Optical-Domain Performance Monitoring for Next Generation Optical Networks
Project Award Date: 09-01-2006
ITTC researchers are refining their multi-functional optical system performance monitor using coherent heterodyne detection. In addition to performing high-resolution optical spectrum analyzing, the system is capable of monitoring chromatic dispersion and PMD at each wavelength channel. Improvements include finding a practical method to relate the detailed spectral information of an optical signal to the corresponding time-domain feature and predict waveform distortion of an optical signal from the detailed optical spectrum change measured by the coherent OSA. This work will have significant values both academically and practically. Secondly, the technique they develop for the measurement of chromatic dispersion using coherent detection is limited to a maximum of 1250 ps/nm accumulated dispersion in a l0Gb/s system. Although this is sufficient for most of the conventional long-haul optical systems where residual dispersions have to be low, it will not be sufficient to support the optical transmitter/receivers recently developed by Nortel, which have extremely high dispersion tolerance. Additional improvement is certainly needed to extend the dispersion measurement range. Third, ITTC researchers have demonstrated PMD monitoring only to the first order. In order to monitor second order PMD, they will need to select more than two frequency components from the signal spectrum. To demonstrate this capability, additional experiments are necessary.
Because of the ultra-high spectral resolution in the MHz level, this spectrum analyzer is able to precisely measure the spectral shape of an optical signal and provide information such as modulation data rate, modulation format, and optical signal-to-noise ratio. ITTC researchers have specifically measured spectrum of optical signal with various modulation formats using the coherent OSA and their differences in the detailed spectral features can be identified. This same coherent detection setup was also used to measure chromatic dispersion and PMD that an optical channel experiences without the access to the input side of the fiber. The accuracy of these measurements has been verified by the comparison between the experiments and the theoretical calculations. This coherent optical performance monitor is flexible and can be used in most of the existing and future optical network architecture, while providing sufficient information for network maintenance and quality control. The PMD monitoring technique developed under this support is of particular interest because of is simplicity and accuracy.
Compared to electrical domain performance monitoring, signal processing in optical domain is data-rate transparent, flexible to various signal modulation format, independent of transmission equipment venders, and is capable of operating in hybrid optical networks across the boundary of different service operators. Existing optical performance monitors are made of low-resolution optical spectrum analyzers. They are capable of monitoring signal optical power at each channel, signal wavelength, and optical signal-to-noise ratio. For future dynamic optical networks, more parameters may need to be monitored in order to ensure the quality of service.
Primary Sponsor(s): Nortel Networks