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Quasi-light Storage for Optical Data Packets
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Four-dimensional QPSK modulation transmission scheme based on entropy-coding-aided symbol selection.

Junjie Cai, Bo Liu, Jianxin Ren

    Optics Express
    |July 30, 2025
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    Summary
    This summary is machine-generated.

    We introduce a novel four-dimensional quadrature phase shift keying (4D-SS-QPSK) scheme using entropy coding for improved signal transmission efficiency. This method enhances receiver sensitivity in fiber optic systems.

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    Area of Science:

    • Optical Communications
    • Digital Signal Processing
    • Information Theory

    Background:

    • Traditional Quadrature Phase Shift Keying (QPSK) suffers from inefficient utilization of high-dimensional space.
    • Bit-interleaved coded modulation (BICM) is a standard technique in digital communication.

    Purpose of the Study:

    • To propose and evaluate a novel four-dimensional quadrature phase shift keying (4D-SS-QPSK) modulation scheme.
    • To enhance spectral efficiency and receiver sensitivity in intensity modulation/direct detection (IM/DD) systems.

    Main Methods:

    • Integration of Huffman coding with bit-interleaved coded modulation (BICM) for non-uniform signal generation.
    • Aggregation of three QPSK signals and one BPSK signal into a four-dimensional phase unit.
    • Symbol subset selection aided by source entropy (SE) and mapping onto a predefined four-dimensional subset.

    Main Results:

    • Demonstration in a 2-km IM/DD seven-core fiber transmission system at 14.175 Gb/s.
    • Achieved a receiver optical power of -10.4 dBm at the HD-FEC BER limit of 3.8 × 10⁻³.
    • Obtained approximately 0.7 dB receiver sensitivity gain over 3D-SS-QPSK and 0.5 dB over 4D-SS-QPSK without BICM.

    Conclusions:

    • The proposed 4D-SS-QPSK scheme effectively overcomes the limitations of traditional QPSK in high-dimensional space utilization.
    • The entropy-coding-aided symbol selection significantly improves receiver sensitivity and transmission efficiency.
    • This modulation scheme offers a promising advancement for future high-speed optical communication systems.