Increasing the system capacity and spectral efficiency(SE)per unit bandwidth is one of the ultimate goals for data network designers,especially when using technologies compatible with current embedded fiber infrastructures.Among these,the polarizationdivision-multiplexing(PDM)scheme,which supports two independent data channels on a single wavelength with orthogonal polarization states,has become a standard one in most state-of-art telecommunication systems.Currently,however,only two polarization states(that is,PDM)can be used,setting a barrier for further SE improvement.Assisted by coherent detection and digital signal processing,we propose and experimentally demonstrate a scheme for pseudo-PDM of four states(PPDM-4)by manipulation of four linearly polarized data channels with the same wavelength.Without any modification of the fiber link,we successfully transmit a 100-Gb s−1 PPDM-4 differential-phase-shift-keying signal over a 150-km single-mode fiber link.Such a method is expected to open new possibilities to fully explore the use of polarization freedom for capacity and SE improvement over existing fiber systems.
Zhi-Yu ChenLian-Shan YanYan PanLin JiangAn-Lin YiWei PanBin Luo
We propose a vertical cavity semiconductor emitting laser(VCSEL)using a coupled-cavity(CC)design to broaden the bandwidths of gain and delay spectra.The structure is formed by constructing a passive cavity coupled with the active cavity.By rendering the strength of the two resonant cavities,the increased gain bandwidth by 340%and the increased delay bandwidth by 800%are achieved as compared with the signal-cavity(SC)VCSEL.The wideband spectra present more square-like passband which is expected for slow light system.By using it,a 20 Gbit/s super Gaussian signal is delayed by about 13 ps with high quality.
提出了一种新型的基于波长双环路结构的光电振荡器方案.在此方案中,利用两个激光器产生两束波长不同的连续光,分别通过两段长度不同的光纤构成双环路结构,利用光学游标效应可以获得单一的起振模式.通过理论分析可知,不同波长的两束光载波在耦合时,几乎不会产生随机拍噪声.实验中,获得了X波段(8—12 GHz)内频率可调谐的高质量微波信号.通过测量,信号的边模抑制比达到60 d B,相位噪声为-132.6d Bc/Hz@10 k Hz.同时,利用锁相环技术,通过光纤拉伸器有效补偿系统的腔长漂移,因此振荡频率的稳定性得到极大改善.系统的频率漂移在2 h内小于±84.3 m Hz.另外,测得的微波线宽为5.3 m Hz,Q值在1012量级,具有很高的谱纯度.
