Examples

Multi-Dimensional Time-Domain Hybrid Modulation using Golay Coding

  • Description

    Modulation formats making use of the four dimensions of the optical field (4D modulation) can offer improved sensitivity compared to the classical dual-polarization encoding where the orthogonal polarization of the light are encoded separately. The dimension of such modulation schemes can be extended using the time dimension, i.e. by defining symbols over several time-slots. In coherent transmission systems, the dimension of the resulting modulation scheme is Nx4 where N is the number of time-slots. Such time-domain hybrid encoding can be used to improve the signal sensitivity or robustness against a particular effect such as polarization [1] or fiber nonlinearities [2] by introducing redundancy in the successive time slots in a similar way to that of a FEC code.

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  • Typical Results

    In this example, the time-domain hybrid coding is achieved using the extended Golay code [3]. The simulation schematic is reported in Figure 1. The extended Golay code is a linear error-correcting code mapping 12-bit message into 24-bit code-words. In [4] it was proposed to map these 24 bits onto a 24D hypercube consisting of 6 consecutive DP-QPSK symbols (6x4 dimensions). The new format was shown to present an improved power efficiency compared to classical dual-polarization and 4D modulation such as polarization-switched QPSK at the same bit-rate. The performance of this particular mapping as well as the one of an alternative mapping on a 16D hypercube (4 consecutive DP-8QAM symbols, each carrying 6 bits/symbol, see Figure 2 ) are reported in Figure 3 . The Time-Domain hybrid modulation combined with Golay-coding presents an improved sensitivity of around 3dB compared to their dual-polarization counterparts at the same bit-rate.

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  • Further Information

    Keywords: Coherent, QAM, Golay, coded modulation, time hybrid

    Similar demonstrations are available in VPItransmissionMaker Optical Systems and on the VPIphotonics Forum.

    [1] S. Mumtaz et al., 'Alamouti Code against PDL in Polarization Multiplexed Systems', Signal Processing in Photonic Communications, Optical Society of America, 2011.
    [2] A. D. Shiner et al., 'Demonstration of an 8-dimensional modulation format with reduced inter-channel nonlinearities in a polarization multiplexed coherent system', Optics Express, pp.20366-74, August 2014.
    [3] https://en.wikipedia.org/wiki/Binary_Golay_code
    [4] D. S. Millar et al., 'A 24-dimensional modulation format achieving 6 dB asymptotic power efficiency.', Signal Processing in Photonic Communications, Optical Society of America, 2013.

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