Abstract:
A system and method for the direct inspection of an optical module. The system includes an optical receiver and/or an optical transmitter, an alignment means precisely dimensioned to interface with a predetermined optical coupling device, and electrical connection means operative to energize an optical coupling device or to receive an electrical output from an optical coupling device. These components may be integrated into a testing probe head. To inspect, the optical module is optically interfaced using precisely dimensioned alignment means, electrically interfacing the optical coupling device to energize the optical coupling device and/or to receive an electrical output from said predetermined optical coupling device. Further, the optical module is either electrically energized and the optical output measures, or optically energized and the electrical output measured. The measured optical or electrical output is compared to the expected output based on the electrical or optical energy applied.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The invention relates generally to the field of electronics manufacturing and, more specifically, to a method and apparatus for the optical testing of an optical coupling module.  
           [0003]    2. Description of Related Art  
           [0004]    In an optical coupling device, such as an optical module, the coupling quality is directly related to the precise positioning of the optical element. To inspect the optical coupling quality of optical module, precising or alignment holes are utilized. Typically, conventional physical (x,y) position measurements are made of the alignment holes. Using this data, and the presumed relative position of the optical element in the optical module, the optical coupling quality of the optical module can be estimated to a certain level of accuracy.  
           [0005]    This method has certain drawbacks. Primarily among them, the mechanical position of the alignment holes is only a rough approximation of the optical coupling quality of the optical module. Mechanical alignments such as surface flatness, drill perpendicularity, camber, die tilt and the interactions are not considered when measuring the x,y position of the hole nor can they be derived. Measurement of these other mechanical alignments and their combined effect on the overall optical coupling quality is laborious and remains an approximation. Because of this approximation, some unacceptable products may be passed while some suitable products may be rejected. Therefore, a reliable, accurate, direct measurement of optical coupling quality is desired.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    To overcome these and other deficiencies in the prior art the present invention describes a system and method for the direct inspection of an optical module. The system comprises either or both of an optical receiver and an optical transmitter, an alignment means precisely dimensioned to interface with a predetermined optical coupling device, and electrical connection means operative to energize an optical coupling device or to receive an electrical output from an optical coupling device. These components may be integrated into a testing probe head.  
           [0007]    The method according to the present invention comprises using precisely dimensioned alignment means to optically interface with a predetermined optical coupling device, electrically interfacing said optical coupling device to either energize said predetermined optical coupling device or to receive an electrical output from said predetermined optical coupling device. The method further comprises either electrically energizing the optical coupling device and measuring an optical output therefrom, or optically energizing the optical coupling device and measuring an electrical output therefrom, and comparing the optical or electrical output from said optical coupling device to the optical or electrical output expected based on the electrical or optical energy applied. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    These and other features, benefits and advantages of the present invention will become apparent by reference to the following text and figures, with like reference numbers referring to like structures across the views, wherein:  
         [0009]    [0009]FIG. 1 illustrates a side elevation view of a test probe system according to the current invention in position to test an optical coupling device; and  
         [0010]    [0010]FIG. 2 illustrates a plan view of an optical coupling device to be inspected according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    Referring now to FIG. 2, an optical coupling device to be inspected, generally  10 , is illustrated. The optical module  12  may be positioned on a flex frame surface  20  after fabrication. The flex frame surface may be provided with electrical interface fingers  22 , although any suitable means for electrically interfacing with an electrical contact portion  13 , such as a plurality of wire bonding pads, of optical module  12  is acceptable.  
         [0012]    The optical module  12  may be provided with one or more alignment holes  16 ,  18 . These alignment holes  16 ,  18  are formed at a predetermined position of optical module  12 . Shown in FIG. 2 as through holes, alignment holes  16 ,  18  may pass only partially through optical module  12 . Alignment holes  16 ,  18  may also be positioned elsewhere on optical module  12 , for example out to the perimeter. The alignment holes  16 ,  18  may be any suitable shape, such as the circular shape illustrated in FIG. 2.  
         [0013]    The optical module  12  has an optical element  14  located at a predetermined position of optical module  12 . Optical element  14  may be either a transmitting element  14   a , for example a laser diode array, defining a transmitting optical module  12   a . Optical element  14  may also be a receiving element  14   b , for example a photodiode, defining a receiving optical module  12   b.    
         [0014]    The use of the optical coupling device  10  will be described. In the case of a transmitting device, the transmitting optical module  12   a  is charged via the electrical contact portion  13 , and light is emitted from transmitting element  14   a . The intensity of light emitted from transmitting element  14   a  may be fixed, or may vary according to the nature of the charge applied to the electrical contact portion  13 . For example, the intensity may be proportionally, exponentially, or in some other way related, to either the voltage or current applied. The intensity may also be dictated by a digitally or otherwise coded electrical input to the transmitting optical module  12   a.    
         [0015]    In the case of a receiving device, light is incident upon the receiving element  14   b , after which the receiving optical module  12   b  would generally produce an output via the electrical contact portion  13 . The receiving optical module  12   b  may be designed such that the light intensity can vary the nature of the charge output through the electrical contact portion  13 . The relationship between the light intensity received and the electrical output may be fixed, may vary proportionally, exponentially or according to some other relationship, or may be digitally or otherwise electrically encoded.  
         [0016]    In the case of either the transmitting or receiving device, the optical module  12  may be designed to operate only in a predetermined portion of the electromagnetic (EM) spectrum, such as IR or UV. It may also have some inherent or designed threshold before the optical element  14  becomes active relative to the electrical contact portion  13 .  
         [0017]    Referring now to FIG. 1, the system and method for inspecting the optical coupling device  10  will now be described. Optical module  12  is shown positioned on a flex frame surface  20 . Probe head  50  is shown positioned above optical module  12  in a position to take a measurement of optical coupling quality.  
         [0018]    Probe head  50  has one or more alignment means  52 , such as alignment pins, the number, size and position of which are predetermined to physically interface with a selected optical module  12 . Alignment means may also be pins or other structural elements, such as an inverse mold, dimensioned to physically interface with the exterior of a predetermined optical module  12 , for example where optical module  12  is not provided with alignment holes  16 ,  18 . Alignment means  52  may also comprise a machine vision system  53 , either solely or as a supplement to one of the physical embodiments already described. The probe head  50  may also have an optical conduit means  54 , such as a fiber optic connector, for optically interfacing the probe head  50  with the optical module  12  being tested. The probe head may also be provided with either or both of an optical receiver  56  and an optical transmitter  58 .  
         [0019]    In one embodiment, optical receiver  56  and optical transmitter  58  are provided integral to probe head  50 ; which is to say these are physically connected so as to move together as a single unit. In an alternate embodiment, however, an optical receiver  56 ′ and/or optical transmitter  58 ′ are provided remotely to the probe head  50 , and communicate with optical conduit  54  via an interface cable  60 . In yet another alternate embodiment optical coupling means  54  is omitted, and an optical receiver  56 ″ and/or optical transmitter  58 ″ is positioned to optically interface the optical module  12  directly. The probe head  50  may also be provided with more than one transmitter or receiver, for example ones operative in an IR or UV band of the EM spectrum.  
         [0020]    Probe head  50  may also be provided with electrical connection means  62  for electrically interfacing optical module  12 . Electrical connection means  62  may be a probe for interfacing via electrical interface fingers  22 , a connector or harness, or any other suitable connection means. However, electrical connection means  62  need not be provided integral to the probe head. In an alternate embodiment, electrical connection means  62  may be a separate component, and/or integrated into a means for holding optical module  12  in position for testing, which might include a movable stage  66 .  
         [0021]    In any of the above cases, the alignment means  52 , and either optical conduit means  54  or one of an optical receiver  56 ″ and an optical transmitter  58 ″, are precisely positioned to superior dimensional accuracy corresponding to the optical module  12  being tested. Therefore, any deficiency in optical coupling quality can be accurately presumed to result from dimensional errors of the optical module  12 .  
         [0022]    The testing method according to the present invention will now be described. Probe head  50  is positioned as shown in FIG. 1 by aligning the alignment means  52  with alignment holes  16 ,  18  of optical module  12 . By virtue of the dimensional accuracy of the probe head, the optical element  14  should be in position to optically interface with the optical conduit means  54 . At the same time, electrical connection means  62  is interfaced with the electrical contact portion  13  of optical module  12 , for example through electrical interface fingers  22 .  
         [0023]    In the case of testing a transmitting optical module  12   a , once in position, the transmitting optical module  12   a  is energized by the electrical connection means  62  to produce a given optical output at transmitting element  14   a . The optical output is collected, for example via optical coupling means  54 , and directed to optical receiver  56 . In this context, “collected” will be understood to include channeling, as for measurement, not solely capacitive capture and storage of the optical energy. The quantity of light collected by optical receiver  56  is compared to the given optical output. This ratio is the measure of optical coupling quality of transmitting optical module  12   a.    
         [0024]    Because of the superior dimensional accuracy of the probe head  50 , any misalignment between transmitting element  14   a  and optical coupling means  54  can be attributed to defects in the location of the transmitting element  14   a . Moreover, regardless of the true position of transmitting element  14   a , the critical measure of the functionality of transmitting optical module  12   a  is the amount of light delivered to the expected location above the transmitting optical module  12   a , which is directly measured by the present invention.  
         [0025]    In the case of testing a receiving optical module  12   b , once the probe head  50  and electrical connection means  62  are in position, optical transmitter  58  is energized to supply a known quantity of light energy to an expected position above receiving optical module  12   b . The electrical output from the receiving optical module  12   b  is collected via electrical connection means  62 . In this context, “collected” will be understood to include channeling, as for measurement, not solely capacitive capture and storage of the electrical energy. The collected electrical output of receiving optical module  12   b  is compared to the expected electrical output, given the known quantity of light applied to the receiving element  14   b . This ratio is the measure of optical coupling quality of the receiving optical module  12   b . Again, regardless of the true position of receiving element  14   b , the critical measure of the functionality of receiving optical module  12   b  is the electrical output derived from a given amount of light delivered to the expected location above the receiving optical module  12   b , which is directly measured by the present invention.  
         [0026]    To position probe head  50  above optical module  12  for testing, the probe head  50  may be attached to a motion control device  64 , preferably one having at least three axes of motion. Alternately, the probe head  50  may be fixed and the optical module may be mounted on a movable stage  66 , again preferably having at least three axes of motion. Alternately, the motion control device  64  and a movable stage  66  may be combined to achieve up to three or more axes of relative motion between probe head  50  and optical module  12 . When either or both of motion control device  64  and movable stage  66  are used in automated testing, it is particularly useful for the alignment means  52  to include a machine vision system  53 , irrespective of any other physical alignment components, to aid in the control of probe head  50 .  
         [0027]    The invention has been described herein with reference to particular exemplary embodiments. Certain alterations and modifications may be apparent to those skilled in the art, without departing from the scope of the invention. The exemplary embodiments are meant to be illustrative, not limiting of the scope of the invention, which is defined by the appended claims.