Double-stage phase-diversity (DSPD) scheme for coherent optical fiber communications

我们研究了由本课题组组长和S。山下本课题的主要目的是建立其基础技术，并开发其在光通信系统中的应用。在DSPD和外差方案中获得了几乎相同的灵敏度。从理论和实验两方面研究了光路不平衡对灵敏度的影响，发现光路不平衡对灵敏度影响不大。它在频域复用系统中的应用。研究了它在超长距离光纤放大器系统中的应用，发现它在超长距离光纤放大器系统中具有良好的噪声性能。除了 关于我们 在此基础上，对光纤放大器本身的噪声特性进行了计算和测量，结果表明后向ASE使光纤放大器的噪声特性下降，并成功地对微带线的形状进行了优化，使微带线作为插入DSPD接收机中频级的群时延均衡器，几乎可以理想地补偿光纤的色散。仿真结果表明，DSPD方案的传输距离受到光纤受激布里渊散射（SBS）的限制。NVe提出了两种抑制SBS的方案：一种是利用光扩频技术，另一种是利用光隔离器，并对这两种方案进行了理论和实验研究。我们还研究了DSPD方案中不可缺少的光学器件和系统，以及这些器件和系统的测量和维护技术。如上所述，本项目的每个课题都取得了丰硕的成果。少

We have studied double-stage phase-diversity (DSPD) scheme for coherent optical fiber communications co-invented by the head investigator and Mr. S. Yamashita. Establishment of its fundamental techniques and development of its application to optical communications systems are the main purposes of this project.For the establishment of its fundamental techniques, we have constructed an experimental setup and measured bit-error-rate. Nearly same sensitivities have been obtained in DSPD and heterodyne scheme. Sensitivity degradation by optical circuit imbalance has been studied both theoretically and experimentally, and it was found that the imbalance does not affect the sensitivity severely. Its application to frequency domain multiplex systems. has also been studied, and it has been shown that this is suitable to such systems.We have studied its application to ultra-long haul systems with optical fiber amplifiers, and found that it has excellent noise performance in such systems. Besides … More , the noise performance of optical fiber amplifier itself have been calculated and measured ; it has been shown that the backward ASE degrades its noise characteristics.As an group-delay equalizer to be inserted in the intermediate-frequency stage of a DSPD receiver, the shape of microstrip line have successfully been optimized to compensate the fiber chromatic dispersion almost ideally. The results of simulation has indicated the possibility of long-distance transmission over 10, 000km.The transmission distance in DSPD scheme is thus limited by stimulated Brillouin scattering (SBS) in optical fiber. NVe have proposed two schemes for SBS suppression ; one using optical spread-spectrum and the other using optical isolators, and studied these theoretically and experimentally.We have also studied the optical devices and systems which are indispensable in the DSPD scheme, and the techniques for measurement and maintenance of these.As described above, fruitful results have been obtained on each subject of this project. Less