Fault Localization of PON Yeung Chue Hei ( ) Lam Yi Kwan ( )

Network Structure FTTX (fiber to the X) Passive (PON) Multiplexing (→P2MP) TDM WDM

Goals Maintain service quality 1/3 of service disruptions are due to fiber cable Fault can be a disaster Assisting reparation Reduce lost Efficiency Not affecting the other service

Challenges High resolution VS high DR capabilities Measurement time Point-to-multipoint problem

Solutions for TDM-PONs P2P Active By-pass Passive By-pass Integrated OTDR functionality P2MP Tunable OTDR and wavelength selective reflectors Conventional OTDR and controlled reference reflections Brillouin OTDR

Solutions for WDM-PONs Tunable OTDR/multi-wavelength source and optical reflector Re-using existing light sources Commercial multi-wavelength OTDR

Other solutions Optical Code-division Multiplexing Optical Frequency Domain Reflectometry

Measuring the Individual Attenuation Distribution of Passive Branched Optical Networks Kuniaki Tanaka, Mitsuhiro Tateda, Senior Member, IEEE, and Yasuyuki Inoue, Member, IEEE IEEE PHOTONICS TECHNOLOGY LETTERS, VOL 8, NO 7, JULY 1996

Reference Reflector

Conventional OTDR Specially designed branched networks Transmission line lengths differ with each other Cannot test branched fiber losses individually Go to the subscriber terminals after branching and measure the transmission loss directly

Passive By-pass

“New” method

Arrayed Waveguide Grating (AWG)

Optical Splitter/Router Module

OTDR Configuration

OTDR Traces

Fiber Fault Identification for Branched Access Networks Using a Wavelength- Sweeping Monitoring Source Chun-Kit Chan, Frank Tong, Lian-Kuan Chen, Keang-Po Ho, Dennis Lam

Introduction Conventional OTDR cannot differentiate Rayleigh backscattered light from different branches Multiwavelength OTDR is expensive

Fiber Identification Scheme

To avoid pulse collision (2nL/c) < 1/(Nf) Eg. N=8, f=1kHz, n=1.5, max L=12.5km

Experiment 1 x 4 branched optical network Data channels: 1548nm, 1551nm 1Gb/s PRBS NRZ L1=8.8km, L2=L3=6.6km, L4 is unmonitored FBG: nm, 1558nm, nm 3dB passband: 0.4nm, 0.8nm, 0.9nm Sawtoothed signal: 2kHz

Summary Makes use of FBGs No additional monitoring source Both time and frequency domain With OTDR techniques, can locate exact fiber cut position

Q&A Thank you for your attention!

Active by-pass

Passive by-pass

Global analysis

Tunable OTDR and Wavelength Selective Reflector

Controlled reference reflections with convention OTDR

Brillouin OTDR (BOTDR)

Tunable OTDR/multi-wavelength source and optical reflector

Re-using existing light sources

Commercial multi-wavelength OTDR

OTDR

Principle of OTDR Operation Launch short duration light pulses into a fiber and then measure the optical signal returned to the instrument.

Block Diagram of OTDR

OTDR Fiber Signature

Features Straight lines distributed Rayleigh backscattering Positive spikes discrete reflections Steps bends or splices

Events Reflective events Fresnel reflections Mechanical splices Connectors Cracks Non-reflective events Bends Fusion splices

Dynamic Range

Attenuation and Event Dead Zone

Attenuation dead zone vs OTDR receiver bandwidth

DR and Dead zone High dynamic range mode larger pulse width increasing the strength of the received signal, better DR, better sensitivity larger dead zone lower resolution High resolution mode smaller pulse width smaller DR, less sensitive smaller dead zone higher resolution

Ghost Events echoes generated by multiple reflections only solution: avoid high reflectivity connectors Dirty or scratched connectors the repetition rate of the laser pulses is too fast (echoes from consecutive pulses may overlap)

Ghost Events connector Aconnector Bfiber end

Gainer Event If the backscatter after the loss event is higher than before the event, a “gainer” will occur. Backscatter information does not always precisely indicate what happens to a forward traveling signal. fiber A fiber B splice Insertion loss position of splice

Remote Fiber Test System Remote test unit, control unit Optical test access unit share on test equipment Controlled by computer databases and computing algorithm. Reference file created and saved in the data base