The vacuum degree is the key parameter reflecting the quality and performance of vacuum glass. This investigation proposed a novel method, based on digital holography, to detect the vacuum degree of vacuum glass. The detection system was composed of an optical pressure sensor, a Mach–Zehnder interferometer and software. The results showed that the deformation of monocrystalline silicon film in an optical pressure sensor could respond to the attenuation of the vacuum degree of vacuum glass. Using 239 groups of experimental data, pressure differences were shown to have a good linear relationship with the optical pressure sensor’s deformations; pressure differences were linearly fitted to obtain the numerical relationship between pressure difference and deformation and to calculate the vacuum degree of the vacuum glass. Measuring the vacuum degree of vacuum glass under three different conditions proved that the digital holographic detection system could measure the vacuum degree of vacuum glass quickly and accurately. The optical pressure sensor’s deformation measuring range was less than 4.5 μm, the measuring range of the corresponding pressure difference was less than 2600 pa, and the measuring accuracy’s order of magnitude was 10 pa. This method has potential market applications.
Based on scalar diffraction theory and the geometric structure of liquid crystal on silicon (LCoS), we study the impulse responses and image depth of focus in a holographic three-dimensional (3D) display system. Theoretical expressions of the impulse response and the depth of focus of reconstructed 3D images are obtained, and experimental verifications of the imaging properties are performed. The results indicated that the images formed by holographic display based on the LCoS device were periodic image fields surrounding optical axes. The widths of the image fields were directly proportional to the wavelength and diffraction distance, and inversely proportional to the pixel size of the LCoS device. Based on the features of holographic 3D imaging and focal depth, we enhance currently popular hologram calculation methods of 3D objects to improve the computing speed of hologram calculation.
In this Letter, we demonstrate a 1 × 4 low-crosstalk silicon photonics cascaded arrayed waveguide grating, which is fabricated on a silicon-on-insulator wafer with a 220-nm-thick top silicon layer and a 2 μm buried oxide layer. The measured on-chip transmission loss of this cascaded arrayed waveguide grating is ∼4.0 dB, and the fiber-towaveguide coupling loss is 1.8 dB/facet. The measured channel spacing is 6.4 nm. The adjacent crosstalk by characterization is very low, only −33.2 dB. Compared to the normal single silicon photonics arrayed waveguide grating with a crosstalk of ∼ −12.5 dB, the crosstalk of more than 20 dB is dramatically improved in this cascaded device.OCIS [1] , a planar concave grating [2,3] , an arrayed waveguide grating (AWG) [4] , and so on. Compared to other basic structures, AWGs have a better optical performance, such as low insertion loss, good channel spacing uniformity, low crosstalk, etc. So, AWG is a widely used multiplexer/de-multiplexer in optical communication systems. Due to the compatibility of the refractive index with standard optical fibers, silica-based AWGs are the most common commercial multiplexer/ de-multiplexer. However, it is hard to realize monolithic integration with other high-speed active devices, although silica-based AWGs have good optical performances as a multiplexer/de-multiplexer.In recent decades, silicon photonics have attracted much attention because silicon materials can be used to fabricate monolithic integration circuits with passive/ active devices, and the process is compatible with complementary metal oxide semiconductor technology [5][6][7] . Silicon-based AWGs on silicon-on-insulator (SOI) wafers with a several-microns-thick top silicon layers were demonstrated in the early 2000s. For example, a turningmirror-integrated AWG with a 4.25-μm-thick top silicon layer was reported, and it had a crosstalk of −23 dB [8] . An AWG-based monolithic integration of a mulitiplexer was presented on an SOI wafer with a 2.5-μm-thick top silicon layer, and its crosstalk was better than −25 dB [9] . However, it is hard to achieve high-speed active devices on such micron-scale SOI wafers, and the footprint size is big because of the big bend radius of this kind of silicon waveguide. Subsequently, more attention was focused on silicon nanowire devices. Many nanowire silicon photonics passive/active devices with good performances have been demonstrated on an SOI platform with a thin (220 nm typically) top silicon layer, including mode size converters [10] , ring-based devices [11] , high-speed modulators [12] , high-speed photo-detectors [13] , etc. Silicon nanowire AWGs were also presented in the past decade. In Ref.[14], a compact nanowire AWG was reported. The insertion loss was 2.2 dB, and the crosstalk was −20 dB. A 12-channel flattened-spectral-response AWG was presented on an SOI wafer with a 220-nm-thick top silicon layer, and the crosstalk was −17 dB [15] . In Ref.[16], an athermal silicon nanowire AWG was demonstrated, and the wavelength temperature dependen...
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