Advanced modulation formats like dual-polarization quadrature phase-shift keying (DP-QPSK) along with the digital coherent receiver are enabling optical networks to provide high spectral efficiency (SE) over long-haul transmission reach. The DP-QPSK based dense wavelength division multiplexing (DWDM) system with 37.5 GHz channel spacing can provide extra throughput of 33% compared to 50 GHz channel spacing. However, at 37.5 GHz channel spacing, optical add-drop multiplexers (OADMs) at intermediate nodes, impact the performance of WDM based optical networks in terms of increased BER, thereby reducing transmission reach drastically. In this paper, we have analyzed with the help of numerical simulations, the performance of a differentially encoded eight-channel 112 Gb/s, OADM based DWDM optical network with a channel spacing of 37.5 GHz. We propose that the selection of optimum values of system parameters can result in reducing the impact of crosstalk propagation and narrowband optical filtering introduced by a chain of OADMs at 37.5 GHz channel spacing. The paper exhibited that the selection of optimum values of parameters like filter order of multiplexer and demultiplexer, launch power per channel and filter taps of adaptive equalizer (AE) result in achieving minimum BER on all the channels over a long transmission reach up to 3600 km.

先进的调制格式（如双极化正交相移键控（DP-QPSK））以及数字相干接收机使光网络能够在长距离传输范围内提供高频谱效率（SE）。与50 GHz信道间隔相比，具有37.5 GHz信道间隔的基于DP-QPSK的密集波分复用（DWDM）系统可以提供33％的额外吞吐量。但是，在37.5 GHz的信道间隔处，中间节点的光分插复用器（OADM）就增加的BER影响了基于WDM的光网络的性能，从而大大降低了传输距离。在本文中，我们借助数值模拟分析了信道间隔为37.5 GHz的基于差分编码的八通道112 Gb / s，基于OADM的DWDM光网络的性能。我们建议选择系统参数的最佳值可以减少由OADM链在37.5 GHz信道间隔处引入的串扰传播和窄带光学滤波的影响。该论文展示了对参数的最佳值的选择，例如多路复用器和多路分解器的滤波器阶数，每通道的发射功率以及自适应均衡器（AE）的滤波器抽头，可在长达3600 km的长距离传输中实现所有通道上的BER最小。