WO2012168004A1

WO2012168004A1 - Method and system for supervising point to multipoint passive optical networks based on reflectometry systems

Info

Publication number: WO2012168004A1
Application number: PCT/EP2012/057902
Authority: WO
Inventors: Manuel SÁNCHEZ YANGÜELA; Rafael CANTÓ PALANCAR
Original assignee: Telefonica, S.A.
Priority date: 2011-06-07
Filing date: 2012-04-30
Publication date: 2012-12-13
Also published as: AR086854A1; ES2417954B1; ES2417954R1; ES2417954A2

Abstract

A method and a system for physical layer monitoring in Passive Optical Networks. The method comprises: - injecting a monitoring light signal at an input of a Passive Optical Network, or PON, to circulate there through; - reflecting back, optical reflectors provided at different points of said PON, at least part of said monitoring light signal, in the form of respective reflected light signals; and - analysing said received reflected light signals to perform a physical layer monitoring of the PON; wherein the method is characterised in that it further comprises, in order to perform said supervision simultaneously to the normal operation of the PON based on the injection of a working light signal: a) diverting said monitoring light signal towards an intermediate conditioning unit; and b) at least splitting, at said intermediate conditioning unit, said diverted monitoring light signal, and sending to each branch of said PON at least part of one of the resulting signals of said splitting. The system is arranged for implementing the method of the present invention.

Description

Method and system for supervising point to multipoint passive optical networks based on reflectometry systems

Field of the art

The present invention generally relates, in a first aspect, to a method for physical layer monitoring in point to multipoint Passive Optical Networks (PON) comprising emitting light to the interior of a PON and analysing the light reflected on respective optical reflectors provided at different points of the PON, and more particularly to a method which allows determing the identification and precise location of an impairment in the transmission medium, based on said analysis, by splitting said light and sending to each branch of said PON one of the resulting signals.

A second aspect of the invention relates to a system arranged for implementing the method of the first aspect.

Prior State of the Art

Carriers are now deploying new fibre access networks capable to satisfy high- demanding customer requirements. And most carriers are deploying point to multipoint passive optical access networks, also known as PON (Passive Optical Networks). These PON networks are the base of current standard GPON (Gigabit capable Passive Optical Networks, [1]), XG-GPON (10-Gigabit capable Passive Optical Networks, [2]) and EPON (Ethernet Passive Optical Networks, [3]) systems, the most widespread solutions used to provide broadband access over fibre.

Previously mentioned solutions have been designed to provide broadband access over a point to multipoint passive fiber infrastructure and have been chosen by carriers because they provide high access rates without the investment required by point to point fiber access networks.

In current PON access networks, according to the topology as it will be shown in Figure 1 , MxN Customer Premises are connected to a unique Optical Line Termination (OLT) located at carrier's Central Office. The transmission medium, the fiber, connects the OLT with MxN Optical Network Units (ONUs) located at Customer Premises. To do so, fiber access infrastructure has a point to multipoint topology, using optical power splitters to split the optical signal from the OLT into the different ONUs. Optical splitting can be done at only one point, but for deployment reasons, optical power splitting is typically being done in two levels. For the first level is used only one power splitter, with one input and M outputs. For the second splitting level, there are M optical power splitters, each of them with one input and N outputs.

But PON solutions have a supervision problem. Traditional supervision methods based on reflectometry, which are suitable for point to point topologies, do not work properly in these type networks due to their point to multipoint topology. Reflectometry methods consist of the emission of variable width pulses. The impairments (break, splice, bad contacts...) distributed along the transmission medium (copper, coaxial or fiber) create echoes, which are analyzed at the emission point. The delay between the pulse and its echo permits to estimate the impairment location while the analysis of the echo waveform and spectrum helps to determine the type of impairment which has caused the echo.

These techniques are also applied in PON access networks, as it will be shown in Figure 2. There is an optical signal generator which generates pulses at wavelength λ₀. These optical pulses are injected into the PON network using a circulator and an Automated Optical Distribution Frame. The Automated Distribution Frame permits that the same reflectometry based supervision system can be shared between the multiple PON trees deployed from the same Central Office. The received echoes are sent by the optical circulator to the analyzer.

But due to their point to multipoint topology, where the optical signal at wavelength λ₀ emitted by the light source reaches all the ONUs, it is not possible to univoquely identify the point where the impairment is located. The received echoes generated by impairments in different PON branches can overlap. So, it is possible to determine the distance from the central office where the impairment is, but it is not possible to identify the branch of the PON network where this impairment is located. And if it is not possible to univoquely determine an impairment position, the supervision system does not help to reduce optical access network OpEx.

There are some proposals for impairment location disambiguation, like the usage of narrowband optical filters centered at different wavelengths for each customer. But these solutions are complex due to carrier needs to take into account the center wavelength of filter that has been assigned to each customer.

Description of the Invention

It is necessary to offer an alternative to the state of the art which covers the gaps found therein, particularly related to the lack of proposals which really allow discerning from the different reflections coming from different points of a PON in a cost-effective way and using mature technology.

To that end, the present invention provides, in a first aspect, a method for physical layer monitoring in Passive Optical Networks, comprising:

- injecting a monitoring light signal at an input of a Passive Optical Network, or PON, to circulate there through;

- reflecting back, optical reflectors provided at different points of said PON, at least part of said monitoring light signal, in the form of respective reflected light signals; and

- analysing said received reflected light signals to perform a physical layer monitoring of the PON;

On contrary to the known proposals, the method of the invention, in a characteristic manner it further comprises, in order to perform said supervision simultaneously to the normal operation of the PON based on the injection of a working light signal:

a) diverting said monitoring light signal towards an intermediate conditioning unit; and b) at least splitting, at said intermediate conditioning unit, said diverted monitoring light signal, and sending to each branch of said PON at least part of one of the resulting signals of said splitting.

For a preferred embodiment, the method comprises using wavelength division multiplexing techniques in order to precisely identify the location of an impairment.

Other embodiments of the method of the first aspect of the invention are described according to appended claims 2 to 6, and in a subsequent section related to the detailed description of several embodiments.

A second aspect of the present invention generally comprises:

- a light source arranged for injecting, in a downstream direction, a monitoring light signal at an input of a PON to circulate there through;

- a plurality of optical reflectors provided at different points of said PON for receiving said monitoring light signal and reflecting back at least part thereof, in the form of respective reflected light signals, in an upstream direction;

- at least one power splitter which, in said downstream direction, equally splits said monitoring light signal and a working light signal into splitted signals, each to be sent to one of different branches of said PON;

- light detecting means arranged for receiving said respective reflected light signals from said optical reflectors ; and

- analysis means connected to said light detecting means for analysing said received reflected light signals to perform a physical layer monitoring of the PON; On contrary to the known proposals, the second aspect of the invention, in a characteristic manner it further comprises:

- diverting means for, in said downstream direction, separating said monitoring light signal from said working light signal; and

- an intermediate conditioning unit with an input connected to an output of said diverting means for receiving said diverted monitoring light signal, said intermediate conditioning unit comprising splitting means for, in said downstream direction, splitting said diverted monitoring light signal, where each output of said splitting means is connected to a respective branch of said PON for, in said downstream direction, supplying it with at least part of one of the splitted monitoring light signals.

Other embodiments of the second aspect of the invention are described according to appended claims 2 to 6, and in a subsequent section related to the detailed description of several embodiments 8 to 15.

Brief Description of the Drawings

The previous and other advantages and features will be more fully understood from the following detailed description of embodiments, with reference to the attached drawings, which must be considered in an illustrative and non-limiting manner, in which:

Figure 1 shows current topology of PON access networks.

Figure 2 shows current reflectometry based supervision systems for PON access networks.

Figure 3 shows, according to an embodiment of the system proposed in the invention, one of the options for the modification required in the first level splitter in order to upgrade PON optical power splitters with WDM capabilities in the U-band for point to multipoint passive optical networks remote monitoring.

Figure 4 shows, according to an embodiment of the system proposed in the invention, one of the options for the modification required in the second level splitter in order to upgrade PON optical power splitters with WDM capabilities in the U-band for point to multipoint passive optical networks remote monitoring.

Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 1 1 and Figure 12 show the spectra of the optical signals in the different points of the system proposed in the invention according to Figure 3 and Figure 4.

Figure 13 shows, according to an embodiment of the system proposed in the invention, another option for the modification required in the first level splitter in order to upgrade PON optical power splitters with WDM capabilities in the U-band for point to multipoint passive optical networks remote monitoring.

Figure 14 shows, according to an embodiment of the system proposed in the invention, another option for the modification required in the second level splitter, according to the second aspect of the invention, in order to upgrade PON optical power splitters with WDM capabilities in the U-band for point to multipoint passive optical networks remote monitoring.

Figure 15, Figure 16, Figure 17, Figure 18, Figure 19, Figure 20 and Figure 21 show the spectra of the optical signals in the different points of the system proposed in the invention according to Figure 3 and Figure 4.

Figure 22 shows the proposed reflectometry based supervision system for PON access networks.

In case that optical splitting is performed in only one level, modifications required in power splitters will be any of the presented in Figure 3, Figure 4, Figure 13 or Figure 14.

Detailed Description of Several Embodiments

The proposed invention improves the performance of reflectometry based systems currently used for PON access networks supervision, adding a disambiguation mechanism that allows a univoque identification and location of impairments in a point to multipoint passive access network.

The basic concept of the invention consists of a modification of optical power splitters used in PON networks, upgrading them with WDM capabilities in the U-band (optical signals whose wavelength goes from 1625 nm to 1675 nm), the wavelength range reserved for optical access network supervision [9].

As the splitters used in PON access networks are power splitters they are not wavelength selective and they divide equally all the input downstream power between all the outputs independently the wavelength of the optical input downstream signal. And reciprocally, the splitter combines all the upstream input signals into the common upstream output.

To change a PON access network into a WDM access network in the U-band, the optical access supervision band proposed in standards [9], current invention proposes a modification of power splitters that are currently being deployed by carriers. Modification consists of: -Optical Bandpass Filters (OBFs) or Arrayed Waveguide Gratings (AWG) for U band signals, connected in parallel with optical power splitters.

-WDM couplers to connect the conventional optical power splitter with a U-band OBF or a U-band AWG.

-A broadband light source, as shown in Figure 22, in the reflectometer, working in the

U-band wavelength range, which can feed each PON branch with an specific wavelength in the U-band

The result consists of new optical power splitters capable for reflectometry supervision:

-New reflectometry capable optical power splitters, 100a as shown in Figure 3 or

100b as shown in Figure 13, for the first splitting level.

-New reflectometry capable optical power splitters, 200 as shown in Figure 4 and Figure 14, for the second splitting level.

In the case of PON access networks with a unique splitting level, which is very uncommon, conventional optical power splitters would have to be replaced by reflectometry capable optical power splitter, 200 as shown in Figure 4 and Figure 14 .

The usage of WDM couplers will introduce additional losses, around an additional loss of 3 or 4 dB in the whole access optical budget. But this reduction still allows a standard 10 km coverage area.

There are other proposals for point to multipoint passive optical networks supervision.

But there are clear differences:

- Other solutions use low cost tunable lasers with no intensity modulation and optical wavelength sweep. Current proposal can use a tunable OTDR with variable time length pulses or can work with a wideband optical source.

- Current proposal provides the whole information related to attenuation and attenuation per unit length in all sections of the point to multipoint access network, and it also permits the location of any impairment or optical parameter variation in the optical access network under supervision. Other solutions give the attenuation at both sides of each fiber section of the point to multipoint access network.

- Like other solutions, current proposal uses passive components. But these passive elements (AWGs or OBFs) are co-located with optical passive splitters of PON networks, instead of low cost reflective optical filters at the end of each last drop fiber used in other

PON supervision solutions. - Wavelength assignment in current proposal depends on optical multiplexers parameters or Optical Bandpass filters. In other solutions wavelength assignment depends only on the reflective optical filter centre-wavelength used at each last drop fiber.

As it has been previously explained, the proposed invention improves the performance of reflectometry based systems currently used for PON access networks supervision, adding a disambiguation mechanism that allows a univoque identification and location of impairments in a point to multipoint passive access network.

Current invention proposes two approaches to upgrade PON optical power splitters with WDM capabilities in the U-band, and thus allowing a fully remote supervision of point to multipoint passive optical networks. The invention proposes two approaches for this purpose which are described next.

Proposed invention provides the whole information related to attenuation and attenuation per unit length in all the sections of an optical passive point to multipoint access network, adding passive components like AWGs and/or OBFs to the passive splitters used in PON. It also permits the location of any impairment like a fiber cut in any section of the point to multipoint fiber access network (i.e. distance of the cut from the optical access head- end/OLT, splitting level and branch) avoiding the ambiguity inherent to point to multipoint access architectures. It also permits the identification of optical parameters variation in the optical access network under supervision.

The first approach to upgrade PON optical power splitters with WDM capabilities in the U-band for point to multipoint passive optical networks remote monitoring were shown in Figure 3 and Figure 4.

As shown in Figure 3, a 1 :M optical power splitter 120 is connected in parallel to power splitter 7a.

The WDM coupler 1 10 shown in Figure 3 splits the received downstream signals 10a

(S, L and U bands as shown in Figure 5) and sends GPON or XG-PON downstream signals 1 1 (as shown in Figure 6, S and L bands) to splitter 7a, while sends downstream U-band signals 12a (Figure 6) to splitter 120. It combines upstream GPON or XG-PON signals with the received echoes in the U-band.

WDM couplers 140 shown in Figure 3 divide upstream signals between splitters 7a and 120. They send GPON or XG-PON upstream signals (O band of signals 41 , 42, 43 and 49 as shown in Figure 9) to splitter 7a and send the received echoes to splitter 120 output ports. They combine downstream GPON or XG-PON downstream signals 13 (bands S and L shown in Figure 7) with a part of the downstream supervision wavelengths in the U-band and generate signals 41 , 42, 43 and 49 as shown in Figure 9. For echoes disambiguation, the U-band supervision signal 14 spectrum (as shown in Figure 7), at the output ports of splitter 120 is divided into M different optical signals 21 , 22, 23 and 29 (as shown in Figure 8) with non-overlapped spectra. This spectrum division is performed by means of M OBFs 131 , 132, 133 and 139 centered at different wavelengths connected to splitter 120 output ports. Each of the non-overlapped M signals 21 , 22, 23 and 29 contains N optical carriers, as shown in Figure 8.

As shown in Figure 4, a 1 :N Arrayed Waveguide Grating (AWG) 220 is connected in parallel to the optical power splitter 7b.

The WDM coupler 210 shown in Figure 4 splits the received downstream signals 43 (S and L bands, and U, sub-band as shown in Figure 10) and sends GPON or XG-PON downstream signals 61 to splitter 7b, while sends the U, sub-band signal 62 to AWG 220. It combines upstream GPON or XG-PON signals with the received echoes in the U sub-band.

WDM couplers 230 shown in Figure 4 divide upstream signals between splitter 7b and AWG 220. They send GPON or XG-PON upstream signals (O band of signals 91 a, 92a, 93a and 99a as shown in Figure 12) into splitter 7b and send the received echoes (wavelengths λη, λ_ί2, λ,, and λ_ίΝ of signals 91 a, 92a, 93a and 99a respectively) to the AWG 220 output ports. The AWG 220 combines the echoes received from the N fiber drops connected to the output ports of the reflectometry enabled splitter for the second splitting level 200.

Each of these WDM couplers 230 combines downstream GPON or XG-PON downstream signals 63 (S and L bands) with a supervision signal 81 a, 82a, 83a or 89a as shown in Figure 1 1 , and generates signals 91 a, 92a, 93a and 99a, as shown in Figure 12.

Echoes disambiguation is performed by AWG 220. It splits the N wavelengths of the optical signal 62 (as shown in Figure 10) received at its input port and send each of these wavelengths to a different output port, generating signals 81 a, 82a, 83a and 89a as shown in Figure 1 1 .

The whole set constituted by one reflectometry enabled splitter 100a and N reflectometry enabled splitter 200 permits the supervision of MxN customers without any kind of ambiguity, because the use of OBFs and AWGs in the physical path of the optical supervision signals changes the point to multipoint topology of PON access networks into a logical point to point topology for supervision purposes, assigning each customer a specific supervision wavelength different from the rest of wavelengths assigned to the other customers connected to the same OLT 4. The second approach to upgrade PON optical power splitters with WDM capabilities in the U-band for point to multipoint passive optical networks remote monitoring were shown in Figure 13 and Figure 14.

This second option uses a cyclic NxM AWG 130 instead of OBFs 131 , 132, 133 and 139 and optical power splitter 120 shown in Figure 3. In this alternative a NxM cyclic AWG 130 is connected in parallel to optical power splitter 7b.

The WDM coupler 1 10 shown in Figure 13 splits the received downstream signals 10b (S, L and U bands as shown in Figure 15) and sends GPON or XG-PON downstream signals 1 1 (S and L bands as shown in Figure 16) to splitter 7b, while it sends downstream U-band signals 12b (Figure 16) to the cyclic AWG 130.

In fact, U-band signals used in the first approach (signals 12a as shown in Figure 6) and the second one (signals 12b as shown in Figure 16) can be the same, but they are going to be processed in a different way due to the different behaviour of OBFs 131 , 132, 133 and 139 (Figure 3) and a NxM cyclic AWG 130 (Figure 3). It combines upstream GPON or XG- PON signals with the received echoes in the U-band.

WDM couplers 140 shown in Figure 13 divide upstream signals between the splitter 7a and cyclic AWG 130. They send GPON or XG-PON upstream signals (O band of signals 51 , 52, 53 and 59 as shown in Figure 18) to splitter 7b and send the received echoes to AWG 130 output ports.

They combine downstream GPON or XG-PON downstream signals 13 (bands S an L shown in Figure 13) with downstream wavelengths sets 31 , 32, 33 and 39 shown in Figure 17 and generate signals 51 , 52, 53 and 59 as shown in Figure 18.

For echoes disambiguation, the U-band supervision signal 12b spectrum (Figure 17), at the output ports of cyclic AWG 130 is divided into M different non-overlapped wavelength sets Uwi , Uw2, U_Wi and U_WN (31 , 32, 33, 39 respectively as shown in Figure 18). This spectrum division is performed by means of properties of the cyclic MxN AWG 130. So in this second alternative, the mechanism for disambiguation is equivalent but it is performed in a different way than in the first approach.

The scheme of a reflectometry enabled splitter for the second splitting level considered in the second approach was shown in Figure 14. Once again, a 1 :N Arrayed Waveguide Grating (AWG) 220 is connected in parallel to the optical power splitter 7b. In fact, the scheme shown in Figure 14 is the same than the one shown in Figure 4. The only difference is in the spectra of U-band supervision signals. It is different due to the different behaviour of reflectometry enabled splitters for the first splitting level described in Figure 3 and Figure 13. WDM coupler 210 shown in Figure 14 splits the received downstream signals 53 (S and L bands, and U_wi wavelength set shown in Figure 19) and sends GPON or XG-PON downstream signals 61 shown in Figure 10 to splitter 7b, while sends the U_wi wavelength set 72 to AWG 220. It combines upstream GPON or XG-PON signals 61 (O band as shown in Figure 10) with the received echoes in the different wavelength sets in U band.

WDM couplers 230 shown in Figure 4 divide upstream signals between splitter 7b and AWG 220. They send GPON or XG-PON upstream signals (O band of signals 91 b, 92b, 93b and 99b of Figure 21 ) into splitter 7b and send the received echoes (wavelengths λΊ,, λ'₂ί, λ'₅ and λ'_Νί of signals 91 b, 92b, 93b and 99b respectively) to the AWG 220 output ports. The AWG 220 combines the echoes received from the N fiber drops connected to the output ports of the reflectometry enabled splitter for the second splitting level 200.

Each of these WDM couplers 230 combines downstream GPON or XG-PON downstream signals 63 (S and L bands shown in Figure 10) with a supervision signal 81 b, 82b, 83b or 89b (Figure 20), and generates signals 91 b, 92b, 93b and 99b, as shown in Figure 21.

Echoes disambiguation is performed by AWG 220. It splits the N wavelengths of the optical signal 72 (Figure 19) received at its input port and send each of these wavelengths to a different output port, generating signals 81 b, 82b, 83b and 89b as shown in Figure 20.

The whole set constituted by one reflectometry enabled splitter 100a and N reflectometry enabled splitter 200 permits the supervision of MxN customers without any kind of ambiguity, because the usage of a cyclic MxN AWG 130 and 1 xN AWGs 220 in the physical path of the optical supervision signals, changes the point to multipoint topology of PON access networks into a logical point to point topology for supervision purposes, assigning each customer with a specific supervision wavelength different from the rest of wavelengths assigned to the other customers connected to the same OLT 4.

Finally, some additional changes are required in relation to current reflectometry solutions used in PON access networks. These changes affects to the reflectometer installed at Central Office. They are shown in Figure 22 and they consist of:

A change of the optical signal generator 300a shown in Figure 2. This optical signal generator has to be changed by a new one 300b shown in Figure 22 with one of the following features:

- Either a broadband source which covers the whole U-band.

- Or a tunable narrowband optical signal generator (i.e. based on a tunable laser) which can be tuned along the whole U-band. This change is necessary because the proposed solution it is only valid when multiple wavelengths, either simultaneously or alternatively, can be injected for supervision purposes.

And for the same reasons, the analyzer 301 a shown in Figure 2 has to be changed by a new one 301 b with either a broadband U-band receiver or a tunable narrowband receiver that can be tuned along the whole U-band.

- Advantages of the invention

The proposed invention improves the performance of reflectometry based systems currently used for PON access networks supervision. The proposed invention provides a disambiguation mechanism which permits univoquely identify the point where an impairment is.

The disambiguation mechanism is based on the usage of WDM techniques, and upgrading current power splitters in order to permit these splitters to divide U-band broadband supervision signals coming from the Central Office into a set of single wavelengths. Each of them will be injected through a specific splitter output, different from the supervision wavelengths injected through the remainder splitter outputs.

Traditional reflectometry procedures will provide the distance where an impairment is, and the wavelength of the received echo will identify the PON branch where this impairment is located.

This disambiguation mechanism will reduce the cost of PON access network supervision, which is currently very high due to the constraints of current available solutions.

A person skilled in the art could introduce changes and modifications in the embodiments described without departing from the scope of the invention as it is defined in the attached claims.

ACRONYMS

AWG Arrayed Waveguide Grating.

CO Central Office.

CPE Customer Premises Equipment.

GPON Gigabit-capable Passive Optical Networks.

OBF Optical Bandpass Filter.

OLT Optical Line Termination.

ONU Optical Network Unit.

OPEX Operating Expense.

PON Passive Optical Network.

WDM Wavelength Division Multiplexer.

XG-PON 10-Gigabit-capable Passive Optical Networks

REFERENCES

[1] ITU-T G.984.1 : Gigabit-capable passive optical networks (GPON): General characteristics (03/2008) http://www.itu. int/rec/dologin_pub.asp?lang=e&id=T-REC-G.984.1- 200803-l!!PDF-E&type=items

[2] ITU-T G.987.1 10-Gigabit-capable passive optical networks (XG-PON): General requirements (01/2010) http://www.itu. int/rec/dologin_pub.asp?lang=e&id=T-REC-G.987.1 - 201001-I!!PDF-E&type=items

[3] IEEE 802.3ah-2004 Part 3: CSMA/CD Access Method & PHY Specifications Amd: Media Access Control Parameters, Physical Layers, &Mgmt Parameters for Subscriber Access Networks.

[4] ITU-T L.40: Very Optical fibre outside plant maintenance support, monitoring and testing system(10/2000) http://www.itu.int/rec/dologin jDub.asp?lang=e8ud=T-REC-L.40- 200010-l!!PDF-E&type=items [5] ITU-T L.41 : Maintenance wavelength on fibres carryingsignals (05/2000)http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-L.41-200005-l!!PDF- E&type=items

[6] ITU-T L.42: Extending optical fibre solutions into the accessnetwork (05/2003)http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-L.42-200305-l!!PDF- E&type=items

[7] ITU-T L.53: Optical fibre maintenance criteria for accessnetworks (05/2003)http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-L.53-200305-l!!PDF- E&type=items

[8] ITU-T L.58: Physical Optical fibre cables: Special needs for access network (03/2004) http://www.itu. int/rec/dologin_pub.asp?lang=e&id=T-REC-L.58-200403-l!!PDF-E&type=items [9] ITU-T L.66: Optical fibre cable maintenance criteria for in-service fibre testing in access networks (05/2007) http://www.itu. int/rec/dologin_pub.asp?lang=e&id=T-REC-L.66- 200705-l!!PDF-E&type=items

Claims

1. - A method for supervising point to multipoint passive optical network based on reflectometry systems, comprising:

wherein the method is characterised in that it further comprises, in order to perform said supervision simultaneously to the normal operation of the PON based on the injection of a working light signal:

2. - A method as per claim 1 , wherein said step b):

- comprises a wavelenght division multiplexing, which includes said splitting, on said diverted monitoring light signal, according to a specific wavelength or a set of specific wavelengths and sending the resulting signal to the corresponding branch, or

- further comprises filtering each of said resulting splitted signals according to a specific wavelength or a set of specific wavelengths and sending the resulting signal to the corresponding branch.

3. - A method as per claim 2, comprising performing said filtering or wavelenght division multiplexing of each resulting splitted signal according to a different and individualized specific wavelenght or to a different and individualized set of specific wavelenghts.

4.- A method as per claim 3, comprising performing a further filtering or wavelenght division multiplexing, according to a specific wavelength, on each of said resulting signals having said set of specific wavelengths and sending the obtained signal to a corresponding sub-branch of said branch.

5.- A method as per any of the previous claims, comprising performing said diverting of step a) based on a wavelenght division multiplexing applied to both, said working light signal and said monitoring light signal, wherein said working light signal is diverted towards a main path of said PON.

6.- A method as per any of the previous claims, wherein said monitoring light signal is located in the U-band and said working light signal is located in the S-band or L-band.

7.- A system for physical layer monitoring in point to multipoint Passive Optical

Networks, comprising:

- a light source (300b) arranged for injecting, in a downstream direction, a monitoring light signal at an input of a PON to circulate there through;

- at least one power splitter (7a, 7b) which, in said downstream direction, equally splits said monitoring light signal and a working light signal into splitted signals, each to be sent to one of different branches of said PON;

- analysis means (301 b) connected to said light detecting means for analysing said received reflected light signals to perform a physical layer monitoring of the PON;

wherein the system is characterised in that it further comprises:

- diverting means (1 10, 210) for, in said downstream direction, separating said monitoring light signal from said working light signal; and

- an intermediate conditioning unit with an input connected to an output of said diverting means (1 10, 210) for receiving said diverted monitoring light signal, said intermediate conditioning unit comprising splitting means for, in said downstream direction, splitting said diverted monitoring light signal, where each output of said splitting means is connected to a respective branch of said PON for, in said downstream direction, supplying it with at least part of one of the splitted monitoring light signals.

8. - A system as per claim 7, wherein said diverting means comprise at least one wavelength divisor multiplexing coupler (1 10) which separates said working light signal from said monitoring light signal, in said downstream direction.

9. - A system as per claim 7 or 8, wherein said splitting means comprise at least one power splitter (120), said intermediate conditioning unit further comprises a plurality of bandpass filters (131 , 132, 133, 139), each interconnected between an output of said power splitter (120) and one of said PON branches (41 , 42, 43, 49), each bandpass filter working at a specific wavelength or at a set of specific wavelengths for filtering one of the splitted monitoring light signals and delivering each filtered monitoring light signal to the corresponding PON branch (41 , 42, 43, 49), in said downstream direction.

10. - A system as per claim 7 or 8, wherein said intermediate conditioning unit comprise an arrayed waveguide grating, or AWG (130), comprising said splitting means, and arranged for wavelength division multiplexing of said diverted monitoring light signal, according to a specific wavelength or a set of specific wavelengths, and for delivering each wavelength multiplexed monitoring light signal to the corresponding PON branch (51 , 52, 53, 59), in said downstream direction.

1 1. - A system as per claims 9 or 10, comprising a wavelength divisor multiplexing coupler (140) per PON branch, arranged for, in said downstream direction, combining one of said splitted working light signals with one of said filtered monitoring light signals or with one of said wavelength division multiplexed monitoring light signals, and delivering the combined light signal to the PON branch (41 , 42, 43, 49; 51 , 52, 53, 59).

12. - A system as per any of claims 8 to 1 1 , wherein, in an upstream direction:

- said wavelength division multiplexing coupler (1 10) combines said working light signal with said monitoring light signal,

- said power splitter (120) combines said monitoring signal splitted in a plurality of wavelengths,

- said arrayed waveguide grating (130) combines said monitoring signal splited in a plurality of wavelengths and

- said wavelength division multiplexing coupler (140) separates said working light signal from said monitoring light signal.

13. - A system as per any of claims 9 to 12, wherein said diverting means and said intermediate conditioning unit form a first stage, the system comprising a plurality of second stages equal or analogous to said first stage with second diverting means (210) and a second intermediate conditioning unit, each interconnected between each of said PON branches (41 , 42, 43, 49; 51 , 52, 53, 59) and a plurality of corresponding PON sub-branches (91 a, 92a, 93a, 99a; 91 b, 92b, 93b, 99b).

14. - A system as per claim 13, wherein each of said second stages is arranged for splitting and filtering, according to a specific wavelength, said filtered monitoring light signal or wavelength multiplexed monitoring light signal, having said set of specific wavelengths, and for delivering each resulting filtered monitoring light signal having said specific wavelength to said corresponding PON sub-branch (91 a, 92a, 93a, 99a; 91 b, 92b, 93b, 99b), in said downstream direction.

15.- A system as per claim 13, wherein each of said second stages is arranged for wavelength division multiplexing, according to a specific wavelength, said filtered monitoring light signal or wavelength multiplexed monitoring light signal, having said set of specific wavelengths, and for delivering each resulting wavelength multiplexed monitoring light signal having said specific wavelength to the corresponding PON sub-branch (91 a, 92a, 93a, 99a; 91 b, 92b, 93b, 99b), in said downstream direction.