Real-Time Spectrum Monitoring System for Next-Generation High-Capacity Optical Networks

This paper presents new theoretical and experimental results along with in-depth insight into a recently introduced simple real-time optical monitoring (RTOM) system and method, suitable for next-generation high-capacity optical networks. The proposed method employs electro-optic (EO) temporal sampling, followed by dispersion-induced real-time Fourier transformation and high-speed signal acquisition. The fundamentals, main design trade-offs, capabilities, and limitations of the RTOM system are thoroughly examined, including a detailed investigation of detection noise and sampling module extinction ratio (ER) effects on dynamic range. The RTOM design process is explored, and reasonable values for design parameters are identified based on practical and realistic specifications. The RTOM method continuously maps the spectral content of dense-wavelength-division-multiplexed (DWDM) data streams into the time domain, allowing to determine the presence and relative power of individual channels with high frequency resolution (∼30 GHz) and high sensitivity (∼1 dB). Notably, it provides fast measurement update rates (in the MHz range), far surpassing the measurement speed of commercially available optical spectrum analyzers, which is typically in the kHz range and slower. This scheme demonstrates remarkable versatility in performing real-time spectral analysis of DWDM signals across diverse operational conditions, including different modulation formats, bit rates (accommodating up to several hundred Gb/s per channel), various dispersion values in the optical link, and channel spacings from 50 GHz to 100 GHz spanning the entire C-band. The comprehensive evaluation reported here underscores the system's adaptability to diverse network configurations and transmission parameters, positioning it as a powerful tool for advanced optical network monitoring.