Distribution components for a wavelength-sharing network Number:7,522,838 from the United States Patent and Trademark Office (PTO) owispatent In accordance with the teachings of the present invention, distribution components for a wavelength-sharing network are provided. In a particular embodiment, a distribution node for an optical network includes a first distributor operable to receive a first downstream signal comprising at least traffic in a first wavelength and traffic in a second wavelength from an upstream terminal, route the traffic in the first wavelength to a first plurality of downstream terminals, and route the traffic in the second wavelength to a second plurality of downstream terminals. A second distributor is operable to receive a second downstream signal comprising at least traffic in a third wavelength, and forward the traffic in the third wavelength to at least the first plurality of downstream terminals. A first combining element is operable to receive the traffic in the first wavelength from the first distributor, receive the traffic in the third wavelength from the second distributor, and forward the traffic in the first wavelength and the traffic in the third wavelength to the first plurality of downstream terminals. A second combining element operable to receive at least the traffic in the second wavelength from the first distributor and forward the traffic in the second wavelength to the second plurality of downstream terminals.<H Distribution, wavelength, Distribution, co, 7522838.html, Patent, pto, 7522838

Title: Distribution components for a wavelength-sharing network

Abstract: In accordance with the teachings of the present invention, distribution components for a wavelength-sharing network are provided. In a particular embodiment, a distribution node for an optical network includes a first distributor operable to receive a first downstream signal comprising at least traffic in a first wavelength and traffic in a second wavelength from an upstream terminal, route the traffic in the first wavelength to a first plurality of downstream terminals, and route the traffic in the second wavelength to a second plurality of downstream terminals. A second distributor is operable to receive a second downstream signal comprising at least traffic in a third wavelength, and forward the traffic in the third wavelength to at least the first plurality of downstream terminals. A first combining element is operable to receive the traffic in the first wavelength from the first distributor, receive the traffic in the third wavelength from the second distributor, and forward the traffic in the first wavelength and the traffic in the third wavelength to the first plurality of downstream terminals. A second combining element operable to receive at least the traffic in the second wavelength from the first distributor and forward the traffic in the second wavelength to the second plurality of downstream terminals.

Patent Number: 7,522,838 Issued on 04/21/2009 to Bouda, et al.

Inventors: Bouda; Martin (Plano, TX), Naito; Takao (Plano, TX)
Assignee: Fujitsu Limited (Kawasaki, JP)

Appl. No.: 11/347,585

Filed: February 3, 2006

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
60756925	Jan., 2006
60729447	Oct., 2005

Current U.S. Class: 398/72 ; 398/58; 398/66

Current International Class: H04J 14/00 (20060101)

Field of Search: 398/58,66,67,71,72,74

References Cited [Referenced By]

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Primary Examiner: Tran; Dzung D
Attorney, Agent or Firm: Baker Botts L.L.P.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. .sctn. 119(e) of U.S. Provisional Application entitled "Passive Optical Network using Shared Wavelengths," Ser. No. 60/729,447 filed Oct. 20, 2005, and of U.S. Provisional Application entitled "Hybrid Passive Optical Network Components," Ser. No. 60/756,925 filed Jan. 6, 2006.

Claims

What is claimed is:

1. A distribution node for an optical network, comprising: a first distributor operable to: receive a first downstream signal comprising at least traffic in a first wavelength and traffic in a second wavelength from an upstream terminal; route the traffic in the first wavelength to a first plurality of downstream terminals; and route the traffic in the second wavelength to a second plurality of downstream terminals; a second distributor operable to: receive a second downstream signal comprising at least traffic in a third wavelength; and forward the traffic in the third wavelength to at least the first plurality of downstream terminals; a first combining element operable to: receive the traffic in the first wavelength from the first distributor; receive the traffic in the third wavelength from the second distributor; and forward the traffic in the first wavelength and the traffic in the third wavelength to the first plurality of downstream terminals; and a second combining element operable to: receive at least the traffic in the second wavelength from the first distributor; and forward the traffic in the second wavelength to the second plurality of downstream terminals.

2. The distribution node of claim 1, wherein the first distributor comprises a wavelength router and the second distributor is selected from the group consisting of a wavelength router and a primary power splitter.

3. The distribution node of claim 1, wherein at least one of the first and second combining elements is selected from the group consisting of a filter, a coupler, and a combination thereof.

4. The distribution node of claim 1, wherein at least one of the first and second combining elements comprises a coupler.

5. The distribution node of claim 1, wherein at least one of the first and second combining elements comprises a filter.

6. The distribution node of claim 1, further comprising: a first plurality of power splitters operable to receive the traffic in the first wavelength and the traffic in the third wavelength from the first combining element and forward the traffic in the first wavelength and the traffic in the third wavelength to the first plurality of downstream terminals; and a second plurality of power splitters operable to receive the traffic in the second wavelength from the second combining element and forward the traffic in the second wavelength to the second plurality of downstream terminals.

7. The distribution node of claim 1, wherein: the second distributor comprises a primary power splitter and is further operable to: split the traffic in the third wavelength into a first plurality of copies, the first plurality of copies comprising a first copy and a second copy; forward the first copy to the first combining element, wherein the traffic in the third wavelength received by the first combining element is the first copy; and forward the second copy to the second combining element; the first combining element is further operable to: combine the traffic in the first wavelength with the first copy of the traffic in the third wavelength into a first combined signal; split the traffic in the first combined signal into a second plurality of copies; and forward the second plurality of copies to the first plurality of downstream terminals; and the second combining element is further operable to: receive the second copy of the traffic in the third wavelength from the primary power splitter; combine the traffic in the second wavelength with the second copy of the traffic in the third wavelength into a second combined signal; split the traffic in the second combined signal into a third plurality of copies; and forward the third plurality of copies to the second plurality of downstream terminals.

8. The distribution node of claim 7, wherein at least one of the first and second combining elements is selected from the group consisting of a filter, a coupler, and a combination thereof.

9. The distribution node of claim 7, wherein at least one of the first and second combining elements comprises a coupler.

10. The distribution node of claim 7, wherein at least one of the first and second combining elements comprises a filter and an associated coupler.

11. The distribution node of claim 7, further comprising: a first plurality of secondary power splitters operable to receive the second plurality of copies from the first combining element and split the second plurality of copies into a first set of additional copies such that each downstream terminal in the first plurality of downstream terminals receives one copy of the first set of additional copies; and a second plurality of secondary power splitters operable to receive the third plurality of copies from the second combining element and split the third plurality of copies into a second set of additional copies such that each downstream terminal in the second plurality of downstream terminals receives one copy of the second set of additional copies.

12. The distribution node of claim 7, wherein the second distributor is operable to receive an upstream signal comprising at least traffic in a fourth wavelength from the downstream terminals, wherein the downstream terminals share the fourth wavelength for transmission of upstream traffic.

13. A distribution node for an optical network, comprising: a first distributor comprising a plurality of cascaded filters and operable to: receive a downstream signal comprising at least traffic in a first wavelength and traffic in a second wavelength from an upstream terminal; route the traffic in the first wavelength to a first plurality of downstream terminals; and route the traffic in the second wavelength to a second plurality of downstream terminals; and a second distributor operable to: receive a second downstream signal comprising at least traffic in a third wavelength; and forward the traffic in the third wavelength to at least the first plurality of downstream terminals.

14. The distribution node of claim 13, wherein the second distributor comprises a primary power splitter and is further operable to split the traffic in the third wavelength into a first plurality of copies.

15. The distribution node of claim 14, wherein the plurality of cascaded filters comprises at least a first filter and a second filter, wherein: the first filter is operable to: receive at least the traffic in the first wavelength and the traffic in the second wavelength at a first port; receive a first copy of the traffic in the third wavelength from the second distributor at a second port; forward the traffic in the first wavelength and the first copy from a third port to the first plurality of downstream terminals; and forward the traffic in the second wavelength from a fourth port to the second filter; the second filter is operable to: receive the traffic in the second wavelength at a first port; receive a second copy of the traffic in the fourth wavelength from the second distributor at a second port; and forward the traffic in the second wavelength and the second copy from a third port to the second plurality of downstream terminals.

16. The distribution node of claim 15, further comprising: a first secondary power splitter operable to: receive the traffic in the first wavelength and the first copy from the first filter; and split the traffic in the first wavelength and the first copy into a second plurality of copies, such that each downstream terminal in the first plurality of downstream terminals receives a copy; and a second secondary power splitter operable to: receive the traffic in the second wavelength and the second copy from the second filter; and split the traffic in the second wavelength and the second copy into a third plurality of copies, such that each downstream terminal in the second plurality of downstream terminals receives a copy.

17. The distribution node of claim 14, wherein the plurality of cascaded filters comprises at least a first filter and a second filter, wherein: the first filter is operable to: receive at least the traffic in the first wavelength and the traffic in the second wavelength at a first port; forward the traffic in the first wavelength from a second port to the first plurality of downstream terminals; and forward the traffic in the second wavelength from a third port to the second filter; the second filter is operable to: receive the traffic in the second wavelength at a first port; forward the traffic in the second wavelength from a second port to the second plurality of downstream terminals.

18. The distribution node of claim 17, further comprising a first secondary power splitter operable to: receive the traffic in the first wavelength from the first filter and a first copy from the second distributor; and split the traffic in the first wavelength and the first copy into a second plurality of copies, such that each downstream terminal in the first plurality of downstream terminals receives a copy; and a second secondary power splitter operable to: receive the traffic in the second wavelength from the second filter and a second copy from the second distributor; and split the traffic in the second wavelength and the second copy into a third plurality of copies, such that each downstream terminal in the second plurality of downstream terminals receives a copy.

19. The distribution node of claim 13, wherein the second distributor is operable to receive an upstream signal comprising at least traffic in a fourth wavelength from the downstream terminals, wherein the downstream terminals share the fourth wavelength for transmission of upstream traffic.

20. A distribution node for an optical network, comprising: at least one power splitter operable to: receive a downstream signal comprising at least traffic in a first wavelength and traffic in a second wavelength from an upstream terminal; and split the downstream signal into a plurality of copies; and at least a first filter and a second filter, wherein: the first filter is operable to: receive a first copy of the downstream signal from the power splitter; forward the traffic in the first wavelength to a first plurality of downstream terminals; and facilitate the termination of the traffic in the second wavelength; the second filter is operable to: receive a second copy of the downstream signal from the power splitter; forward the traffic in the second wavelength to a second plurality of downstream terminals; and facilitate the termination of the traffic in the first wavelength.

21. The distribution node of claim 20, wherein: the downstream signal further comprises traffic in a third wavelength; the first filter is further operable to forward the traffic in the third wavelength to the first plurality of downstream terminals; and the second filter is further operable to forward the traffic in the third wavelength to the second plurality of downstream terminals.

22. The distribution node of claim 20, further comprising: a first secondary power splitter operable to: receive the traffic in the first wavelength from the first filter; and split the traffic in the first wavelength into a second plurality of copies, such that each downstream terminal in the first plurality of downstream terminals receives a copy; and a second secondary power splitter operable to: receive the traffic in the second wavelength from the second filter; and split the traffic in the second wavelength into a third plurality of copies, such that each downstream terminal in the second plurality of downstream terminals receives a copy.

23. A distribution node for an optical network, comprising: a wavelength router operable to: receive a downstream signal comprising at least traffic in a first wavelength and traffic in a second wavelength from an upstream terminal; route the traffic in the first wavelength to a first downstream terminal; and route the traffic in the second wavelength to a second downstream terminal; a power splitter operable to: receive a downstream signal comprising at least traffic in a third wavelength; and split the traffic in the third wavelength into a plurality of copies for communication to at least the first downstream terminal and the second downstream terminal; a first coupler operable to: combine the traffic in the first wavelength from the wavelength router with a first copy of the traffic in the third wavelength from the power splitter into a first combined signal; and forward the first combined signal to the first downstream terminal; and a second coupler operable to: combine the traffic in the second wavelength from the wavelength router with a second copy of the traffic in the third wavelength from the power splitter into a second combined signal; and forward the second combined signal to the second downstream terminal.

24. The distribution node of claim 23, wherein: the first coupler and the second coupler are each asymmetric couplers; a greater amount of the power loss associated with the first coupler is received by the traffic in the first wavelength than by the first copy traffic in the third wavelength; and a greater amount of the power loss associated with the second coupler is received by the traffic in the second wavelength than by the second copy of the traffic in the third wavelength.

25. The distribution node of claim 24, wherein: the traffic in the first wavelength is associated with a first net power after receiving the associated power loss at the first coupler; the first copy of the traffic in the third wavelength is associated with a second net power after receiving the associated power loss at the first coupler; the first net power is substantially equal to the second net power; the traffic in the second wavelength is associated with a third net power after receiving the associated power loss at the second coupler; the second copy of the traffic in the third wavelength is associated with a fourth net power after receiving the associated power loss at the second coupler; and the third net power is substantially equal to the fourth net power.

26. The distribution node of claim 23, wherein the power splitter is further operable to receive an upstream signal comprising at least traffic in a fourth wavelength from the downstream terminals, wherein the downstream terminals share the fourth wavelength for transmission of upstream traffic.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to optical networks and, more particularly, to distribution components for a wavelength-sharing network.

BACKGROUND

In recent years, a bottlenecking of communication networks has occurred in the portion of the network known as the access network. Bandwidth on longhaul optical networks has increased sharply through new technologies such as WDM and transmission of traffic at greater bit rates. Metropolitan-area networks have also seen a dramatic increase in bandwidth. However, the access network, also known as the last mile of the communications infrastructure connecting a carrier's central office to a residential or commercial customer site, has remained at a relative standstill in terms of affordable bandwidth. The access network thus presently acts as the bottleneck of communication networks, such as the internet.

Power-splitting passive optical networks (PSPONs) offer one solution to the bottleneck issue. PSPONs refer to typical access networks in which an optical line terminal (OLT) at the carrier's central office transmits traffic over one or two downstream wavelengths for broadcast to optical network units (ONUs). An ONU refers to a form of access node that converts optical signals transmitted via fiber to electrical signals that can be transmitted to individual subscribers. PSPONs address the bottleneck issue by providing greater bandwidth at the access network than typical access networks. For example, networks such as digital subscriber line (DSL) networks that transmit traffic over copper telephone wires typically transmit at a rate between approximately 144 kilobits per second (KB/s) and 1.5 megabits per second (MB/s). Conversely, Broadband PONs (BPONs), which are example PSPONs, are currently being deployed to provide hundreds of megabits per second capacity shared by thirty-two users. Gigabit PONs (GPONs), another example of a PSPON, typically operate at speeds of up to 2.5 gigabits per second (GB/s) by using more powerful transmitters, providing even greater bandwidth. Other PSPONs include, for example, asynchronous transfer mode PONs (APONs) and gigabit Ethernet PONs (GEPONs).

Although PSPONs may offer much greater bandwidth than typical access networks such as DSL networks, bandwidth requirements are projected to exceed even the increased capacity offered by typical PSPONs. For example, some streaming video and online gaming applications presently require bit rates of approximately one to ten MB/s, and some IP high definition television and video-on-demand systems presently require bit rates of approximately twenty MB/s. Future demands for bandwidth are projected to be even greater. Thus, a need exists for an access network that provides even greater bandwidth.

Another solution to the present bottlenecking issue that would also satisfy demand for bandwidth for many years to come is using wavelength division multiplexing passive optical networks (WDMPONs). These networks comprise access networks in which each ONU receives and transmits traffic over a dedicated downstream and upstream wavelength, respectively. By transmitting traffic over dedicated wavelengths, WDMPONs dramatically increase network capacity over existing networks (including typical PSPONs). However, WDMPONs tend to be very expensive compared to PSPONs, the technological risks of deployment of WDMPONs are very high, and WDMPONs provide much more bandwidth than is presently demanded.

SUMMARY

In accordance with the teachings of the present invention, distribution components for a wavelength-sharing network are provided. In a particular embodiment, a distribution node for an optical network includes a first distributor operable to receive a first downstream signal comprising at least traffic in a first wavelength and traffic in a second wavelength from an upstream terminal, route the traffic in the first wavelength to a first plurality of downstream terminals, and route the traffic in the second wavelength to a second plurality of downstream terminals. A second distributor is operable to receive a second downstream signal comprising at least traffic in a third wavelength, and forward the traffic in the third wavelength to at least the first plurality of downstream terminals. A first combining element is operable to receive the traffic in the first wavelength from the first distributor, receive the traffic in the third wavelength from the second distributor, and forward the traffic in the first wavelength and the traffic in the third wavelength to the first plurality of downstream terminals. A second combining element operable to receive at least the traffic in the second wavelength from the first distributor and forward the traffic in the second wavelength to the second plurality of downstream terminals.

Technical advantages of one or more embodiments of the present invention may include providing a cost-effective, upgrade path from Power Splitting Passive Optical Networks (PSPONs), such as APONs, BPONs, GPONs, and GEPONs, to WDMPONs. Particular embodiments may provide a passive optical network with more downstream bandwidth than a typical PSPON yet avoid the cost and unreliability of WDMPONs by using a more cost-efficient variation of WDMPON features and components for transmission in the downstream direction. In these embodiments, groups of ONUs may share one or more of the downstream WDM wavelengths (instead of each ONU receiving a dedicated wavelength), allowing for relatively coarse (and thus less expensive) wavelength multiplexing optics in the passive distribution network. A group of ONUs may comprise less than all of the ONUs corresponding to one OLT.

Particular embodiments may further avoid the cost of WDMPONs by providing PSPON features and components for transmissions in the upstream direction. These embodiments may allow full re-use of typical optical components at each ONU. By reusing optical components, these embodiments may avoid the cost of new equipment and labor at the time of upgrade.

Particular embodiments may further avoid the cost of WDMPONs by providing a wavelength router comprising a filter system as opposed to a wavelength router comprising a multiplexer. For example, particular embodiments provide a cascaded filter system. Using cascaded filters and avoiding the use of a costly multiplexer to route downstream wavelengths may provide for a less costly network.

Another technical advantage of particular embodiments of the present invention includes providing efficient power budgeting between the signals that are to be split for broadcast to all ONUs and the signals that are to be routed to wavelength-sharing ONUs. These embodiments may manage the power efficiently by allowing the broadcast signals to receive more power than the routed signals. Thus, the signals in need of more power are allotted more power.

Another technical advantage of particular embodiments of the present invention includes increasing the number of wavelengths available to carry traffic by disabling the analog video distribution system typically provided in PSPONs and multiplex a number of digital data signals in the wavelength range around and including the band originally assigned for analog video broadcast. Particular embodiments may transmit traffic in other bands as well.

Another technical advantage of particular embodiments of the present invention includes providing for an easily upgradeable PSPON. In particular embodiments, configuring a PSPON to include components such as filters coupled to the network through switches may facilitate an upgrade of the PSPON.

It will be understood that the various embodiments of the present invention may include some, all, or none of the enumerated technical advantages. In addition, other technical advantages of the present invention may be readily apparent to one skilled in the art from the figures, description and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating an example power splitting PON (PSPON);

FIG. 2 is a diagram illustrating an example WDMPON;

FIG. 3 is a diagram illustrating an example Hybrid PON with WDM downstream overlay (WDMDO-HPON);

FIG. 4 is a diagram illustrating an example Wavelength Shared Hybrid PON (WS-HPON);

FIG. 5 is a diagram illustrating an example upgradeable PSPON;

FIG. 6 is a diagram illustrating in more detail the example WS-HPON of FIG. 4;

FIG. 7 is a diagram illustrating an example upgrade to the example WS-HPON of FIG. 6;

FIGS. 8A and 8B are diagrams illustrating example remote nodes (RNs) that may be implemented in a WDMDO-HPON;

FIGS. 9A and 9B are diagrams illustrating example RNs that may be implemented in a WS-HPON;

FIGS. 10A and 10B are diagrams illustrating additional example RNs that may be implemented in a WS-HPON;

FIGS. 11A and 11B are diagrams illustrating example components for switching a filter in or out of the line during a network upgrade; and

FIGS. 12A, 12B, 12C and 12D are diagrams illustrating example components for switching filters in or out of the line during a network upgrade.

DETAILED DESCRIPTION

FIG. 1 is a diagram illustrating an example Power Splitting Passive Optical Network (PSPON) 10. Typically, PSPONs have been employed to address the bottlenecking of communications networks in the portion of the network known as the access network. In recent years, bandwidth on longhaul optical networks has increased sharply through new technologies such as wavelength division multiplexing (WDM) and transmission of traffic at greater bit rates. In addition, metropolitan-area networks have also seen a dramatic increase in bandwidth. However, the access network, also known as the last mile of the communications infrastructure connecting a carrier's central office to a residential or commercial customer site, has not seen as great of an increase in affordable bandwidth. The access network thus presently acts as the bottleneck of communication networks, such as the internet.

PSPONs address the bottleneck issue by providing greater bandwidth at the access network than typical access networks. For example, networks such as digital subscriber line (DSL) networks that transmit traffic over copper telephone wires typically transmit at a rate between approximately 144 kilobits per second (KB/s) and 1.5 megabits per second (MB/s). Conversely, BPONs are currently being deployed to provide hundreds of megabits per second capacity shared by thirty-two users. GPONs, which typically operate at speeds of up to 2.5 gigabits per second (GB/s) by using more powerful transmitters, provide even greater bandwidth.

Referring back to PSPON 10 of FIG. 1, PSPON 10 includes an Optical Line Terminal (OLT) 20, optical fiber 30, a Remote Node (RN) 40, and Optical Network Units (ONUs) 50. PSPON 10 refers to typical access networks in which an optical line terminal (OLT) at the carrier's central office transmits traffic over one or two downstream wavelengths for broadcast to optical network units (ONUs). PSPON 10 may be an asynchronous transfer mode PON (APON), a broadband PON (BPON), a gigabit PON (GPON), a gigabit Ethernet PON (GEPON), or any other suitable PSPON. A feature common to all PSPONs 10 is that the outside fiber plant is completely passive.

OLT 20 (which may be an example of an upstream terminal) may reside at the carrier's central office (where it may be coupled to a larger communication network) and includes a transmitter operable to transmit traffic in a downstream wavelength, such as .lamda..sub.d, for broadcast to all ONUs 50, which may reside at or near customer sites. OLT 20 may also include a transmitter operable to transmit traffic in a second downstream wavelength .lamda..sub.v (which may be added to .lamda..sub.d) for broadcast to all ONUs 50. As an example, in typical GPONs, .lamda..sub.v may carry analog video traffic. Alternatively, .lamda..sub.v may carry digital data traffic. OLT 20 also includes a receiver operable to receive traffic from all ONUs 50 in a time-shared upstream wavelength, .lamda..sub.u. In typical PSPONs, downstream traffic in .lamda..sub.d and .lamda..sub.v is transmitted at a greater bit rate than is traffic in .lamda..sub.u, as PSPONs typically provide lower upstream bandwidth than downstream bandwidth. It should be noted that "downstream" traffic refers to traffic traveling in the direction from the OLT (or upstream terminal) to the ONUs (or downstream terminals), and "upstream" traffic refers to traffic traveling in the direction from the ONUs (or downstream terminals) to the OLT (or upstream terminal).

Optical fiber 30 may include any suitable fiber to carry upstream and downstream traffic. In certain PSPONs 10, optical fiber 30 may comprise, for example, bidirectional optical fiber. In other PSPONs 10, optical fiber 30 may comprise two distinct fibers. RN 40 of PSPON 10 (which may also generally be referred to as a distribution node) comprises any suitable power splitter, such as an optical coupler, and connects OLT 20 to ONUs 50. RN 40 is located in any suitable location and is operable to split a downstream signal such that each ONU 50 receives a copy of the downstream signal. Due to the split and other possible power losses, each copy forwarded to an ONU has less than 1/N of the power of the downstream signal received by RN 40, where N refers to the number of ONUs 50. In addition to splitting downstream signals, RN 40 is also operable to combine into one signal upstream, time-shared signals transmitted by ONUs 50. RN 40 is operable to forward the upstream signal to OLT 20.

ONUs 50 (which may be examples of downstream terminals) may include any suitable optical network unit or optical network terminal (ONT) and generally refer to a form of access node that converts optical signals transmitted via fiber to electrical signals that can be transmitted to individual subscribers. Subscribers may include residential and/or commercial customers. Typically, PONs 10 have thirty-two ONUs 50 per OLT 20, and thus, many example PONs may be described as including this number of ONUs. However, any suitable number of ONUs per OLT may be provided. ONUs 50 may include triplexers that comprise two receivers to receive downstream traffic (one for traffic in .lamda..sub.d and the other for traffic in .lamda..sub.v) and one transmitter to transmit upstream traffic in .lamda..sub.u. The transmission rate of the ONU transmitter is typically less than the transmission rate of the OLT transmitter (due to less demand for upstream capacity than for downstream capacity). Each ONU 50 is operable to process its designated downstream traffic and to transmit upstream traffic according to an appropriate time-sharing protocol (such that the traffic transmitted by one ONU in .lamda..sub.u does not collide with the traffic of other ONUs in .lamda..sub.u).

In operation, the OLT 20 of a typical PSPON 10 transmits downstream traffic destined for one or more of ONUs 50 in .lamda..sub.d. OLT 20 may also transmit downstream analog video traffic for broadcast to ONUs 50 in .lamda..sub.v. Traffic in wavelengths .lamda..sub.d and .lamda..sub.v is combined at OLT 20 and travels over optical fiber 30 to RN 40. RN 40 splits the downstream traffic into a suitable number of copies and forwards each copy to a corresponding ONU. Each ONU receives a copy of the downstream traffic in .lamda..sub.d and .lamda..sub.v and processes the signal. Suitable addressing schemes may be used to identify which traffic is destined for which ONU 50. Each ONU 50 may also transmit upstream traffic in .lamda..sub.u along fiber 30 according to a suitable time-sharing protocol (such that upstream traffic does not collide). RN 40 receives the upstream traffic from each ONU 50 and combines the traffic from each ONU 50 into one signal. RN 40 forwards the signal over fiber 30 to OLT 20. OLT 20 receives the signal and processes it.

Although PSPONs may offer much greater bandwidth than typical access networks such as DSL networks, bandwidth requirements are projected to exceed even the increased capacity offered by typical PSPONs. For example, some streaming video and online gaming applications presently require bit rates of approximately one to ten MB/s, and some IP high definition television and video-on-demand systems presently require bit rates of approximately twenty MB/s. Future demands for bandwidth are projected to be even greater. In the past, network operators have met increased demand by increasing the transmission rate of transmitters, such as, for example, by upgrading from BPONs to GPONs. However, a switch to a wavelength division multiplexing PON (WDMPON), in which each ONU would receive and transmit traffic over a dedicated downstream and upstream wavelength, respectively, would dramatically increase network capacity and satisfy the demand for bandwidth for many years to come.

FIG. 2 is a diagram illustrating an example WDMPON 100. WDMPON 100 may include any suitable WDMPON (also referred to as WPON) or Dense WDMPON (DWDMPON). WDMPON 100 includes OLT 120, optical fiber 130, RN 140, and ONUs 150. Common features of WDMPONs include dedicating at least one upstream and one downstream wavelength for each ONU. Thus, WDMPONs are operable to transmit downstream traffic over multiple, dedicated wavelengths from an OLT, each wavelength corresponding to a particular ONU. In addition, each ONU is operable to transmit upstream traffic over a dedicated wavelength, separate from the wavelengths used by the other ONUs 150. Thus, the upstream and downstream bandwidth of WDMPON 100 is N times greater than the bandwidth of a PSPON, where N equals the number of dedicated wavelengths over which traffic is carried in each direction.

Referring back to FIG. 2, OLT 120 of example WDMPON 100 may reside at the carrier's central office and includes multiple transmitters (equal to the number of ONUs 150), each operable to transmit a dedicated downstream wavelength, one of .lamda..sub.1-.lamda..sub.n, carrying traffic for a corresponding ONU 150. OLT 120 also includes multiple receivers (equal to the number of ONUs 150), each operable to receive a dedicated upstream wavelength, one of .lamda..sub.1-.lamda..sub.n, carrying traffic from a corresponding ONU 150. OLT 120 also includes a multiplexer operable to multiplex the downstream wavelengths transmitted by the transmitters of OLT 120 and demultiplex the upstream signal (comprising traffic in multiple wavelengths) that OLT 120 receives from ONUs 150. After demultiplexing the signal, the multiplexer is operable to forward the traffic in each wavelength to a corresponding receiver in OLT 120. It should be noted that .lamda..sub.1-.lamda..sub.n in the downstream direction may (or may not) be transmitted at the same wavelengths as .lamda..sub.1-.lamda..sub.n traveling upstream (despite having similar designation for simplicity of this discussion).

Optical fiber 130 may include any suitable fiber and is operable to carry upstream and downstream traffic. In certain WDMPONs 100, optical fiber 130 may comprise, for example, bidirectional optical fiber. In other WDMPONs 100, optical fiber 130 may comprise two distinct fibers. RN 140 of WDMPON 100 comprises any suitable multiplexer and connects OLT 120 to ONUs 150. RN 140 is located in any suitable location and has one port to receive a downstream signal comprising multiple wavelengths from OLT 120 and multiple ports (equal to the number of ONUs 150) to forward traffic in each wavelength to a corresponding ONU. RN 140 is operable to demultiplex a downstream signal such that each ONU 150 receives traffic over its dedicated downstream wavelength, one of .lamda..sub.1-.lamda..sub.n. RN 140 is also operable to multiplex upstream traffic carried over .lamda..sub.1-.lamda..sub.n into a single upstream signal, the traffic in each wavelength corresponding to one ONU 150. RN 140 is operable to forward the upstream signal to OLT 120.

ONUs 150 may include any suitable optical network unit or ONT and may serve residential and/or commercial customers. Each ONU 150 comprises one receiver to receive downstream traffic over its dedicated downstream wavelength from OLT 120. Each ONU 150 also comprises one transmitter to transmit upst