  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.
