Deep learning model for dynamic color design of all-dielectric metasurfaces.

Silicon nanostructure colors have rapidly developed in recent years, offering high resolution and a broad color gamut that traditional pigments cannot achieve. The reflected colors of metasurfaces are determined by the geometric structure of the unit cell and the refractive index matching layer parameters. It is evident that the design of specific colors involves numerous parameters, making it challenging to achieve through conventional calculations. Therefore, the tandem network instead of conventional electromagnetic simulation is natural. The forward part of the network incorporates feature cross terms to improve accuracy, enabling high-precision predictions of structural colors based on structural parameters. The average color difference between the predicted and actual color values in the L,a,b color space is 1.38. The network has been proven to accurately predict the refractive index and height of the refractive index matching layer during the dynamic tuning process. Additionally, the issue of the inverse network converging to incorrect solutions was addressed by leveraging the characteristics of the activation function. The results show that the color difference between the colors designed by the inverse network compared to the actual colors in the L,a,b color spaces is only 2.22, which meets the requirements for commercial applications.

Speckle wavemeter based on a multi-core fiber and compressive imaging.

Random speckle patterns contain valuable information about the incident light. Researchers have successfully constructed spectrometers and wavemeters by utilizing the speckles generated by inter-mode interferences of a multimode fiber (MMF). However, cameras were often employed to record the speckle data in previous reports. The camera's high cost (especially in the near-infrared range), large size, and low response speed limit the applications in optical communications, metrology, and optical sensing. A seven-core fiber (SCF) was fused with an MMF to capture the speckle pattern, where each core coupled part of the speckle field. Furthermore, we take advantage of the space division multiplexing capability of the SCF by incorporating an optical switch. This allows the variety of speckles generated by the incidence of different cores into the MMF. A convolutional neural network (CNN) regression algorithm was designed to analyze the complicated speckle data. The experimental results show that the proposed wavemeter can resolve adjacent wavelengths of 1 pm with an error of about 0.2 pm. We also discussed how different lengths of MMF influence the wavelength resolution. In conclusion, our research presents a robust and cost-effective approach to a wavelength measurement device by use of a seven-core optical fiber.

Machine learning enabled self-calibration single fiber endoscopic imaging.

Single fiber scanners (SFSs), with the advantages of compact size, versatility, large field of view, and high resolution, have been applied in many areas. However, image distortions persistently impair the imaging quality of the SFS, although many efforts have been made to address the problem. In this Letter, we propose a simple and complete solution by combining the piezoelectric (PZT) self-induction sensor and machine learning algorithms. The PZT tube was utilized as both the actuator and the fiber position sensor. Additionally, the feedback sensor signal was interrogated by a convolution neural network to eliminate the noise. The experimental results show that the predicted fiber trajectory error was below 0.1%. Moreover, this self-calibration SFS has an excellent robustness to temperature changes (20-50°C). It is believed that the proposed solution has removed the biggest barrier for the SFS and greatly improved its performance and stability in complex environments.

Deep-learning-assisted fiber Bragg grating interrogation by random speckles.

Fiber Bragg gratings (FBGs) have been widely employed as a sensor for temperature, vibration, strain, etc. measurements. However, extant methods for FBG interrogation still face challenges in the aspects of sensitivity, measurement speed, and cost. In this Letter, we introduced random speckles as the FBG's reflection spectrum information carrier for demodulation. Instead of the commonly used InGaAs cameras, a quadrant detector (QD) was first utilized to record the speckle patterns in the experiments. Although the speckle images were severely compressed into four channel signals by the QD, the spectral features of the FBGs can still be precisely extracted with the assistance of a deep convolution neural network (CNN). The temperature and vibration experiments were demonstrated with a resolution of 1.2 pm. These results show that the new, to the best of our knowledge, speckle-based demodulation scheme can satisfy the requirements of both high-resolution and high-speed measurements, which should pave a new way for the optical fiber sensors.

Variable-fiber optical power splitter design based on a triangular prism.

Fiber optical power splitters (OPSs) have been widely employed in optical communications, optical sensors, optical measurements, and optical fiber lasers. It has been found that OPSs with variable power ratios can simplify the structure and increase the flexibility of optical systems. In this study, a variable-fiber OPS based on a triangular prism is proposed and demonstrated. By adjusting the output beam width of the prism, the power ratio can be continuously tuned. The optical simulations show that the horizontal displacement design is better than the traditional tilt angle design. Our scheme combines a dual-fiber collimator, a focus lens, and a triangular prism with a vertex angle of 120°. By changing the axial displacement of the prism, the power splitting ratio can be altered from 50:50 to 90:10. The polarization and wavelength dependence of the variable OPS were also investigated.

Study of a fiber spectrometer based on offset fusion.

A near-infrared spectrometer based on offset fused multimode fiber (MMF) is investigated in this study. The light spectrum is recovered by analyzing the speckle images when light is passing through the MMF. In order to generate adequate speckles, a polarization maintaining fiber (PMF) and a 30 cm long MMF are fused with a vertical offset. Seven different offset displacements are implemented in the fiber fusion. The follow-up experiments show that the fiber offset fusion has a significant influence on the spectral correlation and the resolution. Larger offset fusion can excite more high-order modes in the MMF, and it greatly improves the spectrometer's performance. The simulation results also show that more modes are excited in MMF, and the increase of mode number leads to lower correlation coefficients of the neighboring spectral channels. However, large offset fusion increases the fusion and the insertion loss of the whole system, which may bring difficulties in the low-light cases. In addition, an image denoising algorithm based on dynamic threshold filtering and a spectral reconstruction algorithm originated from complete orthogonal decomposition were used to remove the speckle pattern noise and recover the spectrum. The final speckle-based spectrometer has a spectral resolution of 0.6∼0.016nm depending on the different offset fusions.

Salisbury screen optical color filter with ultra-thin titanium nitride film.

Titanium nitride (TiN) is a metal-like refractory material that can be used as a substitution for metals in many applications. In this paper, we report the use of an ultra-thin TiN film in the Salisbury screen structure to spectral selectively absorb visible light for forming an optical color filter. The ultra-thin TiN film functions as a partial reflector as well as a protection capping layer in the structure. Spectral selective perfect absorption color filters with TiN-ZnO-Al multilayer films were fabricated and characterized.

Developmental and neurobehavioral toxicity of 2,2'-methylenebis(6-tert-butyl-4-methylphenol) (antioxidant AO2246) during the early life stage of zebrafish.

BACKGROUND: 2,2'-Methylenebis (4-methyl-6-tert-butylphenol) (AO2246) is a synthetic phenolic antioxidant extensively used in food packaging bags and cosmetics. Recently, AO2246 was detected with unexpectedly high concentrations in plasma and breast milk samples from pregnant and lactating women. Hence, it is essential to conduct a thorough investigation to evaluate the detrimental effects of AO2246 on biota. OBJECTIVE: To investigate the developmental and behavioral toxicity of AO2246 in zebrafish, as well as the molecular mechanisms underlying these effects. METHODS: Zebrafish embryos were exposed to AO2246 at concentrations ranging from 0.05 to 10 µM for up to 6 days postfertilization (dpf). Hatching rate, survival rate, heart rate, and body length were measured. Locomotor behavioral and electrophysiologal analyses were performed. Two fluorescence-labeled transgenic zebrafish lines (endothelium-Tg and macrophage/microglia-Tg) were employed. RNA sequencing was carried out. RESULTS: AO2246 has a 96-hour LC50 value of 3 µM. The exposure of AO2246 resulted in a significant reduction in both hatching rate and heart rate. Analysis of locomotor behavior demonstrated that larvae exposed to AO2246 doses exceeding 2 µM exhibited a significant decrease in both total distance and mean velocity. Electrophysiological recordings demonstrated a noteworthy reduction in spike activity at a concentration of 3 µM, relative to control conditions. The administration of AO2246 at 3 µM elicited morphological reactivity and immune alteration of the midbrain microglia in the macrophage/microglia-transgenic zebrafish line, indicating a potential contribution of neurological disorders to behavioral defects. RNA sequencing analysis revealed altered gene expression profiles at high AO2246 concentrations, particularly the dysregulation of pathways associated with neuronal function. CONCLUSIONS: The present study demonstrates that AO2246 exposure elicits developmental and neurobehavioral toxicity in zebrafish larvae. Specifically, exposure to AO2246 was found to cause disturbances in neuronal electrophysiological activity and neurological disorders, which ultimately led to the impairment of locomotor behavior in zebrafish larvae.

Ultra-Broadband, Polarization-Irrelevant Near-Perfect Absorber Based on Composite Structure.

This paper proposes a near-perfect absorption device based on a cross-shaped titanium nanostructure and a multilayered structure. The multilayered bottom structure consists of alternately SiO2 and Ti. The whole device is put on a TiN substrate. The coupling between cross-shaped titanium nanostructures, and that between the cross-shaped titanium nanostructure and bottom multilayer, can further enhance the absorption at some wavelength where most of the energy is reflected or passes through in the device with a single structure. According to the simulation results, the device presents a nearly perfect absorption in a wavelength range from 300 nm to 2000 nm. The average absorptance in the wavelength range from 500 nm to 1400 nm exceeds 96%. This paper also provides a new idea for realizing perfect absorption, which is extensively used in sensing, controllable thermal emission, solar energy harvesting solar thermo-photovoltaic devices, and optoelectronic metrology.

Ultra-Broadband, Omnidirectional, High-Efficiency Metamaterial Absorber for Capturing Solar Energy.

In this study, we investigated an absorber based on a center-aligned tandem nanopillar array for ultra-broadband solar energy harvesting theoretically. A high-efficiency, omnidirectional absorber was obtained by introducing the center-aligned tandem nanopillar array embedded in an Al2O3 dielectric layer. The multi-coupling modes at different wavelengths were interpreted. The strong absorption can be adjusted by changing the radii and heights of nanopillars. According to the simulation results, the average absorptance of the absorber exceeded 94% in the wavelength range from 300 nm to 2000 nm. In addition, the high-efficiency absorption was insensitive to the incident angle and polarization state. The research not only proposed an absorber which possesses a huge potential value for application areas, such as thermal photovoltaic systems, infrared detection, and isotropic absorption sensors, but also pointed out a new way to design an absorber with high efficiency in an ultrabroad wavelength range.

All-Dielectric Color Filter with Ultra-Narrowed Linewidth.

In this paper, a transmissive color filter with an ultra-narrow full width at half of the maximum is proposed. Exploiting a material with a high index of refraction and an extremely low extinction coefficient in the visible range allows the quality factor of the filter to be improved. Three groups of GaP/SiO2 pairs are used to form a Distributed Brag reflector in a symmetrical Fabry-Pérot cavity. A band-pass filter which is composed of ZnS/SiO2 pairs is also introduced to further promote the purity of the transmissive spectrum. The investigation manifests that a series of tuned spectrum with an ultra-narrow full width at half of the maximum in the full visible range can be obtained by adjusting the thickness of the SiO2 interlayer. The full width at half of the maximum of the transmissive spectrum can reach 2.35 nm. Simultaneously, the transmissive efficiency in the full visible range can keep as high as 0.75. Our research provides a feasible and cost-effective way for realizing filters with ultra-narrowed linewidth.

Core-shell NaErF4@NaYF4 upconversion nanoparticles qualify as a NIR speckle wavemeter for a visible CCD.

Speckle patterns have been widely employed as a method for precisely determining the wavelength of monochromatic light. In order to achieve higher wavelength precision, a variety of optical diffusing waveguides have been investigated with a focus on their wavelength sensitivity. However, it has been a challenge to find a balance among the cost, compactness, precision, and stability of the waveguide. In this work, we designed a compact cylindrical random scattering waveguide (CRSW) as the light diffuser by mixing TiO2 particles and ultra-violate adhesive. In the CRSW, speckle patterns are generated by input light scattering off TiO2 particles multiple times. Additionally, a thin layer of upconversion nanoparticles (UCNPs) was sprayed on the end face of CRSW to allow near-infrared (NIR) light to be converted to visible light, breaking the imaging limitations of visible cameras in the NIR range. We, then, further designed a convolution neural network (CNN) to recognize the wavelength of the speckle patterns with excellent robustness and ability to transfer learning. This resulted in the achievement of a high wavelength precision of 20 kHz (∼0.16 fm) at around 1550 nm with a temperature resistance of ±2 °C. Our results demonstrate a low-cost, compact, and simple NIR wavemeter, which is capable of ultra-high wavelength precision and good temperature stability. It has significant value for applications in high-speed and high-precision laser wavelength measurements.

Highly efficient blue top-emitting device with phase-shift adjustment layer.

The phase shift on the reflection from a semitransparent electrode of a top-emitting organic light-emitting device is utilized in this paper to realize a deep blue emission with high efficiency. The phase shift could be adjusted by changing the thickness of Alq(3) when it was deposited onto the semitransparent electrode of the device. Through simulation it is found that the blue shift of the resonant wavelength occurs in a certain range, which is concerned with Alq(3) thickness and the cavity length between two reflective electrodes. According to the simulation, a blue top-emitting organic light-emitting device with a designed structure was demonstrated experimentally by using such a phase-shift adjustment layer. Finally, the device showed excellent performance both in efficiency (3.4 cd/A at 8 V) and Commission Internationale de l'Eclairage coordinates (0.13, 0.15). The brightness of the device reached 20 000 cd/m(2).