Centralized Monitoring and Fault localization for ...

Centralized Monitoring and Fault localization for Passive Optical Network Nani Fadzlina NaimaN, Mohammad Syuhaimi Ab-Rahman", Hesham A. Bakarmanc, A. Ashrif A. Bakara aDepartment of Electrical, Electronics and System Engineering, Faculty of Engineering and Built Environmental Universiti Kebangsaan Malaysia (UKM), 43600 UKM Bangi, Selangor, Malaysia. b paculty of Electrical Engineering, Universiti Teknologi MARA, 40000 Shah Alam, Selangor, Malaysia. cPhotonic Technology Laboratory; Institute of Microengineering and Nanoelectronics (!MEN), Universiti Kebangsaan Malaysia (UKM), 43600 UKM, Bangi, Selangor, Malaysia. Abstract -A real-time, centralized and cost efficient

monitoring and fault localization system is presented. In this system, a superluminescent diode (SLED) is used as the monitoring signal and the signal is reflected by using different types of fiber Bragg gratings (FBGs); uniform and phase-shifted FBGs as branch identifiers. We demonstrate the enhancement of monitoring wavelength whereas for a distinct center wavelength, it represents the reflection spectrum of two types of FBG or two branches in the network. Thus, more optical network units (ONUs) can be monitored for the specific monitoring source with limited bandwidth. The system is capable to monitor up to 64 ONUs with BER of 10.15• Keyword-monitoring, fault localization, passive optical network, fiber Bragg grating

source as

the

monitoring signal and

no fault

localization is presented. Tunable OTDR has been presented in [4]. However, the high cost tunable OTDR and routing wavelength division multiplexing (WDM) make it difficult to be implemented.

Another approach

using the Brillouin-OTDR (B-OTDR) has been proposed in

[5, 9]. This method requires the

employment

of individually

frequency

shifts

(BFS),

assigned

Brillouin

which are also called

identification fiber as the distribution fiber. This method identifies the branches by the frequency of the peak in the spectrum of all Brillouin scattered light.

This

method is

capable

to be

used

as

monitoring and fault localization system. Optical Frequency Domain Reflectometry (OFDR) monitoring has been conducted in [6, 10].

I.

P

assive

optical

This technique applies simple signal processing on

INTRODUCTION

network

(PON)

has

been

recognized as the best design to implement Fiber-to-the-home (FfTH). As the network is

becoming more complex, fiber monitoring and fault

localization

is

becoming

more

crucial.

Conventional method employs optical time domain reflectometry (OTDR) which is only suitable for point-to-point (P2P) network [1, 2]. For point-to­ multipoint (P2MP) network, it requires engineer to go to the failure site to inject the OTDR signal to the identified distribution fiber to determine the exact failure location. This process is tedious and increase maintenance cost. For the recent years, numerous

monitoring

and

fault

localization

techniques have been proposed [1-8]. In

[3], a monitoring system has been

proposed. Amplified spontaneous emission (ASE) source is used as the monitoring signal. Fiber Bragg grating (FBG) is placed in each distribution fiber and distinct reflection spectrum is used as the branch identifier. A WDM receiver is used to monitor the fiber. However, it used costly ASE

the OFDR trace to realize Bragg wavelength shift of

FBG

which

is

located

in

each

capable to identify faulty branch with measurement time shorter that the OTDR methods, however fault localization is not integrated. In this

paper,

a monitoring and

fault

localization system for time division mUltiplexing (TDM) is presented for Passive Optical Network (PON). A low cost superluminescent diode (SLED) which is the monitoring signal will co-propagate with the downstream signal. Each distribution fiber is assigned an FBG; either uniform or phase-shifted (PS) FBG. The unique reflection spectrum is used as the branch identifier and is monitored using an optical spectrum analyzer (OSA).

This system

employs low cost SLED and it does not need transceiver modification. The wavelength reused concept ensures higher monitoring power and more ONUs can be monitored for the limited monitoring band. This system is also applicable to any network protocol extension.

96

978-1-4673-6075-3/13/$31.00 ©2013 IEEE

each

interferometer (IF) unit. Although this method is

and

it

does

not

need

any

protocol

Control unit (CU)

_____

1

Fig. 1. Design of optical network monitoring and fault localization system. SLED is superluminescent diode,BPF is bandpass filter,ONU is the optical network unit, C is optical coupler and OSA is optical spectrum analyzer. II.

DESIGN PRINCIPLE

The monitoring and fault localization system is shown in Fig. 1. An L-band superluminescent diode (SLED) is used as the monitoring signal in this system. During normal condition, the SLED source and the downstream signal will co-propagate along the network. Two different types of FBGs are inserted at the distribution fiber or branch in the network; either the uniform or phase-shifted (PS) FBG. For instance, the first spectrum with center wavelength of 1570 nm is the reflection spectrums from PS­ FBG and uniform FBG which represent two branches. Two different types of FBG are employed in this system so that wavelength reused concept can be exploited. Two types of FBG are used to obtain different shape of reflection spectrum for the same center or Bragg wavelength. For instance, the first spectrum with center wavelength of 1570 nm is the reflection spectrum from PS-FBG and uniform FBG which represent branch #1 and #2 respectively. The spacing between each spectrum is 1 nm to avoid wavelength shift due to temperature vanatlOns. The reflected spectrum of the FBGs will be monitored using an optical spectrum analyzer (OSA). When a missing signal is detected, it indicates that there is a fiber breakdown at distribution fiber. When the control unit detects the missing signal, it will enable the switch to switch to OTDR for fault localization. For cost efficiency, the same SLED that is filtered using a bandpass filter will be the source for the OTDR. Thus, a fiber

monitoring and fault localization system is realized. The simulation result of this system is discussed in the next section. ill.

RESULT AND DISCUSSION

The reflection spectrum of the FBGs is as shown in Fig. 2 a). It represents 6 FBGs or 6 ONUs in the TDM-PON. For each peak of reflection spectrum, it consists of 2 types of FBG; uniform and phase-shifted FBG (PS-FBG). Thus, three peaks represent reflection spectrum of three uniform FBGs and three PS-FBGs which correspond to 6 ONUs. Fig. 2 a) shows the missing reflection spectrum which indicates that there are fiber breakdown at branch #1,#4 and #6 when compared with the spectrum in Fig. 2 b). Basically, the first missing peak at Bragg wavelength of 1570 nm which is missing is the spectrum of PS-FBG which specifies that there is fiber breakdown at branch #1. At Bragg wavelength of 1571 and 1572 nm, there is no reflection spectrum of the uniform FBG which indicates that there are fiber breakdown at branch #4 and #6 respectively. ·;Oco-------,,--,---,---n

-101:-: jCc: 69 ;���--c-::;;:-:-'-'-'--:--=--��"--:-: =-----':-==-=,-----cl-= -- . 573 x

97

10"6

·50 �·55

m hl

� � ·60 -a

• o "-

·65

A A 72�j�1c-"j= 73..J .7�1.J. 1 jL9 6 c-" l CL1�j'cc 70 �5----'-l �j7�1-ILjL.1� 7 j ----'-.1 .lj= 72-L L5� 5 .LL.l�; � 7 .u . 5 6�9-�

) x 10' 2b) Fig. 2a) The reflection spectrum of 6 different FBGs for 6 ONUs b) The reflection spectrum when there are fiber breakdown at branch #1, #4 and #6 Wavdength(rn

Fig. 3 shows the BER performance of the system as the number of ONUs increase. From the graph, it depicts that for BER of 10-15, 64 ONUs can be monitored. Fig. 4 a) and b) display that for 64 ONUs, the received power at the ONU is -24 dBm and the monitoring power received is -47 dBm respectively. The amplitude of the first spectrum peak decrease as the number of ONUs increase and the peak amplitude of the spectrum for 64 ONU is 60 dBm as displayed in Fig. 4 c). However, the system performance can be enhanced by using a higher power of downstream and monitoring signal or by deploying an amplifier in the network. The major loss is due to the power splitter/combiner insertion loss which increase as the number of ONU increase.

enhanced by increasing the downstream and monitoring signal power and by using an amplifier. In this system, an SLED which is the monitoring signal is reflected by using different types of FBGs, uniform and PS-FBGs. Wavelength reused concept is used whereas for a distinct center wavelength, it represents two types of FBGs or two branches in the network so that more ONUs can be monitored for the specific monitoring source bandwidth. The result of the reflection spectrum is displayed using an OSA. After identifying faulty branch, the switch will turn on the OTDR for fault localization. REFERENCES

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-20 ·30

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�-40 eo

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[7]

No.ofONU

Fig. 3. The BER performance versus number of ONUs

1 ---

·10

Communication, 2009. IconSpace 2009. International Conference on, 2009, pp. 5 1-55.

[8]

Power received at ONU

--l\·IollitorinJl power

-- Amplitude of rdlectlOll spectrum

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III

:S-30

� '40

'"

� .

-60

� � __ -�_ __

-------------------

u

�

- - ----- � bl.� 0

--------------------------------------

W

M

D

TI

�

•

�

[9]

==--=--=---� a

�

�

W

M

No.ofONU

Fig. 4. a) The received power at the ONU b) the monitoring power received and c) the amplitude of the first spectrum versus number of ONUs

IV.

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[ 10]

CONCLUSION

A real-time, centralized and cost efficient monitoring technique and fault localization system has been successfully demonstrated. The system is capable to monitor up to 64 ONUs with BER of lO­ IS. However, the system performance can be

98

M. Bert De,C. Wei, J. Bauwelinck,J. Vandewege, and Q. Xing-Zhi, "Nonintrusive Fiber Monitoring of TOM Optical Networks," Lightwave Technology, Journal of, voL 25, pp. 305-317,2007. N. Honda,D. Iida, H. Izurnita,and Y. Azuma, "In­ Service Line Monitoring System in PONs Using 1650-nm Brillouin OTOR and Fibers With Individually Assigned BFSs," Lightwave Technology, Journal of, voL 27,pp. 4575-4582, 2009. Z. Nianyu, Y. Narnihira,C. Ndiaye, and H. Ito, "Fault Location for Branched Optical Fiber Networks based on OFDR Technique Using FSF Laser as Light Source," in Optical Fiber Communication and the National Fiber Optic Engineers Coriference, 2007, pp. 1-3.