提出以改进型双二进制归零码(MD-RZ)信号作为标记,分别采用差分相移键控非归零码(NRZ-DPSK)信号和差分正交相移键控非归零码(NRZ-DQPSK)信号作为载荷进行正交调制的新方案。然后提出了一种从标记信号中提取和恢复时钟的简单方案。比较了背对背系统中2.5 Gbit/s的MD-RZ标记叠加到10 Gbit/s的NRZ-DPSK载荷和20 Gbit/s的NRZ-DQPSK载荷上的频谱特性,证明了MD-RZ标记占空比越大,光分组信号的频带利用率越高。采用传统的二进制强度调制-直接检测(IM-DD)系统的接收机检测得到了背对背系统中不同占空比的2.5 Gbit/s MD-RZ标记的眼图。结果表明,若采用色散补偿技术,两种光分组信号中的MD-RZ标记能够在长距离传输时克服接收端眼图的失真; 当入纤功率值高于18 dBm时,占空比取值越大,MD-RZ标记的眼开度代价具有越高的传输鲁棒性。

Two novel orthogonal modulation schemes, in which a modified duobinary return-to-zero (MD-RZ) signal was generated as a label for optical switching network, were proposed. In one scheme, a non-return-to-zero differential phase shift keying (NRZ-DPSK) signal was generated as a payload, while in another scheme, a non-return-to-zero differential quadrature phase shift keying (NRZ-DQPSK) format payload was introduced. A simple method, in which the clock was extracted and recovered from label signals, was adopted. The spectra of two optical packet signals in the back-to-back label switching systems with 2.5 Gbit/s label and 10 Gbit/s payload, respectively, are compared. It is shown that the optical packet signal with a larger duty cycle label has higher spectral efficiency. In the back-to-back system, 2.5 Gbit/s MD-RZ labels with different duty cycles can be directly measured by a conventional binary intensity modulation direct detection (IM-DD) receiver. The MD-RZ labels of two optical packet signals can avoid the eye diagram distortion for long-distance transmission if the dispersion can be compensated. When the input power is beyond 18 dBm, the eye-opening penalty of MD-RZ label with a larger duty cycle is more robust in the label-detecting path.