Abstract:
Apparatus comprising: a heat sink, the heat sink comprising: a body formed out of a heat-transmissive material; at least one channel extending through the body, the at least one channel having an inlet port and an outlet port; at least one opening extending through the body, the at least one opening being configured to receive an optical module therein; at least one securement element mounted to the body for releasably securing an optical module within the at least one opening; and at least one alignment element mounted to the body for ensuring appropriate alignment of an optical module received in the at least one opening.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATION 
       [0001]    This patent application claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/989,269, filed May 6, 2014 by ProPhotonix Limited and Adrian Zagoneanu for HEAT SINK FOR OPTICAL MODULE ARRAYS (Attorney&#39;s Docket No. PROPHOTONIX-1 PROV), which patent application is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to optical modules and optical module array assemblies in general, and more particularly to heat sinks for optical modules and optical modules array assemblies. 
       BACKGROUND OF THE INVENTION 
       [0003]    There has been increasing demand for optical modules with higher optical output to use as light sources or for processing applications. 
         [0004]    The operating lifetime of a light source (e.g., a laser diode) is dependent on, among other things, its operating temperature. A high quality light source, operating at 20° C., could have a lifetime in excess of 100,000 hours. However, as the optical power of the light source increases, the amount of heat generated by the light source also increases, and dissipating this heat can present significant technical challenges to the designer, particularly where the optical module is used in an optical module array assembly where a sizable number of optical modules must be packaged in a relatively confined space. 
         [0005]    Failure of a light source is defined as the point in time when the operating current required to maintain a specified output power is increased by some percentage (e.g., 50%) of the original operating current. The output power of a light source is usually measured by a monitor photodiode integrated into the optical module which houses the light source. However, not all optical modules have monitor photodiodes incorporated therein, so the risk of the light source overheating and failing without appropriate detection is substantial. 
         [0006]    This “excessive heat” issue is further compounded by the continuous release of new light sources with higher output powers from light source manufacturers, and the placement of high power optical modules in close proximity to each other so as to form dense arrays in optical module array assemblies. 
         [0007]    To maximize the optical source lifetimes, and to ensure reliable operation of optical modules, it is necessary to provide adequate heat sinking for the optical module and, in particular, for the light source contained in the optical module. 
         [0008]    However, optical modules installed in a heat sink have traditionally been difficult to remove and replace. It would, therefore, be highly beneficial to the user if a defective optical module in an optical module array assembly (having a heat sink) could be easily removed and replaced in the field by a non-technical person in a short period of time without the need for special tools. 
         [0009]    In addition to the foregoing, optical modules require associated electronics, generally in the form of a printed circuit board (PCB), to drive the light source in the optical module. In some cases, an internal PCB is incorporated in each optical module. More commonly, however, optical modules are supplied independently of a PCB, and the optical modules are connected to an external PCB. This approach is particularly popular for optical module array assemblies. In this case, all of the optical modules of the optical module array assembly may be driven by a single external PCB. Each optical module plugs into the external PCB via the back end of the optical source of that optical module. As old optical modules become defective, replacement optical modules can simply be plugged into the existing PCB, leading to significant cost savings. The heat sink typically sits substantially parallel to the PCB, with the optical modules extending through, and mounting to, the heat sink. 
         [0010]    It is important that the optical module plugs into the external PCB correctly. For example, when a optical module having a laser diode is mounted in a heat sink, the laser diode (within the optical module) must be correctly connected to the PCB (i.e., the positive pin of the laser diode must connect to the positive connector of the PCB, and the ground pin of the laser diode must connect to the ground connector of the PCB). Failure to do so results in malfunction of the laser diode and permanent damage to the laser diode when a voltage is applied. 
         [0011]    Therefore, it would also be beneficial to provide a heat sink design suitable for a range of different sizes of optical module array assemblies that allows for easy replacement of defective optical modules and includes features to ensure the proper orientation of the optical modules relative to the PCB for correct electrical connection. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides a novel heat sink for an optical module array assembly in which a defective optical module in the optical module array assembly can be easily removed and replaced in the field by a non-technical person in a short period of time without the need for special tools. 
         [0013]    In addition, the present invention also provides a novel heat sink which is suitable for a range of different sizes of optical module array assemblies, which allows for easy replacement of defective optical modules, and which includes features to ensure proper orientation of the optical modules relative to the PCB for correct electrical connection. 
         [0014]    In one form of the invention, there is provided apparatus comprising: 
         [0015]    a heat sink, said heat sink comprising:
       a body formed out of a heat-transmissive material;   at least one channel extending through said body, said at least one channel having an inlet port and an outlet port;   at least one opening extending through said body, said at least one opening being configured to receive an optical module therein;   at least one securement element mounted to said body for releasably securing an optical module within said at least one opening; and   at least one alignment element mounted to said body for ensuring appropriate alignment of an optical module received in said at least one opening.       
 
         [0021]    In another form of the invention, there is provided a method for providing light, the method comprising: 
         [0022]    providing apparatus comprising:
       a heat sink, said heat sink comprising:
           a body formed out of a heat-transmissive material;   at least one channel extending through said body, said at least one channel having an inlet port and an outlet port;   at least one opening extending through said body, said at least one opening being configured to receive an optical module therein;   at least one securement element mounted to said body for releasably securing an optical module within said at least one opening; and   at least one alignment element mounted to said body for ensuring appropriate alignment of an optical module received in said at least one opening;   
               
 
         [0029]    positioning an optical module in said at least one opening, said at least one securement element releasably securing said optical module within said at least one opening and said at least one alignment element ensuring appropriate alignment of said optical module received in said at least one opening; and 
         [0030]    operating said optical module and passing a fluid through said at least one channel so as to draw off heat from said optical module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
           [0032]      FIGS. 1 and 2  are schematic views showing an optical module formed in accordance with the present invention; 
           [0033]      FIGS. 3 and 4  are schematic views showing a heat sink formed in accordance with the present invention; 
           [0034]      FIGS. 5 and 6  are schematic views showing the optical module of  FIGS. 1 and 2  being releasably locked to the heat sink of  FIGS. 3 and 4  using a spring plunger; 
           [0035]      FIG. 6A  is a schematic view showing further details of the spring plunger shown in  FIGS. 5 and 6 ; 
           [0036]      FIG. 7  is a schematic view showing a heat sink/PCB assembly; 
           [0037]      FIG. 8  is a schematic view showing the back side of a heat sink to which optical modules have been mounted; 
           [0038]      FIG. 9  is a schematic view showing the front side of a heat sink to which an optical module has been mounted; 
           [0039]      FIG. 10  is an exploded schematic view showing various aspects of a two-plate heat sink formed in accordance with the present invention; and 
           [0040]      FIG. 11  is a schematic view showing additional aspects of a two-plate heat sink shown in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Optical Modules 
       [0041]    Looking first at  FIGS. 1 and 2 , there is shown an optical module  5  which may be used in connection with the present invention. Optical module  5  can be based on a wide variety of different light sources  10  such as laser diodes, LEDs, OLEDs, SLEDs, etc. The laser diodes can be single mode laser diodes or multimode laser diodes. The laser diodes can be edge-emitting lasers or vertical-cavity surface-emitting lasers (VCSELs). Optical modules  5  can contain more than one light source  10 , for example, the optical module can contain a 2×2 array of light sources. Optical modules  5  can be any length, e.g., they can be 100 mm in length. Optical modules  5  can be any cross-sectional shape, for example, they can be cylindrical, square, or square with angled edges. In one preferred form of the invention, optical modules  5  comprise a round cross-section such as is shown in  FIGS. 1 and 2 . Typically, optical modules  5  range from 6 mm to 30 mm in diameter. Optical modules  5  can have fixed or adjustable focus mechanisms. Optical modules  5  typically include a light source  10 , e.g., a laser diode; and a lens (or a set of lenses)  15  which typically collimate or focus the light beam emitted by light source  10 . Optical modules  5  may also comprise other optical components such as diffractive optical elements, diffusers, polarizers, etc. 
         [0042]    Optical modules  5  may not include a PCB within body  20  of optical module  5 . In this case, optical module  5  is driven by an external PCB (see below) to which the optical module is electrically connected, e.g., via pins  25  of light source  10 . Even where optical module  5  does not have a PCB included in body  20  of the optical module, and where optical module  5  is driven by an external PCB, the optical module generally does include some onboard electronics for driving light source  10 . These onboard electronics can range from very simple electronics which simply allow for ON/OFF operation of light source  10  to more complex electronics which allow operations such as adjustable power output, Transistor-Transistor Logic (TTL) and/or real-time diagnostics. Optical module  5  can also comprise pressure equalization features, and/or purge mechanisms for removing contaminants that may enter the interior of body  20  of the optical module over time. If desired, optical module  5  can be optically fiber-coupled. Where optical module  5  is optically fiber-coupled, e.g., via an optical fiber  30 , the optical fiber can be of any type, e.g., single mode, multimode, polarization mode, photonic crystal, etc. 
       Heat Sink 
       [0043]    In accordance with the present invention, and looking now at  FIG. 3 , there is provided a novel heat sink  35 . Heat sink  35  is suitable for use with optical module array assemblies of any size, e.g., from one optical module  5  up to thousands of optical modules  5 . The optical modules  5  mounted to heat sink  35  will typically be identical to one another. However, it is also possible for an optical module array assembly to comprise optical modules  5  of varying dimensions, wavelengths, functionalities and/or types and, where this is the case, heat sink  35  is configured to accommodate these varying optical modules. Heat sink  35  comprises a body  40  made of a suitable heat-transmissive material, e.g., brass, steel, aluminum, etc. In one preferred form of the invention, body  40  is manufactured from a single plate  41  formed of metal. 
         [0044]    Optical modules  5  are mounted to heat sink  35  via openings  45  formed in body  40 . Openings  45  can be arranged in 1D or 2D arrays. Openings  45  are preferably symmetrically spaced apart from one another, however, if desired, openings  45  can also be staggered or arranged in a random pattern. Openings  45  vary in size and/or taper according to the external geometry of the bodies  20  of the optical modules  5  which are to be received in heat sink  35 . 
         [0045]    By way of example but not limitation, a 32-channel heat sink  35  is shown in  FIG. 3 . In this form of the invention, body  40  is formed out of aluminum and comprises thirty-two openings  45  that extend from the top face  50  of heat sink  35  to the bottom face  55  ( FIG. 8 ) of heat sink  35 . Generally, the number of openings  45  in heat sink  35  is equal to the number of optical modules  5  which are to be provided in the optical module array assembly. In the example shown in  FIG. 3 , openings  45  are arranged in four rows of eight. 
       Serpentine Channels 
       [0046]    In electronic systems, a heat sink is conventionally a passive heat exchanger that cools a device by dissipating heat into a surrounding medium. A heat sink transfers thermal energy from a higher temperature device (e.g., a laser diode) to a lower temperature medium, e.g., a fluid medium. The fluid medium is frequently air, but it can also be water or mixtures of fluids, e.g., a 15% ethylene glycol-water mixture. 
         [0047]    The present invention comprises a novel fluid-cooled heat sink for use in an optical module array assembly, i.e., the aforementioned heat sink  35 . As seen in  FIG. 4 , heat sink  35  comprises two ports  60 A,  60 B, one of which ( 60 A) is located at one side face  65  of heat sink  35  and the other of which ( 60 B) is located at another, opposite side face  70  of heat sink  35 . One port is an input port and the other port is an output port. The two ports  60 A,  60 B are preferably identical, and hence either port can be used as the input port or the output port. A cooling solution (i.e., the fluid medium) enters heat sink  35  via the input port, travels through serpentine channels  75  formed in heat sink  35 , absorbs heat generated by light sources  10  so as to cool the light sources  10  contained within the optical modules  5  mounted to heat sink  35 , and then exits heat sink  35  via the output port. 
         [0048]    The serpentine channels  75  are disposed within heat sink  35  such that when optical modules  5  sit in the heat sink, serpentine channels  75  are disposed at the same “height” as light sources  10  in optical modules  5 , whereby to maximize cooling of the light sources  10 . In other words, serpentine channels  75  are disposed in heat sink  35  such that the cooling solution (i.e., the fluid medium) flowing within serpentine channels  75  will pass adjacent to light sources  10  disposed in optical modules  5 , whereby to efficiently transfer heat from light sources  10  to the cooling medium. Thus, the “vertical alignment” of serpentine channels  75  with light sources  10  ensures that the cooling solution flowing through serpentine channels  75  flows as close as possible to the primary source of heat emanating from optical modules  5  (i.e., the light sources  10 ) so as to maximize cooling of the optical module array assembly. 
         [0049]    Serpentine channels  75  can be provided in a variety of channel configurations, depending on the particulars of the optical module array assembly, e.g., depending on array type, the size of the optical modules  5  used therein, the output powers of the optical modules  5 , the light sources  10  utilized in the optical modules, etc. It should also be appreciated that serpentine channels  75  can comprise varying dimensions along their length, e.g., so as to increase their surface area and/or the turbulence of the cooling solution at selected locations along serpentine channels  75 . Heat sink  35  can also comprise more than one input port and/or more than one output port if desired. 
         [0050]      FIG. 4  shows an exemplary configuration for the serpentine channels  75  of the exemplary 32-channel heat sink  35  shown in  FIG. 3 . For this particular design, to form serpentine channels  75  of heat sink  35 , three bores  80 A,  80 B,  80 C are drilled straight through body  40  of heat sink  35 , extending from side face  65  to the opposing side face  70 . In order to fluidically connect bores  80 A,  80 B, and  80 C together, two additional bores  85 A,  85 B are drilled part way into body  40  of heat sink  35 , preferably perpendicular to the axis of bores  80 A,  80 B,  80 C, i.e., one bore  85 A is drilled inwardly from front face  90  of heat sink  35  and one bore  85 B is drilled inwardly from back face  95  of heat sink  35 . For purposes of illustration, three bores  80 A,  80 B,  80 C and two bores  85 A,  85 B have been shown in  FIG. 4 , however, it should be appreciated that more (or fewer) bores  80 A,  80 B,  80 C may be provided and more (or fewer) bores  85 A,  85 B may be provided. In general, the number (and configuration) of bores  80 A,  80 B,  80 C, etc., and the number (and configuration) of bores  85 A,  85 B, etc., will depend on the number of openings  45  provided in heat sink  35  and the spatial arrangement of the openings  45  provided in heat sink  35 . 
         [0051]    By placing fluid caps  100  ( FIG. 4 ) to block off some of the exit holes of bores  80 A,  80 B,  80 C, etc., and to block off the exit holes of bores  85 A,  85 B, etc., closed-loop serpentine channels  75  are provided for cooling the optical modules  5  mounted in heat sink  35 . Fluid caps  100  may comprise a threaded screw with an appropriate adhesive so as to form an effective seal, or an adhesive-only barrier, or the welding or braising of a cap within the bores, etc. 
         [0052]    It should be appreciated that it is also possible to provide the serpentine channels  75  of heat sink  35  using other methods of manufacture, e.g., casting, 3D printing, etc. 
       Mounting the Optical Modules to the Heat Sink 
       [0053]    Heat sink  35  must be configured to hold optical modules  5  securely within openings  45  so as to provide good mechanical support for optical modules  5 , to provide good thermal contact between optical modules  5  and heat sink  35  so as to allow for efficient thermal transfer from the optical modules to the heat sink, and to allow for easy removal and replacement of optical modules  5  when they become defective. 
         [0054]    To this end, the present invention preferably comprises a corresponding hole  105  formed in heat sink  35  for every opening  45  formed in heat sink  35 . See  FIGS. 4-6 . These holes  105  preferably extend perpendicular to the longitudinal axes of openings  45  and run from each opening  45  to either the front face  90 , the rear face  95 , or the side faces  65 ,  70  of body  40  of heat sink  35 , depending on the location of openings  45  in body  40 . Spring plungers  110  are disposed at the inner ends of holes  105 , near their associated openings  45 . Spring plungers  110  are well suited for fixturing applications where pressure is required for accurate positioning and indexing of components. With the present invention, when an optical module  5  is advanced into an opening  45  of heat sink  35  by the user, the spring plunger  110  is urged outward in its hole  105 , away from the optical module  5  being inserted into opening  45 . Once optical module  5  is in position in opening  45 , spring plunger  110  returns to its original position (e.g., under the power of a spring) and locks the optical module in position within opening  45  (see  FIGS. 5 and 6 ), firmly holding optical module  5  in place. 
         [0055]    To ensure that spring plunger  110  locks optical module  5  into the correct position, optical module  5  is provided with two unique features. First, the outside surface of body  20  of optical module  5  is provided with an indent  115  ( FIG. 5 ) at the location where spring plunger  110  contacts the optical module. Second, the outer surface of body  20  of optical module  5  comprises a lip  120  ( FIG. 6 ) which acts as a stop as optical module  5  is inserted into opening  20 , thereby ensuring that the optical module is correctly seated in the heat sink, with indents  115  aligned with spring plunger  110 . 
         [0056]    In one preferred form of the invention, and looking now at  FIG. 6A , spring plunger  110  comprises a body  110 A having a longitudinal bore  110 B formed therein. Longitudinal bore  110 B terminates in a tapered opening  110 C at the distal end of body  110 A. A ball  110 D is positioned in longitudinal bore  110 B and is sized so that ball  110 D can protrude out of tapered opening  110 C but cannot pass completely through tapered opening  110 C. A spring  110 E is disposed in longitudinal bore  110 B and biases ball  110 D out tapered opening  110 C. An end cap  110 F captures spring  110 E in longitudinal bore  110 B. In the preferred form of the invention, body  110 A of spring plunger  110  is threaded, and holes  105  in body  40  of heat sink  35  are threaded, so that spring plunger  110  can be adjustably positioned in a hole  105 , i.e., so that the spring-biased ball  110 D yieldably protrudes into an opening  45  of body  40  of heat sink  35 , whereby to yieldably engage an optical module  5  advanced into opening  45 . 
       External PCB 
       [0057]    As discussed above, in many cases, the optical modules  5  of a optical module array assembly are driven by an external PCB. In this situation, it is generally important that the PCB be kept electrically isolated from the heat sink. To this end, it is common for the PCB to be spaced a reasonable distance away from the heat sink. However, if the light sources  10  of the optical modules  5  are driven in TTL at high frequencies, the distance between the external PCB and the light sources  10  needs to be minimized so as to cut down on parasitics. 
         [0058]    In one preferred form of the present invention, and looking now at  FIG. 7 , an external PCB  125  is electrically isolated from (i.e., spaced away from), but attached to, heat sink  35  via a plurality of posts  130 , e.g., four posts at each corner of the PCB/heat sink assembly and four posts spread equally across the middle of the PCB/heat sink assembly. 
         [0059]    The height of posts  130  is set to match the back end of the optical module  5 , such that the back end of the optical module (which contains the pins  25  of each light source  10 ) will connect directly into external PCB  125  when the optical module  5  is mounted to heat sink  35 . In some cases this connection may be made via an adapter. In other configurations, the analog part of external PCB  125  may be connected directly to the light source  10  of the optical module  5  and the digital electronics will reside on external PCB  125 . 
         [0060]    It should be appreciated that the number, height and/or configuration of posts  130  can be varied so as to accommodate different sizes of heat sinks and PCBs. In addition, although one external PCB  125  is shown in  FIG. 7 , a plurality of external PCBs  125  could also be provided (e.g., arranged in a side-by-side configuration). 
       Registration Pins 
       [0061]    It will be appreciated that, in addition to securely mounting optical module  5  in openings  45  in body  40  of heat sink  35 , it is also important that the “back end” of optical module  5  (e.g., the end of optical module  5  where the laser diode is located) be correctly circumferentially orientated within a given opening  45 . More particularly, the “back end” of an optical module  5  generally comprises the exposed pins  25  of light source  10  (e.g., a laser diode). See  FIG. 8 . Pins  25  are configured to be directly connected to (or indirectly connected to) an external PCB  125  so as to drive the various optical modules  5  in heat sink  35 . When placing the optical module  5  in an opening  45  of heat sink  35 , the user must generally orient the optical module  5  correctly (i.e., “circumferentially” correctly) so as to ensure that the electrical pins  25  of the light sources  10  are aligned with their counterpart connectors (e.g., positive connector and ground connector) on external PCB  125 . A mistake can easily occur as the pins  25  typically appear visually identical. A further complication occurs in the field when a user mounting optical module  5  to heat sink  35  and PCB  125  may not have the training and technical knowledge necessary to ensure correct alignment of connector pins  25  to external PCB  125 . 
         [0062]    The present invention solves this problem by combining three elements. First, the light source  10  is positioned within the optical module  5  with a specific orientation during manufacture. Second, the lip  120  of optical module  5  is formed with an indent  135  ( FIG. 9 ). Third, the top face  50  of the body  40  of heat sink  35  comprises a registration pin  140  spatially associated with each opening  45 . When placing optical module  5  into an opening  45  of heat sink  35 , the optical module can only sit fully in an opening  45  if the indent  135  of lip  120  of optical module  5  is aligned with registration pin  140  associated with that opening  45 , so that the registration pin  140  may be received in the indent  135 . See  FIG. 9 . Because light source  10  has been pre-aligned relative to indent  135  of optical module  5  (i.e., during the manufacture of the optical module  5 ), the pins  25  of all of the optical modules  5  in the heat sink  35  will be oriented in the same way and in a predetermined fashion. This allows for light sources  10  of optical modules  5  to be correctly connected to external PCB  125  every time, even when optical modules  5  are being replaced. The user does not have to manually align the pins  25  of the optical modules  5 . 
       Second Embodiment 
       [0063]    In the constructions shown in  FIGS. 3-9 , body  40  of heat sink  35  is shown as being formed by a single plate  41 . However, and looking now at  FIGS. 10 and 11 , body  40  of heat sink  35  can also be formed using two plates  41 A,  41 B instead of one plate  41 . In this form of the invention, the spring plungers  110  for holding the optical modules  5  tightly in the heat sink  35  are preferably located in the bottom plate  41 B. The registration pins  140  are located in top plate  41 A. The serpentine channel  75 , through which the cooling fluid travels, may be drilled out in both plates, e.g., the lower half of serpentine channel  75  may be formed in bottom plate  41 B and the upper half of serpentine channel  75  is formed in top plate  41 A. To ensure that the cooling fluid does not leak out of heat sink  35 , individual O-rings  145  ( FIG. 11 ) may be located around the openings  45  in the heat sink plates  41 A,  41 B. A further primary O-ring  150  ( FIG. 10 ) may be located around the peripheries of the two plates, surrounding all of the optical modules  5 . The two plates  41 A,  41 B are preferably held tightly together via a series of screws  155 . 
       Third Embodiment 
       [0064]    Heat sink  35  can be manufactured such that optical modules  5  are held in place by a screw (e.g., a set screw) rather than by spring plungers  110 . 
         [0065]    Alternatively, optical modules  5  may be held in place by screwing a screw directly through the lip  120  of every optical module  5  into the body  40  of heat sink  35 . If desired, more than one screw can be used to secure each module  5  to body  40  of heat sink  35 . 
       MODIFICATIONS OF THE PREFERRED EMBODIMENTS 
       [0066]    It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.