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The cylindrical vector beams (CVBs) as the spatially orthogonal modes in fiber provide additional degree of freedom for optical fiber communication. The ring-core fibers with a high refractive index area matching with the beam shape of CVBs are suitable for stable transmission of CVBs. We simulate and experimentally characterize the CVBs transmission in ring-core fibers with different geometric structure parameters. We demonstrated the transmission of CVBs from 2nd to 7th orders with mode purities higher than 80% and demonstrate the multiplexing communication of coaxial high order CVBs in ring-core fiber. The model we build to calculate the largest CVB mode number and order supported in the ring-core fiber are consistent with the experimental results of our three ring-core fibers. From the simulation results, the higher order CVB modes show larger effective refractive index differences and less crosstalk compared with the lower orders modes. According to the calculation, it is possible to transmit up to 4 mode groups of high order CVB modes in the ring-core fiber with optimized geometric parameters, given by the effective refractive index threshold of 2 × 10−3.

A cascaded phase-only mask architecture (or an optical diffractive neural network) can be employed for different optical information processing tasks such as pattern recognition, orbital angular momentum (OAM) mode conversion, image salience detection and image encryption. However, for optical encryption and watermarking applications, such a system usually cannot process multiple pairs of input images and output images simultaneously. In our proposed scheme, multiple input images can be simultaneously fed to an optical diffractive neural network (DNN) system and each corresponding output image will be displayed in a non-overlap sub-region in the output imaging plane. Each input image undergoes a different optical transform in an independent channel within the same system. The multiple cascaded phase masks in the system can be effectively optimized by a wavefront matching algorithm. Similar to recent optical pattern recognition and mode conversion works, the orthogonality property is employed to design a multiplexed DNN.