Progress in optical networking has stimulated interest in optical performance monitoring (OPM), particularly regarding signal quality measures such as optical signal-to-noise ratio (SNR), Q-factor, and dispersion. These advanced monitoring methods have the potential to extend fault management and quality-of-service (QoS) monitoring into the optical domain. This paper reviews OPM applications and techniques, while examining the role of OPM as an enabling technology for advances in high-speed and optically switched networks.

Optical performance monitoring

Optical performance monitoring for the next generation optical communication networks

We propose and experimentally demonstrate a nondestructive method to monitor chromatic dispersion (CD) and polarization-mode dispersion (PMD) in traffic-carrying wavelength-division-multiplexing optical systems. Coherent heterodyne detection is used to down convert the spectrum of digitally modulated signal from optical domain into radio-frequency (RF) domain. By analyzing group delay difference and polarization walkoff between different frequency components through proper RF signal processing, both CD and PMD can be precisely determined. Good agreement between experimental results and theoretical values has been obtained.

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Fiber chromatic dispersion and polarization-mode dispersion monitoring using coherent detection

The authors describe a fast spectral polarimeter operating in the lightwave communications band capable of measuring both state-of-polarization and degree-of-polarization of hundreds (up to thousands) of spectral components in parallel within milliseconds. In this paper, the design incorporates fast switching ferroelectric liquid crystals for polarization component selection on the 100-mus scale. Dispersion elements and an arrayed detector are used for wavelength-parallel sensing. Bandwidth of coverage can be scaled from a single wavelength-division multiplexed channel to more than 100 nm, and 256 spectral polarization measurements in under 1 ms are verified. Finally, a calibration algorithm is used to minimize measurement error. This instrument offers unprecedented sensing capability relevant to the monitoring and compensation of polarization-related impairments in high-speed lightwave communications

A Complete Spectral Polarimeter Design for Lightwave Communication Systems

Frequency-selective polarimeters measure the state of polarization of the individual spectral components of a modulated optical signal. They can be used either as stand-alone measuring devices or as parts of adaptive polarization-mode dispersion (PMD) compensators. This paper presents a novel frequency-selective polarimeter based on coherent detection, which has superior accuracy compared to previously proposed direct detection-based counterparts. This is due to the high-frequency resolution and power sensitivity of coherent detection, features that minimize the systematic and random error, respectively, in the measurement of the state of polarization of the individual spectral components of the received optical signal. The accuracy of the measurement is independent of the received signal bit rate and modulation format. The proposed frequency-selective polarimeter is studied both theoretically and experimentally. The primary theoretical contribution of this paper is a unified formalism, which allows the modeling of both direct and coherent detection-based frequency-selective polarimeters. Analytical expressions for the output signal of both types of frequency-selective polarimeters are derived. Based on these expressions, a common algorithm is proposed for the evaluation of the Stokes parameters. In addition, an example error signal is used as a metric in order to test the agreement of the theoretical model with the experimental measurements. The successful operation of the coherent frequency-selective polarimeter is demonstrated experimentally for a 10-Gb/s intensity-modulated nonreturn-to-zero (NRZ) optical signal in the presence of first-order polarization-mode dispersion. There is an excellent agreement between theory and experiment.

Coherent frequency-selective polarimeter for polarization-mode dispersion monitoring

We proposed and demonstrated a coherent heterodyne receiver architecture that can frequency-resolve the Stokes parameters of a modulated signal. We also studied the feasibility of generation of an error signal based on the Stokes parameters variance. We presented experimental results for a 10 Gb/s NRZ signal with first-order polarisation mode dispersion (PMD) and theoretical results for a 40 Gb/s RZ signal with higher-order PMD.

G.A. Piech

Papers

Coherent frequency-selective polarimeter for polarization-mode dispersion monitoring

Coherent heterodyne frequency-selective polarimeter for error signal generation in higher-order PMD compensators