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10 August 2004 Demonstration of high-spectral-efficiency 40-Gb/s optical communications system using 4 bits per symbol coding
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Abstract
Next generation high-capacity (> 40 Gb/s) optical communication systems, whether for fiber or free-space transmission, will likely require high spectral efficiency techniques that enable optimization of performance, SWAP (size, weight and power), as well as the support of critical features such as transmission security. Modulation techniques with high number of bits per symbol coding such as differential quaternary phase-shift-keying (DQPSK) at lower symbol rates are more advantageous than conventional binary on-off keyed format with one bit per symbol coding. DQPSK is more robust to impairments of the transmission medium such as fiber dispersion than 40 Gb/s on-off keying. DQPSK is also less vulnerable to eavesdropping than direct-detection of on-off keyed signals at the physical layer. We report results of a 2-bit/s/Hz spectral efficiency multi-channel transmission system with four bits per symbol coding using 12.5 Gsymbol/s DQPSK and polarization multiplexing by bit-interleaved orthogonal polarizations. Transmission of 14×40 Gb/s 20-GHz spaced optical channels over 4×102 km of standard SMF-28 optical fiber with bit-error-ratio below the forward-error-correction code threshold (10-3) required for error-free operation was achieved. Key enabling components used in the transmission experiment are: DQPSK optical modulator and demodulator, channel demultiplexing tunable band-pass optical filter, and balanced photoreceiver.
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Pak S. Cho, Geof Harston, Chris J. Kerr, Art S. Greenblatt, Arkady Kaplan, Yaakov Achiam, Guy Levy-Yurista, Moti Margalit, Yoav Gross, and Jacob B. Khurgin "Demonstration of high-spectral-efficiency 40-Gb/s optical communications system using 4 bits per symbol coding", Proc. SPIE 5440, Digital Wireless Communications VI, (10 August 2004); https://doi.org/10.1117/12.541574
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