Abstract:
Methods and systems are disclosed related to optical elements. An apparatus for making an optical device can be configured to divide an angular pattern into a plurality of sub-angular regions. Then, micro-wedge configurations can be determined for directing light to the sub-angular regions. Subsequently, an array of micro-wedges can be generated according to the micro-wedge configurations, such that adjacent micro-wedges in the array have different configurations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C. § 120 on and is a Continuation of U.S. patent application Ser. No. 09/507,466 entitled “OPTICAL DEVICE, SYSTEM AND METHOD” filed on Feb. 22, 2000, which is incorporated herein by reference in its entirety.  
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to optics and optical systems and devices. The present invention also relates to a device for forming an homogenized light pattern. The present invention also relates to a method of making an optical device.  
       BACKGROUND OF THE INVENTION  
       [0003]     Known techniques for homogenizing light make use of arrayed micro-lenses, diffractive diffusers, ground glass diffusers, and holographically-generated diffusers. Micro-lens arrays homogenize light by creating an array of overlapping diverging cones of light. Each cone originates from a respective micro-lens and diverges beyond the focal spot of the lens. In the known arrays, the individual lenses are identical to each other. Ground glass diffusers are formed by grinding glass with an abrasive material to generate a light-scattering structure in the glass surface.  
         [0004]     Micro-lens arrays, ground glass diffusers and holographic diffusers all have the disadvantage of not being able to control the angular spread of the homogenized, diverging light. Light in general has an angular spread that is fairly uniform over a desired angular region, but the boundaries of the angular region are blurred. With the known diffuser methods, the energy roll-off at the edge of the desired angular spread can extend well beyond this region.  
         [0005]     Diffractive diffusers can be used to control the angular spread of the output light, but such diffusers are limited with respect to the amount of spread that they can impart to the output light. Due to fabrication limitations for short wavelength sources, visible or below, and limitations in the physics of the structures for longer wavelengths the maximum angular spread is limited. Further, diffractive diffusers used in their traditional binary form can include a significant amount of background energy and the patterns must be symmetric about the optical axis.  
         [0006]     Thus, there is a need for a device which can homogenize light while controlling a broad angular spread of the homogenized, diverging light beam. Additionally, there is a need for a method of making an improved device for homogenizing light.  
       SUMMARY OF THE INVENTION  
       [0007]     The disadvantages of the prior art are overcome to a great extent by the present invention. The present invention relates to an optical device formed of a plurality of optical elements. The elements may be used to direct portions of an incident light beam in predetermined, respective directions. The optical elements may be formed adjacent to each other in a two-dimensional array. Adjacent elements may have different shapes. The locations of the elements in the array may be essentially random with respect to the directions of the corresponding light beam portions.  
         [0008]     According to preferred embodiments of the invention, the optical elements may be formed of transparent or reflective materials. The output surfaces of the respective elements may be flat and planar or they may be curved and non-planar.  
         [0009]     According to another aspect of the invention, the optical device may be used to form an angular pattern. Alternatively, the device may be used to split the incoming beam into sub-beams.  
         [0010]     The present invention also relates to an optical system that has a light source and an optical homogenizing device. The optical device may be formed of a large number of micro-wedges. The wedges may be used to form respective non-adjacent portions of a desired angular pattern. In a preferred embodiment of the invention, adjacent wedges may be formed with different three-dimensional conjurations.  
         [0011]     The present invention also relates to a method of making a multi-faceted optical device. The method includes the steps of (1) dividing an angular pattern into sub-angular regions, (2) determining micro-wedge configurations for directing beam portions to the sub-angular regions, and (3) generating an array of micro-wedges, according to the determined configurations, such that adjacent wedges have different configurations.  
         [0012]     According to another aspect of the invention, the two-dimensional arrangement or ordering of the wedges in the device-array is essentially random with respect to the two-dimensional arrangement of the sub-angular regions in the pattern. According to this aspect of the invention, the respective micro-wedge configurations may be assigned to random locations in the array. Thus, the relative positions or order of the wedges in the array has essentially no relationship to the relative positions or order of the sub-angular regions in the pattern. According to yet another aspect of the invention, the output surface slopes for the micro-wedges are calculated by a programmed general-purpose computer based on the locations of the respective sub-angular regions in the desired pattern.  
         [0013]     In a preferred embodiment of the invention, appropriate phase tare surfaces may be used to divide the output surfaces of the micro-wedges into stepped or terraced surfaces, to thereby reduce the overall thickness of the optical device.  
         [0014]     According to yet another aspect of the invention, an optical homogenizing device is formed of a tiled array of sub-devices, where each sub-device has randomly arranged micro-wedges. The tiled device may be used, for example, to handle large diameter input beams.  
         [0015]     Thus, the present invention provides a method and apparatus for homogenizing a beam of light. The invention makes use of micro-structures in an array where each optical element or micro-wedge is different from its adjacent neighbor in size and slope. The array of different micro-wedges can homogenize light sources without the disadvantages of the prior art. Various combinations and alterations to the micro-wedge array may include: adding a phase bias to the micro-wedges to further scramble the incoming beam; and adding a lens function to the surface of the array or to the back surface of the device.  
         [0016]     The present invention may be used to homogenize light sources, perform beam splitting operations, and/or to redirect light in a given direction.  
         [0017]     These and other advantages and features of the invention will become apparent from the following detailed description of the invention which is provided in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a schematic perspective view of an optical system constructed in accordance with a preferred embodiment of the invention.  
         [0019]      FIG. 2  is a partial plan view of the optical device shown  FIG. 1 .  
         [0020]      FIG. 3  is a cross sectional view of the optical device of  FIG. 2 , taken along the line  3 - 3 .  
         [0021]      FIG. 4  illustrates a method of making the optical device of  FIGS. 2 and 3 .  
         [0022]      FIG. 5  is a perspective view of another optical device constructed in accordance with the present invention.  
         [0023]      FIG. 6  is a partial cross sectional view of yet another optical device constructed in accordance with the present invention.  
         [0024]      FIG. 7  is a partial cross sectional view of yet another optical device constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]     Referring now to the drawings, where like reference numerals designate like elements, there is shown in  FIG. 1  an optical system  10  constructed in accordance with a preferred embodiment of the invention. The optical system  10  has a light source  12  for generating a light beam  14 , and an optical device  16  for homogenizing the beam  14 . In operation, the device  16  may be used to form an angular pattern  18 . In the illustrated embodiment, the pattern constitutes the letter “H.” In alternative embodiments, the device  16  may be used to form a wide variety of patterns, including for example a split beam pattern.  
         [0026]     In a preferred embodiment of the invention, the optical device  16  is formed of an array of optical wedges  22 ,  24 . The wedges  22 ,  24  receive incident portions of the input beam  14  and direct the beam portions  46 ,  48  toward respective portions  50 ,  52  of the angular pattern  18 .  
         [0027]     As shown in more detail in  FIG. 2 , the optical device  16  may be formed of numerous square or rectangular-shaped micro-wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44 . Although only twelve wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  are shown in  FIG. 2 , the optical device  16  may have ten thousand or more wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  distributed randomly across its output surface. The configuration (i.e., three-dimensional shape) and slope of each wedge  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  may be different than the configuration and slope of each adjacent wedge  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44 . In a preferred embodiment of the invention, the wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  have flat, planar optical output surfaces ( FIG. 3 ). The present invention should not be limited, however, to the preferred embodiments shown and described herein in detail.  
         [0028]     In a preferred embodiment of the invention, the areas of adjacent wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  are made unequal by selecting the lengths of the edges  142  appropriately. As shown in  FIG. 2 , for example, the lengths L 1  and L 2  of edges (or boundaries)  142  extending in a first direction may be made not equal to each other (L 1 ≠L 12 ). Similarly, the lengths L 3  and L 4  of edges  142  that extend in the orthogonal direction may be made not equal to each other (L 3 ≠L 4 ). By constructing the wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  in different sizes by making their side edges  142  of different lengths, interference effects may be reduced.  
         [0029]     The arrows  60  in  FIG. 2  represent the direction of increasing thickness for the respective wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  (where thickness is measured in a direction perpendicular to the plane of the page). Thus, the first wedge  22  increases in thickness from left to right in  FIG. 2 , whereas the second wedge  24  increases in thickness from top to bottom as viewed in  FIG. 2 . A third wedge  26  increases in thickness in a direction toward the lower left corner of  FIG. 2 . A fourth wedge  32  increases in thickness in a direction toward the upper left corner of  FIG. 2 .  
         [0030]     Phase tare surfaces  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84  may be provided to reduce the overall thickness of the optical device  16 . Thus, the first wedge  22  is separated by a tare surface  70  into first and second portions  90 ,  92 . The slopes ( 60 ) of the first and second portions  90 ,  92  may be equal to each other. That is, the planar output surfaces of the first and second portions  90 ,  92  may be parallel to each other. Likewise, the second wedge  24  is separated by a tare surface  72  into first and second parallel portions  94 ,  96 . The slopes (designated by arrows  60 ) of the two portion  94 ,  96  may be equal to each other.  
         [0031]     The tare surfaces  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84  in effect operate to fold the output surfaces of the micro-wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44 . The tare surfaces  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84  may be especially useful when the slopes ( 60 ) of the wedge output surfaces are relatively great. The heights of the tare surfaces  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84  (measured in the direction from top to bottom as viewed in  FIG. 3 ) may be a function of the wavelength of the incident light, if desired. For example, the heights of the tare surfaces  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84  may be integer multiples of the wavelength of the incoming light beam  14 .  
         [0032]     As shown in  FIG. 3 , the phase tare surfaces  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84  may lie in planes that are essentially parallel to the propagation direction of the input beam  14 . In  FIG. 3 , the surfaces of the micro-wedges located behind the cross sectional line  3 - 3  are not shown for the sake of clarity of illustration. In other words,  FIG. 3  represents only a thin slice of the optical device  16  taken along the line  3 - 3 .  
         [0033]     In operation, the light source  12  transmits the input beam  14  toward the optical device  16 . The input beam  14  may have an uneven intensity distribution across its cross section. The beam  14  is directed onto the optical device  16  such that portions of the beam  14  are incident on respective wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44 . The wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  direct the beam portions  46 ,  48  in predetermined directions to form an homogenized angular pattern  18 . The homogenized pattern  18  may have a substantially uniform light intensity distribution. The beam portions  46 ,  48  are transmitted in different directions since each wedge  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  is different from its adjacent and neighboring wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  in size and/or slope ( 60 ). Thus, the light output  46 ,  48  of each wedge  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  is directed or angled toward a particular sub-angular region  50 ,  52  of the desired angular spread  18 . Although the angular spread or pattern  18  is shown as the letter “H” in  FIG. 1 , the optical device  16  also may be used to split the input light beam  14  and/or to form a variety of other patterns.  
         [0034]     Referring now to  FIG. 4 , a preferred method of making the optical device  16  includes the step of dividing the desired pattern  18  into small sub-angular regions (Step  150 ). The size of the incident beam  14  may be used to determine an appropriate number of sub-angular regions into which the pattern  18  should be divided. If the cross sectional area of the beam  14  is relatively large, then a relatively large number of sub-angular regions may be employed. If the cross,sectional area of the beam  14  is relatively small, then a relatively small number of sub-angular regions may be employed. Although only two sub-angular regions  50 ,  52  are shown in  FIG. 1  for the sake of clarity, the present invention may be practiced by dividing the entire pattern  18  in to ten thousand or more such sub-angular regions. The number of sub-angular regions may be related to the number of wedges to be formed in the optical device  16 .  
         [0035]     Then, using appropriate geometric calculations, a slope and a three dimensional configuration for each wedge is determined such that the wedge will direct a portion of the input beam to a respective sub-angular region (Step  152 ). Then, a location within the device  16  is randomly chosen for each calculated wedge configuration (Step  154 ). The random placement of the wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  in the optical device  16  causes the pattern  18  to have a uniform intensity. In other words, the random location of the wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  causes the input beam  14  to be homogenized.  
         [0036]     The output surfaces of the wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  may then be formed in a suitable substrate (e.g., glass) by gray scale photolithography, a suitable direct write method (e.g., electron beam or laser), or by another suitable technique (Step  156 ).  
         [0037]     If the number of sub-angular regions in the pattern  18  is less than the number of micro-wedges desired to be arrayed in the device  16 , then some of the wedges may have the same slope and size. The similar wedges will direct light energy to the same location or sub-angular region. However, the wedges with similar slopes, sizes and shapes are preferably not located adjacent one another.  
         [0038]     The illustrated optical device  16  may be used to increase the amount of angular spread in the pattern  18  while maintaining a well defined pattern boundary  158  ( FIG. 1 ). For example, at a wavelength of two hundred forty eight, nanometers, with efficiencies of from eighty five percent to ninety five percent, depending on the shape of the output pattern  18 , a half angle of approximately seven degrees is obtainable.  
         [0039]     In addition, the device  16  may be used efficiently over a broad wavelength band, including but not limited to white light. This is an advantage over diffractive diffusers since diffractive diffusers are tuned to a particular wavelength and have decreased efficiency at different wavelengths.  
         [0040]     According to another embodiment of the invention, an optical device  100  ( FIG. 5 ) may be formed of a tiled array of smaller devices  16 . The tiled device  100  may be used, for example, to handle large diameter input beams. The size of each tile  16  may be slightly different from the neighboring tiles  16  to eliminate interference effects that might otherwise be caused by a repeating pattern. The intensity of light transmitted through each tile  16  may be different, which may cause a slight change in the amount of energy imparted to each sub-angular region in the pattern  18 . This effect is reduced, however, by the random placement of wedges within each tile  16 .  
         [0041]     For certain desired angular regions, the number of sub-angular regions required to fill the region can be very large (for example, greater than ten thousand) which requires a very large number of micro-wedges. In these instances, the input beam  14  should have a small diameter to illuminate all portions of the tiles  16 . By decreasing the size of the individual micro-wedges, the input beam size can be reduced. The size of the wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  preferably should not be so small, however, as to cause the diffraction angle defined by the wedge apertures to become too great.  
         [0042]     As shown in  FIG. 6 , the output surfaces  130  of an optical device  16 ′ may have slight curvatures. The surfaces  130  may be spherical, parabolic or the like. The output surfaces  130  may be separated by tare surfaces, and discontinuities  132  similar to the tare surfaces and rectangular facet boundaries shown in  FIGS. 2 and 3 . The slight curvatures shown in  FIG. 6  produce narrow bands of angles instead of single angles. The illustrated curvatures can help to improve the filling of large angular patterns  18  with fewer facets in the optical device  16 ′. The embodiment shown in  FIG. 6  otherwise operates similarly to the embodiment shown in  FIGS. 1-3 .  
         [0043]      FIG. 7  displays an optical device  16 ″ employed in a reflection mode. In this embodiment, the input light  14  is propagated into a micro-wedge array  16 ″. A mirror coating  122  is used on the array output surfaces which reflects the input light  14  to direct beam portions  46 ′,  48 ′toward the respective portions of the desired pattern  18 .  
         [0044]     The present invention may also be employed with a phase bias device or an optical lens  140  as shown schematically in  FIG. 1 . The lens  140  may be separate from the optical device  16  or it may be constructed as an integral part of the optical device  16 . The lens  140  may be on either side of the micro-wedges  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44 . The lens  140  may be used, for example, to perform an optical Fourier-transform operation.  
         [0045]     According to yet another aspect of the invention, the facet boundaries  142  ( FIG. 2 ) of each micro-wedge  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 ,  44  may be randomized to further reduce the effects of discontinuities at the boundaries  142 .  
         [0046]     Reference has been made to preferred embodiments in describing the invention. However, additions, deletions, substitutions, or other modifications which would fall within the scope of the invention defined in the claims may be implemented by those skilled in the art without departing from the spirit or scope of the invention. Accordingly, the invention is not to be considered as limited by the foregoing description, but is only limited by the scope of the appended claims.