Light Field Distribution Research Articles

Technology of static oblique lithography used to improve the fidelity of lithography pattern based on DMD projection lithography

This paper proposes a static oblique lithography (SOL) strategy based on conventional digital micromirror device (DMD) projection lithography. This strategy combines the oblique lithography on oblique scanning lithography with static lithography to ensure that we can produce high fidelity microstructures with very smooth curved edges in all directions and more accurate relative line positions. Not only does the single-axis high-precision micromotion stage of this strategy enable a significant reduction in fabrication cost, but also enables the lithography of subpixel-width curves with smooth edges used our improved sub-pattern quantization strategy. The intensity distribution of the actual diffracted light field at the focal point of the helical zone plate fabricated by the SOL is highly matched with the intensity distribution of the designed simulated light field. This shows that the SOL can play an important role in the field of micro-optical device fabrication.

Dual Function Modification of Cs2CO3 for Efficient Perovskite Solar Cells.

Organic-inorganic hybrid perovskite solar cells (PeSCs) attract much attention in the field of solar cells due to their excellent photovoltaic performance. Many efforts have been devoted to improving their power conversion efficiency (PCE). However, few works focus on simultaneously improving their electrical and optical property. Herein, a simple strategy is proposed to improve the PCE from 19.8% of a reference device to 22.9%, by utilizing cesium carbonate (Cs2CO3) to modify indium tin oxide (ITO) substrate. The insertion of a Cs2CO3-modification layer between ITO substrate and SnO2 electron transport layer simultaneously offers two benefits: improving the electron extraction capability and adjusting the light field distribution in the device. The optical optimization effect of Cs2CO3 revealed in this work has not been reported before. This work provides a new and simple strategy to obtain high performance PeSCs by improving the electrical and optical properties of the devices at the same time.

Measuring of Transverse Energy Flows in a Focus of an Aluminum Lens

In this study, we theoretically and experimentally investigate the propagation of a second-order cylindrical vector beam through an aluminum lens which forms a tight focus at the distance of the wavelength. Simulation by the finite-difference time-domain method and the Richards–Wolf formulae produces light field distributions which coincide with experimental measurements provided with scanning near-field optical microscopy. We demonstrate that a pyramidal metallized cantilever with a hole is more sensitive to the transversal component of intensity than to the full intensity or to the Umov–Poynting vector in areas of reverse energy flow.

Ultrathin Film Amorphous Silicon Solar Cell Performance using Rigorous Coupled Wave Analysis Method

The issues related to global energy needs and environmental safeties as well as health crisis are some of the major challenges faced by the human, which make us to generate new pollution-free and sustainable energy sources. For that the optical functional nanostructures can be manipulated the confined light at the nanoscale level. These characteristics are emerging and leading candidate for the solar energy conversion. The combination of photonic (dielectric) and plasmonic (metallic) nanostructures are responsible for the development of better optical performance in solar cells. Here, the enhancement of light trapping within the thin active region is the primary goal. In this work, we have studied the influence of front-ITO (rectangular) and back-Ag (triangular) nanogratings were incorporated with ultrathin film amorphous silicon (a-Si) solar cell by using rigorous coupled wave analysis (RCWA) method. The improvement of light absorption, scattering (large angle), diffraction and field distributions (TE/TM) were demonstrated by the addition of single and dual nanogratings structures. Significantly, the plasmonic (noble metal) nanogratings are located at the bottom of the cell structure as a backside reflector which is helpful for the omni-directional reflection and increased the path length (life time) of the photons due to that the collection of the charge carriers were enhanced. Further, the proposed solar cell structure has optimized and compared to a back-Ag, front-ITO and dual nanogratings based ultrathin film amorphous silicon solar cell. Finally, the obtained results were evidenced for the assistance of photonic and plasmonic modes and achieved the highest current density (Jsc) of 23.82 mA/cm2(TE) and 22.75 mA/cm2 (TM) with in 50 nm thin active layers by integration of (dual) cell structures.

High-contrast phase imaging based on nonlinear holographic hot image model

Imaging for weak-phase objects is a challenging issue in the linear imaging process. Here, we demonstrate a high-contrast phase imaging method based on a nonlinear holographic hot image model. Due to the nonlinear Kerr effect, the holographic hot image can transform a weak phase into strong amplitude as a signal amplifier. The phase information is iteratively obtained from the light field distribution of the holographic hot image. The strong signal-to-noise ratio helps improve the imaging contrast. Using a tunable photorefractive crystal, we numerically and experimentally demonstrate the advantage of this method for imaging weak-phase objects. For the determined sample, our method doubles the imaging contrast. As far as we know, this is the first report using the nonlinear holographic hot image for imaging technology. This study can provide a potential strategy to achieve high-contrast imaging for various weak-phase objects applied in biomedical imaging, semiconductor metrology, and photolithography.

Investigation of three topological edge states in honeycomb lattices based on graphene plasmonic crystal

In this article, three categories of the edge states in the honeycomb lattice are investigated theoretically by using the effective tight-binding Hamiltonian. The edge-bulk corresponding dispersions of zigzag, bearded, and armchair edge states analytically. The actual edge-bulk corresponding and the light field distribution of the graphene plasmonic crystals are obtained by solving Maxwell equations with boundary conditions, which are in good agreement with the analytical results. The proposed plasmonic structures provide guidance for designing the frequency range dependent property of topological structures, and show the potential applications in topological robust devices.

High Performance Ge-on-Si Photodetector With Optimized Light Field Distribution by Dual-Injection

This paper proposed a photodetector with a dual-injection structure. Input power is splitted into two beams by a 3 dB beam splitter at the incident end and then coupled into the photodetector, which can make the light field distribution in the germanium absorption layer more uniform. With the same active area structure, the responsivity of the dual-injection structure can be increased by 45.73% at 108.33 mW, the saturated optical power could be induced by 44.76%, and the bandwidth can be improved by 6.74 GHz at 20 mW comparing with the single-injection structure. The dual-injection structure improves the performance of the device without increasing the complexity.

Design of Ultra-High Extinction Ratio TM- and TE-Pass Polarizers Based on Si-Sc0.2Sb2Te3 Hybrid Waveguide.

The selective polarizers play an important role in silicon-based integrated circuits. The previous polarizers based on silicon waveguides have the defects of large scale and low extinction ratio. In this work, TM- and TE-pass polarizers only 10 μm long were developed based on phase-change material of Sc0.2Sb2Te3 (SST) hybrid silicon waveguide, where several SST bars with a varied distance was designed. Because of the excellent characteristics of the refractive index of the material, ultra-high extinction ratios (ERs) were achieved. A 3-D finite element simulation was carried out to optimize the structure of the polarizers, and the distribution of light field, as well as the transmission behavior of TE and TM modes in the two polarizers, was further demonstrated in detail. When the SST is crystalline, the unwanted mode can be attenuated, while the wanted mode can pass through with low loss. Compared with the GST-based polarizers, the proposed ones achieved high extinction ratios of ~43.12 dB (TM-pass one) and ~44.21 dB (TE-pass one), respectively; at the same time, ILs for the wanted modes could be negligible. The design of high-performance polarizers paves a new way for applications of all-optical integrated circuits.

Vectorial metasurface holography

Tailoring light properties using metasurfaces made of optically thin and subwavelength structure arrays has led to a variety of innovative optical components with intriguing functionalities. Transmitted/reflected light field distribution with exquisite nanoscale resolution achievable with metasurfaces has been utilized to encode holographic complex amplitude, leading to arbitrary holographic intensity profile in the plane of interest. Vectorial metasurface holography, which not only controls the intensity profile, but also modifies the polarization distributions of the light field, has recently attracted enormous attention due to their promising applications in photonics and optics. Here, we review the recent progresses of the vectorial metasurface holography, from the basic concept to the practical implementation. Moreover, vectorial metasurfaces can also be multiplexed with other degrees of freedom, such as wavelength and nonlinearity, enriching and broadening its applications in both civil and military field.

Focus shaping by tightly focusing locally linear polarized vortex beams with Pancharatnam–Berry tailored

Based on vector diffraction theory, we demonstrated that the three-dimensional spatial separation of the two foci can be achieved by modulating the polarization distribution of the input vector light field. The Pancharatnam–Berry tailored vector light field combined with a vortex phase can realize both foci possess vortices of arbitrary topological charges. The simulation results show that the tightly focused vector vortex beam can generate two vortices with independent topological charges, and the spatial distance between the two vortex foci can be adjusted. Moreover, the focal field distribution with optical cage or flat-topped profile can be easily obtained by appropriately choosing the polarized structure and vortex phase of the input beams. We generate a perfect optical cage that is almost surrounded by uniform light intensity. The flat-topped focus can be formed by focusing of a single vortex, as well as the superposition focusing of the two vortices. These engineered focus profiles may find potential applications in optical imaging, laser micromachining, particle trapping and manipulations.

The Application of the Combination of Virtual and Reality in the Film Space Performance

In order to improve the effect of film space performance, this paper applies the combination of virtual and reality to the film space performance processing. Moreover, this paper analyzes the light field distribution of the three-dimensional object in space, and modulates the projected image projected on it with the spectral characteristics of the optical screen to finally restore the light field of the original object. In addition, this paper uses the multi-projection method to study the recovery process of the cylindrical microlens array screen to the light field, and divides and reorganizes the multi-view image of the scene shot by the camera array to obtain the correct projected image. Finally, this paper applies the space processing algorithm based on the combination of virtual and reality to the film space performance processing, and uses experimental research to verify the reliability of the method proposed in this paper.

Tapered-open-cavity-based in-line Mach-Zehnder interferometer for highly sensitive axial-strain measurement.

An in-line Mach-Zehnder interferometer based on a multimode-fiber-assisted tapered open-cavity (TOC) is proposed. Light field distributions of the TOC were investigated using beam propagation method with different offsets and diameters of the taper waist. Bias and uniform taper (BT and UT)-based structures were fabricated and compared using one- and two-step arc-discharge methods, and comprehensive tests were then conducted considering axial-strain. The experimental results show that the UT structure has more than -45 pm/µɛ linear wavelength shift with the applied axial-strain. Owing to its compact size and low cost, the proposed sensor is promising for axial-strain-related high-precision engineering applications.

Light-Field Imaging Reconstruction Using Deep Learning Enabling Intelligent Autonomous Transportation System

Light-field (LF) cameras, also known as plenoptic cameras, permit the recording of the 4D LF distribution of target scenes. However, many times, surface errors of a microlens array (MLA) are responsible for degradation in the images captured by a plenoptic camera. Additionally, the limited pixel count of the sensor can cause missing parallax information. The aforementioned issues are crucial for creating accurate maps for Intelligent Autonomous Transport System (IATS), because they cause loss of LF information, and need to be addressed. To tackle this problem, a learning-based framework by directly simulating the LF distribution is proposed. A high-dimensional convolution layer with densely sampled LFs in 4D space and considering a soft activation function based on ReLU segmentation correction is used to generate a superresolution (SR) LF image, improving the convergence rate in the deep learning network. Experimental results show that our proposed LF image reconstruction framework outperforms the existing state-of-the-art approaches; specifically, it is effective for learning the LF distribution and generating high-quality LF images. Different image quality assessment methods are used to evaluate the performance of the proposed framework, such as PSNR, SSIM, IWSSIM, FSIM, GFM, MDFM, and HDR-VDP. Additionally, the computational efficiency was evaluated in terms of number of parameters and FLOPs, and experimental results demonstrated that our proposed framework reached the highest performance in most of the datasets used.

Study on the Light Field Regulation of UVC-LED Disinfection for Cold Chain Transportation

In this paper, the pain point that cold chain transportation urgently needs for an efficient disinfection method is pointed out. Thus, this work aims at solving the problems and improving the disinfection efficiency in cold chain transportation. While Ultraviolet-C (UVC) irradiation is an effective method by which to kill viruses, it is difficult to apply the commonly used UVC-LED disinfection light source to ice-covered cold chain transportation due to its uneven light field distribution. Thus, the light field regulation of UVC-LED disinfection for cold chain transportation is studied. A UVC-LED chip with a wavelength of 275 nm was used as a light source, and parallel light was obtained by collimating lenses. Then, microlens array homogenization technology was used to shape the UVC light into a uniform light spot, with an energy space uniformity rate of 96.4%. Moreover, a simulation was conducted to compare the effects of the ice layer on the absorption of UVC light. Finally, an experiment was carried out to verify that the disinfection efficiency can be increased nearly by 30% with the proposed system by disinfecting E. coli (Escherichia coli), and the results indicate that the proposed system is an effective disinfection solution during cold chain transportation.

Temporal effect on tight focusing, optical force and spin torque of high-order vector-vortex beams

We theoretically study the dependence of the light field distributions, optical force and spin torque of high-order vector-vortex (HOVV) beams focused by a high numerical aperture objective on ultrafast variable time (0–400 fs). It is accomplished by the fast Fourier transform, time-dependent vectorial diffraction theory and Rayleigh scattering model. Firstly, it is shown that the light field patterns of tightly focused HOVV beams can be quasi-periodically reshaped by adjusting the intrinsic fleeting time. We further examine the three-dimensional (3D) distributions of optical force on a Rayleigh particle (with a size much smaller than the light wavelength) in the focal volume induced from tightly focused HOVV beams, which reveals that the distinct vector-vortex light fields as a function of ultrafast time endow the capability of the selective trapping for particles. Beyond that, we proceed to the 3D spin torque on the given particle, which makes the conversions between transverse and longitudinal spin torques possible, resulting in the 3D spatial rotation within an ultrafast timescale. Additionally, it is found that the vortex order plays a pivotal role in steering the focused light fields and related optical forces and spin torques. The proposed pathway and acquired results not only provide a novel degree of freedom for the ultrafast control of light fields, but also have potential applications in integrated spectroscopic analysis, ultrafast optical tweezers and spanners, and high-speed optical measurements.

Temperature compensated fiber-optic liquid level sensor by micro-sphere based in-line Michelson interferometer

In this paper, a novel micro-sphere based in-line Michelson interferometer is proposed and completed experimentally through arc-discharge technique. The light field distributions are theoretically investigated to gain optimal core offset and diameter of micro-sphere. Multiple fabricated samples are compared and the comprehensive tests are then performed in terms of liquid level and temperature. The experimental results show that obvious blue shift of fringes is demonstrated with the rise of liquid level and the average sensitivity reaches 62.6 pm/mm with high linearity in the range of 0–40 mm. Moreover, owing to highly-consistent temperature response (∼99.5%), the crosstalk caused by ambient temperature is eliminated by differential method and the measurement error is compressed within 1.33%. Due to the merits of compactness, low cost, ease of fabrication and operation, our sensor is very potential in the liquid-level related engineering applications.

Single-frame measurement of complete spatiotemporal field of ultrashort laser pulses using frequency domain separate spectral interferometry

The spatiotemporal coupling distortion of large aperture ultra-high peak power laser will degrade the pulsed beam in both near-field and far-field. To accurately predict the light field distribution at the focus and compensate for the spatiotemporal coupling distortion, a single-frame measurement of full three-dimensional spatiotemporal coupling distortion is proposed based on the frequency domain separate spatial-spectral interference. The setup requires only a slit array attached to the front of an Imaging spectroradiometer. The whole procedure of carrier frequency distinguished spectral interference measurement is simulated in this study. The simulation results prove that the presented measuring method is correct and effective. The effectiveness of this method will be further verified experimentally in next step.

Inclined and gradient Al component AlGaN nanostructures with enhanced photoelectric performance for solar-blind UV detectors

This paper designs an AlGaN nanoarray model with different Al composition distributions, and studies the effects of geometric parameters on its optical response and quantum efficiency. COMSOL Multiphysics software was used to calculate and analyze the influence of the axis inclination on the light absorption efficiency and light field distribution of the nanostructures. Compared with vertical nanostructures, tilted structure arrays have better light absorption characteristics, and the photoelectric response of gradient Al composition AlGaN photocathode is more significant at the wavelength region of 200–300 nm. Simulation studies have found that the dense nanostructured array will reabsorb part of the emitted electrons, and the use of an auxiliary external electric field can effectively improve the collection efficiency of the photocathode. Finally, when the external electric field is 2.5 V/μm, the nanowire height is 800 nm and the incident angle is 10°, the GaN-Al0.365Ga0.635N layered nanostructure array can achieve an electrical response efficiency of 30.93%.

Study on scattering light field distribution of optical element in-surface defects based on Mueller matrix

For precise optical elements, the size of in-surface defects is at the nanometer scale. When incident light illuminates in-surface defects on optical elements, strong diffraction and scattering effects are produced, and this greatly reduces the beam quality in optical systems. In this study, a three-dimensional model of the in-surface defects of K9 optical components was established. On this basis, a theoretical model of electromagnetic scattering between the defect and the incident and scattering fields was constructed. The 4 × 4-order scattering Mueller matrix light field distributions of incident light modulated by different-sized defects were obtained by numerical simulations, and the influencing factors were analyzed. These simulations provide a theoretical basis and a reference for the manufacture of precision optical elements and a scale calibration for surface quality detection methods.

Intensity-Modulated Fiber-Optic Strain Sensor Using Multimode Fiber and Microfiber Joint-Assisted Micro-Cavity Interferometer

In this paper, a novel micro-cavity based Mach-Zehnder interferometer is proposed by joint-assistance of microfiber and multimode fiber (MMF). The light field distribution is comprehensively investigated, and the quantitative beam expansion range and the length of MMF are obtained. Under the optimized fabrication parameters, a joint-assisted micro-cavity structure is experimentally completed and the axial strain tests are performed. The experimental results show that obvious intensity responses of fringes are exhibited in the range from 0 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$300~ {\mu \varepsilon }$ </tex-math></inline-formula> , but with gradually reduced wavelength sensitivities. It is found that a near-zero wavelength drift exists in the fringe of 1589.83 nm with the intensity sensitivity of ~0.02 dB/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mu \varepsilon }$ </tex-math></inline-formula> . Besides, the corresponding temperature response is −81 pm/°C with a slight fluctuation of ~0.003 dB/°C. Such high discrimination between axial strain and temperature brings <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 0.5~ {\mu \varepsilon }$ </tex-math></inline-formula> detection resolution and ultra-low temperature crosstalk ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 0.15~ {\mu \varepsilon }/^{ {\circ }}\text{C}$ </tex-math></inline-formula> ), simultaneously. With the merits of high sensitivity and practicality, our sensor is very promising and potential in high-precision axial-strain related engineering monitoring and sensing.