This paper proposed a transmission two-dimensional (2D) slanted grating based on a double-layer cylindrical structure. We used rigorous coupled-wave analysis (RCWA) and simulated annealing algorithm (SA) to optimize the grating parameters. Results show that the diffraction efficiency of the (-1,0) and (0,-1) order exceed 35% under normal incidence in the range of 429–468 nm wavelength for TE and TM polarization. Meanwhile, the total diffraction efficiency can reach up to 78%. We also discuss the tolerances for the grating parameters to ensure high quality manufacturing processes. The relatively large tolerances ensure fabrication of the two-dimensional slanted grating and provides the possibility for practical applications. The proposed 2D slanted grating can be applied to 2D exit pupil expansion, which is of great importance in AR/VR applications.
With the release of IphoneX, compact 3D optical measurement has become a popular technology. An important application of compact 3D optical measurement is to realize 3D imaging of targets. A compact three-dimensional optical measuring instrument can project a coded or structured light pattern onto an object to achieve the purpose of three-dimensional imaging. Apple's solution is to design diffractive optical elements using algorithms (such as the Gerchberg-Saxton algorithm) to produce a fan-out staggered dot matrix projection pattern in which some dot matrix produce a lateral offset from adjacent dot matrix. In this paper, a new method is proposed to generate the interlaced lattice projection pattern, i. e. the transverse odd-even combinational Dammann grating method. This method produces the above pattern by two Dammann gratings placed perpendicular to the optical axis, which is different from the scheme proposed by Apple. The advantage of this scheme is that the overal structure is simple and the design cost is reduced, so it is easy to mass-produce, and its lateral combinational structure is conducive to the miniaturization and integration of devices, so it is convenient to integrate in various interconnected devices. For example, mobile phones with 3D face recognition using this technology are not only easy to use, but also highly secure.
Grating theory is normally designed for nano/microoptics applications. If we consider the further smaller size, we might enter the area of picometer optics. Although it seems picometer optics might be the frontier of developing nanooptics devices into the next step, it is hard to make picometer optical devices previously. We will report a series of three works that can lead us into the picometer scale. The first is to fabricate high-density gratings whose periods can be controlled to be slightly different in picometer range, which is done by rotating Dammann grating in a microrad angle for achieving the grating period continuously tuned in picometer scale. The second is to propose carrier pico-grating array for measuring the distances of the moving grating, which can be done in picometer accuracy. The third is to measure the wavefront of two-beam interferences in picometer accuracy, which is far beyond the current normal laser interferometer. Initial experimental results demonstrated that the wavefront has been measured with 250pm linear phase difference, which is impossible to obtain with the traditional laser interferometer. Taking consideration of these picometer works together, we believe that picometer optics should come with these picometer optical tools further extended in the near future.
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