A ) is provided by four corner terminals  44 ,  45 ,  46  and  47  for applying voltages V 1 , V 2 , V 3  and V 4 , respectively, to the electrically resistive electrode  43 . 
         [0066]    As can be seen in the schematic of  FIG. 5 , similar to the embodiment  10  of  FIG. 1A , the embodiment  50 , its liquid crystal layer  42  is similarly sandwiched between a highly conductive electrode layer  48  and the aforementioned electrically resistive electrode layer  43 . Similarly and again for the sake of simplicity, the electrically resistive electrode layer  43  is considered to have a uniform resistivity over its entire surface. Both electrode layers  43  and  48  are considered to be transparent to the passing of coherent, monochromic and parallel incident light  49  ( 15  in the embodiment  10  of  FIG. 1A ). The highly conductive electrode layer  48  is grounded at a certain point, such as at ground  51 , as shown in  FIG. 5 . A diffraction grating layer  52  ( 23  in the embodiment  10  of  FIG. 1A ) is positioned over the electrically resistive layer  43 . 
         [0067]    As was previously indicated, the four corners of the electrically resistive electrode  43  are provided with terminals  44 ,  45 ,  46  and  47  which are connected to an electronic circuitry to be described below for applying voltages V 1 , V 2 , V 3  and V 4 , respectively, as shown in  FIG. 5 . As a result, for the considered uniform electrical resistivity of the electrode layer  43 , a linearly varying electric potential pattern is then distributed over the surface of the electrode layer  43 , as shown in  FIG. 6 . In which case, the electric field along the width and length of the liquid crystal layer  42  between the electrically resistive electrode layer  43  and the highly conductive and grounded (or any reference voltage) layer  48  will be similarly linearly varied. As a result, the liquid crystal layer  42  will shift the phase of the incoming coherent, monochromic and parallel incident light  49  proportionally to the applied varying electric field levels, the pattern of which corresponds to the pattern of the potential distribution of  FIG. 6  over the surface of electrically resistive electrode layer  43 , as shown in  FIG. 5  by the plane  53  for the incident light  54  that has passed through the liquid crystal layer  42 . The magnitude of the phase shift along the length and width of the liquid crystal layer  42  of the incident light  49  is dependent on the level of the voltages V 1 , V 2 , V 3  and V 4 ,  FIGS. 5 and 6 , as was similarly described for the embodiment  10  of  FIG. 1A . 
         [0068]    It will be appreciated by those skilled in the art that the diffraction grating layer  52 ,  FIG. 5 , may be designed to project a varieties of strip patterns. For example, circular hole patterns may be used to project a series of concentered circle strip patterns shown in solid lines  55  in  FIG. 7  over the object, which for the sake of simplicity is considered to be a flat plane and parallel to the plane of the diffraction grating layer  52 . Now by applying different voltages V 1 , V 2 , V 3  and V 4  to the terminals  44 ,  45 ,  46  and  47 , respectively, for example as shown in  FIG. 6 , the previously described phase shifting of the said incident light  49 ,  FIG. 5 , will cause the projected circle strip patterns  55  to be shifted depending on the relative magnitudes of the applied voltages, for example, as shown by dashed lines  56  and indicated by the shifting arrow  57  in  FIG. 7 . 
         [0069]    Another example of diffraction grating patterns that may be used for the diffraction grating layer  52 ,  FIG. 5 , is shown in the schematic of  FIG. 8 . In this example, diffraction grating layer  58  alone is shown (without the remaining components of the device of the embodiment  50  of  FIG. 5 ). The incident coherent, monochromic and parallel light  59  passing through the diffraction grating layer  58  (e.g., causing the diffracting light  61 ) will then project a two-dimensional grid pattern  60  over the aforementioned object as was previously described. Now by applying different voltages V 1 , V 2 , V 3  and V 4  to the terminals  44 ,  45 ,  46  and  47 , respectively, for example as shown in  FIG. 6 , the previously described phase shifting of the incident light  49 ,  FIG. 5 , will cause the projected grid pattern  60  to be similarly shifted to the right or left and/or up and down depending on the relative magnitudes of the applied voltages. 
         [0070]    It will be appreciated by those skilled in the art that the amount of the shifting of the circular strip patterns  55  of  FIG. 7  and the grid pattern  60  of  FIG. 8  are similarly dependent on the relative magnitudes of the applied voltages V 1 , V 2 , V 3  and V 4 ; the characteristics of the liquid crystal layer  42 , and the diffraction grating pattern,  FIG. 5 . 
         [0071]    It will also be appreciated by those skilled in the art that the voltage V 1 , V 2 , V 3  and V 4  may be varied over time using any arbitrary profile, and that the projected circular strip patterns  55  of  FIG. 7  and the grid pattern  60  of  FIG. 8  would then similarly generate a two-dimensional scanning (i.e., shift to the right and left and/or up and down) of the surface of the object. 
         [0072]    It will be appreciated by those skilled in the art that the phase shifting ability of a thin layer of liquid crystal such as those described for the above methods and devices for projecting scanning patterns over objects is rather limited and the resulting angle between the incident wave front and the phase shifted wave front is relatively small. Thus, multiple strips (sections) of scanning pattern projection devices, such as those shown in the cross-sectional views of  FIGS. 1A or 4 , can be assembled in series as shown in the cross-sectional view of  FIG. 9 . In the cross-sectional view of  FIG. 9  only two such sections of the device shown in  FIG. 4 , each with a width of L are shown to be provided. It is, however, appreciated by those skilled in the art as many such sections may be provided in a device to achieve the required span of the projected scanning pattern. 
         [0073]      FIG. 10  illustrates a cross-sectional view of a single device section of the scanning pattern projection device of  FIG. 9 . In the device of  FIG. 9  for projecting scanning patterns over objects, each section of the device is constructed as the diffractive elements that work in reflection configuration as illustrated in cross-sectional view  FIG. 4 . It is, however, appreciated by those skilled in the art that the device sections of the scanning pattern projection device of  FIG. 9  may also be constructed as described for the device of  FIG. 1A  for operation with through passing incident light. In either case, the incident light is considered to be coherent, monochromic and parallel. 
         [0074]    In the cross-sectional view of  FIG. 10 , all components of the device are considered to be as those described for the cross-sectional view of  FIG. 4 . In  FIG. 10 , the device section is shown to have a width of L, and a diffractive grating period of a. 
         [0075]    It will be appreciated by those skilled in the art that if the required deflective angle between the incident wave front and the phase-shifted wave front φ max  (as shown in  FIG. 10 ) and when the maximum phase shift angle for the liquid crystal layer can provide is φ max , then the length of device L has to be smaller than 
         [0000]    
       
         
           
             
               
                 L 
                 max 
               
               = 
               
                 
                   
                     φ 
                     max 
                   
                    
                   λ 
                 
                 
                   2 
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                   tan 
                    
                   
                       
                   
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                     ϕ 
                     max 
                   
                 
               
             
             , 
           
         
       
     
         [0000]    where λ is the wavelength of the incident coherent, monochromic and parallel light. It is also appreciated by those skilled in the art that the device can deflect wave front in both positive and negative direction, thereby the total deflection range is 2φ max , i.e., from −φ max  to φ max . 
         [0076]    For example, consider the case in which the maximum deflective angle between the incident wave front and the phase-shifted wave front is to be φ max  shown in  FIG. 10 . In this example, the incident light is considered to have a wavelength λ=633 nm, while the diffractive grating period is considered to be α=3.3μm (i.e., 300 lines per millimeter), which makes the diffraction angle for each grating,  FIG. 3 , for a 
         [0000]    
       
         
           
             
               θ 
               inc 
             
             = 
             
               
                 0 
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                 to 
                  
                 
                     
                 
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                 be 
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                    
                   
                     λ 
                     a 
                   
                 
                 = 
                 
                   11 
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                     ° 
                     . 
                   
                 
               
             
           
         
       
     
         [0000]    Thus, in order to scan the entire range, the deflected wave front angle range should not be less than less than 11° and therefore the deflective angle between the incident wave front and the phase-shifted wave front φ max  should not be less than 5.5° . It is noted that the current maximum phase shifting capability of liquid crystal layer φ max  is given to be 8 π. 
         [0077]    In the reflection configuration shown in  FIG. 10 , the light waves pass the liquid crystal layer twice, therefore the above currently available maximum phase shifting between the incident and the reflected light wave becomes 16 π. As a result, the maximum length of device section shown in  FIG. 10  to achieve full scan is given as 
         [0000]    
       
         
           
             
               L 
               max 
             
             = 
             
               
                 
                   
                     φ 
                     max 
                   
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                   λ 
                 
                 
                   2 
                    
                   π 
                    
                   
                       
                   
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               = 
               
                 53 
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                 μ 
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                   m 
                   . 
                 
               
             
           
         
       
     
         [0078]    It will also be appreciated by those skilled in the art that in order to generate a continuous phase shifting across multiple sections of a scanning pattern projection device,  FIG. 9 , and considering the practical limitations in achieving absolute phase shifting across each section, one has to provide for an appropriate phase offset between each pair of sections. In  FIG. 11 , the desired phase shifted wave front is shown with a dotted line  62  making a deflective angle between the incident wave front and the phase-shifted wave front φ. As can be seen in  FIG. 11 , the required continuous phase shifting indicated by the dotted line cannot generally be achieved between the first and second sections of the scanning pattern projection device. To achieve phase-shifted wave front continuity, a proper phase offset Δφ 1 ,  FIG. 11 , must be provided between the two sections of the scanning pattern projection device. It will be appreciated by those skilled in the art that the phase offset Δφ 1 =n 1 λ, where n 1  is an integer and λ is the wavelength. Similarly, phase shifted wave front continuity between other sections of the scanning pattern projection device is achieved, making the scanning pattern projection device capable of providing continuous phase shifting along all present sections of the device. It will be appreciated by those skilled in the art that to achieve the above continuous phase shifting across multiple sections of scanning pattern projection device,  FIG. 9 , the voltage difference V 2 -V 1  should be the same as the voltage difference V 4 -V 3 . And that the difference between the voltages V 3  and V 2  must be such that it would cause the phase offset Δφ 1 ,  FIG. 11 . Similarly, the voltage difference across all sections of scanning pattern projection device must be the same as the voltage difference V 2 -V 1 , while the voltage differences between the adjacent electrically resistive electrode top layers ( 33  in  FIG. 4 ) must be such that they would provide for the required aforementioned phase offsets between the adjacent sections to ensure a continuous phase shifting across multiple sections of scanning pattern projection device. 
         [0079]    It will also be appreciated by those skilled in the art that by varying the voltages V 1 , V 2 , V 3  and V 4  as a function of time in the embodiment of  FIG. 9  while keeping their aforementioned relationship to ensure continuous phase shifting, a desired scanning (shifting) of the light patterns  21 ,  FIG. 1C , over the projected object is obtained. 
         [0080]    In an alternative embodiment of that shown in  FIG. 12 , the top and bottom electrode sections (layers  33  and  32  in  FIG. 4 ) are made out of previously described electrically resistive electrode layers, otherwise they are constructed as the device of  FIG. 4 . The voltages to the electrically resistive electrode layers are then applied as described below to achieve a phase shifting as the one described for the embodiment of  FIG. 9  and shown in  FIG. 11 . It is noted that in the embodiment of  FIG. 9 , the voltages applied to each scanning pattern projection device section is controlled separately, i.e., for the case of the two sections shown in  FIG. 9 , the voltages V 1 , V 2 , V 3  and V 4  applied to the top electrically resistive electrode layer sections are controlled as was previously described while the opposite electrode layers are connected to a common ground, thereby generating the desired electric field gradient across the liquid crystal layer. In the embodiment of  FIG. 12 , however, shared voltages V 1  and V 2  are applied to the top electrically resistive electrode layers. And to provide for the aforementioned required phase shift offset between the device sections to achieve a continuous phase shifting along all sections of the scanning pattern projection device, bias voltages V 3  and V 4  are applied to the opposite electrodes as shown in  FIG. 12 . As a result, for a scanning pattern projection device constructed with n sections, it would only require n+2 voltage control signals to achieve a continuous phase shifting along all sections of the scanning pattern projection device. 
         [0081]    It will be appreciated by those skilled in the art that by varying the voltages V 1 , V 2 , V 3  and V 4  as a function of time in the embodiment of  FIG. 12  while keeping their aforementioned relationship to ensure continuous phase shifting, a desired scanning (shifting) of the light patterns  21 ,  FIG. 1C , over the projected object is obtained. 
         [0082]    It will also be appreciated by those skilled in the art that the voltages applied to the electrically conductive electrodes in all the above embodiments, for example the voltages V 1 , V 2 , V 3  and V 4  in the embodiments of  FIGS. 1A, 4, 5, 9, 10 and 12 , are relative to the device ground. 
         [0083]    In all the above embodiments, the electrically resistive electrode layers are considered to have a constant electrical resistance along the width and length of the electrodes and that the thickness of the liquid crustal layers to be also constant. It will be, however, appreciated by those skilled in the art that the electrical resistance of the electrically resistive electrode layers may also be varied along their width and/or along their lengths. As a result, a desired non-uniform voltage and thereby phase shifting can be obtained along the width and/or length of each electrode layer. For example, by providing different electrical resistivity on the electrically resistive electrode layers of two adjacent sections of a scanning pattern projection device such as the one shown in  FIG. 9 , each section would provide a different phase shifting profile along the width L of the section as shown in  FIG. 13 . It will also be appreciated by those skilled in the art that by varying the electrical resistivity of the different sections of a scanning pattern projection device along their width and/or length, the phase shifting profile over the entire surface of the scanning pattern projection device may be arbitrarily shaped, as long as they are monotonically decreasing due to the increasing total resistance from each high voltage end of the electrode. In the embodiment of  FIG. 13 , two self-coherent incident waves are shown to pass through the aforementioned adjacent two sections. As a result, two different diffraction patterns are projected onto the object surface. The difference between the deflected wave front of the two incident waves is controllable by varying the voltages applied to the electrically resistive electrode layers as was previously described to obtain the desired variation in the diffraction pattern. 
         [0084]    It will also be appreciated that similar variation in the phase shifting may be obtained by varying the thickness of the liquid crystal layer along the width and/or length of different sections of a scanning pattern projection device. One advantage of this method is that it can create a non-monotonically decreasing (increasing) phase shifting profile, as shown in  FIG. 14 . 
         [0085]    It will also be appreciated by those skilled in the art that the electrodes layers of the scanning pattern projection device sections besides being electrically resistive, may also be fabricated with combined inductance and/or capacitance and/or semiconductor characteristic. Such added electrical inductance or capacitances may be more local or may be distributed over certain region of the electrode layer to achieve certain regional pattern scanning effects. As a result, the scanning pattern projection device can be provided with a controllable dynamics phase shifting response by providing properly controlled input voltage excitations to the electrode layers. Noting that in the aforementioned embodiments, electrode layers were considered to have uniform resistivity along the width (and/or length) of the device sections considered, thereby causing the voltage to drop uniformly along the width (and/or length) of each section of the scanning pattern projection device. Then if, for example, a uniform inductance is provided over the conductive electrode layer, then the change in voltage along the width (and/or length) of each section of the scanning pattern projection device becomes proportional to the rate of change of the passing current at each point along the width (and/or length) of the section. In general and with the current technology, it is difficult to fabricate electrode layers with zero or even very low electrical resistivity. As a result, in general combinations of effects will be experienced depending on the resistivity and inductivity distribution over the surface of the electrode layer and the applied voltage profiles as a function of time in each section of the scanning pattern projection device. In practice, one may therefore design the electrode layers within their practical limitations to achieve optimal projected pattern scanning characteristics depending on the selected patterns and the application at hand. 
         [0086]    While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.