As an important means to obtain three-dimensional depth information of target, optical measurement has been widely used in face recognition, machine manufacturing, aerospace and other related fields in the past decades. Optical three-dimensional imaging and depth measurement is a fast and non-contact method for reconstructing three-dimensional imaging and depth measurement of objects based on optical means and digital image processing analysis. In this paper, a three-dimensional measurement module of transversely rotating combined Dammann grating is proposed, which generates interleaved high-density dot-matrix structured light for three-dimensional imaging and measurement. The measurement module consists of integrated components of laser and beam expander, collimating lens, four transversely rotating combined Dammann gratings with different beam splitting ratios, and objective lens. The laser emits a laser beam which is collimated by a collimating lens. Four Dammann gratings are used to generate four non-staggered dot-matrix by splitting them, and then the high-density staggered projection dot-matrix for three-dimensional measurement and imaging are projected by the objective lens. The measurement module has the advantages of simple structure, high output dot-matrix density, staggered projection dot-matrix edges, and easy integration into mobile devices. This technology may reduce the complexity, number of optical elements, power consumption and cost of structured light projectors in mobile and fixed 3D sensors.
In this paper, we propose a two-dimensional metal-dielectric grating with dielectric nanodisks on a thin gold film structure for refractive index sensing due to its near unity absorption at 1050 nm wavelength. The perfect absorption mainly originates from excitation of the horizontal magnetic dipole mode in the metal-dielectric structure. The results show that the sensitivity and full width half maximum are 560 nm/RIU and 11.13 nm over the sensing range of 1.33 to 1.38, respectively. Obviously, the corresponding figure of merit is calculated to be 50.3 RIU-1, which shows a high sensing performance. Moreover, it also shows excellent performance by measuring the light intensity change in the reflected light at a certain wavelength. The proposed structure has great potential application in biological sensing, integrated photodetectors, chemical applications and so on.
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.
The direct laser writing lithography technology is an efficient way to make the large-sized diffraction gratings. It has the advantages of high efficiency, low cost and high flexibility. For further improvement the performance of the direct laser writing technology, we introduced the two-dimensional Dammann grating into the direct laser writing system. The Dammann grating can create a finite array of uniform intensity spots so that the efficiency of the writing can be increased. In addition, we also proposed a way of rotating the two-dimensional Dammann grating. By the geometric relationship, the expressions of the rotation angle can be derived. Considering the efficiency, the uniformity and the price of the 1D Dammann, we proposed the rotating 2D Dammann grating technology based on the 1D Dammann grating. While the rotation angles of 1D Dammann grating and the 2D Dammann grating are different. The efficiency of laser writing based on 2D Dammann is quite higher than the 1D-Dammann laser writing. We can use this method to fabricate the large-sized diffraction gratings efficiently.
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