Patent Publication Number: US-11658763-B2

Title: Wavelength division multiplexing module

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/706,969, filed Sep. 18, 2017, now U.S. Pat. No. 10,439,750; which is a continuation of U.S. patent application Ser. No. 14/930,332, filed Nov. 2, 2015, now U.S. Pat. No. 9,768,900; which is a continuation of U.S. patent application Ser. No. 14/157,644, filed Jan. 17, 2014, now U.S. Pat. No. 9,197,346; which is a continuation of U.S. patent application Ser. No. 13/362,210, filed Jan. 31, 2012, now U.S. Pat. No. 8,660,429; which is a continuation of U.S. patent application Ser. No. 12/360,719, filed Jan. 27, 2009, now U.S. Pat. No. 8,107,816; which application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/024,450, filed Jan. 29, 2008, which applications are hereby incorporated by reference in their entireties. 
    
    
     FIELD 
     The present disclosure generally relates to fiber optic telecommunications equipment. More specifically, the present disclosure relates to modules for housing fiber optic telecommunications equipment. 
     BACKGROUND 
     In fiber optic telecommunications systems, it is common for optical fibers of transmission cables to be split into multiple strands, either by optical splitting of a signal carried by a single stranded cable or by fanning out the individual fibers of a multi-strand cable. Further, when such systems are installed, it is known to provide excess capacity in the installations to support future growth and utilization of the fibers. Often in these installations, modules including splitters or fanouts are used to provide the connection between transmission fibers and customer fibers. To reduce the cost and complexity of the initial installation and still provide options for future expansion, a module mounting chassis capable of mounting multiple modules may be used in such an installation. 
     While a chassis may accept several modules, the initial installation may only include fewer modules mounted in the chassis, or enough to serve current needs. These chassis may be configured with limited access to one or more sides, or may be mounted in cramped locations. In addition, some of these chassis may be pre-configured with the maximum capacity of transmission cables to accommodate and link to modules which may be installed in the future. Since it is desirable to have access to components within the chassis for cleaning during the installation of a new module, some provision or feature of the chassis will desirably permit a user to access and clean the connectors of these pre-connectorized and pre-installed transmission cables. 
     It is also desirable for the chassis to be configured to ensure that modules are installed correctly and aligned with other components within the chassis to mate with the pre-connectorized and pre-installed transmission cables. 
     In fiber-optic communications, it is also common for optical signals of transmission cables to be multiplexed. Wavelength division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths of laser light to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional communications over one strand of fiber. 
     A WDM system uses a multiplexer at the transmitter to join signals together and a demultiplexer at the receiver to split them apart. With the right type of fiber, it is possible to have a device that does both simultaneously, and can function as an optical add-drop multiplexer. WDM systems allow expansion of the capacity of the network without laying more fiber. 
     WDM systems are divided in different wavelength patterns: 1) conventional WDM; 2) dense WDM (DWDM); and 3) coarse WDM (CWDM). WDM, DWDM and CWDM are based on the same concept of using multiple wavelengths of light on a single fiber, but differ in the spacing of the wavelengths, number of channels, and the ability to amplify the multiplexed signals in the optical space. 
     In certain telecommunications applications, it might be desirable to combine wavelength division multiplexing technology with fiber optic signal splitting technology. 
     SUMMARY 
     The present invention relates to telecommunications equipment that combines wavelength division multiplexing technology and fiber optic signal splitting technology and packages it in a modular format. The module of the present disclosure includes an input for inputting a fiber optic signal to be split into multiple strands, an input for inputting a fiber optic signal to be demultiplexed into different wavelengths of laserlight, and an output for outputting a combination signal wherein a split signal and a demultiplexed wavelength are combined into a single output fiber. 
     According to one aspect, the module includes within the interior an optical multiplexer/demultiplexer, a fiber optic splitter, and an optical device for combining a split signal and a demultiplexed wavelength into an output fiber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the description, illustrate several aspects of the inventive features and together with the detailed description, serve to explain the principles of the disclosure. A brief description of the drawings is as follows: 
         FIG.  1    is an exploded view of a fiber optic wavelength-division multiplexing (WDM) module having features that are examples of inventive aspects in accordance with the present disclosure; 
         FIG.  2    illustrates the WDM module of  FIG.  1    in a fully assembled configuration including the input and the output signals going into and a coming out of, respectively, the module; 
         FIG.  3    is a right side view of the WDM module of  FIG.  1   ; 
         FIG.  4    is a left side view of the WDM module of  FIG.  1   ; 
         FIG.  5    is an exploded view of a module housing of the WDM module of  FIG.  1   ; 
         FIG.  6    is a perspective view of a splice holder/cable management structure of the WDM module of  FIG.  1   ; 
         FIG.  7    is a bottom view of the splice holder/cable management structure of  FIG.  6   ; 
         FIG.  8    is a front view of the splice holder/cable management structure of  FIG.  6   ; 
         FIG.  9    is a perspective view of another cable management structure of the WDM module of  FIG.  1   ; 
         FIG.  10    is a top view of the cable management structure of  FIG.  9   ; 
         FIG.  11    is a front view of the cable management structure of  FIG.  9   ; 
         FIG.  12    is a schematic view illustrating the fiber optic circuit of the WDM module of  FIG.  1   ; 
         FIG.  13    is a diagram illustrating a fiber optic splitter configured for use in the WDM module of  FIG.  1   ; 
         FIG.  14    is a diagram illustrating a multiplexer chip configured for use in the WDM module of  FIG.  1   ; 
         FIG.  15    is a diagram illustrating an optical add/drop filter configured for use in the WDM module of  FIG.  1   , the add/drop filter configured to combine a split signal and a demultiplexed wavelength into a single output fiber; 
         FIG.  16    is an exploded view of an input connection for inputting a signal into the splitter of the WDM module of  FIG.  1   ; 
         FIG.  17    illustrates the input connection of  FIG.  16    in a fully assembled configuration; 
         FIG.  18    illustrates an input connection in a fully assembled configuration for inputting a signal into the multiplexer chip of the WDM module to be demultiplexed into different wavelengths of laserlight; 
         FIG.  19    is a diagram illustrating the input connection of  FIG.  17    with the fiber optic circuit of the fiber optic splitter configured for use with the WDM module; 
         FIG.  20    is a diagram illustrating the input connection of  FIG.  18    with the fiber optic circuit of the multiplexer chip configured for use with the WDM module; 
         FIG.  21    is an exploded view of an output connection for outputting a signal from the WDM module of  FIG.  1   ; 
         FIG.  22    illustrates the output connection of  FIG.  21    in a fully assembled configuration; 
         FIG.  23    illustrates an example routing of a fiber optic cable from an input connection of the WDM module to an input location of the fiber optic splitter within the WDM module; 
         FIG.  24    illustrates an example routing of a fiber optic cable from an output location of the fiber optic splitter to an input location of an optical add/drop filter that is configured to combine a split signal and a demultiplexed wavelength into a single output fiber; 
         FIG.  25    illustrates an example routing of a fiber optic cable from an input connection of the WDM module to an input location of the multiplexer chip within the WDM module; 
         FIG.  26    illustrates an example routing of a fiber optic cable from an output location of the multiplexer chip to an input location of an optical add/drop filter that is configured to combine a split signal and a demultiplexed wavelength into a single output fiber; 
         FIG.  27    illustrates an example routing of a fiber optic cable from an output location of the optical add/drop filter that is configured to combine a split signal and a demultiplexed wavelength to an output connection of the WDM module; and 
         FIG.  28    is a diagram illustrating an example positioning of a plurality of output connections of the WDM module among a plurality of filler crimp tubes. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary aspects of the present disclosure which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or similar parts. 
       FIGS.  1 - 4    illustrate a telecommunications module  10  having features that are examples of inventive aspects in accordance with the present disclosure. Since one of the telecommunications equipment housed by the module  10  is a fiber optic wavelength division multiplexer/demultiplexer, the telecommunications module  10  may also be referred to herein as a fiber optic wavelength division multiplexing (WDM) module  10 . The WDM module  10  is configured to be inserted within a telecommunications chassis similar to the chassis shown and described in commonly-owned U.S. Pat. No. 7,536,075, the disclosure of which is incorporated herein by reference in its entirety. As will be described in further detail below, the WDM module  10  is also configured to be inserted into the telecommunications chassis in a similar manner to that shown and described in the U.S. patent application Ser. No. 11/975,905. 
     The WDM module  10  of the present disclosure is configured to power split an input signal into a plurality of signals. The WDM module  10  is also configured to demultiplex a second input signal into a plurality of wavelengths. An optical device  22  (e.g., an optical add/drop filter, a single channel filter, etc.) within the module  10  is configured to combine one of the power split signals and one of the demultiplexed wavelengths into a combination output signal that is output through the module  10 . The powersplitting function, the demultiplexing function and the signal combination function are all performed within the module  10 . 
     Referring to  FIG.  1   , the WDM module  10  is shown in an exploded orientation. WDM module  10  includes a module housing  12  that includes a main housing portion  14  and a removable cover  16 . The module housing  12  including the main housing portion  14  and the removable cover  16  is illustrated separately in  FIG.  5   , without the internal components of the module  10 . 
     Still referring to  FIG.  1   , the WDM module  10  is configured to house a fiber optic splitter  18 , a multiplexer/demultiplexer chip  20 , and a plurality of optical devices  22  configured to combine a split signal and a demultiplexed wavelength into a single output signal. According to one embodiment, the optical devices  22  that are configured to combine a split signal and a demultiplexed wavelength into a single output signal may be optical add/drop filters. Optical add/drop filters and their uses are known in the art. The optical add/drop filters may also be called single channel filters. Other types of devices performing the same function are possible. 
     The fiber optic splitter  18  is adapted to power split a first input fiber optic signal entering the module  10  into multiple strands. The multiplexer/demultiplexer chip  20  is configured to demultiplex a second input fiber optic signal entering the module  10  into different wavelengths of laserlight. Each of the optical devices  22  (e.g., add/drop filters) is configured to combine one of the split signals and one of the demultiplexed wavelengths into a single output fiber. Each of the combination signals are then output from the module  10 . In the embodiment shown, the fiber optic splitter  18  is a 1×8 splitter and the multiplexer/demultiplexer  20  is an 8-channel chip. Accordingly, in the embodiment of the module  10  shown, 1 splitter input signal and 1 multiplexer input signal get output as 8 separate combination signals. 
     A fiber optic circuit diagram of the WDM module  10  of  FIGS.  1 - 4    is shown in  FIG.  12   .  FIG.  13    diagrammatically illustrates the fiber optic splitter  18  configured for use in the WDM module  10 .  FIG.  14    diagrammatically illustrates the multiplexer chip  20  configured for use in the WDM module  10 .  FIG.  15    diagrammatically illustrates one of the add/drop filters  22  configured for use in the WDM module  10  of  FIG.  1   , wherein the add/drop filter  22  is configured to combine a split signal and a demultiplexed wavelength into an output signal. 
     According to one example embodiment shown in  FIG.  12   , a signal input into the fiber optic splitter  18  gets split into 8 separate signals, each separate signal being the same as the original input signal. It should be noted that in other embodiments, the fiber optic splitter  18  may power split the signal into different power levels, rather than into the same signal. From an output  24  of the splitter  18 , each of the split signals get spliced into an input  26  (i.e., PASS leg) of each of the add/drop filters  22 . Likewise, a signal input into the multiplexer chip  20  gets demultiplexed into 8 different wavelengths. Each wavelength gets output from the multiplexer chip  20  as a separate signal and is spliced into another input  28  (i.e., REF leg) of the each of the add/drop filters  22 . The signals from the splitter  18  and the multiplexer chip  20  are combined at the add/drop filters  22  and output from the add/drop filters  22  (e.g., at COM leg) as 8 combination signals. 
       FIG.  2    illustrates the WDM module  10  with the two input signal cables  30 ,  32  going into the module  10  and the eight combination output signal cables (each one designated as “ 34 ”) coming out. As shown, the input cables  30 ,  32  and the output cables  34  may be connectorized and be forwarded on to appropriate locations through fiber optic adapters  36 . As shown in  FIG.  2   , the module housing  12  includes a cable exit  38  for outputting the combination fiber optic signals out of the module  10  and to customers. 
     Referring back to  FIG.  1   , the WDM module  10  includes a number of cable management/routing features for correctly orienting the cables within the module  10 , as will be described in further detail below. One such feature is a splice holder/cable management structure  40  that is configured to house the plurality of fiber optic splices  42  within the module  10  and also route fiber optic cables through the module  10  (shown in further detail in  FIGS.  6 - 8   ). Another cable routing feature is a cable management structure  44 . In the depicted embodiment, the cable management structure is shown located between the fiber optic splitter  18  and the add/drop filters  22  (shown in further detail in  FIGS.  9 - 11   ). In other embodiments, the cable management structure  44  could be located between the fiber optic splitter  18  and the bottom wall  54  of the module  10 . A fiber retainer  46  that is removably mounted to the main housing portion  14  of the module housing  12  is also shown in  FIG.  1   . The fiber retainer  46  helps keep cables spooled around a first radius limiter  48  within the main housing  14  of the module  10 . 
       FIGS.  2 - 4    illustrate the module  10  in a fully assembled configuration with the cover  16  mounted on the main housing portion  14 . 
       FIG.  5    illustrates the housing  12  of the module  10  in isolation, with the internal features of the module  10  removed therefrom. Referring to  FIG.  5   , the main housing portion  14  defines a first sidewall  50  extending between a top wall  52 , a bottom wall  54 , a rear wall  56 , and a front wall  58 . Removable cover  16  defines a second sidewall  60  of the module housing  12  and closes off an open side  62  of the module main housing portion  14 . Cover  16  is mounted to main housing portion  14  by fasteners through fastener holes  64  in the cover  16  and fastener mounts  66  defined on main housing portion  14 . The cover  16  may include a label  68  placed thereon with indicia relating to the module  10  (see  FIGS.  1  and  3   ). 
     The main housing portion  14  defines a top mounting flange  70  and a bottom mounting flange  72  of the WDM module  10  extending from the top and bottom walls  52 ,  54 , respectively. As discussed previously, the WDM module  10  of the present application is configured for insertion into a chassis similar to the one described in U.S. patent application Ser. No. 11/975,905 and in a similar manner to that described therein. As such, similar to the modules and the chassis described in U.S. patent application Ser. No. 11/975,905, the bottom flange  72  and a corresponding slot on the chassis are smaller in size than top flange  70  and the corresponding top slot on the chassis. Bottom slot of the chassis is sized such that, while bottom flange  72  fits into the bottom slot of the chassis, the larger top flange  70  does not fit. This ensures that the WDM module  10  is positioned within a front opening of a chassis in a particular desired orientation to correctly position the cable inputs and the outputs relative to the chassis. 
     It should also be noted that while the housing  12  of the WDM module  10  of the present application is configured similarly to those of the modules shown in described in U.S. patent application Ser. No. 11/975,905 for mounting purposes, the WDM module  10  of the present application has certain differences. The WDM module housing  12  of the present application has the depth of two of the modules of U.S. patent application Ser. No. 11/975,905. As such, the WDM module  10  of the present application occupies two mounting locations within a chassis such as the chassis shown in U.S. patent application Ser. No. 11/975,905. 
     Still referring to  FIG.  5   , the rear wall  56  of main housing portion  14  includes a curved portion  74  configured to provide bend radius protection to cables within interior of the module  10 . Similar to modules of U.S. patent application Ser. No. 11/975,905, the rear wall  56  of main housing  14  includes an inset portion  76 . The inset portion  76  might be used to accommodate a pair of fiber optic connectors protruding out of the rear wall  56 , if, for example, a rear input configuration is desired instead of a front input configuration. It should be noted that in the depicted embodiment, the WDM module  10  includes a front input configuration. Thus, the slots  78  for receiving fiber optic connectors at the rear wall  56  may be covered with inserts  80  (see  FIG.  5   ). In U.S. patent application Ser. No. 11/975,905, the modules are shown with a rear input configuration wherein rear fiber optic connectors protrude from the rear wall at the inset portion of the module housing. As noted before, a rear input configuration is certainly one option for the WDM module  10  of the present application. In such a configuration, fiber optic connectors protruding rearwardly from rear wall  56  would mate with fiber optic adapters of adapter assemblies that are mounted within the chassis. 
     Still referring to  FIG.  5   , in the depicted embodiment, the input connections  82 ,  84  are provided at the front of the module main housing  14 .  FIG.  16    illustrates an exploded view of an input connection  82  for inputting a signal into the splitter  18  of the WDM module  10  and  FIG.  17    illustrates the input connection  82  of  FIG.  16    in a fully assembled configuration.  FIG.  19    is a diagram illustrating the input connection  82  with the fiber optic splitter  18  configured for use in the WDM module  10 . 
       FIG.  18    illustrates a fully assembled view of the input connection  84  for inputting a signal into the multiplexer chip  20  of the WDM module  10  to be demultiplexed into different wavelengths of laserlight.  FIG.  20    is a diagram illustrating the input connection  84  with the multiplexer chip  20  configured for use in the WDM module  10 . 
     As shown in  FIGS.  16 - 20   , each input connection  82 ,  84  (whether for the fiber optic splitter  18  or the multiplexer chip  20 ) includes a boot  86  that mates with a crimp element  88 . The crimp element  88  defines a circumferential notch  90  (i.e., recessed portion). The circumferential notch  90  is slidably inserted into a slot  92  defined on an insert piece  59  that is fastened to the front wall  58  of the main housing portion  14  with fasteners (see  FIGS.  1  and  5   ). The crimp elements  88  of the input connections  82 ,  84  are captured by the cover  16  when the cover  16  is mounted on the main housing  14 . 
     As mentioned previously, the embodiment of the WDM module  10  illustrated includes the cable exit  38  at the front of module main housing  14  (see  FIG.  1   ). The cable exit  38  is slidably mounted to main housing  14  of the WDM module  10  and is captured by the cover  16  when cover  16  is mounted to main housing  14 . The cable exit  38  defines a protruding rear lip  94  that is slidably inserted into a slot  96  defined around a front aperture  98  defined at the front wall  58  for accommodating the cable exit  38 . The cable exit  38  permits telecommunications cables within the module  10  to be directed outside of the module  10 . The cable exit  38  is preferably sized to fit within the profile of the WDM module  10  to preserve the density of a telecommunications assembly having a plurality of modules  10  mounted adjacent to each other. 
     The front wall  58  of the module main housing  14  is angled with regard to a front opening of a chassis, which may aid in directing cables entering and exiting the WDM module  10  toward a desired location. In other embodiments, front walls could be made generally parallel to a front of chassis within the scope of the present disclosure. 
     As noted above, the WDM module  10  of the present application includes similar features to those modules shown and described in U.S. patent application Ser. No. 11/975,905 for mounting purposes. As such, the main housing portion  14  includes an integrally formed flexible latch  100  (i.e., cantilever arm) that is adapted to engage a portion of a chassis to hold module  10  within a front opening of the chassis. Flexible latch  100  also deflects to permit withdrawal of the module  10  from a chassis. The flexible latch  100  of the module  10  is constructed similarly to that of modules of U.S. patent application Ser. No. 11/975,905 and includes a finger grip tab  102 , a front latching tab  104  and a rear latching tab  106  that cooperate with a bulkhead at a mounting location of a chassis. The WDM module  10  also includes a fixed grip tab  108  opposing and adjacent to flexible latch  100  to aid removal of module  10  from chassis. Fixed grip tab  108  is preferably positioned on module  10  opposite latch  100  so that a user may apply opposing force on latch  100  and fixed grip tab  108  to securely grasp module  10  and remove it from a chassis with two adjacent fingers of the hand. The insertion of the WDM module  10  into a chassis is similar to that of modules described in U.S. patent application Ser. No. 11/975,905. 
     Now referring back to  FIG.  5   , within interior of main housing  14 , module includes a first radius limiter  48  adjacent the curved portion  74  of rear wall  56  of main housing  14 . The WDM module  10  includes a second radius limiter  110  adjacent front wall  58  of housing  12  near the cable exit  38 . As will be discussed in further detail below, the radius limiters  48 ,  110  provide bend-protection to fiber cables within the module  10  while providing cable management/routing functionality. 
     Still referring to  FIG.  5   , the module main housing  14  also includes integrally formed crimp holders  112  (e.g., slots) adjacent the front wall  58  of housing  14  underneath the second radius limiter  110 . Crimp elements  114  (see  FIGS.  21 - 22   ) crimped to the ends of cables that are extending from the output locations  116  of the add/drop filters  22  are slidably received into the crimp holders  114 . Crimp elements  114  include square flanges  118  between which are defined recessed portions  120 . The crimp holders  112  include complementary structure to the crimp elements  114  such that once the crimp elements  114  are slidably inserted into the crimp holders  112 , the crimp elements  114  are prevented from moving in a longitudinal direction due to the flanges  118 . Once slidably inserted, crimp elements  114  are held in place by the cover  16  that is mounted on the module main housing  14 . The assembly of an output connection  122  for outputting a signal from the WDM module  10  is shown in detail in  FIGS.  21  and  22   . A crimp element  114  is crimped and terminated to a cable in a manner commonly known in the art. 
     In the embodiment shown, there are four crimp holding slots  112 , each slot  112  being able to accommodate up to eight crimp elements  114  (see  FIG.  28   ). Since there are eight combination output signals in the embodiment of the WDM module  10  shown, the output cables  34  occupy eight crimp holding positions  124 . The rest of the positions  124  may be filled with dummy crimp elements or inserts/fillers that are not connected to cables, making sure the crimp elements  114  crimped to active output cables  34  do not slide out of the slots  112 . In  FIG.  28   , one example positioning of a plurality of “active” crimp elements  114  among filler crimp elements is shown. 
     In the embodiment of the module shown, the crimp holders  112  provide the capacity for up to thirty-two crimp elements  114  connected to output cables  34 . Thus, the WDM module  10  of the present disclosure could house, if desired, a 1×32 fiber optic splitter and a 32 channel multiplexer. Also, the configuration of the module housing  12  can certainly be modified to accommodate other number of inputs or outputs, as desired. In addition, other complementary shapes between the crimp elements  114  and the crimp holders  112  are possible to provide a slidable fit and to prevent axial movement of the crimp elements  114  within the crimp holders  112 . 
     Still referring to  FIG.  5   , the first radius limiter  48  defines a curved wall  126 . The curved wall  126  includes a first end  128  and a second end  130 . The first and second ends  128 ,  130  of the curved wall  126  act as guides in positioning the multiplexer chip  20  within the main housing  14  (see  FIGS.  23 - 27   ). Also as shown in  FIGS.  23 - 27   , the bottom wall  54  of the module main housing  14 , the ends  128 ,  130  of the curved wall  126  of the first radius limiter  48 , the splice holder  40  adjacent the top wall  52  of the module main housing  14  and a tab  132  extending from the crimp holding structure  112  define a frame structure around the multiplexer chip  20  for correctly positioning the multiplexer chip  20  within the interior of the main housing portion  14 . As shown in  FIGS.  1  and  23 - 27   , once the multiplexer chip  20  is placed within the main housing portion  14 , the fiber optic splitter  18  and the add/drop filters  22  are placed next adjacent thereto and held within the module  10  against the chip  20  by the removable cover  16 . 
     As noted above, the fiber retainer  46  may be placed on the main housing portion  14  to keep cables wrapped around the first radius limiter  48 . The fiber retainer  46  is planar and includes a circular shape to match the contour of the curved portion  74  of the rear wall  56  of the main housing  14 . The fiber retainer  46  includes three tabs  134  positioned around the periphery. The three tabs  134  are placed within slots  136  formed around the curved portion  74  of the rear wall  56 . The fiber retainer  46  includes a circular opening  138  which accommodates a portion of the first radius limiter  48  that protrudes through the opening  138 . When the fiber retainer  46  is placed on the main housing portion  14 , it lies flush with the main housing portion  14  and is held thereagainst by the cover  16 . 
       FIG.  5    also illustrates the cover  16  of the WDM module  10 . The cover  16  is configured to be fastened to the module main housing portion  14 . The cover  16  defines a similar contour as the main housing portion  14  and captures the internal components within the module  14 . The cover  16  includes protruding portions  140  defined around the periphery and slots  142  defined between the protruding portions  140  that intermate with corresponding structures located around the periphery of the main housing  14  for correctly placing the cover  16  onto the main housing  14 . 
       FIGS.  6 - 8    illustrate the splice holder/cable management structure  40  of the WDM module  10  in detail. The splice holder/cable management structure  40  is configured to be placed within the module  10  between the top wall  52  and the multiplexer chip  20  (see  FIGS.  1  and  23 - 27   ). The splice holder  40  includes a first wall  144  and second and third integral sidewalls  146 ,  148  extending perpendicularly from the first wall  144 . The second and third sidewalls  146 ,  148  define a channel  150  thereinbetween for guiding fiber optic cables therethrough. When the splice holder/cable management structure  40  is placed within the module  10 , the third wall  148  rests against the multiplexer chip  20  (see  FIGS.  23 - 27   ). And, when mounted, the second wall  146  and the top wall  52  of the main housing portion  14  of the module  10  define a pocket  152  for placing the fiber optic splice elements  42  therein. The second wall  146  keeps the fiber optic splice elements  42  in the pocket  152  separated from the fiber optic cables passing through the channel  150  defined between the second and third sidewalls  146 ,  148 . In this manner, any epoxy residue remaining in the splice area is kept away from the cables passing through the channel  150 . 
     As will be discussed in further detail below, when the module input  82  for the splitter  18  is first routed to the fiber optic splitter input  154  (see  FIG.  23   ), the cable may pass through the pocket  152 , over the splice elements  42 . Similarly, the module input  84  for the multiplexer chip  20  may pass through the pocket  152 , over the splice elements  42 , when being routed to the input location  158  of the multiplexer chip (see  FIG.  25   ). 
     Still referring to  FIGS.  6 - 8   , the third wall  148  of the splice holder/cable management structure  40  may include an inset portion defined by a notch  160  for accommodating fiber optic cables wrapped around a spool  162  defined by the first radius limiter  48 . The notch  160  on the third wall  148  allows for expansion of fiber optic cables around the spool  162 . 
       FIGS.  9 - 11    illustrate the cable management structure  44  of the WDM module  10 . The cable management structure  44  is configured to be placed into the module  10  after the placement of the multiplexer chip  20 . In one embodiment, the cable management structure  44  is configured to be located between the fiber optic splitter  18  and the add/drop filters  22 . As mentioned previously, in other embodiments, the cable management structure  44  may be located between the fiber optic splitter  18  and the bottom wall  54  of the module housing  14 . The cable management structure  44  includes a U-shaped configuration with a first wall  164  and integral second and third sidewalls  166 ,  168  defining a channel  170  thereinbetween. The channel  170  guides fiber optic cables therethrough when routed within the module  10  as will be discussed in further detail below. 
     Now referring back to  FIG.  1   , when the module  10  is assembled, the multiplexer chip  20  is placed into the main housing  14  first. The fiber optic splitter  18  and the add/drop filters  22  are placed after the multiplexer chip  20  with the splitter  18  being separated from the add/drop filters  22  by the cable management structure  44 . As noted previously, the cable management structure  44  may be located between the splitter  18  and the bottom wall  54  of the main housing  14 . Splice elements  42  are located adjacent the top wall  52  of the main housing  14  and are separated from the multiplexer chip  20  by the splice holder/cable management structure  40 . The fiber retainer  46  is placed on the first radius limiter  48  after the fiber cables have been routed to keep the fiber cables wrapped around the spool  162  of the first radius limiter  48 . The cover  16  holds the internal components of the module  10  within the housing  12 . 
     The WDM module  10  is shown in  FIGS.  23 - 27    with the cover  16  and the fiber retainer  46  removed from the main housing portion  14  to illustrate the internal components and the routing of the cables therein. It should be noted that the routing of the cables illustrated in  FIGS.  23 - 27    represents simply one example arrangement for the depicted module  10  and other arrangements are certainly possible. 
     In  FIG.  23   , an example routing arrangement of a first fiber optic cable  172  from an input location  82  of the WDM module  10  to an input location  154  of the fiber optic splitter  18  within the WDM module  10  is illustrated. A first cable  172  extends from the input connection location  82  of the module  10  upwardly toward the splice holder/cable management structure  40  and through the pocket  152  defined at the splice location, over the splice elements  42  (not shown in  FIG.  23   ). From the splice holder/cable management structure  40 , the first cable  172  extends downwardly and around the first radius limiter  48  and is spooled around the first radius limiter  48  as many times as necessary. After leaving the first radius limiter  48 , the first cable  172  extends toward the front of the module  10  upwardly and around the second radius limiter  110 . From the second radius limiter  110 , the first cable  172  extends downwardly and to the input location  154  of the fiber optic splitter  18 . The fiber optic splitter  18  splits the optical signal into a plurality of signals. In the given embodiment, a 1×8 splitter is used, and, thus the signal from the first cable  172  may be split into eight signals. 
     It should be noted that various different types of fiber optic splitters may be used within the module  10 . According to one embodiment, the fiber optic splitters may split an input signal into a plurality of the same signals. In other embodiments, fiber optic splitters that split the input signal into different power levels (i.e., different ratios), rather than into the same signal, may be used. 
     In  FIG.  24   , an example routing of a fiber optic cable  174  from an output location  24  of the fiber optic splitter  18  to an input location  26  of an add/drop filter  22  that is configured to combine a split signal and a demultiplexed wavelength into a single output signal is illustrated. It should be noted that only one of the eight fiber cables  174  from the splitter  18  to the add/drop filter  22  is illustrated for clarity purposes. Other seven of the split signals carried by seven other fiber cables  174  would follow a similar path to the one that will be described. 
     Referring to  FIG.  24   , the second cable  174  extends from the output location  24  of the splitter  18  and upwardly around the first radius limiter  48 . The second cable  174  is spooled around the first radius limiter  48  as many times as needed. From the first radius limiter  48 , the second cable  174  starts to extend toward the splice holder/cable management structure  40  and is spliced at the splice location to a third cable  176 . The third cable  176  extends toward the front of the module  10  from the splice location and around the second radius limiter  110 . From the second radius limiter  110 , the third cable  176  extends downwardly and through the channel  170  formed by the cable management structure  44  located between the splitter  18  and the add/drop filters  22  and toward the rear of the module  10 . From the channel  170 , the third cable  176  goes upwardly around the first radius limiter  48  as many times as needed and through the channel  150  defined by the splice holder/cable management structure  40  toward the front of the module  10 . From the splice holder/cable management structure  40 , the third cable  176  goes around the second radius limiter  110  once again and downwardly to the input location  26  of the add/drop filter  22  (i.e., the PASS leg of the filter  22 ). 
     In  FIG.  25   , an example routing of a fiber optic cable  178  from an input location  84  of the WDM module  10  to an input location  158  of the multiplexer chip  20  within the WDM module  10  is illustrated. 
     Referring to  FIG.  25   , the fourth cable  178  extends from the input connection  84  of the module  10  upwardly toward the splice holder/cable management structure  40  and through the pocket  152  defined at the splice location, over the splice elements  42  (not shown in  FIG.  25   ). From there, the fourth cable  178  extends downwardly and around the first radius limiter  48  and is spooled around the first radius limiter  48  as many times as needed. After leaving the first radius limiter  48 , the fourth cable  178  ends up at the input location  158  of the multiplexer chip  20 . The multiplexer chip  20  demultiplexes the optical signal carried by the fourth cable  178  into different wavelengths of laserlight. In the given embodiment, an 8-channel multiplexer chip is used, and, thus, the signal from the fourth cable  178  will be demultiplexed into eight different wavelengths. 
     In  FIG.  26   , an example routing of a fiber optic cable  180  from an output location  182  of the multiplexer chip  20  to an input location  28  of an add/drop filter  22  that is configured to combine a split signal and a demultiplexed wavelength into a single output signal is illustrated. It should be noted that routing of only one of the eight fiber cables  180  from the multiplexer chip  20  to the add/drop filter  22  is illustrated for clarity purposes. Other seven of the cables  180  carrying the other seven demultiplexed wavelengths would follow a similar path to the one that will be described. 
     Referring to  FIG.  26   , the fifth cable  180  extends from the output location  182  of the multiplexer chip  20  and upwardly and around the second radius limiter  110 . From the second radius limiter  110 , the fifth cable  180  extends toward the rear of the module  10  through the channel  150  defined by the splice holder/cable management structure  40 . From the splice holder/cable management structure  40 , the fifth cable  180  extends downwardly around the first radius limiter  48  as many times as needed. From the first radius limiter  48 , the fifth cable  180  extends toward the front of the module  10  through the channel  170  formed by the cable management structure  44 . From the cable management structure  44 , the fifth cable  180  extends upwardly toward the second radius limiter  110  and around the second radius limiter  110 . From the second radius limiter  110 , the fifth cable  180  extends toward the splice holder/cable management structure  40  and is spliced at the splice location to a sixth cable  184 . The sixth cable  184  extends from the splice location toward the rear of the module  10  and around the first radius limiter  48 . The sixth cable  184  is spooled around the first radius limiter  48  as many times as needed. From the first radius limiter  48 , the sixth cable  184  extends toward the front of the module  10  to the input location  28  of the add/drop filter  22  (i.e., REF leg of the filter  22 ). 
     In  FIG.  27   , an example routing of a fiber optic cable  186  from an output location  116  of the add/drop filter  22  (i.e., COM leg of filter  22 ) that is configured to combine a split signal and a demultiplexed wavelength to an output signal of the WDM module  10  is illustrated. 
     Referring to  FIG.  27   , the seventh cable  186  carrying a combination signal extends from the output  116  of the add/drop filter  22  toward the rear of the module  10 . The seventh cable  186  extends upwardly around the first radius limiter  48  and is spooled around the first radius limiter  48  as many time as needed. From the first radius limiter  48 , the seventh cable  186  extends toward the front of the module  10  through the channel  150  defined by the splice holder/cable management structure  40 . From the splice holder/cable management structure  40 , the seventh cable  186  is led to the crimp holders  112  of the module  10  and is crimped to a crimp element  114 . The eighth cable  34  (i.e., output cable  34 ) extends from the other end of the crimp element  114  to the cable exit  38  of the module  10 . It should be noted that the routing for only one of the cables going from the add/drop filter output  116  to the module output has been described for clarity purposes. There are eight add/drop filters  22  for combining a split signal and a demultiplexed wavelength. Each of the cables extending from each add/drop filter output  116  to the module exit  38  may follow a similar path to that described above. 
     As noted above, the routing of the fiber optic cables within module  10  as shown in  FIGS.  23 - 27    is only one example and other ways of routing the cables within the module  10  are possible. 
     As noted previously, according to one embodiment, the WDM module  10  may house an 8-channel wavelength division multiplexing chip. According to another embodiment, the WDM module  10  may house a 4-channel wavelength division multiplexing chip. According to another embodiment, the WDM module  10  may house a 16-channel wavelength division multiplexing chip. In other embodiments, the module  10  may house other types of wavelength division multiplexing chips. In all the embodiments, the WDM module  10  may house fiber optic splitters that are configured to split a signal into a number of signals corresponding to the number of demultiplexed wavelengths. The fiber optic splitters used may power split the signal into the same signals or into different power levels/ratios. 
     The disclosures of the following U.S. Patents are also incorporated herein by reference in their entirety: U.S. Pat. No. 5,363,465, issued Nov. 8, 1994, entitled FIBER OPTIC CONNECTOR MODULE; U.S. Pat. No. 5,317,663, issued May 20, 1993, entitled ONE-PIECE SC ADAPTER; U.S. Pat. No. 7,376,322, issued May 20, 2008, entitled FIBER OPTIC MODULE AND SYSTEM INCLUDING REAR CONNECTORS; U.S. Pat. No. 7,400,813, issued Jul. 15, 2008, entitled FIBER OPTIC SPLITTER MODULE; U.S. Pat. No. 7,376,323, issued May 20, 2008, entitled FIBER OPTIC ADAPTER MODULE; and U.S. Pat. No. 7,346,254, issued Mar. 18, 2008, entitled FIBER OPTIC SPLITTER MODULE WITH CONNECTOR ACCESS. 
     The above specification, examples and data provide a complete description of the manufacture and use of the disclosure. Since many embodiments of the disclosure can be made without departing from the spirit and scope of the inventive aspects, the inventive aspects resides in the claims hereinafter appended.