Abstract:
A pluggable optical module for use with optical communication systems, wherein the pluggable optical module comprises a housing having an opening arranged to receive a subassembly, wherein the subassembly is capable of being removably inserted into the housing.

Description:
FIELD OF THE INVENTION 
     The present invention relates to pluggable optical sub-assemblies for use with optical communications systems. 
     DISCUSSION OF THE BACKGROUND ART 
     Pluggable modules such as optical transmitters, receivers or transceiver are known and their use is becoming more commonplace in optical communications systems. European patent application number 01310415.3 discloses a known pluggable module, which houses both a transmitter and receiver which both fixedly disposed within the module housing. These modules can be easily inserted into a communication system&#39;s rack or chassis, often without having to power down the system. This is known in the art as “hot pluggability”. 
     However, as communications systems evolve it is becoming desirable to change the wavelength or indeed the mode of operation of the module. For example, a system originally operating at 1300 nm using course wavelength division multiplexing (CWDM) may in time need to operate at 1550 nm and use dense wavelength division multiplexing (DWDM). Currently, such a change would require an entirely new module be inserted into the system chassis, or the existing module be removed and re-assembled with new parts to allow for the new functionality. This is both time-consuming and expensive. 
     Furthermore, many of the customer facing parameters of the module, such as physical size and electrical connection are becoming common to all optical modules of a certain type and are previously agreed to under what is known in the industry as “multi source agreements” or are dictated by standards set by, for example, IEEE. 
     Thus it is desirable to make use of the existing module housing and yet be able to easily and inexpensively change the internal functionality of the module. 
     It is an object of the present invention to provide a solution to the above mentioned problem. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a pluggable optical module comprising a housing, said housing being adapted to receive a subassembly, said subassembly capable of being removably inserted into said housing. 
     Thus the present invention provides an easy and inexpensive means for changing the functionality of an optical module. This may be achieved without having to remove the parent module from the system chassis or even having to power down the system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the principle advantages and features of the invention have been described above, a greater understanding and appreciation of the invention may be obtained by referring to the drawings and detailed description of an embodiment, presented by way of example only, in which; 
         FIGS. 1   a  and  1   b  show an embodiment of the present invention, 
         FIGS. 2   a ,  2   b  and  2   c  show an alternative embodiment of the present invention, 
         FIGS. 3   a  and  3   b  show yet a further embodiment of the present invention, 
         FIG. 4  shows an exposed view of a possible internal configuration of the pluggable subassembly shown in  FIG. 1   a,    
         FIG. 5  shows an exposed view of a further possible internal configuration of the pluggable subassembly shown in  FIG. 1   a,    
         FIG. 6  shows a more detailed view of an example of the electrical connection means of the pluggable subassembly shown in  FIG. 1   a , and 
         FIGS. 7 and 8  show examples of means for detecting the type of pluggable subassembly. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As seen in  FIG. 1   a , the present invention comprises a pluggable module  10 , which has outer physical parameters common to all types of transceivers or transponder made according to an agreed standard. For example, the module seen in  FIGS. 1   a  and  1   b  is designed according to the DWDM pluggable transceiver MSA (http://www.hotplugdwdm.org/msa.htm). Module  10  is easily inserted into a system chassis via the grooves  12  disposed by either side of the module. Electrical connection between the module and the system is established via electrical connectors  14  disposed at the rear of the module. Now according to the present invention, module  10  is arranged to receive, for example, via an opening  13  in front plane  16  a pluggable subassembly  18 . The subassembly could be a receiver subassembly or a transmitter subassembly. The module could be arranged to receive one pluggable subassembly, for example, a transmitter assembly, or two subassemblies, such as a transmitter subassembly and a receiver subassembly. The subassembly could also be a transceiver subassembly. The subassembly may have a latch  19  disposed at the front in order to aid in the insertion and/or removal of the subassembly from the parent module  10 . The subassembly may include some local means for retaining the subassembly within the parent module. Furthermore, the parent module and subassembly may be arranged so that the subassembly can be inserted or removed from the parent module without having to power down the module or host system, thus being hot pluggable. 
       FIG. 1   a  shows the subassembly  18  just prior to being inserted into opening  13  in the parent module and  FIG. 1   b  shows the subassembly fully inserted into the parent module. 
     The subassembly  18  of  FIGS. 1   a  and  1   b  may be, for example, a CWDM type optical transmitter operating at 1300 nm. Should the operator wish to change the configuration of his system to for example, to a DWDM system operating at 1550 nm, the CWDW subassembly can be easily removed and a new optical transmitter subassembly configured to operate as a DWDM system at 1550 nm inserted. Alternatively, the CWDM wavelength could be the same as the DWDM wavelength with the operator simply wanting to swap a 1550 nm CWDM part for a 1550 DWDM part. Similarly, an operator customer may wish to change a 1300 nm CWDM part for a 1550 CWDM part. Furthermore, as will be appreciated by the person skilled in the art, the wavelengths of the subassemblies could vary anywhere between 1270 nm to 1620 nm or beyond, depending on the system&#39;s requirements. This applies to both CWDM and DWDM subassemblies. Alternatively, it may be desirable to change the receiver subassembly from a PIN type receiver to an APD based receiver. 
       FIGS. 2   a ,  2   b  and  2   c  show an alternative embodiment of the present invention in which the parent module  20  is of a type known in the industry as Small Form-Factor Pluggable and has external features which conform to industry standards known as SFP (Small form-factor pluggable transceiver MSA) (http)://schelto.com/SFP/SFP%20MSA.pdf). As with the embodiment shown in  FIGS. 1   a  and  1   b , it is possible to have a pluggable transmitter subassembly  28   a , a pluggable receiving subassembly  28   b , or both. Here the latch  29  is part of the parent module to aid in inserting and removing the parent from a host system chassis. The latch may also function to hold the subassemblies securely in place. 
     In  FIGS. 3   a  and  3   b  yet a further embodiment of the present invention is shown in which the pluggable subassembly  38  is inserted into a suitable configured opening  33  in a top surface  31  of the parent module  30 . The subassembly can snap fit into place with electrical connections being established between the subassembly and the parent module via suitable designed electrical connection on the underside  35  of the subassembly. For example, a BGA (Bulk Grid Array) type connector could be used. As with the previous embodiments, the parent module can be configured to accept either a transmitter subassembly, receiver subassembly, or both. 
     As previously stated, the subassembly could be a transceiver or receiving subassembly. The subassembly could be suitable for DWDM or CWDM operation. For example, as seen in  FIG. 4 , the subassembly of the type shown in  FIGS. 1   a  and  1   b  is shown with its internal components exposed. In this example the subassembly  40  is a transmitter configured for DWDM operation comprising a laser  41 , optics  42 , wavelength isolator  43 , temperature sensor  44 , and a temperature control  45  such as a TEC (thermoelectric cooler). As will be appreciated components can be added or removed from the subassembly depending on the specific requirements of the subassembly. For example, as seen in  FIG. 5 , subassembly  50  is configured for CWDM operation and comprises a laser  51  and optics  52 . 
     Both the subassemblies  40  and  50  of  FIGS. 4 and 5  have electrical connectors  46 ,  56  disposed at the rear of the subassembly which make electrical connection with electrical sockets  48 ,  58  disposed on PCBs  49 ,  59  respectively. 
     As seen in  FIG. 6 , an alternative electrical connector  66  may be used with receiver subassembly  60  and electrically connected to the parent module via electrical socket  68  located on PCB  69 , much the same way as for transmitter subassemblies. 
     PCBs  49 ,  59 ,  69  are located within the parent modules and may form the base onto which a variety of other components required by the parent module are disposed. For example as seen in  FIGS. 7 and 8  an integrated circuit (IC)  75 ,  78  may also be located on the PCB  59 ,  79 . The IC may be configured to examine the subassembly once it has been plugged into the parent module to identify what type of subassembly is present, for example a CWDM or DWDM transmitter. Similarly, the IC  75  could identify whether the receiver subassembly  70  contained a PIN or ADP type detector. 
     Once identification of the specific configuration of the subassembly had been determined, preprogrammed operating parameters could be executed and the transceiver or transponder module could begin to function accordingly. 
     Advantageously, the present invention allows for optical transceiver and transponder modules to be easily and inexpensively upgraded from one wavelength to another or from CWDM to DWDM configuration without replacing the entire module. 
     It is not intended that the present invention be limited to the above embodiments and other modifications and variations are envisaged within the scope of the claims.