6. Conclusion
6.2. Future research prospect
In current optical communication systems, besides the fiber link noise and interference, transceiver impairments and imperfect characteristics limits the further improvement for the transmission capacity. On the other hand, high baud rate, complex modulation format, multi-dimension modulation multiplexing and advanced signal processing are being researched hotly to improve the spectrum efficiency and signal quality at the receiver. Many problems may exist in the
use of this techniques. To solve it, research works of the behavior modeling and character measurement for the optical transceivers need future efforts:
1: For the nonlinearity issue of electrical amplifier, the compensation scheme based on the proposed model requires algorithm research. It is expecting to efficiently compensate the nonlinear distortions and improve the transmission performance based on the proposed model. For current nonlinear behavior model, the complexity is still high, which is suitable for distortion analysis and penalty evaluation. However, for the nonlinearity compensation and implementation in real applications, model simplification research may be needed so as to reduce the required power consumption and cost.
2: As optical transceiver operates, the impairments and distortions would change due to the module aging or operation condition varying, for example bandwidth change, delay change or gain change due to temperature varying. The behavior modeling and measurement based on adaptive methods for these dynamic impairments is required research to improve the robustness and reliability of optical transceiver.
3: The powerful machine learning or neural network models can provide a kind of behavior model and description manner for the complex or inextricable problems. For the complex impairments in optical transceiver, such as the nonlinearity, the dynamic distortions or the quantization and sampling imperfections in DAC and ADC, machine learning or neural network models could be researched to model, measure and mitigate the penalties and improve the transmission capacity of optical transceivers.
For future optical transceivers, the balance among high capacity, low cost and low power consumption is always required. Signal processing algorithms can provide an optimal solution for such balance. Research works of behavior modeling and measurement for the distortions and impairments for the optical transceivers in various application scenarios might become more and more important for the future high speed, dynamic, flexible and high efficiency communication systems.
87
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Acknowledgement
First of all I would like to thank Professor Kazutoshi Kato, Professor Yuji Oki and Professor Shunji Kimura for their supervision, inspiration, and guidance. I am greatly grateful to them, I simply say: thank you so much.
I would like to acknowledge Fujitsu Research and Development Center for providing me the experiment instruments and environments. I offer my sincere thanks to the research group members in Fujitsu for their valuable helps, communications and comments. Special thanks to Dr.
Tao Zhenning who helped me a lot in the research of this work.
I would also like to thank my parents for their never ending support, love and care.
Finally, my deepest gratitude goes to my wife Wenyun Ji for her selfless love, support and understanding.