The multilevel anticounterfeiting QR code readily integrates the advantages of excitation wavelength-dependent PL emissions, a strong red afterglow and sensitive excitation power-dependent UCL emissions in one overall device.
We present a quad-channel waveguide-based near-eye display as an ultra-wide-angle architecture for the metaverse. The core concept is to divide one field of view into four by placing the couplers within the regions, where only the subsets of field of view are located. Compared to its counterparts, including the single-, double- and triple- channels, our quad-channel waveguide can push the envelope of field of view further. With the aid of k-space diagram, the upper limit of field of view is illustrated and deduced. The design rules of the waveguide, sawtooth grating as the in-coupler, and slanted grating as the out-coupler are expounded. Through the rigorous coupled-wave analysis, the diffraction efficiencies of gratings can be calculated and optimized. As an overall evaluation, its key performance indicators are summarized as follows. Field of view is 100° (diagonal), eye relief is 10 mm, exit pupil is 11.5 × 11.5 mm2, average transmittance is 2.56%, and average uniformity is 75%.
This presented paper describes a high-precision goniometer system with a ring laser gyro (RLG). The principle of the goniometer is introduced. The key techniques for improving the measuring accuracy are analyzed. As the central element of the goniometer, RLG is investigated, including its error items, such as scalefactor, bias and random walk coefficient. The experimental results are provided.
This article analyses the trends in viewership of four popular videos over approximately 500 samples in time on the bilibili, a video platform. According to the statistical law, it is found that the number of video views obeys a non-homogeneous Poisson distribution. To further explore the time-varying patterns of playback volume, describing the impact of changes in viewership and the growing Internet market on video views, we built a model for online video popularity, and verified it with actual data. This model reveals the dissemination mechanism of online video. The findings provide theoretical support for facilitating or inhibiting the dissemination of video.
Dual-frequency heterodyne interferometer has been widely applied in many fields. It is also an important part for measuring position error in the system that laser simultaneously measure six degree of freedom geometric motion errors of a linear guide. To segregate the heat source, simplify the optical path and obtain a convenient delivery, a polarization maintain fiber (PMF) is used in the system for linking the laser source and the measurement section. However, the nonlinear error caused by PMF will reduce the measurement accuracy, and cannot be ignored in ultra-precision measurement. In this paper, a measurement model for analyzing the nonlinear error caused by the axis misalignment between the laser source and PMF was established with the Jones Matrix. Experiments were performed for verifying and calculating. The results show that the measuring error caused by nonlinear error is less than 2 nm with the axis misalignment being up to 10 degrees.
Considering the compensation of thermo-optic coefficients (TOC) between GaN-based cavity and TiO 2 photonic crystal (PhC) layer, we have theoretically designed a photonic crystal surface emitting laser (PCSEL) with temperature-insensitive wavelength. The structure includes a freestanding GaN membrane with embedded multiple InGaN/GaN quantum well (QW) layer and the top TiO 2 PhC layer. The high refractive index (RI) of PhC and the freestanding membrane cavity structure cooperate to enable a stronger field-coupling in PhC, thus fulfill the athermal coupling condition. Interestingly, the wavelength temperature dependence is only 0.0015 nm/°C for such PCSEL with a 82% PhC confinement factor, and its athermal property is proportional to the field confinement factor in TiO 2 PhC layer. To illustrate, a general formula has been developed after the investigations of thermo-optic effect and thermal expansion effect.
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