Patent Publication Number: US-2022231779-A1

Title: Passive optical network distribution systems and components thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 16/939,309, filed Jul. 27, 2020, which is a continuation of application Ser. No. 16/298,564, filed Mar. 11, 2019, now U.S. Pat. No. 10,727,972, which is a continuation of application Ser. No. 15/443,851, filed Feb. 27, 2017, now U.S. Pat. No. 10,230,484, which is a continuation of application Ser. No. 14/636,497, filed Mar. 3, 2015, now U.S. Pat. No. 9,584,248, which application claims the benefit of provisional application Ser. No. 61/947,210, filed Mar. 3, 2014, which applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present application relates generally to distribution of passive optical network services, and in particular to passive optical network distribution systems and components thereof. 
     BACKGROUND 
     Passive optical networks are becoming prevalent in part because service providers want to deliver high bandwidth communication capabilities to customers. Passive optical networks are a desirable choice for delivering high speed communication data because they may not employ active electronic devices, such as amplifiers and repeaters, between a central office and a subscriber termination. The absence of active electronic devices may decrease network complexity and cost and may increase network reliability. 
     Passive optical networks may take one or more signals from incoming fiber(s) and make it available to a number of output fibers. For example, a distribution cable may include 24 optical fibers and may run from a central office to a distribution location, such as an equipment enclosure. At the equipment enclosure, each fiber in the distribution cable may be split into a number of outgoing fibers which are made available to subscribers. For example, passive optical networks may employ 1:2, 1:4, 1:8, 1:16 and 1:32 splitting ratios for each fiber, for making optical data available to subscriber locations. 
     In a traditional gigabit passive optical network, a single transmit wavelength and a single receive wavelength are used in each 1:32 split, requiring 32 subscribers to share bandwidth on a single fiber. However, in other systems, such as WDM systems, dedicated wavelengths are used for each subscriber. Conversion between gigabit and WDM systems requires substantial reconfiguration of the optical network to take advantage of the dedicated wavelength system. In certain instances, replacing wires leading to subscriber locations would be required. Such re-cabling is costly and time-consuming. 
     For these and other reasons, improvements are desirable. 
     SUMMARY 
     In accordance with the following disclosure, the above and other issues are addressed by the following: 
     In a first aspect, a system for delivering multiple passive optical network services is disclosed. One system includes a first optical transmission service comprising a common wavelength pair routed from a source to each of a plurality of subscribers and a second optical transmission service comprising a plurality of unique wavelength pairs, each of the unique wavelength pairs assigned to a subscriber among the plurality of subscribers. The system includes a splitter optically connected to first fiber carrying the first optical transmission service, the splitter including a plurality of outputs each delivering the first optical transmission service, and a wavelength division multiplexer connected to a second fiber, the wavelength division multiplexer separating each of the unique wavelength pairs of the second optical transmission service onto separate optical fibers. The system further includes a plurality of second wavelength division multiplexers optically connected to a different output of the plurality of outputs of the splitter and to a different one of the unique wavelength pairs from the wavelength division multiplexer, thereby combining a unique wavelength pair and a common wavelength pair onto a single fiber to be delivered to a subscriber. The system further includes a band-pass filter receiving the single fiber including the unique wavelength pair and the common wavelength pair, the band-pass filter delivering one of the unique wavelength pair and the common wavelength pair to the subscriber. 
     In a second aspect, a system for delivering multiple passive optical network services includes a first optical transmission service and a second optical transmission service received on a common fiber, the first optical transmission service comprising a common wavelength pair routed from a source to each of a plurality of subscribers and the second optical transmission service comprising a plurality of unique wavelength pairs, each of the unique wavelength pairs assigned to a subscriber among the plurality of subscribers. The system further includes a splitter positioned at a terminal optically connected between a central office and a subscriber, the splitter configured to receive the single fiber and output a plurality of optical connections passing the common wavelength pair and each of the plurality of unique wavelength pairs to each of a plurality of subscribers. The system also includes a filter at each of a plurality of subscribers, the filter selected to deliver either the common wavelength pair or one of the plurality of unique wavelength pairs to the subscriber associated with the filter. 
     In a third aspect, an optical termination enclosure is located between a signal distribution source and a plurality of subscribers. The optical termination enclosure includes a splitter optically connected to a first fiber carrying a first optical transmission service comprising a common wavelength pair to be routed from the source to each of the plurality of subscribers, the splitter including a plurality of outputs each configured to deliver the first optical transmission service through hardened multi-fiber optical connectors of the optical termination enclosure. The enclosure further includes a wavelength division multiplexer connected to a second fiber carrying a second optical transmission service comprising a plurality of unique wavelength pairs, each of the unique wavelength pairs to be assigned to a subscriber among the plurality of subscribers, wherein the wavelength division multiplexer is configured to separate each of the unique wavelength pairs of the second optical transmission service onto separate optical fibers which are output from the optical termination enclosure through hardened multi-fiber optical connectors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a system for delivery of multiple passive optical network services, according to one embodiment of the present disclosure; 
         FIG. 2  shows a schematic view of a system for configurable delivery of passive optical network services, according to one embodiment of the present disclosure; 
         FIG. 3  shows a schematic view of a system for configurable delivery of passive optical network services, according to a second embodiment of the present disclosure; 
         FIGS. 4A-4B  show schematic views of subscriber equipment usable with the systems of  FIGS. 2-3 , according to one example embodiment of the present disclosure; 
         FIGS. 5A-5B  show schematic views of subscriber equipment usable with the systems of  FIGS. 2-3 , according to one example embodiment of the present disclosure; 
         FIG. 6  shows a schematic view of a system for configurable delivery of selectable passive optical network services, according to a further embodiment of the present disclosure; 
         FIG. 7  shows a schematic view of a system for configurable delivery of selectable passive optical network services, according to a further embodiment of the present disclosure; 
         FIG. 8  shows a schematic view of a system for configurable delivery of selectable passive optical network services, according to a further embodiment of the present disclosure; 
         FIG. 9  shows a schematic view of a system for configurable delivery of GPON-based passive optical network services, according to a further embodiment of the present disclosure; 
         FIG. 10  shows a schematic view of a system for configurable delivery of WDM-based passive optical network services, according to a further embodiment of the present disclosure; 
         FIGS. 11A-11C  schematically illustrate a variety of different fiber deployment configurations for delivering WDM-based passive optical network services according to the present disclosure; and 
         FIG. 12  schematically illustrates an example method and system for providing deferred delivery of WDM-based passive optical network services according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed invention. 
     In general, the present disclosure relates to delivery of one or more selectable passive optical network services to a single endpoint, such as a household, a business, or other entity requiring a telecommunications connection to a distribution hub. The present disclosure describes a variety of passive optical network configurations which allow for selective use of one or more of the passive optical network services, thereby allowing selective upgrading of endpoints based on customer desires or requirements. The methods and systems of the present disclosure allow use of the same optical fibers already deployed to customer homes. 
     The present disclosure is designed to enable providers of data/video/voice services who have currently deployed fiber-to-the-premise (FTTP) distribution networks for those services, be able to upgrade customers to higher data rate &amp; bandwidth service(s) while maintaining the other services in their current delivery format. For example, a service provider may upgrade its data service to deliver individual customers with a dedicated 1 Gbps or 10 Gbps data line via a DWDM passive optical network (DWDM PON) while continuing to deliver voice and video to that same customer on its traditional gigabit PON (GPON). However, both would be delivered to the customer premise on the same already installed fiber. In this example, the service provider would not have to upgrade all of its delivery equipment to work with the new DWDM PON system but can use the fiber network that is already deployed in the field to deliver all of these services. Additionally, the present disclosure allows for switchover of individual customers from a GPON network to a WDM-based PON network, thereby providing a dedicated service (e.g., 1 Gbps or 10 Gbps service) to that customer rather than requiring the customer to connect via a time-shared optical network with other subscribers, thereby reducing the effective bandwidth available to that subscriber. 
     Referring now to  FIG. 1 , a generalized network in which aspects of the methods and systems of the present disclosure may be implemented. The network  10  as shown is a passive optical network (PON) such as can contain various fiber-to-the-premise (FTTP) systems. The network  10  connects a source  102 , such as a central office of a telecommunications provider, to various subscribers  104 , allowing the subscribers high speed data communications to other subscribers within the network and outside of the network (through other communication channels of the source). The network  10  includes a number of fiber optic components  103  that allow the network to route specific fiber optic signals to a subset of the entire subscriber base, thereby allowing the central office  102  to manage bandwidth concerns. The components can include, for example, splices, splitters, wavelength division multiplexers, repeaters, filters, and other optical components. These components may be modularly added or removed from the fiber optic system, such as by placing various combinations of such equipment in a fiber distribution hub or other modularly extensible system. The systems of the present disclosure breakout multifiber cable down to single fiber, limited wavelength spectra to allow a small number of users to share a particular available bandwidth. For example, in the case of gigabit PON, 32 subscribers  104  typically share a single wavelength for transmitting and receiving data with the source  102 . In the case of a WDM-based PON, each subscriber has a dedicated wavelength pair which it uses to communicate with the source  102 , thereby effectively increasing the bandwidth to that subscriber as compared to gigabit PON by eliminating competing traffic using that subscriber&#39;s communication wavelength. 
     Referring now to  FIGS. 2-10 , various systems for delivery of multiple passive optical network services are shown. These systems can be located within the network  10  of  FIG. 1 , and provide at least a portion of the connecting optical components used to connect a source  102  to subscribers  104 . 
     Referring now to  FIG. 2 , a schematic view of a system  100  for delivery of multiple passive optical network services is shown, according to one embodiment of the present disclosure. The system  100  connects optical fibers from a source  102 , shown as a central office or OLT, to one or more subscribers  104 , shown as customers or ONT connections. The system receives an initial distribution fiber  106  leading from the source  102 , on which all spectra of optical transmission coexist. That initial distribution fiber  106  can include, for example, both GPON services (e.g., operating on 1310 nm uplink and 1490 downlink optical frequencies) as well as a spectrum usable for WDM-based PON distribution. At the system  100 , which can be implemented at a terminal or other location between a central office  102  and subscribers  104   a - n,  the fiber  106  is received at a wavelength division multiplexer  108 , which separates the GPON service wavelengths from the WDM-based PON wavelengths. The GPON wavelengths are routed to a splitter  110 , which power-splits the GPON signal up to 32 or more ways (one per subscriber). The WDM-based PON wavelengths are routed to a cyclic arrayed waveguide grating (AWG)  112  that operates as a WDM to split uplink and downlink wavelengths (λ C , λ L , respectively) onto separate fibers. Those separate fibers can then be routed to a 2:1 WDM  114  which combines one WDM wavelength pair with one output from the splitter  110 , to provide an output of the system  100  a combined GPON and WDM-PON signal. That signal can then be selectively connected to a subscriber  104 , as shown. 
     Generally, in the configuration shown in  FIG. 2 , a single fiber is disposed between the central office  102  and the system  100  (e.g., the terminal). This fiber will carry combined GPON and C-band/L-band WDM-PON services, with 32 C-Band and 32 L-Band wavelengths used. The terminal will, in this embodiment, include 35 or more optical components, with WDM  108 , splitter  110 , AWG  112 , and 32 separate 2:1 WDMs  114 . This allows for delivery of a single fiber to a subscriber  104 , with no need to change any connections at the terminal when transferring between GPON and WDM-PON services; only a change to an end unit is contemplated, as illustrated in  FIGS. 4A-4B and 5A-5B , described below. 
     Additionally, it is noted that the loss levels at the system  100  will typically be expected to be about 7-8 dB on the WDM-PON signals, due to passage through WDMs  108 ,  114 , as well as AWG  112 . By way of contrast, loss on the GPON signals may be on the level of 18-20 dB, due to the power split component of splitter  110 . 
     Referring now to  FIG. 3 , an alternative configuration for a system  150  is shown. System  150  generally corresponds to system  100  of  FIG. 2 , but rather than using a single fiber  106  between the central office, separate fibers  106   a - b  are used for the GPON and WDM-PON services, respectively. This eliminates the WDM  108  at the system  150 , thereby simplifying and cost-reducing that terminal implementation, and reducing the loss involved (while trading off the requirement of an additional fiber between the central office  102  and the system  150 ). 
     Referring to  FIGS. 4A-4B , an example implementation of equipment used at a subscriber  104  is shown, and which allows for transitioning between GPON and WDM-PON services.  FIGS. 4A-4B  illustrate an arrangement in which a subscriber receives an input fiber connection which may include signals at both GPON and WDM-PON wavelengths. When the subscriber is registered for GPON services, that subscriber may utilize the configuration in  FIG. 4A  in which a filter  160  receives signals and filters the WDM-PON signals, passing GPON signals to a home unit. Similarly, the system can include a transmitter/receiver  170  that is configured to transmit and receive at GPON wavelengths (e.g., 1310/1490 nm). 
     When converting to WDM-PON, a subscriber will generally substitute that equipment for new equipment that includes a filter  165  tailored to the wavelengths selected for that subscriber, and a transmitter/receiver  175  that also falls within that band. In some embodiments, the selected wavelengths are close together (e.g., do not have intervening used wavelengths) such that a band-pass filter allows passage of both uplink and downlink (transmit and receive) wavelengths, while blocking wavelengths dedicated to other subscribers or which are used for GPON. 
       FIGS. 5A-5B  illustrate an alternative configuration for equipment used at a subscriber  104  for transitioning between GPON and WDM-PON services. In this embodiment, rather than using a transmitter and receiver within a particular band passable by filter  160 , a transmitter  190  can be configured to transmit either of GPON or WDM-PON services. As such, in some cases a subscriber could be allocated dedicated uplink wavelength and downlink wavelength, or only a dedicated downlink wavelength in alternative embodiments. In particular, as shown in  FIG. 5A , a receiver  180  and transmitter  190  are configured for use at GPON wavelengths (1310 nm uplink and 1490 nm wavelength downlink). In  FIG. 5B , a receiver  185  can be tuned to a particular WDM frequency, and a transmitter  195  can either be within a band matched to filter  165  (which also encompasses the receiver  185 ), or can be configured to transmit on some other frequency, for example a return dedicated wavelength for WDM-PON or a GPON wavelength. 
     In alternative embodiments beyond those described in connection with  FIGS. 4A-4B and 5A-5B , other arrangements can be used at subscriber premises for selecting from between GPON and WDM-PON services. For example, in some cases, different filters can be used for uplink and downlink wavelengths, and a transmitter from the subscriber may be tunable to a desirable uplink wavelength to avoid the requirement of replacing subscriber systems when switching from GPON to WDM-PON. In still further arrangements, a subscriber may be switched from GPON to WDM-PON for only downlink wavelengths, and may have a shared uplink wavelength on the GPON service if both services are delivered to that subscriber concurrently. Such arrangements could be enabled by different combinations of filters and selected transmission systems at the subscriber used for generating uplink signals having one or more predetermined wavelengths. In a still further example embodiment, a white light transmitter could be paired with a filter either preconfigured to pass L-band (uplink) wavelengths or that is configurable to pass tunable uplink wavelengths back to the terminal (e.g., terminals  100 ,  150 , or those discussed below) to the central office  102 . 
       FIG. 6-7  illustrate further arrangements of a system for configurable delivery of passive optical network services, according to further embodiments of the present disclosure. In general,  FIG. 6  illustrates a system  200  in which, rather than using a WDM  114  to route both GPON and WDM-PON signals to a subscriber  104 , a 6-port WDM  120  can be used, which can combine GPON signals with multiple wavelengths output from AWG  112 . As such, a number of WDMs is reduced, thereby cost-reducing the overall system  200 . In particular, rather than using 35 passive components in system  100 , system  200  utilizes 19 components. 
       FIG. 7  illustrates an analogous variant of  FIG. 6  as is shown in  FIG. 3  relative to  FIG. 2 ; that is, in  FIG. 7 , two input fibers  106   a - b  are used and routed to system  250 , which eliminates WDM  108  from that system. 
       FIG. 8  illustrates a further variation of a system  300  for delivering passive optical network services to a subscriber  104 . In system  300 , a received combined signal on fiber  106  is routed to WDM  108 , which separates GPON signals from WDM-PON signals as discussed above. The GPON signals are routed to 1×32 splitter  110 , while the WDM-PON signals are routed to a filter array  302 , which is illustrated as a plurality of filters  302   a - n  which each selectively pass a narrow band of wavelengths. As such, the filter array  302  operates as a wavelength division multiplexer that separates (or combines) an inbound wavelength onto separate “channels” that include both C-Band and L-Band wavelengths. Such wavelength bands can be multiplexed with GPON signals at WDM  114  to deliver either GPON, WDM-PON, or combined services to a particular subscriber  104 , thereby again avoiding the requirement of service at a particular subscriber to switch over to an “upgraded” WDM-PON service. In alternative embodiments, and analogous to those described above, a further variation of  FIG. 8  would involve delivering WDM-PON and GPON services on separate fibers to the system  300 , thereby removing the WDM  108 . 
     Referring to  FIGS. 9-10 , a further possible system  400  is shown, according to an example embodiment. In the example of  FIG. 9 , a system  400 , such as an outside plant terminal, can receive combined GPON and WDM-PON services on an input fiber  106 , and split that signal using splitter  402 , which can be, in some embodiments, a 1×32 power splitter. Each output signal of that splitter, which retains the GPON and all WDM-PON wavelengths, would then be delivered to a subscriber. In the arrangement of  FIG. 9 , a GPON subscriber would include GPON equipment, including a GPON filter  460 , at the subscriber premises, thereby filtering out all WDM-PON wavelengths (shown as C-band wavelengths λ C1 -λ CN , and L-band wavelengths λ L1 -λ LN ). The subscriber would then also be configured to deliver GPON return signals, such as may be accomplished using any of the subscriber configurations illustrated in  FIG. 4A or 5A . 
     By way of contrast to  FIG. 9 , in  FIG. 10 , a WDM band-pass filter  465  can be installed at the subscriber  104 , such that the GPON and other non-selected WDM-PON wavelengths are filtered, and a particular set of C-band and L-band wavelengths (shown as λ C1 , λ L1 ) are allowed to pass through for use by the subscriber  104 . 
     In comparison to the arrangements of  FIGS. 2-3 and 6-8 , the arrangement of  FIGS. 9-10  delivers all WDM-PON wavelengths to each subscriber, and therefore the filter  465  at each WDM-PON subscriber must be uniquely usable by that subscriber (e.g., physically keyed or otherwise uniquely identifiable) such that no two subscribers utilize the same downlink or uplink wavelengths to avoid collision of data from those subscribers (e.g., because in the WDM-PON case, no time division multiplexing is provided because it is presumed that the service is dedicated to a specific subscriber). Additionally, although the design at the system  400  of the terminal is simplified, other arrangements may be selected for other reasons. For example, the arrangement of  FIGS. 9-10  may be disadvantaged for WDM-PON subscribers, since each of the WDM-PON signals is power-split at splitter  402 . In the other arrangements discussed herein, WDM-PON signals are not power-split in this manner. 
     In each of the above cases, although some reconfiguration of equipment at a subscriber may be required, in the variety of example embodiments provided herein, little or no reconfiguration of connections at a terminal between a central office  102  and a subscriber  104  is required, thereby simplifying maintenance and/or configuration services that would otherwise be performed by a service provider. Furthermore, installation of new equipment at a subscriber could be performed either by providing a self-install kit to a subscriber or by installing an automatically or remotely configurable filter and/or transmission system that utilizes a tunable optical transmitter at the subscriber to vary the L-band (uplink) frequency that is used. 
     Overall, in each of the above-described situations, GPON subscribers can each utilize common equipment at the subscriber premises, since those subscribers will utilize the same uplink and downlink frequencies. However, as subscribers migrate to WDM-PON systems, those subscribers will receive dedicated wavelengths and will utilize a preconfigured or tunable system at assigned L-band and C-band (uplink and downlink) wavelengths. Such subscribers can be managed using a wavelength assignment or tracking system that validates that user&#39;s dedicated WDM-PON wavelength, for example using a tracking application. 
     In various examples of the present disclosure, delivery of gigabit passive optical networks and WDM passive optical networks are considered; however, deployment of additional types of optical networks is possible as well using the systems and techniques disclosed herein. For example the present disclosure also relates to delivery of other types of systems with different wavelengths and parallelism, such as various WDM-PON arrangements. Furthermore, other embodiments are possible as well which include different levels and combinations of splitters, filters, and wavelength division multiplexers. Examples of other variations are described in U.S. Pat. No. 8,559,818, the disclosure of which is hereby incorporated by reference in its entirety. 
     In the embodiments disclosed herein, the systems for delivery of multiple passive optical network services are illustrated as passive optical modules. However, it is understood that the system can be configured from a number of separate components, and could include additional passive or active optical components. Furthermore, additional optical networking components can be incorporated into networks having the systems described herein. 
     Additionally, it is noted that the uplink and downlink wavelengths can be configured in various ways. For example, in some embodiments (e.g., as discussed in connection with at least  FIGS. 8-10 , C-band and L-band wavelengths are adjacent one another, meaning that no other C-band or L-band wavelength assigned to a different subscriber of the subscribers connected to the terminal are provided between those wavelengths. In alternative arrangements in which an AWG is configured to route individual wavelengths or wavelength bands to a particular output, various wavelength combinations may be used, which may or may not be adjacent. This is also the case if, on uplink, the GPON services are used, with a non-dedicated uplink channel. 
     Through use of the systems disclosed herein, a provider of passive optical network services can connect multiple services to a single subscriber location while avoiding laying additional fibers to those locations. A provider or maintainer of an optical network such as are disclosed herein can install the splitters, filters, and wavelength division multiplexers as described herein to split a common wavelength pair into a number of fibers, and to separate unique wavelength pairs onto a corresponding number of fibers. The fibers carrying the common wavelength pair can be joined to each one of the fibers carrying different unique wavelength pairs to allow connection of a subscriber to either one or both services by using a single preexisting optical fiber connected to the subscriber. 
     Referring now to  FIGS. 11A-11C , a variety of fiber deployment configurations for delivering WDM-based passive optical network services according to the present disclosure are schematically illustrated. The systems illustrated in  FIGS. 11A-11C  allow for convenient switchover of individual customers/subscribers from a GPON network to a WDM-based PON network.  FIGS. 11A-11C  relate to configurations or systems where the switchover includes a change of the physical connection at a terminal located between a source such as the central office and a subscriber location. In contrast, the systems described above may include additional components at the terminal locations to allow the subscribers to change between GPON and WDM-PON services without a physical connection change at the terminal. 
     According to the configuration illustrated in  FIG. 11A , an outside equipment enclosure, depicted in the form of an optical termination enclosure (OTE)  502 , may receive a distribution fiber leading from a source such as a central office including both GPON services (e.g., operating on 1310 nm uplink and 1490 downlink optical frequencies) as well as a spectrum usable for WDM-based PON distribution (or separate fibers for the GPON and WDM-PON services as shown above). According to the example deployment system  500  illustrated in  FIG. 11A , the depicted OTE  502  includes a splitter  504  (e.g., 1×32) for power splitting the GPON signal. The WDM-based PON wavelengths are routed to a cyclic arrayed waveguide grating (AWG)  506  in the OTE  502  that operates as a WDM to split dedicated pairs of uplink and downlink wavelengths (λ C , λ L , respectively) onto separate fibers. 
     The OTE  502 , as depicted, may output GPON and WDM-PON signals through connectors such as hardened multi-fiber optic connectors (HMFOC)  508  leading to further outside equipment enclosures such as multiport service terminals (MST)  510  servicing a number of subscribers. In the depicted embodiment, each MST  510  is shown with eight ports  512  for servicing eight subscribers. 
     According to the switchover configuration illustrated in  FIG. 11A , an MST location may receive an upgraded WDM-PON signal by unplugging connectorized cabling from a GPON based output  514  and plugging the connectorized cabling into a WDM-PON based output  516  at the OTE location. 
       FIG. 11B  illustrates a variation of the switchover configuration shown in  FIG. 11A , wherein two MST&#39;s  510   a,    510   b,  one dedicated to GPON-based service and one dedicated to WDM-PON service, respectively, are deployed in the field. Subscribers desiring a service upgrade are switched from the GPON dedicated MST  510   a  to the WDM-PON dedicated MST  510   b.  In this configuration, if a single subscriber wants to upgrade its service, the entire MST location does not have to be switched over to the WDM-PON based signal and the subscriber can be independently upgraded. 
     When all of the subscribers/customers of the GPON dedicated MST  510   a  have switched over the WDM-PON dedicated MST  510   b,  the now “empty” MST  510   a  can be used for future service upgrades. For example, the “empty” MST  510   a  can now be used for a different signal such as a 10 Gbps data line if the equipment at the OTE  502  is also upgraded accordingly (e.g., the splitter  504  removed and replaced by other WDM-type equipment that can split the required uplink and downlink wavelengths onto separate fibers). Thus, the already existing, but empty, MST&#39;s can now be used to provide convenient signal upgrade switchovers with equipment changes only at the OTE location. 
       FIG. 11C  illustrates a variation of the configurations of  FIGS. 11A and 11B , wherein a cable  520  carrying both GPON and WDM-PON based signals are initially deployed, ready for future signal switchovers. The fibers  522  of the cable can be terminated with HMFOC&#39;s  508  at both ends. The remote end  524  of the cable  520  can be used for either of the switchover methods described in  FIG. 11A  (one MST switched over) or  11 B (dedicated MST&#39;s for each of the type of signals). 
       FIG. 12  illustrates a system  600  that is a variation of the systems  100 ,  150  described above with respect to  FIGS. 2 and 3 . The system  600  of  FIG. 12  illustrates a method for deferred delivery of WDM-based passive optical network services according to the present disclosure. 
     Even though the system  600  of  FIG. 12  is configured for connecting optical fibers from a source, such as a central office or OLT, to one or more subscribers, such as customers or ONT connections, the system  600  of  FIG. 12  is set up to defer the WDM-based PON service until a future desired time for the subscribers. 
     Similar to  FIG. 3 , the system  600  of  FIG. 12  may receive separate fibers  606   a,    606   b  for the GPON and WDM-PON services, respectively. However, the GPON and the WDM-PON services may be housed in separate housings  602 ,  604 , respectively, and the WDM-PON services may not be fully incorporated into the system  600  until the two separate housings are physically connected. According to one example embodiment, the housing  604  carrying the AWG  608 , which operates as a WDM to split uplink and downlink wavelengths onto separate fibers may be provided a piece of modular equipment that may need to be physically connected to the housing  602  carrying the power splitter. 
     In the specific system  600  shown in  FIG. 12 , the GPON wavelengths are routed to a splitter  610 , which power-splits the GPON signal up to n ways (one per subscriber). There are n number of WDM&#39;s  612  housed within the same housing  602 . As described above with respect to the systems of  FIGS. 2 and 3 , the WDM&#39;s  612  are configured to combine an output from the power splitter  610  with a WDM wavelength pair. However, the fibers  614  carrying the WDM wavelength pairs are not relayed directly from the AWG  608 . The fibers  614  carrying the WDM wavelength pairs are patched to a first connector  616  that has a connection location  618  exposed to an exterior of the housing  602  carrying the power splitter  610  and the WDM&#39;s  612 . The first connector  616  may be provided as a multi-fiber connector (MPO). Other connectors may also be used. 
     Similarly, fibers  620  carrying the WDM wavelength pairs that have been split by the AWG  608  are also patched to a second connector  622  that is configured to mate with the first connector  616  when the two housings  602 ,  604  are mated. The second connector  622  may also be an MPO connector. Other connectors that are configured to mate with the first connector can also be used. 
     In this manner, a shared signal being forwarded to a subscriber can be upgraded to a combined GPON and WDM-PON signal by a modular connection provided between the two housings  602 ,  604  when the upgrade is desired. 
     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.