Djordjevic Ivan B, Arabaci Murat, Xu Lei, Wang Ting
University of Arizona, Department of Electrical & Computer Engineering, Tucson, Arizona 85721, USA.
Opt Express. 2011 Mar 28;19(7):6845-57. doi: 10.1364/OE.19.006845.
The multidimensional channel capacity studies indicate that the employment of multiple photon degrees of freedom-such as subcarrier, amplitude, phase, polarization, and space-can improve the spectral efficiency by several orders of magnitude higher than that claimed in any fiber-optic experiment reported to date. This dramatic increase in spectral efficiency through multiple photon degrees of freedom can provide revolutionary capabilities for future optical networks. Moreover, photons can carry both spin angular momentum (SAM) associated with polarization, and orbital angular momentum (OAM) associated with the azimuthal phase of the complex electric field. Because OAM eigenstates are orthogonal, an arbitrary number of bits per photon can be transmitted in principle. The ability to generate the OAM modes, such as Bessel modes, in multimode fibers (MMFs) will allow realization of fiber-optic communication networks with ultra-high bits-per-photon efficiencies. To this end, we propose here a spatial-domain-based multidimensional coded-modulation scheme as an enabling technology for multi-Tb/s serial optical transport. To demonstrate the capabilities of the proposed scheme, we show that an eight-dimensional (8D) spatial-domain-based coded modulation scheme outperforms a prior-art 128-point 4D scheme by 3.88 dB at BER of 10(-8) while providing 120 Gb/s higher aggregate information bit rate. The proposed 8D scheme also outperforms its conventional polarization-multiplexed QAM counterpart by even a larger, and indeed striking, margin of 8.39 dB (also at the BER of 10(-8)).
多维信道容量研究表明，利用多个光子自由度，如子载波、幅度、相位、偏振和空间等，可以将频谱效率提高几个数量级，比迄今为止报道的任何光纤实验所宣称的效率都要高。通过多个光子自由度实现的频谱效率的显著提高，可为未来光网络提供变革性的能力。此外，光子既可以携带与偏振相关的自旋角动量（SAM），也可以携带与复电场的方位角相位相关的轨道角动量（OAM）。由于OAM本征态是正交的，原则上每个光子可以传输任意数量的比特。在多模光纤（MMF）中生成诸如贝塞尔模式等OAM模式的能力，将使实现具有超高每光子比特效率的光纤通信网络成为可能。为此，我们在此提出一种基于空间域的多维编码调制方案，作为实现多太比特每秒串行光传输的 enabling 技术。为了证明所提方案的能力，我们表明，在误码率为10^(-8)时，一种基于空间域的八维（8D）编码调制方案比现有技术的128点4D方案性能优3.88 dB，同时提供高120 Gb/s的总信息比特率。所提的8D方案比其传统的偏振复用QAM对应方案性能优幅度更大，达到惊人的8.39 dB（同样在误码率为10^(-8)时）。
