Patent Application
20150372757
Optical data transceiver modules convert optical signals received via an optical fiber into electrical signals, and convert electrical signals into optical signals for transmission via an optical fiber. In the transmitter portion of a transceiver module, an opto-electronic light source such as a laser performs the electrical-to-optical signal conversion. In the receiver portion of the transceiver module, an opto-electronic light detector such as a photodiode performs the optical-to-electrical signal conversion. A transceiver module commonly also includes optical elements, such as lenses, as well as electrical circuitry such as drivers and receivers. A transceiver module also includes one or more fiber ports to which an optical fiber cable is connected. The light source, light detector, optical elements and electrical circuitry are mounted within a module housing. The one or more fiber ports are located on the module housing.
Demand continues for transceiver modules having increasingly higher data rates. Achieving high data rates in a transceiver module requires high precision in the optical alignment among lenses, light sources, light detectors, and other elements in the optical path. Aligning such elements during the transceiver module manufacturing process is only part of the challenge facing practitioners in the art. A related challenge is maintaining the elements in such alignment. One impediment to maintaining alignment is known as epoxy cure drift. Once a lens has been aligned with the light source or light detector, it needs to be secured in place. Epoxy is commonly used to adhere the lens in place. An epoxy that maintains high adhesion strength even when subjected to high temperatures, humidity and mechanical forces is commonly employed to withstand such conditions, which can occur during normal use of the transceiver module. Such high-strength epoxy or “structural epoxy” commonly requires a higher temperature to fully cure than adhesives having lower adhesion strength, such as room temperature-cure epoxies and light-cure epoxies. However, epoxy cure drift can occur if the high curing temperature causes the lens to thermally expand out of alignment.
Various transceiver module configurations are known. One type of transceiver module configuration is known as Small Form Factor Pluggable (SFP). Such SFP transceiver modules include an elongated housing having a substantially rectangular cross-sectional shape. A forward end of the housing is connectable to an optical fiber cable. A rearward end of the housing has an array of electrical contacts that can be plugged into a mating connector when the rearward end is inserted or plugged into a slot of a network switch or other device. An SFP transceiver module having four parallel transmit channels and four parallel receive channels is commonly referred to as Quad SFP or QSFP.
In some transceiver modules, the light source and light detector are mounted on a printed circuit board (PCB) with their optical axes normal to the plane of the PCB. As these device optical axes are perpendicular to the ends of the optical fibers, there is a need to redirect or “turn” the signal path 90 degrees between the fibers and the device optical axes. In some transceiver modules, a 90-degree signal path turn is accomplished in the electrical domain by, for example, a flex circuit. In other transceiver modules, the turn is accomplished in the optical domain by a reflective surface.
It would be desirable to provide an improved method for achieving and maintaining optical alignment among elements in an optical data transceiver module.
Embodiments of the present invention relate to a method for making an electro-optical assembly of an optical communications module, in which elements in the optical signal path are aligned relative to a lens mounting frame. In an exemplary embodiment, the lens mounting frame has a generally planar shape and a perimeter surrounding an interior opening. The perimeter has a frame lower surface defining a first plane and a frame upper surface defining a second plane. The frame upper surface bears fiducial markings. The lens mounting frame is attached to the surface of the printed circuit board (PCB) by attaching the frame lower surface to the surface of the PCB.
An opto-electronic device is then aligned relative to the lens mounting frame by detecting the fiducial markings and moving the opto-electronic device into an aligned opto-electronic device position in response to detection of the fiducial markings. The opto-electronic device is secured to the surface of the PCB in the aligned opto-electronic device position.
A bottom lens device is then aligned relative to the lens mounting frame by detecting the fiducial markings and moving the bottom lens device into an aligned lens device position over the opto-electronic device in response to detection of the fiducial markings. The bottom lens device is secured in the aligned lens device position.
A top lens device is then attached to the lens mounting frame by placing a base portion of the top lens device in contact with the frame upper surface.
Other systems, methods, features, and advantages will be or become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the specification, and be protected by the accompanying claims.
The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention.
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Although in the exemplary embodiment upper surface 32 has an indented section 38, in other embodiments (not shown) such an upper surface of such a lens mounting frame need not have an indented section. Also, in other embodiments, any other suitable portion of the upper surface of such a lens mounting frame can bear fiducial markings. Although in the exemplary embodiment there are four fiducial markings 40 arranged in a linear array, in other embodiments there can be any other suitable number of such fiducial markings arranged in any other suitable manner.
Fiducial markings 40 are molded into lens mounting frame 30 or otherwise co-formed with the remainder of lens mounting frame 30. That is, the same mold (not shown) and molding process step that produces the remainder of lens mounting frame 30 at the same time produces (i.e., co-forms) fiducial markings 40. Note that as lens mounting frame 30 in the exemplary embodiment consists of the molded plastic material, lens mounting frame 30 is a solid mass of such material. That is, in lens mounting frame 30 nothing but the molded plastic material exists between fiducial markings 40 and alignment holes 36. This molded characteristic of lens mounting frame 30 thus ensures that the relative locations or positioning between fiducial markings 40 and alignment holes 36 can be fixed with high precision.
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Each fiducial marking 40 can comprise a circular pit or similar feature that is readily optically detectable by a robotic pick-and-place machine or similar manufacturing system (not shown). The use of fiducial markings 40 in the manufacturing process is described in further detail below.
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Opto-electronic light source 44 can be, for example, a vertical cavity surface-emitting laser (VCSEL) chip with an array of (e.g., four) laser elements (not individually shown for purposes of clarity). In operation, the laser elements emit light beams, i.e., optical transmit signals, along respective optical axes normal to the surface of PCB 24. Opto-electronic light detector 46 can be, for example, a PIN photodiode chip with an array of (e.g., four) photodiode elements (not individually shown for purposes of clarity). In operation, the photodiode elements detect light beams, i.e., optical receive signals, along respective optical axes normal to the surface of PCB 24.
Additional electronic elements, such as a driver chip 48 and a receiver chip 50, can also be die-attached to the surface of PCB 24. Opto-electronic light source 44 and opto-electronic light detector 46, as well as driver chip 48 and receiver chip 50, can be electrically interconnected to each other and to printed circuit pads 52 on PCB 24 by wirebonding. Printed circuit pads 52 are coupled to circuit traces (not shown for purposes of clarity) in PCB 24, and such circuit traces are, in turn, coupled to electrical contact pads 26 (
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More specifically, the robotic pick-and-place machine can optically detect fiducial markings 40 and move transmit bottom lens device 62 and receive bottom lens device 64 into respective aligned positions in response to detection of fiducial markings 40. That is, the pick- and place machine determines the difference between detected positions of fiducial markings 40 and the position of transmit bottom lens device 62 and uses this difference as feedback to move or reposition transmit bottom lens device 72 until transmit bottom lens device 62 arrives at its predetermined aligned position relative to fiducial markings 40. Likewise, the pick- and place machine determines the difference between detected positions of fiducial markings 40 and the position of receive bottom lens device 64 and uses this difference as feedback to move or reposition receive bottom lens device 64 until receive bottom lens device 64 arrives at its predetermined aligned position relative to fiducial markings 40. Transmit bottom lens device 62 and receive bottom lens device 64 are secured to the surface of PCB 24 in these aligned positions by, for example, epoxy. Significantly, a structural epoxy that would require curing at high temperature is not used to secure transmit bottom lens device 62 and receive bottom lens device 64. As transmit bottom lens device 62 and receive bottom lens device 64 are not subject to mechanical forces during normal use of optical communications module 10, a structural epoxy is not needed. Rather, a light-curable epoxy or a room-temperature-curable epoxy can be used, as the curing of such epoxies produces little to no epoxy cure drift from the aligned positions. Such non-structural epoxies are also referred to as tacking epoxies.
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Top lens device 68 has a transmit fiber port 70 and a receive fiber port 72. Transmit and receive fiber ports 70 and 72 include arrays of lenslets 74 and 76, respectively. In operation, lenslets 74 focus the transmit optical signals on the ends of transmit fibers (not shown) of MPO connector 20 (
Two alignment posts 78 extend from the lower surface of top lens device 68. Alignment posts 78 are molded into top lens device 68, i.e., co-formed with the remainder of top lens device 68, in a manner similar to that described above in which alignment holes 36 and fiducials 38 are co-formed with the remainder of lens mounting frame 30. That is, the same mold (not shown) and molding process step that produces the remainder of top lens device 68 at the same time produces alignment posts 78. Note that as top lens device 68 in the exemplary embodiment consists of the molded plastic material, top lens device 68 is a solid mass of such material. That is, in top lens device 68 nothing but the molded plastic material exists between alignment posts 78 and lenslets 74 and 76. This molded characteristic of top lens device 68 thus ensures that the relative locations or positioning between alignment posts 78 and lenslets 74 and 76 can be fixed with high precision.
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It should be noted that the above-described features obviate aligning top lens device 68 with lens mounting frame 30 by any other means than the mating of alignment posts 78 with alignment holes 36. That is, the mating of alignment posts 78 with alignment holes 36 is by itself a sufficient (passive) alignment method, and no additional alignment methods, such as an active method involving feedback, need be performed.
Top lens device 68 can be secured to lens mounting frame 30 by structural epoxy or laser welding. Lens mounting frame 30 can be optically opaque to facilitate laser welding by directing a laser beam (not shown) through top lens device 68 and into lens mounting frame 30. Due to its opacity, lens mounting frame 30 absorbs the laser energy and transforms it into heat, which fuses the lower surface of top lens device 68 to the upper surface of lens mounting frame 30 to form a weld. Such methods for securing top lens device 68 to lens mounting frame 68 do not affect the above-described alignment, since the mating of alignment posts 78 with alignment holes 36 retains top lens device 68 in alignment during any further securing steps. There is no epoxy cure drift.
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Note that a space or air gap exists in cavity 82 between transmit bottom lens device 62 and the interior of top lens device 68. That is, transmit bottom lens device 62 extends into cavity 82 but does not contact any portion of top lens device 68. Although not shown in
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Plugging MPO connector 20 into optical communications module 10 in preparation for the above-described operation can cause MPO connector 20 to exert mechanical forces upon top lens device 68. Although not shown for purposes of clarity, the end of MPO connector 20 has bores that receive guide pins 94 and 96. Such a mechanical connection can transmit mechanical forces from MPO connector 20 to top lens device 68. By spacing or separating top lens device 68 from bottom lens devices 62 and 64, mechanical forces acting upon top lens device 68 are not directly transferred to bottom lens devices 62 and 64 but rather are directly transferred to lens mounting frame 30 and then from lens mounting frame 30 to PCB 24.
It should be noted that good alignment among elements in the transmit optical path 86 depends to a greater extent upon good alignment between transmit bottom lens device 62 and opto-electronic light source 44 than it does upon good alignment between other elements in transmit optical path 86. Likewise, good alignment among elements in the receive optical path 88 depends to a greater extent upon good alignment between receive bottom lens device 64 and opto-electronic light detector 46 than it does upon good alignment between other elements in receive optical path 88. Thus, spacing or separating top lens device 68 from bottom lens devices 62 and 64 helps minimize adverse effects of mechanical forces upon top lens device 68 while not significantly sacrificing optical alignment.
Spacing or separating top lens device 68 from bottom lens devices 62 and 64 also facilitates providing features that inhibit back reflection of the optical signals. The region 100 in
The exemplary method described above with regard to
One or more illustrative embodiments of the invention have been described above. However, it is to be understood that the invention is defined by the appended claims and is not limited to the specific embodiments described.
