Light Intensity Distribution Research Articles

Optical trapping of multiple particles based on a rotationally-symmetric power-exponent-phase vortex beam.

In this paper, the optical trapping of multiple particles based on a rotationally-symmetric power-exponent-phase vortex beam (RSPEPVB) was introduced and demonstrated. Based on the theories of tight focusing and optical force, the optical force model of RSPEPVB was established to analyze the optical trapping force of tightly focused RSPEPVB. Then, an experimental setup of optical tweezer, by utilizing the RSPEPVB, was built to demonstrate that the optical tweezer of RSPEPVBs can achieve the optical trapping of multiple particles, and the number of captured particles is equal to the topological charge l of RSPEPVB, which shows that the RSPEPVBs can achieve multi-particles trapping with controllable number. Moreover, compared to vortex beam, the captured particles by RSPEPVB will not rotate around the circular light intensity distribution. The results will provide a new option for optical trapping of multiple particles in biomedicine, laser cooling and so on.

Effect of Grating Ruling Machine System Errors on Grating Spectral Performance

Grating groove functions scalar theory can describe the light source through the grating interference and diffraction effect of the physical phenomenon of splitting light. It can be used to represent the distribution of the complex amplitude of the illumination light source on the diffraction screen under the action of the diffraction grating and display the information on the diffracted light position and intensity distribution. As a result, the effect of groove error on the intensity of grating ghost lines and stray light is analyzed. This paper presents an energy solution and analysis of the grating periodic groove error utilizing the grating scalar diffraction theory. Based on this, the effect of the core components of the grating ruling machines, such as screw and worm gear, on the stray light and ghost line of the grating is analyzed. Finally, the random groove error is analyzed. The analysis results show that the worm gear error is an important reason for the appearance of ghost lines in the machine ruling grating, and the lead screw error and random grooving error are the main reasons for the stray light produced by the grating. We optimize the worm gear, lead screw, and error compensation system of the grating ruling machine to effectively improve the ruling quality of the grating.

Bit Error Rate Analysis in Atmospheric Turbulence Channel of Synthetic Double Vortex Beam

Random phase screen method was used to simulate the light intensity and phase distribution of the synthesized double vortex beams transmitted in atmospheric turbulence given the light intensity characteristics and phase characteristics of double Laguerre–Gaussian beams (DLGB) generated by coaxial superposition. Results show that the scintillation coefficient decreases initially, and then increases with the topological charge difference of the double vortex beam, and the topological charge difference is related to the number of split spots. When the number of split spots is small, the intensity distribution is concentrated, exhibiting a good penetrating effect on atmospheric turbulence.

Polychromic light source for the realization of multispectral processing method of skin malignant lesions images

When diagnosing oncological skin diseases, the problem of untimely detection of pathologies remains relevant. Modern diagnostic methods have a number of disadvantages associated with the limited capabilities of human vision, high requirements for non-invasive studies and digital representation of the results obtained for their transmission over communication channels. The most important tasks of early binary diagnostics of skin neoplasms can be solved using bioradiophotonics methods. The paper considers the author’s multispectral method for processing images of skin areas using a new specialized polychrome light source with software control of the radiation wavelength. The principle of operation of such a source is analyzed and the use of a set of LEDs with a special arrangement is justified which makes it possible to direct a beam of light of any wavelength in one direction. The choice of the wavelength ranges used for LEDs is confirmed, the first version of the layout of such a light source is described, and its optical and structural diagrams are given. It is shown that the optimal way of the wavelength programmable control is its coarse tuning by switching LEDs and fine tuning by acousto-optic tunable filters installed at the source output. A number of test images of a pigment spot on the skin with a size of 40 × 30 mm with wavelengths ranging from near ultraviolet to near infrared ranges using a black and white camera are presented. With digital processing, received monochromatic images, histogram equalization and median filtering of images were carried out to expand the dynamic range of brightness levels and minimize distortion caused by the unevenness of the skin area under study and the presence of shadow illumination. Graphs of the amplitude intensity distribution in the original and filtered images are obtained for the selected wavelengths of the LEDs. It is shown that the presence of a skin neoplasm can be judged by the dips in the light intensity distribution curve. The radial arrangement of LEDs on the board is justified to minimize shadow illumination when illuminating the skin. The conducted studies of multispectral image processing using a realized polychrome light source contribute to the development of new methods for the early diagnosis of skin neoplasms based on photonics and optoelectronics and can find practical application in medical technologies.

Consistent pattern printing of the gap structure in femtosecond laser DMD projection lithography.

Maskless lithography technologies have been developed and played an important role in the fabrication of functional micronano devices for microelectronics, biochips and photonics. Optical projection lithography based on digital micromirror device (DMD) is an efficient maskless lithography technology that can rapidly fabricate complex structures. The precise modulation of gap width by DMD maskless optical projection lithography (MOPL) using femtosecond laser becomes important for achieving micronano structures. Herein, we have investigated the relationship between the structure morphology and the light intensity distribution at the image plane by multi-slit diffraction model and Abbe imaging principle, and optimized the gap width more accurately by modulating exposure energy. The aperture diameter of the objective lens has a substantial effect on the pattern consistency. The continuously adjustable structural gap widths of 2144 nm, 2158 nm and 1703 nm corresponding to 6, 12, 24 pixels are obtained by varying the exposure energy in the home-built MOPL system. However, the ideal gap structure cannot be obtained only by adjusting the exposure energy when the gap width is small, such as 1 or 2 pixels. Furthermore, we have proposed an alternative way to achieve fine gap structures through the structural decomposition design and precise control of exposure energy in different regions without changing the MOPL optical system. This study would provide a promising protocol for fabricating gap microstructures with controllable configuration using MOPL technique.

Improved photoacoustic images via wavefront shaping modulation based on the scattering structure.

Multispectral optoacoustic tomography (MSOT) has become the dominant technical solution for photoacoustic imaging (PAI). However, the laser source of fiber output in the current MSOT method is typically a TEM00 Gaussian beam, which is prone to artifacts and incomplete due to the uneven distribution of the irradiated light intensity. Here, we propose a novel method to improve the quality of photoacoustic image reconstruction by modulating the wavefront shaping of the incident laser beam based on the designed scattering structure. In the experiment, we add the designed scattering structure to the current hemispherical photoacoustic transducer array device. Through experiments and simulations, we investigate and compare the effects of different scattering structures on laser intensity modulation. The results show that an ED1-C20 diffusion structure with a scattering angle of 20 degrees has the most effective modulation of the beam intensity distribution. And we choose gold nanoparticles of 50-100 nanometers (nm) diameters and index finger capillary vessels respectively as the medium of PAI. We obtain the highest ratio of PAI area increases of gold nanoparticles and index finger to devices compare without scattering structure is 29.69% and 634.94%, respectively. Experimental results demonstrate that our method is significantly higher quality than traditional methods, which has great potential for theoretical application in medical PAI.

Optimization of Light Field for Generation of Vortex Knot

The theory of knots and links focuses on the embedding mode of one or several closed curves in three-dimensional Euclidean space. In an electromagnetic field system, all-optical knots or links composed of phase or polarization singularities have been verified theoretically and experimentally. Recent studies have shown that robust topological all-optical coding can be achieved by using optical knots and links. However, in the current design of optical knots and links based on phase or polarization singularities, the amplitude of light between adjacent singularities is relatively weak. This brings great pressure to detection of optical knots and links and limits their applications. Here, we propose a new optimization method in theory. Compared with the existing design methods, our design method improves the relative intensity distribution of light between adjacent singularities. We verify the feasibility of our design results in experiments. Our study reduces the detection difficulty of optical knots and links, and has a positive significance for promotion of applications of optical knots and links.

System for Non-Contact and Multispectral Examination of Blood Supply to Cutaneous Tissue

The presented system for non-contact examination of tissue perfusion is one of the tools for complex examination of human body tissues (skin, subcutaneous) and their mutual interactions, including blood flow and activity under various external stimuli. In our system, optical radiation, with wavelengths of 525 nm, 625 nm, and 940 nm, was used to investigate the perfusion and properties of skin tissue. Our work presents that it is possible to obtain comprehensive information about the cardiovascular system and skin tissue perfusion by a suitable combination of wavelengths, light intensity, and homogeneous illumination distribution with a properly chosen sensing device—a camera. The proposed system consists of an illumination device that emits light of the three wavelengths mentioned above and thus makes it possible to investigate the skin tissue structures and their interrelationships in terms of their blood supply and interactions with each other.

Mode Recognition of Orbital Angular Momentum Based on Attention Pyramid Convolutional Neural Network

In an effort to address the problem of the insufficient accuracy of existing orbital angular momentum (OAM) detection systems for vortex optical communication, an OAM mode detection technology based on an attention pyramid convolution neural network (AP-CNN) is proposed. By introducing fine-grained image classification, the low-level detailed features of the similar light intensity distribution of vortex beam superposition and plane wave interferograms are fully utilized. Using ResNet18 as the backbone of AP-CNN, a dual path structure with an attention pyramid is adopted to detect subtle differences in the light intensity in images. Under different turbulence intensities and transmission distances, the detection accuracy and system bit error rate of basic CNN with three convolution layers and two full connection layers, i.e., ResNet18 and ResNet18, with a specified mapping relationship and AP-CNN, are numerically analyzed. Compared to ResNet18, AP-CNN achieves up to a 7% improvement of accuracy and a 3% reduction of incorrect mode identification in the confusion matrix of superimposed vortex modes. The accuracy of single OAM mode detection based on AP-CNN can be effectively improved by 5.5% compared with ResNet18 at a transmission distance of 2 km in strong atmospheric turbulence. The proposed OAM detection scheme may find important applications in optical communications and remote sensing.

Optical bone densitometry insensitive to skin thickness.

Skin thickness, including the adipose layer, which varies from individual to individual, affects the bone density measurement using light. In this study, we proposed a method to measure skin thickness using light and to correct the bias caused by differences in skin thickness and verified the proposed method by experiments using a phantom. We measured simulated skin of different thicknesses and bovine trabecular bone of different bone mineral densities (BMDs) using an optical system consisting of lasers of 850 and 515nm wavelengths, lenses, and slits. Although the slope of the light intensity distribution formed on the surface of the material when irradiated by the 850nm laser is affected by the thickness of the skin phantom. The difference of the intensity distribution peaks (δy) between the 850 and 515nm lasers was strongly correlated with the thickness of the skin phantom. The coefficient of determination between the measurements and the BMD was improved by correcting the 850nm laser measurements with δy. This result suggests that the method is applicable to optical bone densitometry, which is insensitive to differences in skin thickness.

Refined Test and Evaluation Method of Side Viewing Angle of LED Display Module

In order to classify light-emitting diode (LED) display units with a specific luminous direction and improve the uniformity of the display screen, this paper proposes a classification method for the basic component of the LED display, i.e., the display module. According to the relationship between the light intensity distribution and the viewing angle of the packaged LED, the brightness inflection point was used as the fixed position of the two side array cameras, and the shooting was carried out from the normal direction of the display module and from the viewing angle directions of the left and right sides, respectively. The established classification model of the relative deviation between classes was used to evaluate the luminous consistency of the display module. The LED display module was directly classified according to the side viewing angle. The experiment considered the matching with human vision and controlled the number of product types. The results show that the brightness uniformity of the display module selected by this method increased by 3.31%, which basically ensures that the yield is not reduced due to the inconsistency of the side viewing angle, and this improvement can be judged in advance without building a screen, which not only saves time but also reduces manpower. This method has been stably and feasibly applied to engineering practice and can be classified according to customers’ requirements for LED display perspective.

Research and Implementation of Indoor 3D Positioning Algorithm Based on LED Visible Light Communication and Corresponding Parameter Estimation.

In the era of mobile Internet, the application of various positioning-based location service systems is becoming more and more common. In addition, the traditional radio positioning system is limited in the use of special environments such as mines, hospitals, and gas stations, and long-term electromagnetic radiation can cause potential damage to the human body. Compared with the traditional wireless positioning technology, VLC-based positioning technology has a good application prospect in the field of indoor wireless positioning. Compared with traditional radio positioning technology, the use of VLC technology to achieve indoor positioning is different in that the system design and layout need to consider the basic needs of indoor lighting; that is, the layout of multiple visible light sources in the room should meet the minimum illumination requirements of any area of the room. Since the layout structure of the light source that only considers the lighting requirements or only considers the positioning accuracy requirements is not the same, in the design process of the indoor visible light wireless positioning system, it is necessary to consider the overall optimization layout of multiple indoor visible light sources under the conditions of lighting and positioning constraints. This paper mainly optimizes indoor positioning from the aspects of light source layout, reflected light intensity distribution, and noise model.

Micro sliding friction model considering periodic variation stress distribution of contact surface and experimental verification

Micro sliding phenomenon widely exists in the operation process of mechanical systems, and the micro sliding friction mechanism is always a research hotspot. In this work, based on the total reflection method, a measuring device for interface contact behavior under two-dimensional (2D) vibration is built. The stress distribution is characterized by the light intensity distribution of the contact image, and the interface contact behavior in the 2D vibration process is studied. It is found that the vibration angle of the normal direction of the contact surface and its fluctuation affect the interface friction coefficient, the tangential stiffness, and the fluctuation amplitude of the stress distribution. Then they will affect the change of friction state and energy dissipation in the process of micro sliding. Further, an improved micro sliding friction model is proposed based on the experimental analysis, with the nonlinear change of contact parameters caused by the normal contact stress distribution fluctuation taken into account. This model considers the interface tangential stiffness fluctuation, friction coefficient hysteresis, and stress distribution fluctuation, whose simulation results are consistent well with the experimental results. It is found that considering the nonlinear effect of a certain contact parameter alone may bring a greater error to the prediction of friction behavior. Only by integrating multiple contact parameters can the accuracy of friction prediction is improved.

Comparison of temperature, current density, and light intensity distributions of nano-resistor patterns for an improved solid state incandescent light emitting device simulation model

The solid-state incandescent light-emitting device is an emerging optoelectronic device that is made on a silicon wafer using IC compatible materials and processes. Light emission takes place by thermal excitation of numerous nano-sized, high-resistivity conductive paths, i.e., nano-resistors, formed from the dielectric breakdown of an MOS capacitor. A simulation method that uses comsol multiphysics, python, and matlab to predict the temperature, current density, and light intensity distributions of various nano-resistor patterns in the device is presented. The Joule heating and blackbody radiation effects are correlated to the temperature and light emission profiles. The effect of mesh quality and depth on these distributions is also investigated. Electrical and optoelectronic properties of the nano-resistors calculated from this new program are consistent with the experimental results.

Propagation properties of controllable anomalous hollow beams in strongly nonlocal nonlinear media

The evolution properties of controllable anomalous hollow beams (CAHBs) in strongly nonlocal nonlinear medium are studied theoretically and numerically. The CAHB has a circular light intensity distribution, but there is a solid light intensity peak in the center. By changing initial parameters, the central and peripheral light intensities can be adjusted, so the CAHB can represent many different types of beams. The CAHBs in strongly nonlocal media shows a very rich variety of propagation characteristics. The transmission evolution properties of CAHBs, such as the light intensity distribution, the beam width and the on-axis light intensity, are mainly studied. The results show that by choosing appropriate initial parameters, the light intensity pattern of CAHBs can remain unchanged and form solitons, but also change periodically. The beam width of CAHBs can be widened or compressed in two transverse directions at the same time, or widened in one direction and compressed in the other direction. Some typical transmission characteristics are illustrated by numerical simulation, and the role of various parameters in transmission evolution is analyzed.

Characterizing interference effects of vortex beams based on the Sagnac interferometer

Orbital angular momentum (OAM) of photons has applications both in classical and quantum information due to its features of optical vortex and infinite dimensions. This paper studies the interference effects of optical vortex beams carrying mixed, conjugate, and single-mode OAM states based on the Sagnac interferometer with light sources of a laser and single photon. We compare our results with numerical simulations and show that the light intensity distribution and phase characteristics can directly characterize the absolute value of the topological charge (TC) carried by vortex beams. Furthermore, our scheme can also classify the photon with positive and negative signs of TC in the mixed mode OAM state by changing the relative phase. The results not only extend the manipulation methods for high-dimensional quantum states, but also lay a solid foundation for the application of vortex beams in a single-photon field.

Simulation of Light Intensity and Nano-Resistor Distribution in SSI-LEDs Using Python as a Framework

The solid-state incandescent LED is a device that emits broad spectrum warm white light from nano-resistors through black body radiation. Previously, the steady state operation of the device was simulated with the finite element analysis method using COMSOL Multiphysics, while the light intensity distribution was separately simulated using MATLAB. There were limitations in these studies with respect to the number, size variation, and distribution of nano-resistors. In this paper, a new Python framework is developed to simulate light emission and perform COMSOL simulations for the same nano-resistor arrangement. The framework circumvents the nano-resistor count and distribution limitations in previous studies. This allows for more sophisticated simulations of many more nano-resistors than previously possible, and investigation into the effect of nano-resistor count on the device.

Focusing properties and focal shift of vortex Hermite-cosh-Gaussian beams

In this work, we investigate the focusing properties of a vortex Hermite-cosh-Gaussian beam (vHChGB) passing through a converging lens system. The analytical propagation equation as well as the beam width expression of a focused vHChGB is derived based on the Huygens-Fresnel diffraction principle. From the obtained formulae, the effects of the Gaussian Fresnel number NF and the initial beam parameters, namely the beam order, the decentered parameter b, and the vortex charge number m, on the structure of the light intensity distribution and the beam spot size in the focal region are analyzed numerically. It is shown that the focal shift, which is determined from the minimum beam spot width criterion, is strongly dependent on the Fresnel number NF. And it is affected by the parameter b and the vortex charge m but is nearly insensitive to the beam order n. For a fixed value of NF, the focal shift is smaller when b or m is larger. The focal shift decreases monotonously with the increase of NF until it vanishes asymptotically for large values of NF. The obtained results may be useful for the applications of vHChGB in beam shaping and beam focusing.

Recognition of high-resolution optical vortex modes with deep residual learning

Optical vortex beams with fractional orbital angular momentum (OAM) can greatly enhance the channel capacity in free-space optical communication. However, high precision measurement of fractional OAM modes is always difficult, especially under the influence of atmospheric turbulence (AT). In this work, we identify the high-resolution OAM modes down to 0.01 using an improved residual neural network (ResNet) architecture based convolutional neural network (CNN). Experimentally, using a single cylindrical lens, the light intensity distribution can be readily converted into a diffraction pattern containing significant features trained into a CNN model. For the fractional OAM modes from 5.0 to 5.9 over a long propagation distance of 1500 m, at 0.1 resolution, our model's predicting accuracy is up to 99.07% under strong AT, ${C}_{\mathrm{n}}^{2}=1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\phantom{\rule{4pt}{0ex}}{\mathrm{m}}^{\ensuremath{-}2/3}$. At 0.01 resolution, the accuracy is as high as 86.98% under intermediate AT, ${C}_{\mathrm{n}}^{2}=1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{4pt}{0ex}}{\mathrm{m}}^{\ensuremath{-}2/3}$, and exceeds 73.78% under strong AT, ${C}_{\mathrm{n}}^{2}=1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\phantom{\rule{4pt}{0ex}}{\mathrm{m}}^{\ensuremath{-}2/3}$. So, these results may have great implications in free-space optical communication.

Single-shot time-of-flight ranging with sub-wavelength accuracy using vortex beam

Time-of-flight (TOF) ranging has been widely used for accurate measurement in science and industry. Existing TOF schemes implemented in the time or frequency domain require continuous measurements to achieve high accuracy. However, the minimum acquisition time for continuous measurement limited the improvement of the acquisition rate. Here, we show that vortex beams provide a route to transfer TOF into the rotation of the spatial intensity distribution of light which can be detected in a single-shot manner. This mechanism enables ranging systems with acquisition rates exceeding one gigahertz and sub-wavelength accuracy. We demonstrate single-shot depth measurements with an accuracy of 51 nanometers, allowing for ultrafast acquisition of displacement in one nanosecond with the same accuracy. These results open up the possibility of improving acquisition rate and accuracy independently through measurement in the space domain.