Measurement of Linear Optical Crosstalk for Bit Error Rate Estimation by using Spread Spectrum Measurement Symbols

T. Welsch and K. Jobmann (Germany)


performance monitoring, crosstalk supervision, spread spectrum


The transmission quality of an all optical transmission degrades with various optical effects like amplifier noise, dispersion, linear and nonlinear crosstalk. We use spread spectrum measurement symbols for leveling the small signal parts arisen by linear crosstalk during the running transmission. This paper presents the measurement of linear optical in-band crosstalk degrading an optical PCM-480 transmission at 34,368Mbit/s. We show how to measure the ratio between payload transmission level and crosstalk level with an accuracy better than 0,4 dB in a wide dynamic range. The bit error rate (BER) measurable payload degradation due to the crosstalk effect occurs at different crosstalk levels depending on the optical system reserve. Aside from a bit error rate estimation based on the measured crosstalk level, an ascertainment and a supervision of crosstalk level limits is possible where no degrading in bit error rate occurs. In our measurements we could identify and precisely quantify the crosstalk effects from 20 dB before any degrading in bit error rate occurs. These results confirmed the possibility of using the spread spectrum measurement symbols for cost sensitive early warning and in-service supervision of all optical WDM cross-connects with high channel numbers.

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