CDM-Based -OTDR for Rapid TDM- and WDM-PON Monitoring

A novel OTDR-system is introduced, which enables a significant reduction of measurement times in TDM- and WDM-PON measurements compared to a conventional λ-OTDR. It has the ability to measure multiple wavelengths simultaneously with just one receiver photodiode. The working principle is similar to a code division multiplexing transmission system. Furthermore, the measurement time is not only reduced by the simultaneous measurements on different wavelengths but also by means of coding gain, which reduces the OTDR averaging time. The coding gain has its origin in the correlation of signals based on complete complementary codes. In an experiment, measurements were performed, which provided results 15 times faster than with a conventional λ-OTDR. Further improvements are possible with different measurement parameters.