Abstract: The deployment of optical fibre for telecommunication network grows rapidly as it promises greater capacity of data transmission. Therefore, a good monitoring system is required to ensure that the optical fibre is in good condition and providing maximum service availability. Active fibre monitoring system has been developed based on optical time domain reflectometer (OTDR) to overcome the limitation of its passive monitoring counterpart. A monitoring wavelength of 1625/1650 nm are normally deployed apart from the wavelengths used for data traffic transmission. Active fibre monitoring provides real-time monitoring so that any failure will results in faster restoration. However, the utilization of both traffic and OTDR in the wavelength-division multiplexing (WDM) system will affect the dynamic range of the OTDR caused by backscattered stimulated Raman scattering (SRS). This study implemented a software simulation model and hardware experimentation to investigate and mitigate the backscattered SRS signal in OTDR active fibre monitoring using 1650 nm wavelength. The investigation was carried out by developing basic OTDR active fibre monitoring system to observe the SRS backscattered noise, power depletion, and amplification using software simulation. The obtained results indicate that the booster amplifier link contributes the highest backscattered SRS including amplified spontaneous emission (ASE) noise. The simulation setup was also used to mitigate the backscattered SRS by placing a chirped fibre Bragg grating (CFBG) at the OTDR to allow only 1650 nm OTDR signal to be received by the OTDR leaving other unwanted signal or noise behind. This mitigation successfully reduces other backscattered signals approximately by 4 dB. Finally, a proof-of-concept hardware experiment is developed to test the feasibility of the proposed technique. The result shows that the OTDR trace for booster amplifier setup was distorted with OTDR penalty of 3.4 dB due to the backscattered noise. By mitigating the backscattered noise, the distortion in the trace was reduced and the OTDR penalty also reduced to 0.41 dB. Hence, coupling an OTDR into a WDM system requires an additional filter to suppress the backscattered noise, and subsequently improving the OTDR active fibre monitoring performance.

Keywords: Backscattered SRS, OTDR active monitoring, point-to-point transmission, optical access networks.

Acknowledgements: This work is funded by Fundamental Research Grant (FRGS), Ministry of Higher Education, Malaysia, No. FRGS/1/2020/TK0/UPM/02/10. The authors would also like to thank TMR&D and Kumpulan ABEX Sdn. Bhd. in providing the facilities for hardware experimentation.

Biography: Siti Barirah Ahmad Anas obtained her PhD from University of Essex, UK in 2009 in the field of Electronic Systems Engineering. She completed her Master of Science in 2003 and Bachelor of Engineering in 1999 from Universiti Putra Malaysia and University of Strathclyde, UK, respectively. She currently works as an Associate Professor at the Department of Computer and Communication Systems Engineering, Faculty of Engineering, Universiti Putra Malaysia. She is also an associate researcher of Wireless and Photonics Networks (WiPNET) Research Centre of Excellence, UPM. Dr. Anas is also a Senior Member of the Institute of Electronics and Electrical Engineers (IEEE). She has been actively involved and served the society since 2002. Currently, she is the Vice-Chair of IEEE Photonics Society Malaysia Chapter for 2021 – 2022 term. She has co-authored more than 90 journal and conference papers, local and internationally. Her research interests include but not limited to optical access networks, fault monitoring in optical networks, visible light communication, free space optics, optical code division multiple access and optical orthogonal frequency division multiplexing.