Broadband, Low-Crosstalk, and Massive-Channels OAM Modes De/Multiplexing Based on Optical Diffraction Neural Network.

Optical communication technology based on the wavelength, time, polarization, and complex amplitude of light is approaching a bottleneck, while the spatial dimension is relatively unexplored. Orbital angular momentum (OAM) beams are an important group of spatial light beams that are promising for increasing the optical communication capacity based on their orthogonality. To effectively utilize this spatial dimension of light, broadband and low-crosstalk OAM mode de/multiplexing devices are indispensable. In this work, by exploiting an optical diffraction neural network, a low-crosstalk OAM de/multiplexer operating in the full C+L band is developed and demonstrated. The device can support 16 OAM modes (l=±1 to ±8) with 5 phase plates (8-level phase), and the designed insertion loss and average intermode crosstalk are better than -2.8 and -30.9 dB, respectively. In particular, multiplexing and demultiplexing are experimentally performed on the same device. The measured average insertion loss in mutltiplexing and demulteplexing is -6.1 to -5.4 and -6.8 to -5.8 dB, respectively, and the corresponding average intermode crosstalk is -27.2 to -22.7 and -26.5 to -22.4 dB. The results in this work have great application prospects for the design of mode de/multiplexers and mode division multiplexing communication systems. [ABSTRACT FROM AUTHOR]