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Characterizing Advanced Modulation Formats Using An Optical Sampling Approach

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Characterizing Advanced Modulation Formats Using An Optical Sampling Approach

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  • Author: Francois Robitaille
With bandwidth demand growing and fi ber availability going down, carriers and equipment manufacturers have no choice but to turn to high-speed optical transmission systems to increase network capacity. However, traditional one-bit-per-symbol modulation schemes, such as OOK or DPSK, do not offer the spectral effi ciency necessary to signifi cantly increase the overall data-carrying capacity of optical fi bers. Moreover, if scaled up to much higher transmission speeds, these traditional modulation formats become very sensitive to chromatic dispersion (CD) and polarization-mode dispersion (PMD), rendering them unusable on existing networks. Last August, the infl uential Optical Internetworking Forum (OIF) recommended using fully coherent four-bit-per-symbol DP-QPSK (dual-polarization quadrature phase-shift keying) modulation format for 100 Gbit/s system design, since it is both spectrally effi cient and highly resilient to CD and PMD (when coupled with suitable signal processing algorithms). In addition, the industry is already seriously looking at longer-term evolution with modulation schemes such as 16-QAM and OFDM.

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