Nonlinear photonic crystals can be employed to generate holographic images in nonlinear optical processes. However, due to the limit of binary structure, the process of holographic imaging will lose part of the amplitude information and cause image hollowing, thus the imaging quality is reduced. Generative adversarial network, a deep learning network based on game theory, is used to restore images. The results of restoration show high similarity to the original images, effectively weakening the effect of image hollowing, suppressing the diffraction effect, and restoring grayscale values. This image post-processing approach completes the field of application of nonlinear holographic imaging, which is useful for non-visible source imaging, crosstalk avoidance, optical encryption, and so on.
The atmospheric turbulence disturbs the phase fronts of orbital angular momentum (OAM) beams, which significantly affects the detection of beam modes. In this paper, we propose a method based on the convolutional neural network (CNN) to detect OAM modes in atmospheric turbulence. This method does not require a separate system to suppress the influence of atmospheric turbulence. The propagation of multimode OAM beams in atmospheric turbulence is simulated by setting several random phase screens in the transmission channel. We select three levels of atmospheric turbulence. In all these cases, the predicted error of the trained CNN is lower than 2 ×10-5 , which indicates that our network can detect the mode distribution in multimode OAM beams efficiently and accurately. We believe that this approach for detecting OAM modes holds great promise for potential applications and will provide widespread benefits for many optical fields.
Optical modulation of terahertz surface plasmon polaritons (THz SPPs) propagating in an intrinsic indium antimonide surface is demonstrated in this paper. The modulation is mediated by the modification of free carrier density with optical illumination. Simulation and experimental results show that a THz modulator can be realized by tuning the propagation lengths of THz SPPs, which could be controlled to be larger or shorter than the distance of two razor blades used for the coupling of the THz wave and the THz SPPs. In comparison with conventional THz modulation approaches, this method of manufacturing is simpler and the switching bandwidth is wider. The maximum modulation frequency of the modulators is anticipated to be above gigahertz, thus leading to the possibility of communication applications using the THz baseband.
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