The optical three-dimension measurement methods have been widely used in face recognition, machine vision, biomedical imaging, virtual reality and aerospace with the advantages of fast speed, high precision and non-contact measurement. Recently, the trend of structured light 3D reconstruction tends to be real-time with improving accuracy and reducing the dependence of time domain. The structured light coding is an active measurement method which could provide abundant feature points. The 2D gold matrix is a spatial coding method and it provides a new type of structured light for optical 3D measurement. This scheme provides the dynamic 2D spatial information based on the fast decoding from the encoded projected light. Here, we proposed a binocular stereo vision system based on the structured light encoded by 2D gold matrix. Only a pair of images, which could be captured in real-time by the two cameras, are needed for 3D reconstruction. The experiment shows that the decoding success rate is up to 99.48% for non-planar object. The system is simple in structure and low in cost. It is expected to be applied to real-time 3D measurement fields such as face recognition and biomedical imaging in the future.
An encapsulated metal-dielectric grating is proposed for realization of reflective broadband polarization-independent 1×2 beam splitter under normal incidence. One can quickly choose a grating structure to realize ultrabroad working waveband by using unified designing method for low-dispersion materials based on the diffraction efficiency map versus the normalized period and depth. Moreover, the center wavelength can be flexibly changed. As an example, a reflective ultrabroadband polarization-independent 1×2 beam splitters operating at wavelength of 1550 nm is designed under normal incidence. The simulation results indicated that a bandwidth of 144 nm could be achieved for the total efficiency over 92%. This kind of broadband polarization-independent 1×2 beam splitters could be found in a variety of applications, such as ultrashort pulse splitting, coherent beam combination, complex vector beam shaping, and also high precision displacement measurement.
Diffraction grating is widely used in a variety of applications, and the grating must have good quality. In various methods of making large-sized gratings, laser direct writing has obvious advantages. Our research group uses the parallel direct laser writing technology to produce a sinusoidal grating with a size of 100×100mm and line number of 1780 per millimeter. Firstly, the grating is analyzed theoretically to find a groove depth where the sinusoidal grating can reach its highest efficiency, then the grating is produced by laser direct writing and finally coated with a layer of gold. In this paper, we introduce the fabrication and efficiency measurement of grating, and estimate its uniformity. We get 16×16 data points which is divided into 4×3 area from the measurement. For each small area, the efficiency is measured and processed by software, obtaining the efficiency distribution diagram. Most efficiencies are around 90%, which is close to the theoretical calculation. Meanwhile, the efficiency distribution is uniform. Experimental results demonstrated that the developed parallel direct laser writing technology is feasible for writing large-size grating.
Orthogonal crossed gratings, or two-dimensional (2D) gratings are key optical elements in plane optical encoders. In this paper, Scanning Dammann lithography (SDL) was implemented to fabricate gold-coated 2D gratings by stepping and scanning a 2D air-bearing stage and rotating Dammann gratings. A displacement measurement interferometer (DMI) was applied to monitor the 2D stage which ensured the positioning accuracy of exposing. A series of experiments by varying the exposure dose were conducted. The atomic force microscope (AFM) results indicted the duty cycle changed with the exposure dose. A 2D gold-coated grating with a size 100*100mm was also fabricated. Since it is straightforward to extend the size of the substrate up to hundreds of millimeters, SDL is a promising method to fabricate large-sized 2D gratings with controllable duty cycle.
A wide-band two-port polarization-independent beam splitter is designed and analyzed at the incident wavelength of 1550nm. Diffraction efficiencies are 49.67%/49.57% and 48.69%/48.88% for TE and TM polarizations in the 0th and the -1st, respectively. Usually, it’s difficult for two-port beam splitter to achieve wide bandwidth for both polarizations. In this paper, the presented grating has advantages of wide incident wavelength range of 110nm and angular bandwidth of 8.8° with good splitting ratio uniformity for both polarizations, particularly TE polarization. Moreover, the aspect ratio of the grating depth to the ridge width is low, which can be etched relatively easily and effectively. This wide-band splitter should be highly interesting for practical applications.