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Tom Ako

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A simulation tool for optical time domain reflectometry (OTDR) monitoring of passive optical networks


The potential growth of telecommunication traffic with 90% per year makes present-day service providers to remove copper cables from the last miles in telecom networks and shift towards Passive all-Optical Networks (PON) for broadband access [1]. To respect the subscriber’s requirements for high-quality service, a PON demands a reliable monitoring system for the identification, localization, and loss quantification of existing faults in the network. The challenging problem, which network providers encounter today, is that Optical Time Domain Reflectometry (OTDR) [2], which is generally used to test faults (see Figure 1), is an inappropriate monitoring method in a PON. Indeed, OTDR measurements carried out from the central office cannot distinguish between the superposition of the backreflected Rayleigh signals originating from the different branches after the fiber distribution hub. Consequently, it is not possible to localize the faults after the splitter and technicians will have to perform expensive truck roll measurements to identify possible failures. We now want set up a simulation tool to generate OTDR traces of PON networks including splitters, with the aim of developing a remote monitoring method enabling OTDR measurements from the central office, eliminating the need for expensive truck rolls. 

Figure 3: Commercial OTDR device (© Yokogawa) 


Remote monitoring based on timing signatures will allow to filter out the discrete Rayleigh reflections form only one of the splitter branches. As such, this would make it possible to locate discrete events such as connectors, non-ideal splices and even fiber breakage along the fiber behind a splitter. Furthermore, the technique requires only an OTDR analyzer at the CO eliminating potentially expensive truck roll measurements.

To test the capabilities and, more importantly, the limitations of such a method requires the generation of detailed OTDR traces [3] of typical PON networks. In this work, you will generate such OTDR traces of PON network lay-outs via computer simulations. Additionally, limitations of current OTDR equipment such as a limited dynamic range, dead zone and noise floor, will be introduced into the simulator in order to come to realistic results.

To validate your simulation code, you will set up experimentally a small PON network and perform an OTDR measurement, which you will cross-check with your simulation results. Finally, you will use your code to check whether fiber Bragg gratings (FBGs) can be used as reflective elements to generate timing signatures of the different branches of a PON, to enable remote monitoring from the central office.

Link to webpage or article related to the subject (optional):

[1] FTTH Handbook Fourth Edition D&O Committee. Available at:


[2] Anderson, D. R.Johnson, L.Bell, Florian G, “Troubleshooting optical-fiber networks : understanding and using your Optical Time Domain Reflectometer”, Elsevier Academic Press,Boston, 2004.

[3] OTDR and backscattering measurements. Available at:



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