The optical combiner is an important part of the optical see-through augmented reality display system. Waveguide is an appropriate solution due to its advantages such as light weight and compact structure. Because grating has replicability, it is a promising solution to the waveguide’s coupler for mass-production. In this paper, a grating coupler for waveguide is designed by using the rigorous coupled wave analysis (RCWA) to increase the accuracy of the simulation due to the critical dimension is similar to the wavelength. The uniformity of the diffraction efficiency is considered as an important parameter for a better displaying performance. The downhill algorithm is used to optimize the parameters of the grating. In order to obtain a large field of view, the thickness of the grating should be controlled carefully. Finally, two gratings are designed for the waveguide which can extend pupil horizontally. The displaying performance of the waveguide is simulated, and the grating couplers are fabricated by the nanoimprint lithography method. The characteristics of the gratings are tested such as transmittance and diffraction efficiency. The results show the proposed gratings can be utilized for waveguide’s coupler. It is believed that our results will give a better alternative for the augmented reality display system.
Fourier ptychographic microscopy (FPM) is a recently developed computational imaging technology, which achieves high-resolution imaging with a wide filed-of-view by overcoming the limitation of the optical spatial-bandwidth-product (SBP). In the traditional FPM system, the aberration of the optical system is ignored, which may significantly degrade the reconstruction results. In this paper, we propose a novel FPM reconstruction method based on the forward neural network models with aberration correction, termed FNN-AC. Zernike polynomials are used to indicate the wavefront aberration in our method.Both the spectrum of the sample and coefficients of different Zernike modes are treated as the learnable weights in the trainable layers.By minimizing the loss function in the training process, the coefficients of different Zernike modes can be trained, which can be used to correct the aberration of the optical system. Simulation has been performed to verify the effectiveness of the FNN-AC.
It is a meaningful but challenging issue that designing illumination optics for extended sources directly. A number of direct design methods developed specifically to deal with prescribed intensity designs usually fail to produce satisfactory illumination in the near field where the influence of lens size on the irradiance distribution cannot be ignored. In this paper, a direct method of designing aspherical lenses for extended sources is introduced to achieve specified irradiance characteristics. And various types of prescribed irradiance distributions are shown in this paper to verify the broad applicability and high efficiency of the direct design method, especially two examples of producing discontinuous irradiance distributions are analyzed in detail.
In compressive spectral imaging, three-dimensional spatio-spectral data cubes are recovered from two-dimensional projections. The quality of the compressive-sensing-based reconstruction is dependent on the coherence of the sensing matrix, which is determined by the system projection and the sparse prior. Studies on the optimization of the system projection, which mainly deals with the coded aperture, successfully decreases the coherence of the sensing matrix and improves the reconstruction quality. However, the optimization of the sparse prior considering the relationship between the system projection and the sparse prior remains a challenge. In this paper, we propose a gradient-descent-based sparse prior optimization algorithm for the coherence minimization of the sensing matrix in compressive spectral imaging. The Frobenius norm coherence is introduced as the cost function for the optimization, and the overcomplete dictionary is chosen as the sparse prior to solve the optimal sparse representation in the reconstruction as it provides higher degree of freedom for optimization compared to common orthogonal bases. The optimized dictionary effectively decreases the coherence of the sensing matrix from 0.880 to 0.604 and significantly improves the quantitative image quality metrics of the reconstructed hyperspectral images with the corresponding peak signal-to-noise ratio (PSNR) increased by 9 dB, the structural similarity (SSIM) above 0.98, and the spectrum angular mapper (SAM) below 0.1. Furthermore, the requirement of the sampling snapshots is reduced, which is shown by similar image quality metrics between the reconstructed hyperspectral images of only 1 snapshot with the optimized dictionary and of more than 5 snapshots with the non-optimized dictionary.
Direct design of illumination optics for extended light sources is challenging but rewarding. Most of the current direct methods, which are developed specifically for the treatment of prescribed intensity designs, usually cannot yield acceptable illumination in the near field where the influence of lens size on the irradiance distribution cannot be ignored. Here, for the first time, to the best of our knowledge, we develop a direct method for designing aspherical illumination lenses with prescribed irradiance properties for extended sources in 3D geometry. The proposed method is valid in both near field and far field. The proposed method is numerically and experimentally evaluated. The results obtained show the effectiveness of the proposed method.
Freeform surfaces are optical surfaces without linear or rotational symmetry. Their high degrees of design freedom liberate designers and engineers from restrictions on optical surface geometry, yielding compact and lightweight imaging systems with excellent optical performance. Freeform optics have become a competitive tool in the design of optical seethrough head-mounted display (OST-HMD) systems. In this paper, we present two different OST-HMD systems which have different optical different configurations and both employ freeform optics to correct and balance optical aberrations. In the optimization design of the two OST-HMD systems, we start from a spherical imaging system with an on-axis configuration, and then tilt and decenter each optical surface to find a starting point. In the final state of optimization, the order of each XY polynomial used to represent the freeform surface is gradually increased. The modulation transfer functions of the two OST-HMD systems are evaluated and the three-dimensional models of the two systems are also presented.
Two freeform surfaces provide more degrees of freedom in designing illumination optics and can yield a better solution. The existing methods for point-like sources are mostly valid in designing one freeform surface. Designing two freeform surfaces for point-like sources still remains a challenging issue. In this letter we develop a general formulation of designing two freeform lens surfaces for point-like sources. The proposed method is very robust in designing freeform lenses with two elaborately designed surfaces. The examples clearly show that using two freeform surfaces yields better solutions to challenging illumination problems with ultra-high energy efficiency.