Abstract:
In one aspect, an illumination device for illuminating a desired portion of a target object includes a light source and one or more diffractive, holographic optical elements disposed in an optical path between said light source and the target for forming a discrete illumination field on the target. In a further aspect, a method for illuminating a desired portion of a target object to be illuminated includes providing a source of light and arranging a diffractive, holographic and diffractive optical element in an optical path between said source of light and said target. The optical element is configured to deliver a selected pattern of light to an illumination field at a selected working distance away from the combined holographic and diffractive optical element. A target object to be illuminated is positioned in the optical axis at a distance approximately equal to said working distance.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit under 35 U.S.C. § 119(e) of U.S. provisional application Serial No. 60/327,210 filed Oct. 4, 2001. Said provisional application is incorporated herein by reference in its entirety. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0002]    In the accompanying drawings:  
           [0003]    [0003]FIG. 1 is a cross-sectional view of an exemplary ring illuminator according to one aspect of the present invention;  
           [0004]    [0004]FIG. 2 is a perspective view of the ring illuminator shown in FIG. 1;  
           [0005]    [0005]FIG. 3 is an exploded view of the ring illuminator shown in FIGS. 1 and 2;  
           [0006]    [0006]FIG. 4 is a fragmentary view of the ring illuminator shown in FIGS.  1 - 3 ;  
           [0007]    [0007]FIG. 5 is a perspective view of a generally donut-shaped hybrid diffractive and holographic optical element with a pattern type;  
           [0008]    [0008]FIG. 6 illustrates a sleeve incorporating an optical element in accordance with a further aspect of the present invention;  
           [0009]    [0009]FIGS. 7 and 8 illustrate an illumination system operable for both machine vision alignment and photo-induced bonding applications;  
           [0010]    [0010]FIG. 9 is an enlarged, fragmentary view of the combined illumination/photocuring system of FIGS. 7 and 8;  
           [0011]    [0011]FIG. 10 shows an off-axis illuminator in accordance with yet a further aspect of the present invention including a beam splitter and hybrid diffractive and holographic optical element; and  
           [0012]    [0012]FIG. 11 shows a dual-sided hybrid HOE element for use with the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS  
       [0013]    With reference to FIGS.  1 - 4 , there is shown an exemplary ring illumination device  10  according to the present invention for illumination an object  12  to be observed, inspected, imaged, or the like. Exemplary surfaces  12  to be illuminated include, but are not limited to, circuit boards, integrated circuits, fiber optic devices, micro electro mechanical systems (MEMS), micro optic assemblies, and so forth.  
         [0014]    The present device finds utility in structuring light into a desired shape such as a geometric shape and directing the light to a desired location to produce a uniform or pseudo-uniform illumination field on an area of the surface to optimize illumination for all manner of viewing applications including, but not limited to, machine vision applications, imaging applications, human visual inspection, reading bar codes or other machine readable code, characters and so forth, applications involving high-speed strobe inspection of moving products along a production line, spectroscopic applications, manual or automated alignment or orientation of objects prior to processing, handling, machining, bonding, imaging and so forth, metrology, machine alignment, matching recognition, fiducial recognition and alignment, object recognition and inspection applications, and like applications.  
         [0015]    The device  10  includes an upper housing shell  14  and a base housing shell  24  adapted to house and/or support the other components of the invention. A fastener  28 , such as a set screw, clamp, or the like, is provided on the housing to aid in positioning the device  10 . A printed circuit board  16  is electrically coupled to a power source  50  or other power source such as a battery power source and has mounted thereon a plurality of light or illumination sources  18  radially spaced about an optical axis  20 .  
         [0016]    Although the light sources  18  are depicted in the exemplary embodiment as light emitting diodes, it will be recognized that any other light source may be utilized, including but not limited laser light sources, diode lasers, organic light emitting diodes (OLEDs), incandescent lamps, and so forth. The light sources  18  may be monochromatic or broad spectrum, uniform or nonuniform in intensity profile, dispersive or collimated, coherent or noncoherent, etc.  
         [0017]    The light sources  18  may be of the same wavelength or different wavelengths. For example, multiple wavelengths of illumination may be provided within a single illumination ring or array which may be selectively turned on and off to provide selectable wavelengths for different illumination activities or applications.  
         [0018]    In an alternative embodiment, the light sources may be located remotely of the device  10 , e.g., wherein one or more light sources are directed to the plurality of radially spaced apart positions via optical fiber(s), or the like.  
         [0019]    Although the light sources  18  are depicted as a circular array, it will be recognized that arrays of any configuration or shape may be employed, such as rectangular or other geometric shape, or any other desired shape or pattern.  
         [0020]    The base  24  includes a plurality of openings  26  radially spaced apart about an opening  22  centered about the optical axis  20 , each in alignment with an adjacent light source  18 . The housing of the device  10  supports diffractive optics comprising a plurality of individual holographic optical elements (HOEs)  30  disposed at each aperture  26 .  
         [0021]    Although the present invention will be described in reference to the preferred embodiments wherein the diffractive optics comprise individual holographic elements, e.g., that are computer generated, it will be recognized that diffractive Fresnel zone plate designs that mimic standard geometric optics, with the added attributes of being able to direct the beam at specific angles to illuminate a desired target region, may also be employed.  
         [0022]    In certain embodiments, hybrid diffractive and holographic optical elements  30  are contemplated. Referring now to FIG. 11, a hybrid optical element  30  operable to embody the present invention includes a diffractive zone plate design or pattern formed on a first surface  32  of the element  30  and hologram such as a computer-generated hologram formed on a second surface  34  of the element  30  opposite the first surface. Alternatively, in still other embodiments, the hologram and diffractive pattern can be combined onto a single surface of the element  30 .  
         [0023]    With continued reference to FIGS.  1 - 4 , each HOE  30  receives light from the light source  18  and directs and shapes the light beam onto the target  12 , thereby providing uniform illumination of the target  12  from multiple directions. Depending on the particular application, the HOE  30  may be a commercially available optical element, or, may be customized to a particular application.  
         [0024]    The HOE optical elements  30  are selected in accordance with specific working and intensity distribution requirements as dictated by the end use. The hybrid holographic diffractive optical element  30  incorporates computer-generated holographic and diffractive elements to form a selected illumination pattern or structure, e.g., a selected field size and working distance matched to a focal length or operational working distance of an optical visions system and/or the working distance of a light source used for photo curing of light-sensitive bonding materials.  
         [0025]    Commercially available HOE optical elements may be employed in connection with the present invention, or, they may be created by standard or customized, computer-generated holographic/diffractive mathematical equations. The optical elements  30  may be formed from any optical material, selected to allow for transmission of the particular wavelengths of interest, such as gallium arsenide, gallium phosphide, germanium, zinc selenide, zinc sulfide, glass, fused silica, quartz, borosilicate glass (e.g., Pyrex®), polymeric materials such as Lexan®, polycarbonate, and the like. The elements  30  may be formed via any process for creating the desired surface relief pattern, including, for example, standard semiconductor lithography and etching techniques, embossing, molding techniques, such as injection molding, and so forth.  
         [0026]    The elements  30  are selected to tailor the light to a selected or desired beam shape, profile, direction, and working distance onto a selected target  12 . In a preferred embodiment, the optical elements  30  are removable and may be exchanged for use with multiple applications.  
         [0027]    In certain embodiments, the present invention may be achieved by replacing the standard diffusion optics of a conventional ring illumination with the HOE elements  30  in accordance with the present invention. Alternatively, the HOE elements  30  are employed with a customized light source.  
         [0028]    In the depicted embodiment, the device  10  further includes a central opening or aperture  36  aligned with the optical axis  20  of viewing optics  38 , which receives light reflected from the object  12  to be imaged, inspected, etc. The viewing optics  38  may include, for example, a camera, video camera, CCD array, film camera, digital camera, microscope, photomultiplier tube array, or other photosensitive array.  
         [0029]    The illumination field provided by the present invention can be formed into specialized shapes and specified working distances away from the HOE  30  array. With specific reference to FIG. 2, there appears some exemplary illumination shapes which may be achieved employing the illumination device in accordance with the present invention. Exemplary embodiments include circular- or disc-shaped ( 40 ), ring-shaped ( 42 ), rectangular ( 44 ), and rectangular ring-shaped ( 46 ), illumination patterns. However, it will be recognized that virtually any geometric shape, irregular shapes, or regular or irregular discontinuous pattern may be achieved by the present invention. Likewise, for any pattern, a desired intensity profile may be achieved, i.e., uniform or pseudo uniform (or some otherwise desirable intensity profile). For example, the beam shape and intensity profile may be selected to provide optimum illumination for specific machine vision, photo bonding, or other applications.  
         [0030]    In certain embodiments, the formation of a discontinuous pattern of structured light allows the simultaneous illumination of several specific sites, such as several specific sites within the field of view of a vision system for inspection, or, for allowing the photo curing of light activated adhesives and/or bonding agents at specific positions over a part or parts of a device to be bonded.  
         [0031]    With reference now to FIG. 5, there is shown an alternative embodiment in which the HOE elements  30 ′ are integral with a base portion  24 ′, and which may be interchanged with the base housing portion  24  and elements  30  of FIGS.  1 - 4 . For example, the base plate  24 ′ may be formed of a polymeric or other optical material with the elements  30 ′ stamped, etched, or molded directly thereon. In the same manner as described above by way of reference to FIGS.  1 - 4 , the integral base  24 ′ and elements  30 ′ the base plate  24 ′ may optionally have a diffractive pattern and a holographic pattern disposed on opposing sides thereof, or, optionally, hologram and diffractive patterns may be superimposed on a single surface of the base plate  24 ′.  
         [0032]    With reference to FIGS.  1 - 5 , it may be desirable to observe and/or image fluorescent emission from the target object  12 . In such cases, a spectral filter can optionally be provided along the optical axis  20  which blocks the laser illumination light wavelength and which passes the fluorescent emission light to the viewing optics  38 .  
         [0033]    Referring now to FIG. 6, a beam-shaping or wave front enhancement device  60  in accordance with a further aspect of the present invention includes a sleeve  62  that is incorporated or slipped onto the end of an illumination source  64  to structure light from the source  64  into a desired illumination pattern  66  via a holographic optical element  68 . In the depicted embodiment, the illumination source  64  is a fiber optic that is used to transport light, e.g., ultraviolet radiation for photo curing light-sensitive adhesives for bonding applications. The element  68  may be as described above by way of reference to the element  30  (FIGS.  1 - 4  and  11 ).  
         [0034]    The sleeve  62  may be removably attached to the source  64  and exchanged to provide for different illumination fields and use in different applications. For example, in the illustrated embodiment, the sleeve  62  may be replaced with a sleeve  62 ′ or  62 ″, for example, having elements  68 ′ and  68 ″, respectively, to provide selected illumination fields  66 ′ and  66 ″, respectively. As set forth above, any geometric shape or irregular shape is contemplated, including rings or bands, continuous and discontinuous illumination fields, as well as various intensities and intensity profiles, angles, and working distances.  
         [0035]    Referring now to FIGS.  7 - 9 , a combined light curing and machine vision system  70  is shown which incorporates both imaging and photobonding operations into a single system which allows optimized illumination for precise vision inspection, alignment and subsequent photo bonding of components within the field of view of a camera scope system, e.g., on automated assembly or automated bonding system work piece. The light curing system  70  may be, for example, of a type used for bonding optical fiber  72  to a target region  74  of a waveguide material  76 , such as a polymer or solid state waveguide devices, or, similar fiber optic bonding or fiber attachment processes used in the communications market.  
         [0036]    The system  70  includes a gripper  78  which moves the fiber  72  within a field of illumination  84  shaped using an illumination device  80  incorporating a HOE element  82  in accordance with this teaching. In certain embodiments, the illumination device may be a ring illuminator incorporating HOE elements, such as ring illuminator as described above by way of reference to FIGS.  1 - 5 . Alternatively, an illuminator employing a single light source is also contemplated.  
         [0037]    The illumination device  80  may be used in conjunction with viewing optics  86  and imaging electronics  88  such as a camera, CCD or other photo sensor array, or the like, and a computer-based information handling system  90  for the automatic, optimal alignment of the fiber  72  to the waveguide substrate  74 . Once the fiber  72  is optimally positioned, the illumination system  80  provides an optimized illumination field  84  to bond the fiber to the waveguide material, e.g., using a photo-sensitive or photo-activated adhesive or bonding materials.  
         [0038]    The same wavelengths of light may be used for both the alignment and bonding operations. In preferred embodiments, the light source is an ultraviolet (UV) source, most preferably UV light in the range between about 150 nm to about 465 nm. Most preferably, the light source is a pulsed laser source with a pulse width ranging on the order of nanoseconds to milliseconds, depending on the radiation source.  
         [0039]    When the illumination system  80  includes multiple light sources, such as a ring illuminator of a type detailed above, the machine vision optics may view the target along an optical axis passing centrally between the plural light sources. However, an illumination system  80  having a single illumination source is also contemplated, e.g., wherein the sensing optics are located adjacent to the light source and the HOE  82 .  
         [0040]    Light sources of differing wavelengths may be selectively employed for alignment purposes and for bonding purposes, e.g., wherein the light of an appropriate wavelength is selectively actuated by the computer system  90  under preprogrammed control.  
         [0041]    In still a further embodiment, the illumination device  80  carrying the HOE  82  may be used solely for the bonding illumination and wherein the illumination used for the automatic alignment of the fiber  72  may use a separate light source, ambient lighting, etc. Likewise, the optics used for the automated alignment may be incorporated into or optically coupled to the illumination device  80  or may be separately located therefrom. Finally, in still another embodiment, the machine vision viewing optics may be optically coupled to the fiber  72  itself for the automated alignment, with the illumination device  80  providing the bonding illumination and, optionally, providing illumination for the machine vision alignment.  
         [0042]    Referring now to FIG. 10, there appears an illumination system  100  according to yet a further embodiment of the present invention. A light source  102  such as a laser light source directs light along a first axis  104 . A lens or other optical element  106  may be used to focus or expand the beam and/or to provide a collimated beam, etc., which is then transmitted to a HOE element  108  which is designed to produce a patterned or shaped illumination field  110  which is uniform or otherwise has desired intensity characteristics at a desired or selected operational working distance  112  therefrom. The HOE  108  may be as described above.  
         [0043]    The beam producing the desired illumination field  112  is folded, e.g., 45 degrees, by a beam splitter, dichroic mirror, or the like  114 , along an optical axis  116  onto the target object  118  to be illuminated. Viewing optics  120 , such as a camera, microscope, etc., as described are used to view and/or image the illuminated target  118  along the optical axis  116 .  
         [0044]    With continued reference to FIG. 10, in certain embodiments wherein fluorescent emission from the target object  118  is to be observed, the beam splitter  118  may be a dichroic mirror which reflects and/or blocks passage of the incident radiation and which passes the fluorescence radiation. Additionally or alternatively, a spectral filter can optionally be provided along the optical axis  116  between the beam splitter  114  and the viewing optics  120  which blocks the laser illumination light and passes the fluorescent emission light to the viewing optics, e.g., for forming an image of the fluorescent emission.  
         [0045]    Although the HOE in accordance with this teaching has been described in reference to transmissive optical elements, it will be understood that the reflective HOE optical elements can also be employed. For example, the optical elements can be coated to allow for reflection and still retain their diffractive properties. In cases where the illumination light source cannot be readily placed behind the HOE element, it will be understood that reflective configurations may be employed.  
         [0046]    Likewise, it will be recognized that any further means of delivering or steering the light energy to the sample may be used, including prisms, mirrors, lenses, optical fibers, optical crystals, filters, and the like, and any arrangements, combinations, and/or equivalents thereof.  
         [0047]    The invention has been described with reference to the preferred embodiment. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.