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Line-structured laser sensors used in gear measuring provide a new way to acquire the perfect 3-D information of the complicated tooth flank with modification. This method leads to a series of problems, such as incident light occlusion, multiple reflection, system calibration and so on. The incident light occlusion poses severe problem on the integrity of the gear flank data acquired by the line-structured laser sensors. To understand the influence of the incident light occlusion during the cylindrical gear measuring and improve the efficiency of the measurement, this article analyzes this problem in depth. According to the position relation between the line-structure laser sensor and the gear, the projection theory is used to illustrate the incident light occlusion process between adjacent teeth and the model of the occlusion is built up. Four experiments are conducted to verify the validity of the model. This model applies to the cylindrical gear with different parameters. The influence of the modification on incident light occlusion zone could be ignored. On the basis of this model, the influence of the offset and the setting angle of the sensor on the incident light occlusion problem is thoroughly discussed, which gives a guide to control route planning and data acquiring during measuring the perfect information of the tooth flank.

As the communication distance changes, the received signal strength of an underwater optical communication system will change, and the range of its variation may not only exceed the dynamic range of the photoelectric detection device but also cause the reliability of communication to change due to the change in the received signal-to-noise ratio. In order to maintain better communication over a longer distance, this paper proposes a rate-adaptive method for underwater optical communication with joint control in the photoelectric domain. In the optical domain, the incident light’s power is adaptively adjusted by controlling the transmittance of the liquid crystal light valve to reduce saturation distortion. In the electrical domain, the constellation distribution is optimized according to the desired probability mass function, and the modulation order is adjusted in real time by estimating the received signal-to-noise ratio of the link. The simulation results show that under the forward error correction (FEC) threshold, the proposed method increases the dynamic range of the photomultiplier tube (PMT) by about 10 dB and expands the dynamic range of the system’s communication distance.

It is important to study environmental effects on the properties of solar cells because solar cells are usually used in open environments. If the surface morphology of a solar cell changes, the angle of incident light will change depending on its photoelectric properties. So, in this paper, the photoelectric properties of silicon solar cells covered with upright pyramids with different base angles were investigated depending on the angle of incident light. From the obtained results, it was found that when the angle of incident light is varied from 0º to 80º, the short circuit current densities of planar and pyramidal textured silicon solar cells with base angles of pyramids of 50.4º and 70.4º decrease to 82.6, 88.8, 89.8 %, the open circuit voltages decrease to 10.5, 12.8, 14.1 % and the fill factors decrease to 1.9, 2.2 and 3.2 %. The efficiency of a silicon solar cell covered with pyramids with a base angle of 70.40 is better than those of planar and other textured silicon solar cells in the range of incident light angles from 0º to 80º, although the dependence of its photoelectric parameters on the angle of incident light increases.

Meta-holographic encryption is a potentially important technique for information security. Despite rapid progresses in multi-tasked meta-holograms, the number of information channels available in metasurfaces is limited, making meta-holographic encryption vulnerable to some attacking algorithms. Herein, we demonstrate a re-programmable metasurface that can produce arbitrary holographic images for optical encryption. The encrypted information is divided into two matrices. These two matrices are imposed to the incident light and the metasurface, respectively. While the all-dielectric metasurface is static, the phase matrix of incident light provides additional degrees of freedom to precisely control the eventual functions at will. With a single Si metasurface, arbitrary holographic images and videos have been transported and decrypted. We hope that this work paves a more promising way to optical information encryption and authentication. Here, the authors demonstrate a re-programmable metasurface that can produce arbitrary holographic images for optical encryption. The encrypted information is divided into two matrices and defined to the incident laser to produce arbitrary holographic images.

Aiming at solving the problem of color distortion existing in the dark original pruning algorithm, an improved transmittance computation approach separated for each color channel is proposed. Firstly, the influence of the incident light frequency on the transmittance of each color channel is analyzed based on Beer-Lambert law. Meanwhile, the proportional relationship among the transmittance of each channel is deduced. Secondly, the image is resumed to improve the operation efficiency. After that, the image is pretreated to get the refined transmittance. Finally, the transmittance of all the color channels is obtained through the proportional relationship. And the corresponding transmittance is used to recover the image on each channel. Thus, the image defogging is realized. We evaluate the proposed algorithm qualitatively and quantitatively. From the subjective results, the proposed algorithm has better visual effect than that of the other algorithms, and our method has more details compared to the other two methods. While from the objective results, the proposed approach can achieve natural image color without high saturation, and reduce the running time by 4 to 10 times compared with several state-of-art algorithms. The proposed algorithm can obtain a higher color fidelity and a better image color in terms of e, r¯\\[ \\overline{r} \\] and H. The proposed method is obviously superior to those of the others in terms of no-reference quality evaluator in spatial domain and has the highest average PSNR value.

Phase-change materials (PCMs) offer a compelling platform for active metaoptics, owing to their large index contrast and fast yet stable phase transition attributes. Despite recent advances in phase-change metasurfaces, a fully integrable solution that combines pronounced tuning measures, i.e., efficiency, dynamic range, speed, and power consumption, is still elusive. Here, we demonstrate an in situ electrically driven tunable metasurface by harnessing the full potential of a PCM alloy, Ge 2 Sb 2 Te 5 (GST), to realize non-volatile, reversible, multilevel, fast, and remarkable optical modulation in the near-infrared spectral range. Such a reprogrammable platform presents a record eleven-fold change in the reflectance (absolute reflectance contrast reaching 80%), unprecedented quasi-continuous spectral tuning over 250 nm, and switching speed that can potentially reach a few kHz. Our scalable heterostructure architecture capitalizes on the integration of a robust resistive microheater decoupled from an optically smart metasurface enabling good modal overlap with an ultrathin layer of the largest index contrast PCM to sustain high scattering efficiency even after several reversible phase transitions. We further experimentally demonstrate an electrically reconfigurable phase-change gradient metasurface capable of steering an incident light beam into different diffraction orders. This work represents a critical advance towards the development of fully integrable dynamic metasurfaces and their potential for beamforming applications. The authors demonstrate an efficient platform for electrically driven reconfigurable metasurfaces by using Ge 2 Sb 2 Te 5 to realize non-volatile, reversible, multilevel, and fast optical modulation and wavefront engineering in the near-infrared spectral range.

Plasmonic nanostructures hold promise for the realization of ultra-thin sub-wavelength devices, reducing power operating thresholds and enabling nonlinear optical functionality in metasurfaces. However, this promise is substantially undercut by absorption introduced by resistive losses, causing the metasurface community to turn away from plasmonics in favour of alternative material platforms (e.g., dielectrics) that provide weaker field enhancement, but more tolerable losses. Here, we report a plasmonic metasurface with a quality-factor ( Q -factor) of 2340 in the telecommunication C band by exploiting surface lattice resonances (SLRs), exceeding the record by an order of magnitude. Additionally, we show that SLRs retain many of the same benefits as localized plasmonic resonances, such as field enhancement and strong confinement of light along the metal surface. Our results demonstrate that SLRs provide an exciting and unexplored method to tailor incident light fields, and could pave the way to flexible wavelength-scale devices for any optical resonating application. Metallic nanostructures are useful in many optical devices due to their nonlinear properties and responses to interaction with light. Here the authors demonstrate a metasurface of gold nanoparticle arrays with ultra-narrow surface lattice resonances of high quality-factor that operates in the telecommunication band.

With the further miniaturization and integration of multi-dimensional optical information detection devices, polarization-sensitive photodetectors based on anisotropic low-dimension materials have attractive potential applications. However, the performance of these devices is restricted by intrinsic property of materials leading to a small polarization ratio of the detectors. Here, we construct a black phosphorus (BP) homojunction photodetector defined by ferroelectric domains with ultra-sensitive polarization photoresponse. With the modulation of ferroelectric field, the BP exhibits anisotropic dispersion changes, leading an increased photothermalelectric (PTE) current in the armchair (AC) direction. Moreover, the PN junction can promote the PTE current and accelerate carrier separation. As a result, the BP photodetector demonstrates an ultrahigh polarization ratio (PR) of 288 at 1450 nm incident light, a large photoresponsivity of 1.06 A/W, and a high detectivity of 1.27 × 10 11 cmHz 1/2 W −1 at room temperature. This work reveals the great potential of BP in future polarized light detection. Integrated polarization-sensitive photodetectors are important for sensing applications and optical communication. Here, the authors report the realization of 2D black phosphorus homojunction photodetectors defined by ferroelectric substrates, showing polarization ratios up to 288 and high responsivity in the near-infrared.

Relying on abrupt phase discontinuities, metasurfaces characterized by a transversely inhomogeneous surface impedance profile have been recently explored as an ultrathin platform to generate arbitrary wave fronts over subwavelength thicknesses. Here, we outline fundamental limitations of passive gradient metasurfaces in molding the impinging wave and show that local phase compensation is essentially insufficient to realize arbitrary wave manipulation, but full-wave designs should be considered. These findings represent a critical step towards realistic and highly efficient conformal wave manipulation beyond the scope of ray optics, enabling unprecedented nanoscale light molding.

Recent advances in photoredox catalysis have made it possible to achieve various challenging synthetic transformations, polymerizations and surface modifications 1 – 3 . All of these reactions require ultraviolet- or visible-light stimuli; however, the use of visible-light irradiation has intrinsic challenges. For example, the penetration of visible light through most reaction media is very low, leading to problems in large-scale reactions. Moreover, reactants can compete with photocatalysts for the absorption of incident light, limiting the scope of the reactions. These problems can be overcome by the use of near-infrared light, which has a much higher penetration depth through various media, notably biological tissue 4 . Here we demonstrate various photoredox transformations under infrared radiation by utilizing the photophysical process of triplet fusion upconversion, a mechanism by which two low-energy photons are converted into a higher-energy photon. We show that this is a general strategy applicable to a wide range of photoredox reactions. We tune the upconversion components to adjust the output light, accessing both orange light and blue light from low-energy infrared light, by pairwise manipulation of the sensitizer and annihilator. We further demonstrate that the annihilator itself can be used as a photocatalyst, thus simplifying the reaction. This approach enables catalysis of high-energy transformations through several opaque barriers using low-energy infrared light. Photoredox transformations are achieved with infrared light by using triplet fusion upconversion that converts infrared into visible light, enabling the use of photoredox chemistry on larger scales and through barriers that are impenetrable by visible light.