Devices for Transmitter, Wave-Propagation, and Receiver in Coherent Optical Communication Systems

提高信号激光器和局域激光器的光谱纯度是实现实用相干光通信系统的关键一步。研究了1/f噪声对半导体激光器光谱扩展的影响，结果如下： 在高功率限制下，最窄线宽由1/f噪声确定。由于1/f噪声在高比特率系统中是无害的，因此实现高功率状态并保持高纵模稳定性至关重要。调频也是相干光通信系统的关键技术。我们证明了具有分离电极结构的DFB激光器适用于频率调制。我们开发了两种分析具有不对称折射率分布的保偏光纤的方法：一种是基于有限元方法，另一种是基于边界积分方法。两者都用于新的折射率分布的设计。我们提出了两种对策来应对传输信号的偏振波动。一种是偏振复合方案，另一种是偏振分集方案。后者在实际系统中特别有用，因为功率损失小于0.5dB，并且可以在同一接收器中实现相位分集。

The improvement of the spectral purity of the sdignal laser and the local laser is a crucial step to realize practical coherent optical communication systems. The effect of the 1/f noise on the spectral spread of semiconductor lasers is investigated, and the results are given in the following: In the high power limit, the narrowest linewidth is determined from the 1/f noise. Since the 1/f noise is harmless in the high bit-rate system, it is most important to achieve the high power state keeping a high longitudinal mode stability.The frequency modulation is also a key technology in coherent optical communication systems. We show that DFB lasers haveing the separated-electrode structure are suitable for frequency modulation.We develop two methods for analyzing polarization maintaining optical fibers with the asymmetrical refractive-index distribution: One is based upon the finite-element method, and the other the boundary-integral method. Both are used for the design of new refractive-index distributions.We propose two countermeasures to cope with the polarization fluctuation of the transmitted signal. One is the polarization recombining scheme, and the other is the polarization diversity scheme. The latter is especially useful in practical systems, because the power penalty is less than 0.5dB and the phase diversity can be implemented in the same receiver.