| Optical-domain performance monitor (OPM) will be a key component to monitor the performance of future optical networks. Compared to electrical domain performance monitoring, OPM has a number of advantages such as wavelength and data-rate transparency. It is also applicable to various different optical modulation formats. An OPM can be shared by many wavelength channels and therefore it is especially advantageous for applications in wavelength-division multiplexed (WDM) optical networks with large channel count.; In this dissertation, we first investigate the current states of performance monitoring in WDM optical networks, and the importance of performance monitoring in the optical domain. Then, we present a novel optical-domain performance monitoring architecture which consists of an ultra fine-resolution optical spectrum analyzer (OSA), a chromatic dispersion (CD) monitor, and a polarization-mode dispersion (PMD) monitor. In the design of OSA, we demonstrate a novel technique based on coherent detection to achieve ultra fine spectral resolution. It can be used to measure channel wavelength, signal optical power and optical signal-to-noise ratio (OSNR) in WDM systems. Its ultra fine resolution also enables the measurement of channel data-rates and optical modulation formats in optical domain, which are important for future dynamic optical networks. As for the designs of CD and PMD monitors, coherent detection technique is also used. Coherent detection down converts the spectrum of digitally modulated optical signal in the system from optical domain into electrical domain, and by applying proper RF signal processing, both CD and PMD can be determined. Many conventional methods measuring CD and PMD require the access to both sides of the fiber system, while the technique we proposed only requires the access to the receiver end. Therefore, it is non-destructive and can be deployed in various locations within an optical network. At the same time, coherent detection also provides high sensitivity and accuracy and it requires less signal optical power in the measurement compared to direct detection. In addition, the monitoring of CD is not affected by the PMD performance of the fiber, and vice versa, which isolates the sources of system performance degradation. This dissertation provides detailed theoretical analysis as well as experimental demonstration on the proposed optical-domain performance monitor. We have also analytically evaluated the impacts of system noise and nonlinearity on the accuracy of the CD monitoring, and the results agree well with numerical simulations.; Combining an ultra fine-resolution OSA with the CD and the PMD monitoring functionalities, a multi-functional optical performance monitor can be built. Such a performance monitor is capable not only of monitoring optical signal to noise ratio, channel power, channel wavelength, signal modulation format and signal data-rate, but also capable of monitoring CD and PMD in ultra dense WDM transmission systems. This technique which is based on coherent detection is promising for optical performance monitor, making non-destructive performance monitoring more practical and reliable. |
