PON monitoring Joint work between Multitel and FPMs/TCTS

1. PON monitoringJoint work between Multitel and FPMs/TCTS e1+ VD-A workshop Barcelona – 26th February 2007

2. Multitel main interests in VD-A • Optical amplification in PON • Remote amplification • Remote pumping • Remote powering • Bi-directional amplification • Monitoring of PON (passive layer) • P2MP (Point-to-Multipoints) architectures => collaboration with FPMs/TCTS labs e1+_VD.A_workshop_Barcelona_Feb07

3. Multitel main interests in VD-A • Optical amplification in PON • Remote amplification • Remote pumping • Remote powering • Bi-directional amplification • Monitoring of PON (passive layer) • P2MP (Point-to-Multipoints) architectures => collaboration with FPMs/TCTS labs e1+_VD.A_workshop_Barcelona_Feb07

4. PON monitoring Main problem to be solved: In-service FTTx networks optical layer monitoring. [To be integrated in the Network Management System] State of the art: two monitoring layers to consider - Active components monitoring : . Each active component uses autodiagnostic functions which are centralized and analysed through the NMS => Alarms below specified threshold levels - Passive components monitoring (Fiber, splitters, connectors, splices) : For the moment, a failure identification and resolution takes a long time. After determining that a fiber break has occured, a qualified technician must be dispatched with an OTDR to the closest access point with visibility to the fault to determine the optical distance to the fault. e1+_VD.A_workshop_Barcelona_Feb07

5. PON monitoring Main problem to be solved: In-service FTTx networks optical layer monitoring. [To be integrated in the Network Management System] State of the art: two monitoring layers to consider - Active components monitoring : . Each active component uses autodiagnostic functions which are centralized and analysed through the NMS (Network Management System) => Alarms below specified threshold levels - Passive components monitoring (Fiber, splitters, connectors, splices) : For the moment, a failure identification and resolution takes a long time. After determining that a fiber break has occured, a qualified technician must be dispatched with an OTDR to the closest access point with visibility to the fault to determine the optical distance to the fault. e1+_VD.A_workshop_Barcelona_Feb07

6. FTTx Networks Monitoring Passive components : Two monitoring methods - Preventive one : Analysis of passive components progressive aging. Makes it possible to anticipate and organize network maintenance, thus reducing OPEX. - Curative one : Automatic diagnostic and location of critical faults. Workflow efficiency enhancement. Main failures reasons : Public works, digging, human mistakes during maintenance operations, local reasons (rodents, …) Failure statistics from installed PONs : No clear data available e1+_VD.A_workshop_Barcelona_Feb07

7. Specifications Main requirements: - Intelligence centralized at the CO - should not impact the PON architecture (e.g. branches of same length) - should maintain colorless ONUs The OTDR system must be fully-automated, enabling the following functions : - PON’s branches monitoring (split ratio and configuration to be determined) - Optical faults and breaks localisation - Faults database updates e1+_VD.A_workshop_Barcelona_Feb07

8. ONU 1550nm 1550nm Mux DeMux Central Office 1310nm 1310nm 1*N Splitter 1625nm OTDR 1625nm SRE Components- OTDR in the Central Office (@ 1625nm to be used in-service)- SRE (element switchable between two reflective states : R=0 and R=100%) Monitoring method e1+_VD.A_workshop_Barcelona_Feb07

9. Monitoring method : Problem to be solved : The OTDR trace shows whether a fault is located on one of the PON’s branches or not. - The useful information is the distance from the CO to the fault. - BUT it is not possible to know which branch contains the fault - ANDthe measured fault is only an apparent one, much weaker than the real one Solution : - Only one SRE in reflective position. Monitoring of each branch in turn - The SRE generates an intense OTDR reflective peak. Its amplitude decreases in case of a fault on the monitored branch - The real fault value is calculated from the apparent loss one, using previous networks’ detected faults database e1+_VD.A_workshop_Barcelona_Feb07

10. 1st year achievements • SRE : • Determination of the best SRE optical design • SRE electronic design • Realistic PON setup construction (split ratio = 16, 32, or even 64) • Statistical study of the OTDR trace for a random break in a PON • Theoritical determination of minimum OTDR performances to detect a given fault in a PON (considering FTTx norms) e1+_VD.A_workshop_Barcelona_Feb07

11. SRE 1* 2 Coupler PON Optical Switch Photodiode + TIA Electronics µP SRE Optical Design Constraints to be considered : - Technical ones : The SRE must switch when it receives a message from the CO When off, the SRE must be only a few reflective (not to interfer with the signal from other branches) - Economical ones : Monitoring system cost reduction In parallel, study of installation cost per user - Best design : Optical configuration that minimizes the number of components Compatible with Planar Lightwave Circuit Technology that enables cost saving by wafer scale process. SOA Coupler SOA e1+_VD.A_workshop_Barcelona_Feb07

12. SRE Electronic Design • For a fully-automated monitoring system, the SRE must have the following functions : • Photodiode output signal amplification (signal sent from the C.O. @ 1625nm, TTL format) - Signal treatment (Micro-controller) : - Address reading - Comparison with SRE address - Delaying reading • Switch commutation during the delaying read. - Switch commutation at the end of the delaying period. e1+_VD.A_workshop_Barcelona_Feb07

13. 1625nm Laser Driver SRE 1 * 2 Optical Coupler RS232 + Electronics Distribution Cable (10km) Feeder Cable (10km) Optical Switch 1 * N PLC Splitter Photodiode + Ampli PC Driver Software DAQ Optical Switch µP Electronics (N=16, 32 and 64 available) GPIB Only 4 SREs on this Setup (low take rate) 1625 nm Monomode OTDR Realistic PON construction Driver Functionalities: Communication between Central Office and SRE OTDR measurements OTDR trace import & treatment Faults database update. e1+_VD.A_workshop_Barcelona_Feb07

14. Statistical study of random fiber breaks • Fiber breaks detection is linked to curative monitoring : • - A fiber break is either reflective & non reflective. - The reflective behaviour is random (depends on the shape of the break, the environnement) The study of numerous fiber breaks makes it possible to trace a statistical profile : This statistic will later be used to evaluate the number of detectable breaks in a given PON, with given OTDR performances – Thus, it will be possible to evaluate the monitoring method limits. . e1+_VD.A_workshop_Barcelona_Feb07

15. Theoritical study of OTDR performances Experimental validation of the OTDR waveform noise (NW) theoritical equation : Measured OTDR Trace Measured Waveform Noise Calculated Waveform Noise e1+_VD.A_workshop_Barcelona_Feb07

16. Theoritical study of OTDR performances Experimental validation of the apparent fault theoritical equation : ATT : Real loss value Hmarche: Apparent loss value e1+_VD.A_workshop_Barcelona_Feb07

17. Theoritical study of OTDR performances Thanks to the two previous results, it is now possible to calculate the apparent fault and the theoritical minimum DR necessary in each of the following cases : Monitored branch loss bound by PON Norms (MIN and MAX values) Other branches loss also bound by PON Norms (MIN and MAX values) 4 extrem combinations considered : MIN/MIN, MIN/MAX, MAX/MIN, MAX/MAX Given Split ratio Given Real fault value (1dB to be consistent with the monitoring system definition) k depends on the OTDR trace analysis method (k=2 here) e1+_VD.A_workshop_Barcelona_Feb07

18. Theoritical study of OTDR performances Results: For N=32 or 64, and for a given real loss value of 1dB, - The apparent fault is, in most cases, lower than the OTDR resolution limit. This is true for all the considered norms. - Even if the apparent fault value is high enough to be visible on the OTDR trace, the necessary DR can vary from 30 to 45 dB. These high values lead to the use of long OTDR pulses, thus highly reducing the OTDR spatial resolution. e1+_VD.A_workshop_Barcelona_Feb07

19. Cases of reflective faults (fibre breaks) In case of reflective faults, the equation giving the minimum DR is : Conclusions: In the same conditions than previous calculation (for non reflective faults), the necessary DR to see a -50dB reflective fault can vary from 20 to 35dB. Other values : -40dB, DR= 12 to 30 dB -30dB, DR= 10 to 25 dB e1+_VD.A_workshop_Barcelona_Feb07

20. In-service monitoring • - If all the branches are the same length, it is possible to use this property to virtually extend the monitored branch. Thus, the backscattered signal from a fault that belongs to this branch is no more in competition with the others branches backscattered signals. It is so the REAL LOSS value that is measured on the OTDR trace. • - Moreover, this technique makes it possible see all the faults affecting the branch at the same time (major advantage in comparison with the SRE technique • - BUT, this technique needs strong OTDR pulses and, thus, a poor spatial resolution • => next steps : can we possibly amplify this secondary trace ? e1+_VD.A_workshop_Barcelona_Feb07

21. PON Potential options • Semiconductor Optical Amplifier : • Could potentially be compatible with RSOA based ONUs • Issue: how to remove the CW component ? • Raman amplification Need of a Raman laser source @ 1455nm to amplifiy OTDR pulses @ 1550nm (much more expensive than an SOA, but shared between N users) e1+_VD.A_workshop_Barcelona_Feb07