Abstract
In this paper, we have explored the feasibility of 8-level pulse amplitude modulation (PAM8) format for realizing beyond 100 Gb/s transmission in a bandwidth-limited intensity modulation and direct-detection (IMDD) system. Generally, Volterra equalizer is a practical algorithm which can be used in bandwidth-limited system to combat the linear and nonlinear impairments. However, we observe that the performance of Volterra equalizer would be restricted by a phenomenon of level-dependent equalized effect, especially in low optical signal-to-noise ratio case. To cope with this problem, a tap coefficient decision directed Volterra equalizer (TDD-Volterra) with multiple sets of tap coefficients is proposed. The optimal set of tap coefficients is selected according to the decision results of input symbols before equalization. By this means, the TDD-Volterra is effective for overcoming the level-dependent equalized effect. By using the proposed TDD-Volterra, 180 Gb/s PAM8 signal is successfully transmitted over 2 km standard single mode fiber in an IMDD system with the 10-dB bandwidth of 17.5 GHz for the first time. The achieved bit error rate (BER) value is below the 7% overhead hard-decision forward error correction threshold of $3.8\times 10 ^{-3}$ . Moreover, the performance comparison among decision-directed least-mean square equalizer, Volterra Equalizer, and TDD-Volterra are analyzed in this paper. The experimental results show that compared to the conventional Volterra equalizer, the algorithm complexity of TDD-Volterra is decreased by over 50% for achieving a given BER value. Our research may provide a solution for beyond 100 Gb/s short-reach applications using bandwidth-limited electro-optical components.
Highlights
New applications such as the 5th generation (5G) wireless communication, virtual reality and cloud computing lead to the explosively increased data traffic
It could be clearly observed that the 10-dB bandwidth of this intensity modulation and direct-detection (IMDD) system is about 17.5 GHz, and the strong filtering effect could be attributed to the cascaded filtering of electrical and optical components used in this system
The feasibility of PAM8 format for realizing the data rate of 180 Gb/s in a bandwidth-limited IMDD system is investigated in both simulation and experiment
Summary
New applications such as the 5th generation (5G) wireless communication, virtual reality and cloud computing lead to the explosively increased data traffic. Some advanced modulations formats such as 4-level pulse amplitude modulation (PAM4) [3], [4], discrete multi-tone (DMT) [5] and carrier-less amplitude and phase modulation (CAP) [6], [7] have been intensively discussed in IMDD systems. These researches show that PAM4 is a better solution by considering the power consumption, the transmission performance and the complexity of transceivers [8], [9]. PAM4 has been adopted for several distance categories in IEEE 200 GbE and 400 GbE
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