查看更多>>摘要：To deal with a terahertz (THz) super-resolution (SR) algorithm based on a convolutional neural network (CNN) without standard training datasets, a complex "zero-shot" SR (CZSSR) reconstruction algorithm is proposed according to the internal image statistics with a five-layer complex CNN model. Instead of relying on pre-training, the proposed method is of sound self-adaptability. Compared with real ZSSR, the peak SNR of CZSSR rose by about 0.94 dB, MSE decreased by 0.042, and SSIM increased by about 40% for the SR result of the measured data. The results show that the CZSSR method can solve the low-resolution problem of a THz imaging system and the shortage of datasets in THz SR based on CNN. Therefore, t his research is of great significance for application in the fields of medical imaging and non-destructive detection. (C) 2022 Optica Publishing Group
查看更多>>摘要：Source and mask optimization (SMO) is a key technique to guarantee the lithographic fidelity for 14-5 nm technology nodes. The balance between lithography fidelity and computational efficiency is a big issue for SMO. Our earlier works of compressive sensing SMO (CS-SMO) effectively accelerated the SMO procedure by sampling monitoring pixels. However, the imaging fidelity of the results of these methods can be further improved. This paper proposes a novel Bayesian compressive sensing source and mask optimization (BCS-SMO) method, to the best of our knowledge, to achieve the goals of fast SMO and high fidelity patterns simultaneously. The SMO procedure can be achieved by solving as a series of re-weighted l(1)-norm reconstruction problems, and the weights can be updated in every iteration. The results demonstrate that, with similar computational efficiency, the BCS-SMO method can significantly improve lithographic fidelity over the current CS-SMO method. (C) 2022 Optica Publishing Group
查看更多>>摘要：We propose a method to construct a compact dual focal-plane optical see-through near-eye display using diffractive waveguides and multiple lenses. A virtual image from a display device is projected into a three-grating waveguide using an objective lens, and a virtual image can be shown at a far distance with an extended eye box. One negative lens is employed to reduce the focus distance of the virtual image, and a corresponding positive lens is used to compensate for the distortion and accommodation errors. Thus, not only can a virtual image with a near distance be achieved, but also a virtual plane with a further distance can be generated by introducing another projection module and waveguide. Only two waveguides and two pieces of lenses are used in front of one eye to obtain a lightweight outlook. To verify the proposed method, a proof-of-concept prototype was developed to provide vivid virtual images at different depths in front of the human eye. (C) 2022 Optica Publishing Group
查看更多>>摘要：A point diffraction interferometer based on silicon nitride waveguide (WG-PDI), adopting a silicon nitride waveguide spherical wave source (WG-SWS) with Si substrate and SiO2 cladding, is proposed for spherical surface testing. The WG-SWS is used to overcome the drawbacks of the existing spherical wave sources, which can generate high accuracy and high numerical aperture spherical reference wave. In this paper, the theory of the WG-PDI is described, and the possible errors introduced by the device are analyzed. In addition, the lateral deviation between the curvature center of the test wave and the curvature center of the reference wave cannot be eliminated in the reflected configuration of the pinhole diffraction interferometer. After analyzing the influence of the systematic error introduced by the lateral deviation, the semi-reflective film was coated on the output facet of the waveguide spherical wave source to realize point diffraction interference without lateral deviation. Finally, the surface error of a spherical surface was measured by WG-PDI. The experimental results agree well with those measured by the ZYGO interferometer. (C) 2022 Optica Publishing Group
查看更多>>摘要：The wide field of view (FOV) of traditional star sensor optical systems restricts the ability to suppress atmospheric background. An optical imaging system for an all-time star sensor based on FOV gated technology is proposed. In this system, a wide FOV telescope is used to observe a large sky area containing multiple stars. A microlens and microshutter array is employed to subdivide the wide FOV and gate a narrow FOV to suppress atmospheric background radiation. Assisted by a common imaging lens, each set of microlens and microshutter elements corresponds to a FOV gated imaging channel. With the rapid switching of gated FOV, multiple stellar images are obtained on a common detection during daytime. As an example, a FOV gated optical imaging system with 0.4 degrees gated FOV and 61 imaging channels is designed. In addition, a simplified prototype is developed, and a preliminary experiment of FOV gated imaging is performed near the ground. The results verify the capability of multiple stellar detections during daytime. The proposed optical imaging system has a strong capability of suppressing atmospheric background radiation and provides sufficient FOV gated imaging channels to enhance the probability of detecting multiple stars. It provides an effective technical way to develop all-time star sensors based on star pattern recognition and enables a completely autonomous attitude determination possible for platforms inside the atmosphere during daytime. (C) 2022 Optica Publishing Group
查看更多>>摘要：Narrowband resonance plays an important role in many optical applications, especially for the development of wavelength-selective properties and enhanced light-matter interaction. In this paper, we demonstrate metal- insulator-metal (MIM) waveguide gratings, which exhibit guided-mode resonance (GMR) with reduced bandwidth in mid-infrared absorption and thermal emission. Our fabricated MIM waveguide grating consists of a copper substrate, a lossless ZnSe film, and a top gold stripe grating. Our measurements reveal strong GMRs with a bandwidth of 1.29% of the central wavelength in both mid-infrared absorption and thermal emission spectra. By varying structural parameters of the MIM waveguide grating, strong absorptions and thermal emissions of GMRs are observed and tuned within the 3-5 mu m wavelength range. These results manifest the great potential of engineering infrared properties by using GMR and could be useful for spectral control in a variety of infrared devices. (C) 2022 Optica Publishing Group
查看更多>>摘要：Multi-beam laser Doppler vibrometers (MB-LDVs) have an advantage over scanning single-beam laser Doppler vibrometers (LDVs) due to the reduction in measurement time and their ability to measure non-stationary and transient events. However, the number of simultaneously interrogated points in current MB-LDVs is limited due to the complexity of the electronic hardware, which increases with the number of measurement channels. Recent developments of high-speed line-scan CMOS cameras suggest that their use in MB-LDVs can reduce the hardware complexity and increase the number of measurement channels. We developed a MB-LDV based on a digital line-scan CMOS camera that simultaneously measures vibrations on a linear array of 99 points. The experimental setup and performance of the developed MB-LDV are discussed in this paper. (C) 2022 Optica Publishing Group
查看更多>>摘要：Due to tremendous design flexibility and ease of light control capability, the photonic crystal fiber offers efficient, flexible, and miniaturized plasmonic biosensors with attractive features. In this work, a high index (GeO2 doped silica) core flat fiber is proposed and analyzed for RI sensing ranging from 1.53 to 1.60. A rectangular analyte channel is created on top of a flat fiber to better handle the liquid analyte. To introduce the plasmonic effect, TiO2 and gold arc deposited to the analyte channel. The sensing performance is carried out for two operating wavelengths, as two peaks are obtained for each analyte. The second operating wavelength shows better sensing performance than the first one. However, the proposed sensor offers average wavelength sensitivity of 5000 nm/RIU with a sensor resolution of 2 x 10(-05) RIU. In addition, the proposed sensor shows identical linearity, which is quite rare in prior sensors. Moreover, the proposed flat sensor provides outstanding detection accuracy of 0.01 nm(-1), detection limit of 79.28 nm, signal to noise ratio of -4.1497 dB, and figure of merit of 50 RIU-1. Owing to outstanding sensing performance and a unique detection range, this sensor can be effectively used in biological and organic analyte sensing applications. (C) 2022 Optica Publishing Group
查看更多>>摘要：Instantaneous frequency measurement (IFM) with single branch detection based on the birefringence effect is proposed and experimentally demonstrated. The unknown microwave frequencies are modulated to pump a length of polarization maintaining fiber. Due to the fiber birefringence effect, the input light signal is decomposed into two orthogonal-polarization signals with a relative time delay. After detection, an amplitude comparison function (ACF) is obtained by comparing the alternating-current and direct-current powers. Therefore, no multipath detection is needed so that the electrical variations in the photonic link can be cancelled out in ACF. A theoretical analysis is given to illustrate the mechanism of the proposed IFM system. The disturbances are investigated and discussed in simulation. A proof-of-concept experiment is carried out for verification with a result of +/- 10.2 GHz over 2.2-5.2 GHz. (C) 2022 Optica Publishing Group
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