基于自零差检测的高速模式复用无源光网络

High Speed Mode-Division-Multiplexing Passive Optical Network Utilizing Self-Homodyne Detection

为满足未来不断发展的接入网络业务需求,提出了一种基于自零差检测的高速模式复用无源光网络方案。在该方案中,少模光纤中的一个空间模式传送信号载波(即导频),其他空间模式用于传输信号。在接收端,导频和信号通过模式解复用器分离,导频作为接收端的本振与信号进行混频,实现自零差检测。借助于低串扰的少模光纤和模式复用/解复用器,接收端无需多入多出技术处理,即可实现导频与信号低串扰的分离。相比于偏振复用的自零差检测,基于模式复用的自零差检测可以有效地提高频谱效率。自零差检测可以有效地抑制激光器相位噪声,大大降低光线路终端或光网络单元对激光器线宽的要求。在接收端,由于不需要额外的本振,信号处理无需进行频偏的补偿,对载波相位恢复的要求也大大降低,从而有效降低了接收端数字信号处理的复杂度。利用该方案实验实现了4×40Gbit/s偏振复用正交频分复用信号经过55km两模式少模光纤和模式复用解复用器后的无误码自零差检测。与背对背传输相比,55km少模光纤引入的Q因子代价小于1dB。

To satisfy the demand of evolving network business in future access networks, a high speed Mode-Division-Multiplexing Passive Optical Network （MDM-PON） scheme utilizing self-homodyne detection is proposed. In the proposed scheme, one of the spatial modes is used to transmit a portion of signal carrier （namely pilot-tone） as the Local Oscillator （LO）, while the others are used for signal-bearing channels. At the receiver, the pilot-tone and the signal are separated by mode demulti- plexer and then sent to the receiver for coherent detection. Due to the low modal-crosstalk Few-Mode Fiber （FMF） and all-fi- ber mode multiplexer/demultiplexer （MUX/DEMUX）, the pilot-tone and the signal can be effectively separated without Multi- ple-Input Multiple-Output （MIMO） processing. Compared with Polarization Division Multiplexing （PDM） self-homodyne de- tection, the spatial efficiency is enhanced. Meanwhile, the self-homodyne detection can effectively suppress the laser phase noise, which relax the requirement for lasers line-width at the Optical Line Terminal or Optical Network Units （OLT/ONUs）. At the receiver side, the Digital Signal Processing （DSP） is also simplified since self-homodyne detection reduces the receiver eomplexity by eliminating the LO from the coherent receiver, removing the need for frequency offset compensation and reduc- ing the requirement for carrier phase recovery by several orders of magnitude. Using the proposed scheme, a proof of concept 4×40 Gbit/s Orthogonal Frequency Division Multiplexing （OFDM） signal transmission over 55 km FMF using low modalcrosstalk two-mode FMF and MUX/DEMUX with error free operation is experimentally demonstrated. Compared with the baek to back case, less than 1 dB Q- factor penalty is observed after transmission over 55-kin FMF.