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

我们研究了山下先生和首席研究员共同发明的用于相干光纤通信的两级相位分集(DSPD)方案。本项目的主要目的是建立其基本技术，并将其应用于光通信系统。为了建立其基本技术，我们搭建了一个实验装置并进行了误码率测试。在DSPD方案和外差方案中获得了几乎相同的灵敏度。从理论和实验两个方面研究了光路不平衡对灵敏度的影响，发现不平衡对灵敏度的影响不大。它在频域多路复用系统中的应用。我们研究了它在带有光纤放大器的超长距离系统中的应用，发现它在这类系统中具有优异的噪声性能。除了…此外，还对光纤放大器本身的噪声性能进行了计算和测量，结果表明后向ASE降低了光纤放大器的噪声特性。作为插入DSPD接收机中频级的群延时均衡器，微带线的形状被成功地优化以补偿光纤的色散。模拟结果表明，DSPD方案的传输距离有可能超过10000公里，因此光纤中的受激布里渊散射(SBS)限制了传输距离。NVE提出了两种抑制受激布里渊散射(SBS)的方案，一种是利用光扩频技术，另一种是利用光隔离器，对它们进行了理论和实验研究，并研究了DSPD方案中必不可少的光学器件和系统，以及它们的测量和维护技术。较少

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