The frontier research of optics is about to enter the field of picometer optics from the current field of micro-nano optics, and picometer measurement is the key to picometer optics research. If we use a laser interferometer with nanoscale resolution to measure a grating with good periodic uniformity and thousands of periods, then for one single period, the resolution can be obtained at picometer scale. Based on this theory, the interference field period is measured by the SRG (scanning reference grating) method, and the periodic average value of picometer accuracy can be measured when the movement of the grating is monitored with a laser interferometer. When we know the grating period of picometer accuracy, we can modulate the holographic interference field by slightly changing the angle of the two beams of light, and make two exposures to make a grating with a slightly different picometer accuracy period, which we call a picometer comb. When the picometer comb is irradiated by the laser beam, interference fringes are generated along the propagation direction, and its period T is inversely proportional to the period difference Δd of the two-exposed picometer comb. This has far-reaching implications for the future of picometer measurement.
A 1×5 transmission grating splitter with triangular structure under normal incidence at the wavelength of 1550 nm is presented in this paper. In order to further increase the efficiency, the material of the designed grating is MgF2. The whole transmitted diffraction efficiency of the gratings is over 99% with uniformity better than 0.3%. The designed parameters of this triangular grating are employed by the rigorous coupled-wave analysis and the simulated annealing algorithm. This grating has a large tolerance for fabrication with better performance, which should be highly interesting for practical applications.
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.
Spectrum plays an essential role in spectral imaging technology. To obtain the spectral information of image, two high - density diffraction gratings which substitute the prism are introduced in the Sagnac loop to form the polarization Sagnac interferometer (PSI). Usually, it’s difficult for prism to achieve wider angle of spectral line and higher resolution, the presented Sagnac loop with high-density gratings has advantages of wide spectral and high resolution. Meanwhile, the dispersion generated by grating is more uniformed than the prism. The two parallel beams exit from the Sagnac loop and the pass through the linear polarizer and finally polymerized on the focal plane array (FPA) by an imaging lens. This compact Sagnac loop with two high-density diffraction gratings is a new way to obtain the spectral-resolved image, which should be interesting for practical applications.
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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