Abstract:
An automatic testing illumination system has advantages of speed, quick calibration ability and therefore high accuracy over conventional illuminators. An spherical light source/concentrator exit port is rapidly and sequentially covered by at least one automated device for affecting the light leaving the exit port. Automation enables a very rapid sequencing of light onto a two or three dimensional array to cut the time for test and evaluation, and to permit very accurate calibration of the illuminator system.

Description:
FIELD OF THE INVENTION 
     This application relates to the field of self contained, portable machines and test equipment for optical detectors, such as CCD and CMOS imaging devices, and more particularly to an automated, compact, efficient illumination system for use with a small integrating sphere which produces light having high spatial uniformity, high resolution MTF target to be used for characterizing the resolution of pixelized devices under test. 
     BACKGROUND OF THE INVENTION 
     One of the fastest growing segments of the electro-optic art involves the use of photo electric detector arrays used in cameras and detectors for consumers, machine imaging and inspection imaging. The advancement in this area has been so extensive and so rapid at the technically advanced side of the market that the technology has enabled individually owned electronic cameras to begin to supplant cameras which use film and chemical development. The more technical side of the electronic imaging industry continues to advance and demands ever increasing sensitivity to produce a product of ever increasing quality. Increased affordability is had through mass production and the lowering of production costs while keeping the product quality high. High product quality is absolutely dependent upon high level testing. 
     To consider a simple electronic camera as an example, the main component is a two dimensional electronic array, typically a silicon-based device having thousands of pixels of a size less than 20 micrometers each. In more advanced applications, the array may be a three dimensional electronic array having an ability to make further measurements on light waves which may have penetrated the surface and which may have interfered with each other, for example. The remaining parts of the camera are far less critical and include a lens, a focusing system for physically moving the lens, and computer memory storage. The quality and suitability of the two dimensional detector array will determine whether the camera will function properly. As it is the most expensive and critical component in the camera, if it is defective, the camera as a whole is virtually worthless. Further, if the optical chip can be identified as rejected or accepted at an early stage of manufacture, before further assembly costs, significant efficiency and cost savings can be attained. 
     The critical need is therefore to properly test two dimensional arrays with as much speed and accuracy as possible to eliminate the defective components very early in the manufacturing process, at each stage before additional value can be added. Quality control is of paramount importance in the products which use two dimensional detector arrays, but even the tightest production and quality testing program cannot achieve its goals without the very most efficient test equipment. This problem is significant for low end products like ordinary digital cameras, but it is acute for high end and specialty two dimensional array products. Commercially available test illuminators can produce uniform illumination so long as the integrating sphere is large, significantly larger than the area occupied by the arrays to be tested. 
     Integrating spheres as commonly used have as their purpose the production of a uniform light source. The larger the integrating sphere, the more uniform light source produced. However, larger integrating spheres which overlie two dimensional arrays are more bulky to operate. Many of the smaller integrating spheres often fail to produce enough uniformity in illumination and do not provide uniform coverage over areas larger than about  24  square millimeters. Currently available illumination test equipment fails to give the greatest efficiency both because of failure in spatial illumination and uniformity and because of losses in illumination intensity resulting in inefficiency. 
     Testing is critical for several reasons. Any further work done on the two dimensional array if it is defective represents both lost time and lost material. Further, the average reasonable number of tests available for a given array are likely to be large in number and to additionally be dependent upon a specific set of testing criteria for the composition of the array, the intended use environment for the array or both. As such, doing really excellent testing translates into a really burdensome time and effort cost. 
     What is therefore needed is a test system which can perform intensive testing of a wide variety of two dimensional arrays, to simulate a further wide variety of operational environments to insure that arrays chosen for further processing are as close to perfect as the intended device requires. 
     The theory behind the operation and use of an integrator begins with the fact that proper evaluation of the functional performance of large two dimensional detector arrays for camera vision requires spatially uniform levels of illumination. Further, filtering and test patterns may be applied to test two dimensional arrays in an attempt to find even the smallest defect in the array. Commercially available simple test illuminators are low in efficiency, large, and bulky, and require an entry setup and calibration for each array tested. Existing illuminators have achieved spatial uniformity approaching a one percent variance taken over a rather small illuminating area. This value is unacceptable where high quality and very tight production control is essential. Without more, the use of a spherical integrator to attempt to statistically randomize the distribution of illumination is simply insufficient. Such conventional reflecting spheres attempt to provide a uniform nearly ideal distribution of light, known as Lambertian distribution, where the reflected intensity is substantially independent of the angle of incidence. However, commercially available test illuminators are low in efficiency, large and bulky and do not provide uniform illumination coverage over the minimum required coverage area. The output or reflective efficiency is a function of the overall area occupied by the radiating lamp, and may be difficult to control. Given this low level of efficiency, attempted compensation requires the use of a very high wattage lamp to power the illumination test system. A heating problem is thus created since about 80% of the energy going into the bulb is given off as waste heat which needs to be dissipated. Heat dissipation by providing openings in the sphere decrease would decrease its efficiency even further. A pure air ventilation system to compensate for the heat load would probably require refrigeration in order to work optimally. Resulting temperature changes from heating will introduce error into the two dimensional array measurement. 
     Where the wall is depended upon for providing the spatial uniformity, the disadvantages are cost, large size and bulk and especially the waste heat energy which is not only a problem in itself, but as a source of error as stray light which can in an unwanted manner heat the two dimensional array. 
     It is desirable to provide a relatively smaller beam cross section so that the homogeneity can be controlled. In the needed integrating sphere system it would be necessary to provide additional optics to accommodate economical filter sizes, and to provide for automated testing. A structure is needed which is portable, efficient, stable, compact and which can in an automated way test thousands of arrays in the minimum time. 
     SUMMARY OF THE INVENTION 
     A structure and system is provided for both avoiding the limitations on the currently available test devices and providing a source of uniform illumination that is compact, efficient and portable, and employing it in a wide variety of test set ups. The advantage to this structure and process, and overall approach is that a relatively cheap, fast, and compact illuminator can be manufactured and which will be so automated that it can be self tested through a high number of data points for a given array, as well as characterize a high number of arrays of one type and then be altered to test a completely different array in a matter of minutes. A light source uses a sphere to create a stream of uniform light through an exit aperture or exit port. A pair of motor driven filter wheels are mounted in front of the exit aperture or exit port along with a motor driven target slide. Control electronics are housed within the same housing as the sphere and provide rapid control for the filter wheels and exit aperture. 
     The advantage of the concept is both forward and reverse oriented. A known test array having known characteristics can be used to calibrate the expected results in order to get a real time indication of the performance and state of the illuminator. Once performance characteristics have been established, a level of performance may be specified before introduction of the two-dimensional arrays to be tested. The mass testing of arrays may then begin. After a reasonable period of time, the test array can be reintroduced to insure that no defects in the illuminator have developed from either changes in the illumination source, heat, or variations in power, and the like. As a result, consistency is assured. 
     During the test, light from the elliptical light source/concentrator is directed through a field homogenizer &amp; shutter, and then through controlled position spectral filter and attenuation wheels, such individual filter and attenuation materials may be commonly commercially available. The spectral filter &amp; attenuation wheels are driven by a filter wheel/shutter drive controller. Light directed through the field homogenizer &amp; shutter, and spectral filter and attenuation wheel is thus further smoothed of its spatial unevenness, before being directed through a lens transfer system to then produce uniform pupil irradiance. 
     The light source is preferably a high temperature tungsten halogen lamp or quartz halogen. The lamp can be chosen from commercially available lamps and is preferably positioned at one focus of a sphere. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, its configuration, construction, and operation will be best further described in the following detailed description, taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematic illustration, from a side view, of the illuminator of the invention and illustrating the preferred arrangement of the elements; and 
     FIG. 2 illustrates a top view of the simplified mechanical embodiment of the automatic illumination testing system  11  seen in FIG. 1; 
     FIG. 3 illustrates a top schematic view of the automatic illumination testing system; 
     FIG. 4 is a perspective view illustrating one mechanical realization of the mechanical aspects of the invention; and 
     FIG. 5 illustrates a sectional view of an integrated lens transfer system housing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The description and operation of the invention will be best described with reference to FIG. 1 which illustrates an automatic illumination testing system  11 . A housing  13  is seen to include an integrating sphere  15  and associated electronics  17  located adjacent the sphere section  15 . The integrating sphere  15  is preferably about six inches in diameter and may be commercially available from Labsphere, Inc. The front of the automatic illumination testing system  11  includes an exit aperture opening  19  from which light generated from the sphere section  15  leaves the housing  13 . The exit aperture opening  19  may have a circular diameter of about one and a half inches. As closely adjacent the aperture opening  19  as possible is a target slide  21  operated by an actuation motor  23 . The target slide  21  is seen as a vertically mounted target slide, but a different embodiment will also be shown later. The target slide  21  has an upper clear or through aperture  25 , and a lower test pattern aperture  27 . The test pattern aperture can be laser cut or have etched images positioned to produce a test pattern of sufficient sharpness and clarity for testing. The ability of a two-dimensional array to reproduce the test pattern is one measure of its level of perfection. 
     To one side of the aperture opening  19  a first wheel  31  is pivotally mounted to the housing  13 , and first wheel  31  may preferably be one of a neutral density filter or frequency filter or a combination of both. The term “frequency filter” is a general term herein and includes frequency selective filters which may include band pass, high pass, low pass, low stop, high stop and band stop filters. First wheel  31  is powered by a first friction drive motor  33  having a drive wheel  35  engaging an outwardly disposed rim  37  of the first wheel  31 . The first wheel  31  may have a radius of about 3.250 inches to enable positioning a series of about six one inch radius apertures  39 . 
     To the other side of the aperture opening  19  a second wheel  41  is pivotally mounted to the housing  13 , and second wheel  31  may also preferably be one of a neutral density filter or frequency filter or a combination of both. Second wheel  41  is seen positioned at the front of and slightly overlapping first wheel  31 . Second wheel  41  is powered by a second friction drive motor  43  having a drive wheel  45  engaging an outwardly disposed rim  47  of the second wheel  41 . The second wheel  41  may also have a radius of about 3.250 inches to enable positioning a series of about six one inch radius apertures  49 , but may differ so long as the through transmissive properties of the first and second wheels  31  and  41  are not compromised. 
     Light emanating from the aperture opening  19  and which has an opportunity to propagate beyond the target slide  21 , and first and second wheels  31  and  41  enter a lens transfer system  51  and including a first lens  53 , second lens  55 , variable aperture  57 , third lens  59 , and fourth lens  61 . 
     The first lens  53 , when operating with 1.5 inch diameter evenly illuminated exit port or exit aperture opening  19  may preferably have an edge diameter of about sixty millimeters, a circular aperture diameter of from about 27.2 millimeters to about 29.0 millimeters, and a thickness of about 18 millimeters. It may have a coating for enhanced transmission of from four hundred to one thousand nanometers. The concave radius is about 234.5 millimeters and opposes a convex radius of about 68.9 millimeters. 
     The second lens  55  is a doublet combination of a double concave lens portion cemented to a double convex lens portion. Second lens  55  has an edge diameter of about 44.0 millimeters, a set of circular aperture diameters of 14.5, 17.41, and 20.4 millimeters. The outer of the double concave surfaces had a concave radius of 17.55 millimeters. The concave surface matching the convex surface of the double convex portion has a same radius of about 167.8 millimeters. The free convex end of the double convex portion has a radius of 31.4 millimeters. The double convex portion lies more adjacent the first lens  53  while the double concave portion lies on the other side and toward the variable aperture  57 . The variable aperture  57  can assume an opening size of from about one inch in diameter to fully shut. 
     The third lens  59  lies on the other side of the variable aperture  57  and also is a doublet combination of a double concave lens portion cemented to a double convex lens portion. Third lens  59  has an edge diameter of about 48.0 millimeters and a set of circular aperture diameters of 13.1, 19.8, and 23.3 millimeters. The outer of the double concave surfaces has a concave radius of 17.55 millimeters. The concave surface matching the convex surface of the double convex portion has a same radius of about 167.8 millimeters. The free convex end of the double convex portion has a radius of 31.4 millimeters. The double concave portion lies more adjacent variable aperture  57  while the double convex portion lies on the other side and toward the fourth lens  61 . 
     The fourth lens  61 , may preferably have an edge diameter of about sixty millimeters, a circular aperture diameter of from about 30.6 millimeters to about 33.0 millimeters, and a thickness of about 18 millimeters. It may have a coating for enhanced transmission of from four hundred to one thousand nanometers. The fourth lens  61  is double convex having a first convex radius of about 729.3 millimeters and faces the third lens  59 . Fourth lens  61  has a second convex radius of about 81.5 millimeters and faces away from the third lens  59  and toward a test area focal plane  65  at which a 3 inch diameter evenly illuminated image of the exit port  19  is utilizable for characterizing a wafer level imaging device  67  which may be a two or three dimensional electronic array. 
     In operation, and by example in the drawings, assuming that the target slide  21  has two positions and that first and second wheels  31  and  41  each have six positions, a total of  72  combined states can be achieved, and quickly. With proper control electronics and sensors, and with the high speed electronics to simultaneously control the target slide  21  and first and second wheels  31  and  41 , as well as to read corresponding outputs created in a wafer level imaging device, a complete test can be performed in a minute. Calibration can occur early and often in the cycle to keep the automatic illumination testing system  11  true to its pre-set standard. 
     In its most simplistic realization, as seen in FIG. 1, the light, after treatment by the lens transfer system  51 , is directed to a support  65 , or other structure containing a two or three dimensional array  67 , and which may hereafter be referred to as a two dimensional array, the term three dimensional array referring to any system which has a depth dependent sensitivity such as by interference, focus, or dimensional location aspect. Once the two dimensional array  67  is positioned on the support  65 , the associated electronics  17  can drive the motors  23 ,  33  &amp;  43  to put the two dimensional array  67  through its test paces automatically. 
     Referring to FIG. 2, a top view of the simplified mechanical embodiment of the automatic illumination testing system  11  seen in FIG. 1 gives a top down more complete view of the light transmission. A bulb  69  which may preferably be a tungsten halogen or other bulb directs light toward the sphere section  15  and thence through the aperture opening  19 . The remainder of the structures of FIG. 2 are the same as was described for FIG.  1 . 
     Referring to FIG. 3, a top schematic view of the automatic illumination testing system  11  is seen, but with various electrical connections which enable a wide variety of modes to be realized using the automated circuitry. The two or three dimensional array  67  is connected into electronics  17  either directly or through another computer  71 . Where computer  71  is utilized, the computer  71  will typically contain special circuitry for characterizing the array  67 . Where the automatic illumination testing system  11  is built as an automated but stand-alone or stand-off system, a working interface between the computer  71 , typically more closely associated with the array  67 , will be had. Nothing will prevent the computer  71  from being included within or as a part of the electronics  17 , especially where it is desired for the automatic illumination testing system  11  to be constructed for direct connection to the array  67 . In this case, the automatic illumination testing system  11  is constructed more as a complete testing device. In most cases, the combination of computer  71  and test stand connection to electronics  17  will be either provided by a manufacturer or highly customized to a manufacturer&#39;s needs. The automatic illumination testing system  11  will be provided as an integrated unit, but with the capability to communicate with and in some cases be controlled by the computer  71 . 
     As is shown in FIG. 3, the bulb  69 , first and second friction drive motors  33  and  43 , target slide motor  21 , and electronics  17 , and a variable aperture motor  73 , are all electrically connected in common. The connection of electronics  17  to the computer  71 , or optionally directly to the array  67  is also had. This connection scheme enables active testing, as well a temporal aspect testing and calibration. 
     Where one of the aspects of the array  67  is its reaction time, the time from initial illumination can be tracked with the schematic of FIG.  3 . The variable aperture motor  73  can be used to test the reaction of the array  67  to different light levels. Further, where the array  67  is an array which has been thoroughly tested, it can be utilized to calibrate the computer  71  and or the electronics  17  in order to even more finely and accurately perform testing. The use of a finely tested array  67  will enable the electronics  17 , likely to contain and include a microprocessor controller, to gauge. the exact output of the bulb  69  and the exact transmissivity of the variable aperture  57  as controlled by the variable aperture motor  73 . Other aspects of operation include assessment of the speed at which the motors  23 ,  33  and  43  operate, as well as perhaps the performance of the sphere section  15 . Bulb  69 , and motors  23 ,  33 ,  43  and  73  can be more exactly controlled. 
     Referring to FIG. 4, a perspective view illustrates one mechanical realization of the mechanical aspects of the invention outside the housing  13  which facilitates quick operability. A quick-change and calibration facilitative assembly  99  shown in FIG. 4 is supported by a base  101 . Base  101  supports a stand  103  which rotationally supports a first wheel  105  having apertures  107 . An axially de-couplable fitting  109  engages a hub  111  of the wheel  105 . A pivotally mounted handle assembly includes a base  115  and pivotally mounted handle  117  having a central aperture  119 . A pair of springs  121  flank the outside of the handle  117 . A bearing ball  123  rotates on a shaft  125  and the bearing ball  123  is engaged by the handle  117  to disengage the de-couplable fitting  109  from the wheel  105  to facilitate a rapid change of the wheel  109 . A motor mount  129  is shown with its motor removed to illustrate that a power shaft would extend through an aperture  131  for mechanical engagement with the shaft  125 , and to help better illustrate the working of the assembly  99 . 
     A pair of stands  141  exist for the support of a lens transfer system assembly  51 , while a base mounted variable aperture motor  143  has a pair of moveable members  145  to move matching structures on the lens transfer system assembly  51 . Also seen is a stand  153  which rotationally supports a second wheel  155  having apertures  157 . An axially de-couplable fitting  159  engages a hub  161  of the wheel  155 . A pivotally mounted handle assembly includes a base  165  and pivotally mounted handle  167  having a central aperture  169 . A pair of springs  171  flank the outside of the handle  167 . A bearing ball  173  rotates on a shaft  175  and the bearing ball  173  is engaged by the handle  167  to disengage the de-couplable fitting  159  from the wheel  155  to facilitate a rapid change of the wheel  159 . A motor mount  179  is shown with its motor  181  which is the same style motor which would also fit motor mount  109 . 
     A pivoting target slide  191  is shown pivotally mounted to a stand  193  and powered by a motor  195 . Rather than vertical displacement, the slide assembly shown uses a simple angular displacement of the pivoting target slide  191 . The displacement near the beam path is almost a slide since the pivot axis is so far displaced from the beam path. 
     Also seen is a target mirror  201  mounted atop a pivoting support  203  and operated by a motor  205 . A target ring  207  is supported by a stand  209  and may be used to either support or guide alignment with a test sensor or calibration instrument. In this manner, even without a test array  67 , the system  11  can, in an automated fashion, provide a self test. The instrument aligned with the target ring  207  can be widely varied depending upon what aspects of the system  11  are to be tested. One mode of operation would include positioning the mirror  201  to direct light through the target ring  207  during start up each new day of testing, to at least give a cursory indication that the system  11  is functioning properly or to link performance between two days of testing to give better quality assurance. 
     Referring to FIG. 5, a sectional view of an integrated lens transfer system housing  221  is used to support the lens transfer system  51  lenses  53 ,  55 ,  59 , and  61  , as well as the variable aperture  57 . The housing  121  is shown atop the supports  141 , and a mechanical extension  231  is seen extending downward for engagement with the pair of moveable members  145  for actuation of the variable aperture  57 . 
     While the present invention has been described in terms of a illuminator system for automatically testing two or three dimensional arrays, one skilled in. the art will realize that the structure and techniques of the present invention can be applied to many similar optical appliances. The present invention may be applied in any situation where light density is to be concentrated, diffused and then used to illuminate a target area, and where an automatic testing sequence is desired to reduce time in testing, enable calibration and increase statistical quality control. 
     Although the invention has been derived with reference to particular illustrative embodiments thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. Therefore, included within the patent warranted hereon are all such changes and modifications as may reasonably and properly be included within the scope of this contribution to the art.