Patent Publication Number: US-8967881-B2

Title: Optical network unit transceiver

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of U.S. patent application Ser. No. 13/652,381, filed Oct. 15, 2012, titled PLUGGABLE OPTICAL NETWORK UNIT TRANSCEIVER, which is a Divisional of U.S. patent application Ser. No. 12/618,504, filed Nov. 13, 2009, titled OPTICAL NETWORK UNIT TRANSCEIVER, which in turn claims the benefit of Singapore Patent Application No. 200808465-9, filed on Nov. 13, 2008, all of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to communication systems. In particular, example embodiments relate to an optical network unit (ONU) transceiver module configured to provide a number of features such as ensuring I/O pin alignment, preventing tilting, and/or positioning the top of the ONU transceiver module at a predetermined height above a host printed circuit board (PCB) having a protruding socket. 
     2. Related Technology 
     Interest in broadband optical access networks is growing, driven by an increasing demand for high-speed multimedia services. Optical access networks are often referred to as fiber-to-the-curb (FTTC), fiber-to-the-building (FTTB), fiber-to-the-premise (FTTP), or fiber-to-the-home (FTTH). Each such network provides an access from a central office to a building, or a home, via optical fibers in an optical cable. As the transmission quantity of such an optical cable is much greater than the bandwidth actually required by each subscriber, passive optical networks (PON) shared between many subscribers through splitters have been developed. 
     Referring to  FIGS. 1A and 1B , a conventional ONU transceiver module  100  and host device  102  are shown. The ONU transceiver module  100  includes input/output (I/O) pins  104  that are plugged into the host device&#39;s  102  internal PCB  106 . The ONU transceiver module includes an RF connector  108  for an RF cable to connect to the ONU transceiver module  100 . More specifically, typical ONU transceiver modules  100  have  20  I/O pins in a row protruding from the bottom of the ONU transceiver modules  100  and the standard RF connector  108  for transmission of an electrical video signal. One example of a standard RF connector used is a SubMiniature B (SMB) connector that protrudes from a side of the ONU transceiver module  100 . 
     The host device  102  includes a protruding connector  110  configured to receive the I/O pins  104  of the ONU transceiver module  100 . Because the protruding connector  110  extends above the PCB  106 , the module  100  has to be raised to a height which is at the same level as the protruding connector  110  to prevent tilting when the module  100  is plugged into the host device  102 . Additionally, proper functioning requires that the I/O pins  104  are plugged into the correct holes of the protruding socket  110 . 
     The conventional module  100  of  FIG. 1A  includes various features to address these two problems, including a plurality of stepped guide pins  112 A- 112 C and a stabilizing rib  114 . Each of the stepped guide pins  112 A- 112 C includes a guiding pin  116 A- 116 C and a stepped portion  118 A- 118 C. The stepped portions  118 A- 118 C and stabilizing rib  114  are configured to rest on the host device  102  PCB  106  to raise the module  100  to the same level as the protruding connector  110  to prevent tilting when the module  100  is plugged into the host device  102 . The guiding pins  116 A- 116 C are configured to be received by guiding holes  120 A- 120 C on the host PCB  106 ; alignment of the guiding pins  116 A- 116 C with the guiding holes  120 A- 120 C aligns the I/O pins  104  with the corresponding holes of the protruding I/O socket  110 . After aligning the guiding pins  116 A- 116 C with the guiding holes  120 A- 120 C, the guiding pins  116 A- 116 C can be received in the guiding holes  120 A- 120 C, allowing the I/O pins  104  to then be inserted into the correct holes of the protruding I/O socket  110 . 
     Each of the stepped guide pins  112 A- 112 C is a separate component that increases the number of separate parts used in assembling the module  100 . Generally speaking, each additional part used in module  100  assembly not only increases the cost of the module  100 , but also increases the processes required to assemble the finished product. Moreover, in the conventional module  100  of  FIG. 1A , holes are formed in the module  100  to receive each of the stepped guiding pins  112 A- 112 C—these holes can weaken the shell structure of the module  100 . Furthermore, the guiding pins  116 A- 116 C are relatively long compared to their diameter such that the guiding pins  116 A- 116 C may be susceptible to breaking or bending. 
     The host device  102  further includes a plurality of posts  122 A and  122 B configured to be coupled to a heatsink (not shown) to dissipate heat away from the module  100 . For the heatsink to operate effectively, the module  100  must be positioned at a predetermined height above the PCB  106  when the module  100  is plugged into the host device  102 . Module designs that do not meet the height requirement have to be raised or lowered to ensure proper contact with the heatsink. 
     SUMMARY 
     In general, example embodiments of the invention relate to ONU transceiver modules configured to address various problems in prior art implementations. For example, disclosed embodiments provide one or more advantages, such as ensuring I/O pin alignment with protruding sockets of host devices, the ability to be positioned at predetermined heights above the host devices, and/or preventing tilting of the ONU transceiver modules when plugged into the host devices. 
     In one example embodiment, a pluggable ONU transceiver module comprises a top shell, a bottom shell configured to mate with the top shell to form a cavity, and a PCB disposed within the cavity. A plurality of I/O pins are coupled to the PCB and are configured to be inserted into a protruding socket of a host device through the bottom shell. The protruding socket is mounted on a PCB of the host device. The pluggable ONU transceiver module further comprises one or more guiding features integrated with the bottom shell and configured to ensure that the I/O pins are inserted correctly into the protruding socket, and means for positioning the top shell at a predetermined height above the PCB of the host device to allow coupling of the top shell to a heatsink of the host device. 
     In another example embodiment, a pluggable ONU transceiver module comprises a top shell, a bottom shell configured to mate with the top shell to form a cavity and further configured to position the top shell at a predetermined height above a PCB of a host device, and a PCB disposed within the cavity. A plurality of I/O pins are coupled to the PCB disposed within the cavity and are configured to be inserted into a protruding socket of the host device through the bottom shell. The protruding socket is mounted on the PCB of the host device. The pluggable ONU transceiver module further comprises an opening formed in the bottom shell and configured to ensure that the I/O pins are inserted correctly into the protruding socket. 
     In yet another example embodiment, a pluggable ONU transceiver module comprises a top shell, a bottom shell configured to mate with the top shell to form a cavity, and a PCB disposed within the cavity. A plurality of I/O pins are coupled to the PCB and are configured to be inserted into a protruding socket of a host device through the bottom shell. The protruding socket is mounted on a PCB of the host device. The pluggable ONU transceiver module further comprises two guiding tabs formed in the bottom shell and configured to ensure that the I/O pins are inserted correctly into corresponding holes in the protruding socket, and means for positioning the top shell at a predetermined height above the PCB of the host device to allow coupling of the top shell to a heatsink of the host device. 
     Additional features of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The features of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify the above and other features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIGS. 1A and 1B  illustrate a conventional pluggable ONU transceiver module and host device having a protruding I/O socket, respectively; 
         FIG. 2  discloses some of the components that may be found in a pluggable ONU transceiver module according to embodiments of the invention; 
         FIGS. 3A-3D  disclose an example of a pluggable ONU transceiver module according to embodiments of the invention; and 
         FIGS. 4A-4C  disclose two more examples of pluggable ONU transceiver modules according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the figures wherein like structures will be provided with like reference designations. It is understood that the figures are diagrammatic and schematic representations of example embodiments of the invention, and are not limiting of the present invention, nor are they necessarily drawn to scale. 
       FIGS. 2-4C  disclose various aspects of some example embodiments. Embodiments of the ONU transceiver module may, among other things, ensure proper insertion of the ONU transceiver module I/O pins into a corresponding host device&#39;s protruding connector, prevent tilting of the ONU transceiver module when plugged into the host device, and/or position the top of the ONU transceiver module at a predetermined height to mate with a heatsink fastened to the host device. Note that the principles disclosed herein can also be applied to other pluggable communication modules where I/O pin alignment, tilt prevention, and/or module height positioning are desired. 
     I. General Aspects of some ONU Transceiver Modules 
       FIG. 2  illustrates some of the components that may be found in an exemplary pluggable ONU transceiver module  200 . The example pluggable ONU transceiver module  200  can include an optical connector  205  configured to connect to an optical network via a single optical fiber  210  for both upstream and downstream optical communication over the single fiber  210 . The single fiber  210  can be a single mode fiber, such as an SMF-28E fiber. The single fiber  210  can also include a fiber pigtail connecting the pluggable ONU transceiver module  200  to the network via another fiber optical connection at another end of the fiber pigtail. 
     The pluggable ONU transceiver module  200  includes an optical triplexer  215  for separating received optical signals from the optical network and for transmitting a transmit optical signal to the optical fiber. For example, the pluggable ONU transceiver module  200  can include a triplexer including collimating ball lenses as disclosed in U.S. patent application Ser. No. 12/031,234, filed Feb. 14, 2008, the contents of which are hereby incorporated by reference herein. 
     The example pluggable ONU transceiver module  200  further includes a first receive line including a first optical receiver  220 , such as a first photodiode. The first receive line further includes a first TIA  225  for amplifying an electrical data signal generated by the first optical receiver  220  from a received optical data signal. The pluggable ONU transceiver module  200  further includes a second receive line including second optical receiver  230 , such as a second photodiode. The second receive line further includes a second TIA  235  for amplifying an electrical video signal generated by the second optical receiver  230 . Examples of optical receivers that may be used for the first and/or second optical receivers  220 ,  230  include photodiodes, avalanche photodetectors, metal-semiconductor-metal detectors, and the like. 
     The pluggable ONU transceiver module  200  further includes a transmit line including a laser  240  for generating an optical data signal from an electrical data signal received from a laser driver  245 . Examples of lasers that can be used for the laser  240  include edge emitting lasers such as double heterostructure, quantum well, strained layer, distributed feedback, and distributed Bragg reflector lasers, as well as vertical cavity surface-emitting lasers (VCSELs), and the like. 
     Thus, the example pluggable ONU transceiver module is configured to transmit and receive digital data signals over the first receive line and the transmit line. The ONU transceiver module is also configured to receive analog video signals over the second receive line. 
     The pluggable ONU transceiver module further includes I/O and video interfaces including I/O contacts  250  and video contacts  255 , respectively. The I/O and video contacts  250  and  255  are electrically coupled directly, or indirectly via additional circuitry and/or a processor  260 , to the laser driver  245 , first post amplifier  225  and the second post amplifier  235 . The I/O contacts  250  can include a single linear array of electrical contacts, while the video contacts  255  can be part of an SMB or other RF connector. 
     The laser  240 , first optical receiver  220 , and second optical receiver  230  each have a different associated wavelength so that the signals received and transmitted thereby may be triplexed. The wavelength associated with the laser  240 , first optical receiver  220  and second optical receiver  230  can be any wavelength between 375 nanometers and 1800 nanometers in some embodiments. For example, the wavelengths associated with the laser  240 , first optical receiver  220 , and second optical receiver  230  can be about 1310 nanometers, about 1490 nanometers, and about 1550 nanometers. The laser  240  can be associated with a signal wavelength of about 1310 nanometers, the first optical receiver  220  receiving digital data signals can be associated with a signal wavelength of about 1490 nanometers, and the second optical receiver  230  receiving analog video signals can be associated with a signal wavelength of about 1550 nanometers. For example, about 1310 nanometers can refer to wavelengths between 1290 and 1330 nanometers, about 1490 nanometers can refer to wavelengths between 1480 and 1500 nanometers, and about 1550 nanometers can refer to wavelengths between 1540 and 1560 nanometers. 
     The video signal can be a CATV video signal which ranges between 55 megahertz and 870 megahertz. The optical video signal can be an internet protocol television (IPTV) signal. The digital data signals can transmit digital data at rates between 1 and 10 Gbp/s or more. For example, the second optical receiver  230  can receive data transmitted at rates of about 2.5 Gbp/s and the laser  240  can transmit digital data at rates of about 1.25 Gbp/s. 
     II. Aspects of some Example Embodiments 
     Referring now to  FIGS. 3A-3D , an example of a pluggable ONU transceiver module  300  is illustrated according to some embodiments of the invention.  FIG. 3A  illustrates an exploded perspective view,  FIGS. 3B and 3C  illustrate upside-down perspective views, and  FIG. 3D  illustrates a side view of the ONU transceiver module  300 . 
     The ONU transceiver module  300  includes a top shell  302  and a bottom shell  304  configured to mate together to form a cavity. As best seen in  FIG. 3A , a PCB  306  is disposed within the cavity, upon which are mounted a triplexer  308  and circuitry  310  that may include a processor or the like. The PCB  306  further includes a plurality of I/O contacts  312 . A plurality of I/O pins  314  are coupled to the PCB  306  via the I/O contacts  312  and are configured to be inserted into a protruding socket  316  on a corresponding host device  318  and to electrically connect the ONU transceiver module  300  to the host device  318 . The ONU transceiver module  300  further includes an optical connector  320  configured to connect to an optical fiber  321  to access an optical network. 
     In some embodiments, the top shell  302  and bottom shell  304  can be secured together using any of a variety of means. In the embodiment of  FIGS. 3A-3D , for example, the top shell  302  includes a plurality of protrusions  322 A- 322 D configured to engage complementary openings  324 A- 324 D formed in the bottom shell  304 . Alternately or additionally, the top shell  302  can be coupled to the bottom shell  304  using one or more screws, bolts, pins, or other fasteners or the like. 
     As shown in  FIG. 3B , a guiding feature  326  is integrated with the bottom shell  304  and is configured to ensure that the plurality of I/O pins  314  are inserted into the correct holes of the protruding socket  316 . In particular, the guiding feature  326  comprises a rectangular opening in the bottom shell  304  that is sized to receive the protruding socket  316 . For instance, the length of the rectangular opening guiding feature  326  can be substantially equal to the length of the protruding socket  316 . According to this embodiment, the I/O pins  314  are positioned within the cavity formed by the top shell  302  and bottom shell  304  such that when the rectangular opening guiding feature  326  is aligned with the protruding socket  316 , each of the I/O pins  314  is automatically aligned with the correct hole of the protruding socket  316 . Because the length of the rectangular opening guiding feature  326  is substantially equal to the length of the protruding socket  316 , the I/O pins  314  are substantially constrained to insert into the correct holes of the protruding socket  316  when the protruding socket  316  is inserted into the rectangular opening guiding feature  326 . 
     The rectangular opening guiding feature  326  allows the protruding socket  316  to be received into the cavity formed by the top shell  302  and bottom shell  304 . In some embodiments, this allows the flat bottom of the bottom shell  304  to rest directly on a PCB  334  of the host device  318 . As such, the bottom shell  304  is configured to prevent the ONU transceiver module  300  from tilting when plugged into the host device  318 . 
     Although the guiding feature  326  is disclosed in  FIG. 3B  as a rectangular opening that is complementary to the shape of the protruding socket  316 , the guiding feature  326  can alternately comprise an opening having a circular, oval, or other shape depending on the shape of the protruding socket  316 . 
     With combined reference to  FIGS. 3A and 3C , in some embodiments of the invention an electromagnetic interference (EMI) shield  328  is positioned between the PCB  306  and bottom shell  304  to substantially prevent the entrance or exit of electromagnetic radiation (EMR) into or out of the ONU transceiver module  300 . As can be seen in  FIG. 3C , which shows the ONU transceiver module  300  without bottom shell  304 , the EMI shield  328  includes individual openings  330  through which each of the I/O pins  314  extends from the PCB  306  downwards (e.g., towards the bottom shell  304 ). Thus, although EMR in some embodiments may pass into our out of the ONU transceiver module  300  through the rectangular opening guiding feature  322  of the bottom shell  304 , the EMI shield  328  is configured to substantially prevent EMR from passing through the EMI shield  328 , which EMR might otherwise adversely affect the PCB  306  and electronic/optoelectronic components mounted thereto in the case of externally generated EMR, or that might adversely affect the host device  318  or other devices external to the ONU transceiver module  300  in the case of internally generated EMR. In other embodiments, the EMI shield  328  can be omitted. 
     With combined reference now to  FIGS. 3A and 3D , additional details according to embodiments of the invention are disclosed. As shown, the host device  318  includes a plurality of posts  332 A and  332 B mounted on the PCB  334  of the host device  318 . Each of the posts  332 A and  332 B includes a threaded through hole configured to receive a screw, bolt or other fastener to secure a heatsink (not shown) to the posts  332 A and  332 B. The heatsink is configured to contact the top of the module  300  to dissipate heat away from the module  300 . To facilitate heat dissipation, the top of the ONU transceiver module  300  is configured to be positioned at a predetermined height H 1  above the PCB  334  of host device  318  when the ONU transceiver module  300  is plugged into the host device  318 . As shown in  FIG. 3D , the predetermined height H 1  extends slightly above the top of the posts  332 A,  332 B. 
     In the embodiment of  FIGS. 3A-3D , the top of the ONU transceiver module  300 , e.g., the top of top shell  302 , is positioned at the predetermined height H 1  above the PCB  334  of host device  318  by bottom shell  304 . The bottom shell  304  can be formed from stamped sheet metal or the like and can be manufactured in a variety of sizes to accommodate a variety of predetermined heights H 1 . The size of the bottom shell  304  can be varied by selecting a desired value for lower height H 2  ( FIG. 3D ) of the bottom shell  304 , without changing any of the other dimensions of the bottom shell  304 . For example, to position the top of the ONU transceiver module  300  at a relatively high predetermined height H 1 , the bottom shell  304  will have a relatively large lower height H 2 . In contrast, to position the top of the ONU transceiver module  300  at a relatively low predetermined height H 1 , the bottom shell  304  will have a relatively small lower height H 2 . Accordingly, the bottom shell  304  serves as one example of a structural implementation of a means for positioning the top of an ONU transceiver module at a predetermined height H 1  above the PCB  334  of host device  318 . 
     In some embodiments, then, the bottom shell  304  provides an integrated solution for (1) ensuring that I/O pins are inserted correctly into the protruding socket of the host device, (2) preventing tilting of pluggable ONU transceiver modules when plugged into host devices with protruding sockets, and (3) positioning the top of the ONU transceiver module at a predetermined height to contact a heatsink. In contrast to conventional solutions for these problems, the bottom shell  304  is an integrated solution comprising a single component that can be assembled to the rest of the ONU transceiver module  300  in a single step. In comparison, prior art solutions include multiple components that are assembled to the rest of the module in multiple steps. Moreover, the bottom shell  304  presents a robust design that is less susceptible to breaking than conventional stepped guiding pins and bottom shells with holes to receive the stepped guiding pins. 
     While  FIGS. 3A-3D  disclose an integrated solution for the problems described above, embodiments of the invention are not limited to integrated solutions. For instance,  FIGS. 4A-4C  disclose two other example ONU transceiver modules according to embodiments of the invention. More specifically,  FIG. 4A  illustrates an exploded perspective view and  FIG. 4B  illustrates an upside-down perspective view of a second example ONU transceiver module  400 A;  FIG. 4C  illustrates an exploded perspective view of a third example ONU transceiver module  400 B. 
     The ONU transceiver module  400 A of  FIGS. 4A and 4B  includes a top shell  402  and bottom shell  404  configured to mate together to form a cavity. As best seen in  FIG. 4A , a PCB  406  is disposed inside the cavity, upon which are mounted a triplexer  408  and circuitry  410 . The PCB  406  further includes a plurality of I/O contacts  412 . A plurality of I/O pins  414  are coupled to the PCB  406  via the I/O contacts  412  and are configured to be inserted into the protruding socket  316  of host device  318  and to electrically connect the ONU transceiver module  400 A to the host device  318 . The ONU transceiver module  400 A additionally includes an optical connector  420  configured to connect to an optical fiber  421  to access an optical network. 
     Top shell  402  includes a plurality of protrusions  422 A- 422 D configured to engage complementary openings  424 A- 424 D formed in the bottom shell  404 , to thereby secure the top shell  402  to the bottom shell  404 . Alternately or additionally, top shell  402  can be coupled to bottom shell  404  using one or more screws, bolts, pins, or other fasteners or the like. 
     As best seen in  FIG. 4B , a plurality of guiding features  426 A,  426 B are integrally formed in the bottom shell  404  and are configured to ensure that the plurality of I/O pins  414  are inserted into the correct holes of the protruding socket  316 . In particular, the guiding features  426 A,  426 B comprise tabs formed by cutting and bending the tabs outwards from the bottom shell  404 . The distance between the tabbed guiding features  426 A,  426 B can be substantially equal to the length of the protruding socket  316 . According to this embodiment, the I/O pins  414  are positioned between the tabbed guiding features  426 A,  426 B such that when the protruding socket  316  is aligned between the tabbed guiding features  426 A,  426 B, each of the I/O pins  414  is automatically aligned with the correct hole of the protruding socket  316 . Because the distance between the tabbed guiding features  426 A,  426 B is substantially equal to the length of the protruding socket  316 , the I/O pins  414  are inserted into the correct holes of the protruding socket  316  when the protruding socket  316  is aligned between the tabbed guiding features  426 A,  426 B. 
     To prevent the ONU transceiver module  400 A from tilting when plugged into the host device  318 , the ONU transceiver module  400 A includes a plurality of tabbed feet  428 A- 428 D integrated into the bottom shell  404 . The tabbed feet  428 A- 428 D are formed in some embodiments during the formation of openings  424 A- 424 D, as will be understood by those skilled in the art in view of the present disclosure. 
     In the embodiment of  FIGS. 4A-4B , the top of the ONU transceiver module  400 A, e.g., the top of top shell  402 , is positioned at a predetermined height above the PCB  334  of host device  318  by top shell  402  to allow proper mating of a heatsink (not shown) secured to posts  332 A,  332 B with the ONU transceiver module  400 A. In particular, top shell  402  can be manufactured in a variety of sizes to accommodate a variety of predetermined heights. The size of the top shell  402  can be varied by selecting a desired thickness for an extension  430  of the top shell  402 , without changing any of the other dimensions of the top shell  402 . For example, to position the top of the ONU transceiver module  400 A at a relatively high predetermined height, the top shell  402  will have a relatively thick extension  430 . In contrast, to position the top of the ONU transceiver module  400 A at a relatively low predetermined height, the top shell  402  will have a relatively thin extension  430 . Accordingly, the top shell  402  serves as a second example of a structural implementation of a means for positioning the top of an ONU transceiver module at a predetermined height above the PCB  334  of host device  318 . 
     Turning to  FIG. 4C , ONU transceiver module  400 B is similar in some respects to ONU transceiver module  400 A of  FIGS. 4A and 4B . In particular, the ONU transceiver module  400 B can include the same bottom shell  404 , PCB  406 , triplexer  408 , circuitry  410 , contacts  412 , I/O pins  414 , optical connector  420 , protrusions  422 A- 422 D, openings  424 A- 424 D, guiding features  426 A,  426 B, and tabbed feet  428 A- 428 D as the ONU transceiver module  400 A of  FIGS. 4A and 4B . Further, the guiding features  426 A,  426 B and tabbed feet  428 A- 428 D of  FIG. 4C  ensure that the I/O pins  414  are inserted correctly into the protruding socket  316  and prevent the ONU transceiver module  400 B from tilting when plugged into the host device  318  in the same way as the guiding features  426 A,  426 B and tabbed feet  428 A- 428 D of  FIGS. 4A and 4B . 
     In contrast, however, the ONU transceiver module  400 B includes a top shell  402 B that is different than the top shell  402  of  FIGS. 4A and 4B . Specifically, the top shell  402 B of  FIG. 4C  lacks the extension  430  of  FIGS. 4A and 4B . Instead, the ONU transceiver module  400 B of  FIG. 4C  includes a separate insert  432  configured to position the top of the ONU transceiver module  400 B at a predetermined height above the PCB  334  of host device  318  to allow proper mating of a heatsink (not shown) secured to posts  332 A,  332 B with the ONU transceiver module  400 B. The insert  432  can be manufactured in a variety of thicknesses to accommodate a variety of predetermined heights H 1  and can be secured to the top shell  402 B. To position the top of the ONU transceiver module  400 B at a relatively high predetermined height, the insert  432  will be relatively thick. In contrast, to position the top of the ONU transceiver module  400 B at a relatively low predetermined height, the insert  432  will be relatively thin. Accordingly, the insert  432  serves as a third example of a structural implementation of a means for positioning the top of an ONU transceiver module at a predetermined height above the PCB  334  of host device  318 . 
     Accordingly, the ONU transceiver modules  400 A and  400 B include a bottom shell  404  configured to (1) ensure that I/O pins are inserted correctly into the protruding socket of the host device via guiding features  426 A,  426 B and (2) prevent tilting of pluggable ONU transceiver modules when plugged into host devices with protruding sockets via tabbed feet  428 A- 428 D. Further, the ONU transceiver modules  400 A and  400 B include means for (3) positioning the top of the ONU transceiver module  400 A or  400 B at a predetermined height to contact a heatsink. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.