WO2009135533A1

WO2009135533A1 - Fibre access network and method

Info

Publication number: WO2009135533A1
Application number: PCT/EP2008/055950
Authority: WO
Inventors: Luca Giorgi; Pierpaolo Ghiggino; Fabio Cavaliere
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2008-05-07
Filing date: 2008-05-15
Publication date: 2009-11-12

Abstract

The present invention relates to optical fibre access networks such as passive optical networks and implementing wave division multiplexing using these networks. There is provided a fibre access network comprisinga passive optical networking optical line terminal (315) coupled to a first port of a first optical filter arrangement (320), a wavelength division multiplexing optical line terminal (305) coupled to a second port of the first optical filter arrangement (320), a fibre network (325, 350) coupled to a third port of the first optical filter arrangement (320), a passive optical networking power splitter (330) coupled to a first port of a second optical filter arrangement (340), the passive optical networking power splitter (330) also coupled to a number of passive optical networking optical network terminals (335),a wavelength division multiplexing splitter (345) coupled to a second port of the second optical filter arrangement (340), the wavelength division multiplexing splitter (345) also coupled to a number of wavelength division multiplexing optical network terminals (335), a third port of the second optical filter arrangement (340) coupled to the fibre network (325, 350), wherein the first and second optical filter arrangements are each arranged to block wavelength division multiplexing optical signals through their respective first ports and to block passive optical networking optical signals though their respective second ports.

Description

FIBRE ACCESS NETWORK AND METHOD

Field of the Invention

The present invention relates to fibre access networks such as passive optical networks and implementing wave division multiplexing using these networks.

Background of the Invention

Optical fibre access networks provide communication facilities to subscribers utilizing an optical network of fibres extending from the subscribers premises to a central office of a network provider or operator. Typically a passive optical network (PON) having a point- to -multi-point architecture is used as this is considered the most cost effective solution. The passive optical network comprises an optical line terminal (OLT) at the central office which is coupled to the point-to-multi-point optical network of fibres. This fibre network uses a number of power splitters to distribute optical fibre to each subscriber whilst relying on the optical signal from the OLT to propagate to optical network terminals (ONT) for each subscriber. Different wavelengths are used for the uplink and downlink optical signals between the passive optical networking OLT and ONT 's - typically 1310nm for upstream and 1490nm for downstream. Various standards have been agreed for different protocols for operating these PON, including GPON (Gigabit passive optical network - ITU-T G.984) and EPON (Ethernet passive optical network - IEEE 802.3ah).

It is widely expected that the next generation of fibre access networks will rely on wavelength divisional multiplexing (WDM) techniques. However, it may be some time before WDM optical components become cost competitive. As such, conventional PONs are likely to continue to be installed in the near future. Various arrangements have been proposed for integrating WDM based fibre access networks into existing conventional PON in order to allow for upgrading the capacity of such PON, when cost-effective WDM optical components become available.

Figure 1 illustrates a fibre access network which interfaces a wavelength division multiplexing passive optical network (WDM PON) with a conventional or non-WDM passive optical network (PON). The fibre access network 100 comprises a WDM OLT 105 coupled to a WDM splitter 120 using a fibre network 110. The WDM splitter splits the signal from the WDM OLT into different wavelengths which are then fed to respective optical fibres coupled to downstream WDM ONT (not shown). One of the ports of the WDM splitter 120 is used to allocate the downstream and the upstream channels of a conventional (non-WDM) PON. However, the respective wavelengths, 1490 nm and 1310 nm, are out of the band (1530 nm - 1560 nm) usually exploited by a dense WDM system. The solution shown in figure 1 uses an active adaptation card 125 for wavelength conversion between 1490 and 1310nm to within the 1530 - 1560nm WDM band. The fibre network 115 coupled to the downstream side of the adaptation card 125 can then be coupled to conventional PON power splitters 130 and PON ONT 135 which use these wavelengths. However this solution is complicated and expensive. An alternative arrangement is to change the optical interfaces at the OLT and the ONT to use the appropriate WDM or non-WDM wavelengths, however this is even more complicated and expensive.

A further solution is shown in Figure 2, which comprises an upgraded fibre access network 200 having both conventional or non-WDM PON and WDM parts. The upgrade components are shown with dashed lines. The network 200 comprises a PON OLT 215 operating at conventional PON wavelengths (1490 and 1310nm) coupled to a WDM combiner 220. The WDM combiner 220 is also coupled to a WDM OLT 205 operating in the 1530 - 1560nm band and to a fibre network 225. The WDM combiner 220 comprises filters associated with different ports so that it blocks conventional PON wavelengths at port B, WDM wavelengths at port A, and allows both PON and WDM wavelengths through port C. The fibre network 225 is coupled to a PON power splitter 230 which power splits the optical signals from the WDM combiner 220 (both PON and WDM optical signals) onto a number of optical fibres 235. These optical fibres 235 are coupled to PON ONT 230A and 230B. In order to upgrade the non-WDM PON (215, 225, 230, 235, 230B, 230A) to include the WDM OLT 205, a second WDM combiner 255 is used together with addition fibre 265 to service WDM ONT 245Y coupled via a WDM splitter 260. Additional fibre 237 may also be added from the PON splitter 230 in order to service new WDM ONT 245X, however this requires a PON bandstop filter to stop the conventional PON wavelengths from passing to the WDM ONT 245X. WDM bandstop filters 250 are used to prevent the WDM optical signals passing to the conventional PON ONT 230A.

Summary of the Invention

There is provided a fibre access network comprising a passive optical networking optical line terminal (PON OLT) coupled to a first port of a first optical filter arrangement such as a WDM combiner, a wavelength division multiplexing optical line terminal (WDM OLT) coupled to a second port of the first optical filter arrangement, and a fibre network coupled to a third port of the first optical filter arrangement. A passive optical networking power splitter is coupled to a first port of a second optical filter arrangement, the passive optical networking power splitter is also coupled to a number of passive optical networking optical network terminals (PON ONT). A wavelength division multiplexing optical network terminal (WDM ONT) is coupled to a second port of the second optical filter arrangement. Optionally a wavelength division multiplexing splitter may also be coupled between the second optical filter arrangement and the wavelength division multiplexing optical network terminal. A third port of the second optical filter arrangement is coupled to the fibre network, and the first and second optical filter arrangements are each arranged to block wavelength division multiplexing optical signals through their respective first ports and to block passive optical networking optical signals though their respective second ports. This fibre access network architecture allows both conventional passive optical networking (PON) and wavelength division multiplexing (WDM) OLT and ONT to communicate with each other over the same fibre network without interfering with each other. The location of the second optical filter arrangement between the passive optical networking power splitter and the first optical filter arrangement also means that wavelength division multiplexing optical signals avoid the losses associated with passing through the passive optical networking power splitter compared with the arrangement of figure 2. This is important in cost effective fibre access networks as these types of power losses limit the reach of the network, or require expensive active components to boost power.

There is also provided a method of adding a wavelength division multiplexing network extension to a passive optical networking access network comprising a passive optical networking optical line terminal (PON OLT) coupled to a passive optical networking power splitter using a fibre network, the passive optical networking power splitter also coupled to a passive optical networking optical network terminal (PON ONT). The method comprises interrupting traffic between the passive optical networking optical line terminal and the passive optical networking optical network terminal, installing a first optical filter arrangement between the passive optical networking optical line terminal and the fibre network, installing a second optical filter arrangement between the passive optical networking power splitter and the fibre network, coupling a fibre extension network to the second optical filter arrangement, coupling a wavelength division multiplexing optical line terminal to the first optical filter arrangement, and re-starting traffic between the passive optical networking optical line terminal and the passive optical networking optical network terminal.

Whilst the method of upgrading an existing PON to include a WDM extension network does require interruption of traffic on the PON, it does have the advantage of reducing power losses compared with existing architectures as discussed above. Also given that maintaining traffic on an access network is less critical for a provider than maintaining traffic on a carrier or backbone network, this method provides a good solution in the access network context. The traffic interruption can be minimised by being performed at night when most subscribers would not be impacted. Another advantage is that the method does require an upgrade of the user equipment (ONT), which would be expensive for the operator and inconvenient for the final user. Also the existing (non-WDM) PON equipment at the OLT remains unchanged.

Once the extension has been installed, traffic carried on the WDM wavelengths or optical signals can be started between the WDM OLT and ONT. Optionally, a WDM splitter may be coupled to the second optical filter arrangement in order to service multiple WDM ONT.

Brief Description of the Drawings

Embodiments will now be described with reference to the following drawings, by way of example only and without intending to be limiting, in which:

Figure 1 illustrates a fibre access network architecture for incorporating a PON into a WDM access network;

Figure 2 illustrates an architecture for upgrading a PON to incorporate a WDM fibre access network extension;

Figure 3 illustrates a fibre access network according to an embodiment; and

Figure 4 is a flow chart of a method for upgrading an existing PON to incorporate a WDM extension. Detailed Description of the Embodiments

A fibre access network according to an embodiment is illustrated in figure 3. The fibre access network 300 comprises a wavelength division multiplexing optical line terminal (WDM OLT) 305, a passive optical networking optical line terminal (PON OLT) 315, a first optical filter arrangement 320, a fibre network 325, a second optical filter arrangement 340, a passive optical networking power splitter 330, a passive optical networking optical network terminal (PON ONT) 335, a wavelength division networking splitter 345, an extension fibre network 350, and a wavelength division multiplexing optical network terminal (WDM ONT) 355.

As is known, an optical line terminal (OLT) is equipment located in a provider's central office which is coupled to optical network equipment (ONT) at each subscriber's premises. Generally an OLT is any equipment used to transmit optical signals to a number of ONT equipment located at respective subscriber's premises. The fibre network architecture used is point-to-multi-point and typically downlink optical signals are broadcast to all ONT and each ONT is allocated a respective timeslot on the uplink. Different OLT and ONT are used for conventional passive optical networking (PON) using a single wavelength for each of the uplink and downlink connections, compared with wavelength division multiplexing (WDM) fibre access networks.

The first and second optical filter arrangements 320 and 340 are implemented in this embodiment as WDM combiners. These are unitary optical components having three ports A, B, C and in which a first port A has a filtering function which blocks WDM optical signals, for example in the 1530 - 1560nm band. A second port B has another filtering function which blocks conventional PON optical signals, for example the 1310 and 1490nm wavelengths. These filtering functions may be bandstop or high and low pass filters for example. The third port C allows both of these WDM and conventional PON optical signals. The WDM combiner is a low insertion loss device, and example commercial products include the Multi Port Micro-optical WDM available from Oplink Communication, California USA, and the EPQA-BGC-0027 PON filter device available from EastPhotonics, Inc Korea. In alternative embodiments, a network of WDM and PON bandstop filters could be used as the first and/or second optical filter arrangements 320 and 340.

Referring again to figure 3, the PON OLT 315 is coupled to a first port A of the WDM combiner 320 such that WDM optical signals are blocked by the WDM combiner. Similarly the WDM OLT is coupled to a second port B of the WDM combiner 320 such that PON optical signals are blocked by the WDM combiner. A third port C of the WDM combiner 320 which does not include the WDM or PON filtering is coupled to the fibre network 325. The fibre network 325 is coupled to a third port C of the second WDM combiner 340, which has a first port A coupled to the PON power splitter 330 and a second port B coupled to the WDM splitter 345. The PON power splitter 330 is coupled to a number of PON ONT 335, and the WDM splitter 345 is coupled to a number of WDM ONT 355 by the extension fibre network 350.

The PON part of the fibre access network 300 comprises the PON OLT 315, the fibre network 325, the PON power splitter 330, and the PON ONT 335. The WDM part of the network 300 comprises the WDM OLT 305, the WDM splitter 345, the extension fibre network 350 and the WDM ONT 355. Both the PON and the WDM parts share the fibre network 325 between the two WDM combiners 320 and 340 which separate the WDM and PON optical signals at the appropriate ports A, B.

This arrangement allows existing PON fibre network 325 to be shared or re-used with a WDM OLT and WDM ONT. Such a network 300 may be initially installed to incorporate both PON and WDM traffic or optical signals, or the WDM part (305, 345, 350, 355) may be added to an existing PON network (315, 325, 330, 335) with the use of the WDM combiners 320, 340 or equivalent structures.

The second WDM combiner 340 is located adjacent the PON power splitter 330 and between the PON power splitter 330 and the first WDM combiner 320. This means that WDM optical signals are not routed through the PON power splitter 330 and instead are routed directly to the WDM splitter 345 and on to the WDM ONT 335. In this way, the substantial power loss that these WDM optical signals or traffic would incur through the PON power splitter is avoided. In other words, power loss of the WDM signals is minimised using this arrangement.

Whilst this arrangement has the disadvantage of requiring PON traffic or optical signal interruption when upgrading an existing PON (315, 325, 330, 335) to include a WDM extension (305, 345, 350, 355), it is believed that this is less significant for an access network, compared for example with a core network where such an interruption may be unacceptable. Thus whilst known arrangements locate a second WDM combiner (340) after a PON power splitter (330) in order to avoid traffic disruption, this necessarily incurs a significant splitting or power loss of the WDM optical signals.

Figure 4 illustrates a method of upgrading an existing PON to include a WDM extension. The method 400 may be applied to the PON part (315, 325, 330, 335) of the fibre access network 300 of Figure 3 in order to add the WDM part (305, 345, 350, 355). This allows existing optical fibre 325 to be re-used whilst substantially upgrading the fibre access network 300. The extent of installed fibre re-use may be quite significant, and this is an especially cost effective upgrade solution as the major cost of providing a fibre access network is the cost of the installed optical fibre. Thus maximising the use of the installed fibre using additional WDM traffic or optical signals effectively reduces the installed optical fibre's cost.

The method 400 of figure 4 of adding a WDM network extension to a PON upgrade comprises interrupting traffic or PON optical signals between the PON OLT 315 and the PON ONT 335 at step 405. This may be implemented in known manner, typically at night in order to minimise subscription impact. A first optical filter arrangement or WDM combiner 320 is then installed between the PON OLT 315 and the fibre network 325 at step 410. The WDM optical signal blocking or first port A is coupled to the PON OLT, and the non-blocking or third port C is coupled to the fibre network. A second optical filter arrangement or WDM combiner 340 is then installed between the PON power splitter 330 and the fibre network 325 at step 415. The WDM optical signal blocking or first port A is coupled to the PON power splitter, and the non-blocking or third port C is coupled to the fibre network. The method may skip steps 420 and 425 to allow for connection of the WDM parts (305, 345, 350, 355) at a later time in order to minimise interruption of the PON traffic. Steps 420 and 425 may then be performed later after restarting the PON traffic at step 430.

The fibre extension network 350 is coupled to the second optical filter arrangement 340 at step 420. The PON optical signal blocking or second port B is typically connected to a WDM splitter 345 which is connected to a WDM ONT 355 by the extension fibre 350. A WDM OLT 305 is coupled to the first optical filter arrangement 320 at step 425. The PON blocking or second port B is coupled to the WDM OLT 305. The PON traffic between the PON OLT 315 and the PON ONT 335 is re-started at step 430. As previously mentioned the WDM OLT 305 and extension network 350 may be coupled to the first and second optical filter arrangements 320 and 340 respectively, after the PON traffic has already been re-started. The WDM traffic or optical signals may then be started between the WDM OLT and the WDM ONT.

Claims

1. A fibre access network comprising: a passive optical networking optical line terminal coupled to a first port of a first optical filter arrangement; a wavelength division multiplexing optical line terminal coupled to a second port of the first optical filter arrangement; a fibre network coupled to a third port of the first optical filter arrangement; a passive optical networking power splitter coupled to a first port of a second optical filter arrangement, the passive optical networking power splitter also coupled to a number of passive optical networking optical network terminals; a number of wavelength division multiplexing optical network terminals coupled to a second port of the second optical filter arrangement; a third port of the second optical filter arrangement coupled to the fibre network; wherein the first and second optical filter arrangements are each arranged to block wavelength division multiplexing optical signals through their respective first ports and to block passive optical networking optical signals though their respective second ports.

2. A fibre access network according to claim 1, further comprising a wavelength division multiplexing splitter coupled between the wavelength division multiplexing optical network terminals and the second port of the second optical filter arrangement.

3. A fibre access network according to claim 1 or 2, wherein the first and/or second optical filter arrangements comprise a wavelength division multiplexing combiner.

4. A fibre access network according to claim 1, 2 or 3, wherein the passive optical networking optical signals are in the range 1310 to 1490 nm and the wavelength division multiplexing optical signals are in the range 1530 to 1565 nm or 1565 nm to 1625 nm.

5. A method of adding a wavelength division multiplexing network extension to a passive optical networking fibre access network comprising a passive optical networking optical line terminal coupled to a passive optical networking power splitter using a fibre network, the passive optical networking power splitter also coupled to a passive optical networking optical network terminal; the method comprising: interrupting traffic between the passive optical networking optical line terminal and the passive optical networking optical network terminal; installing a first optical filter arrangement between the passive optical networking optical line terminal and the fibre network; installing a second optical filter arrangement between the passive optical networking power splitter and the fibre network; coupling a fibre extension network to the second optical filter arrangement; coupling a wavelength division multiplexing optical line terminal to the first optical filter arrangement; re-starting traffic between the passive optical networking optical line terminal and the passive optical networking optical network terminal.

6. A method according to claim 5, wherein the extension fibre network is coupled to a wavelength division multiplexing optical network terminal and the method further comprises starting traffic between the wavelength division multiplexing optical line terminal and the wavelength division multiplexing optical network terminal.

7. A method according to claim 5 or 6, wherein the first and/or second optical filter arrangements comprise a wavelength division multiplexing combiner.

8. A method according to claim 5, 6 or 7, wherein the passive optical networking optical signals are in the range 1310 to 1490 nm and the wavelength division multiplexing optical signals are in the range 1530 to 1565 nm or 1565 nm to 1625 nm.