We experimentally demonstrate the four-fold multiplexing of Hermite–Gaussian (${\mathrm{HG}}_{mn}$) or Laguerre–Gaussian (${\mathrm{LG}}_{lp}$) modes to achieve a 400 Gbit/s quadrature-phase-shift-keyed (QPSK) free-space optical communication link. In this experiment, both modal indices for the HG and LG modes are simultaneously utilized to achieve a larger potential orthogonal modal space. Moreover, we also investigate and compare the effects of aperture size, lateral displacement, and rotation on the system. We measure the degree of performance degradation due to the following: (1) a receiver aperture with a limited size causes power loss and crosstalk for both HG and LG modes; (2) a lateral misalignment between the transmitter and receiver which leads to crosstalk for LG modes, but might not affect ${\mathrm{HG}}_{0n}$ or ${\mathrm{HG}}_{m0}$ modes due to axial symmetry; and (3) a rotational misalignment between the transmitter and receiver which causes crosstalk for the HG modes, but does not tend to affect the LG modes due to azimuthal symmetry.

中文翻译：

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基于Hermite-Gaussian或Laguerre-Gaussian模式的四重复用的400-Gbit / s QPSK自由空间光通信链路，通过改变两个模态指数

我们通过实验证明了Hermite-Gaussian（${\mathrm{HG}}_{米ñ}$）或Laguerre–Gaussian（${\mathrm{LG}}_{升p}$）模式以实现400 Gbit / s正交相移键控（QPSK）自由空间光通信链路。在该实验中，同时使用了HG模式和LG模式的两个模态指数，以实现更大的潜在正交模态空间。此外，我们还研究并比较了孔径大小，横向位移和旋转对系统的影响。我们测量由于以下原因导致的性能下降程度：（1）尺寸受限的接收器孔径会导致HG和LG模式的功率损耗和串扰；（2）发射器和接收器之间的横向未对准会导致LG模式下的串扰，但可能不会影响${\mathrm{HG}}_{0ñ}$ 或者 ${\mathrm{HG}}_{米0}$由于轴向对称而产生的模式；（3）发射器和接收器之间的旋转不对准会导致HG模式产生串扰，但不会因方位角对称而影响LG模式。