Metalenses recently have attracted attention because of their more compact size in comparison with conventional lenses; they can also achieve better optical performance with higher resolution. Duplexer is an interesting function of a metalens that can distinguish different sources and divide them into two parts for specific purposes. In this article, we design tunable duplex metalenses with phase-change material Ge₂Sb₂Te₅ for the first time. Two types of special unit cells are designed to modulate the incident lights, and four metalenses are designed based on the two types of unit cells. Specific phase profiles are calculated for different sections of metalens in which the corresponding unit cells are settled; accordingly, the metalenses can focus the incident lights at any positions according to our design. Moreover, the metalenses become selectable via tuning the state of phase-change material, which means that the output light field can be actively controlled. The proposal of our tunable duplex metalenses will offer new opportunities for active three-dimensional imaging or optical coding.

Recently, the metalens has been investigated for its application in many fields due to its advantages of being much smaller than a conventional lens and is compatible with nano-devices. Although metalenses have extraordinary optical performance, it is still not enough in some occasions such as wavefront detection for adaptive optics and display for large area applications. Using a metalens array is an ideal solution to solve these problems. Unfortunately, the common metalens array cannot be adjusted once it is fabricated, which limits its range of application. In this article, we designed an actively tunable metalens array for the first time by arranging the patterned phase change material Ge₂Sb₂Te₅ (GST) appropriately. For the metalens array designed at the wavelength of 4.6 μm, it had excellent broadband performance in the range from 4.5 μm to 5.2 μm. On the other hand, by tuning the phase state of GST, the focus and display of the metalens array can be controlled, acting as switching on or off. Furthermore, any graphics constructed with patterned focal spots can be achieved when the metalens array has sufficient secondary unit cells. The proposed metalens may have potential application value in the adaptive optics and dynamic display field.

Correction performance of an adaptive optics (AO) system is severely limited by its system latency under high temporal frequency distortions. Wavefront prediction methods has been proven to be an effective way to compensate system delay. A novel wavefront prediction method based on residual learning fusion network (RLFNet) is proposed in this paper. The network is able to eliminate redundant information between adjacent wavefront frames and fuse refined features, which provides a higher prediction accuracy under fewer priori wavefront input. The method is tested on a 1km laser atmospheric transmission experimental setup through high frequency atmospheric turbulence, where wavefront data is collected from a 1kHz Shack-Hartmann wavefront sensor (SHWS). We show that the proposed architecture is able to predict the second frame wavefront after the previous 6 frames with a root-mean-square (RMS) wavefront error reduction up to 53% compare to non-predictive method.

The Shack-Hartmann wavefront sensor produces incorrect wavefront measurements when some sub-spots are weak and missing. In this paper, a method is proposed to predict the centroids of these sub-spots for the Shack-Hartmann wavefront sensor based on the deep neural network. Using the centroid information of present sub-spots, the method is able to predict the absent sub-spots’ positions. The feasibility and effectiveness of this method are verified by a large number of numerical simulations. The method is applied to wavefront measurement of light with non-uniform near-field intensity. The simulation results show that the proposed method is of great help to improve the measurement accuracy and the Strehl ratio of the focal spot. For wavefronts outside of the training sample, the proposed method shows good generalization and adaptability. In addition, the experiment results demonstrate that the proposed method can predict the missing sub-spots’ centroid displacements accurately even though a large proportion of sub-spot is lost randomly.

Light field salient object detection plays an important role in computer vision tasks because of the excellent performance on challenging scenes. However, the imprecise extraction of saliency features from light field imaging puts a negative impact on the accuracy of saliency results, and the invalid fusion of these extracted features makes saliency results lose details, further cutting down their accuracy. In this article, to effectively extract and fuse saliency features of light field imaging, we propose an attention-oriented refinement and fusion network to solve these problems, which mainly includes the attention-oriented refinement module (ARM) and the attention-oriented fusion module (AFM). Specifically, ARM can precisely refine similar features between focal slices and all-focus image, and fully extract abundant structural characteristics of the light field. Subsequently, AFM can efficiently fuse those features extracted by ARM to obtain saliency results with detail information. Furthermore, different dilated convolution layers embedded with ARM and AFM are leveraged to further capture complete saliency results with detail information. Experimental results demonstrate that our proposed method outperforms other 20 state-of-the-art methods and achieves Top-1 accuracies on three light field datasets.

We propose a simple and compact three-wave radial shearing interferometer (TWRSI). This interferometer is constructed by a Gabor zone plate (GZP) and a charge-coupled device (CCD). The nominal plane wavefront under test is diffracted by the GZP into three orders (i.e., a parallel beam, a converging spherical beam, and a diverging spherical beam) leading to an interference pattern. In the imaging plane, three beams can be considered as being the copies of the incident beam, the compressed beam, and the expanded beam, respectively. A CCD detector located in the vicinity of the GZP records this interference pattern. Wavefront can be reconstructed by a single interferogram. The experiment result shows that the proposed method is correct and accurate. This TWRSI is compact, vibration insensitive, suitable for measurement of continuous and transient wavefront.