Optical Principles Research Articles

A novel multifunctional visual sensor based on combined laser structured lights and its anti-jamming detection algorithms

Based on the combined laser structured lights, a novel multifunctional monocular visual sensor was proposed. Firstly, a mathematical model of the proposed visual sensor was established based on the optical triangulation measurement principle. The imaging characteristics of the visual sensor and the influence of structure parameters of the designed visual sensor on the detection errors were studied. Then, the new algorithms were derived for the accurate detection of the welding groove cross-sectional dimensions and the welding torch height even under the circumstances with existing of the installation and robot motion errors, which use only one photograph in monocular vision. Finally, the experiments designed for the detection were carried out. The experimental results show that the proposed visual sensor has high feasibility and anti-jamming capability in the detection, and the errors can also be detected by the sensor simultaneously. Therefore, this novel visual sensor could be applied for the improvement of precision and intelligence in the robotic welding manufacturing.

Mechanically controlled quantum interference in graphene break junctions.

The ability to detect and distinguish quantum interference signatures is important for both fundamental research and for the realization of devices such as electron resonators1, interferometers2 and interference-based spin filters3. Consistent with the principles of subwavelength optics, the wave nature of electrons can give rise to various types of interference effects4, such as Fabry-Pérot resonances5, Fano resonances6 and the Aharonov-Bohm effect7. Quantum interference conductance oscillations8 have, indeed, been predicted for multiwall carbon nanotube shuttles and telescopes, and arise from atomic-scale displacements between the inner and outer tubes9,10. Previous theoretical work on graphene bilayers indicates that these systems may display similar interference features as a function of the relative position of the two sheets11,12. Experimental verification is, however, still lacking. Graphene nanoconstrictions represent an ideal model system to study quantum transport phenomena13-15 due to the electronic coherence16 and the transverse confinement of the carriers17. Here, we demonstrate the fabrication of bowtie-shaped nanoconstrictions with mechanically controlled break junctions made from a single layer of graphene. Their electrical conductance displays pronounced oscillations at room temperature, with amplitudes that modulate over an order of magnitude as a function of subnanometre displacements. Surprisingly, the oscillations exhibit a period larger than the graphene lattice constant. Charge-transport calculations show that the periodicity originates from a combination of the quantum interference and lattice commensuration effects of two graphene layers that slide across each other. Our results provide direct experimental observation of a Fabry-Pérot-like interference of electron waves that are partially reflected and/or transmitted at the edges of the graphene bilayer overlap region.

Design of LED Collimating Light Source Based on Simulation Surface Model

According to the principle of geometrical optics, a LED collimating light source based on surface model is designed. First, establish a collimator lens mathematical model, then the single light-emitting diode model and the light model were imported into Tracepro software for simulation verification. At last the influence of the size of light-emitting diode on the half - intensity angle and the luminous efficiency were analyzed. The results show that the collimating lens control the halfintensity angle of the light-emitting diode source under 3 degrees. The luminous efficiency of the collimating lens is about 90.6% under consideration of material absorption and other losses.

Dispersion control for temporal contrast optimization

We investigate the temporal contrast of the Light Wave Synthesizer 20 (LWS-20): a powerful, few-cycle source based on the optical parametric synthesizer principle. Saturation effects in the RF amplifier driving the acousto-optic programmable dispersive filter (AOPDF) were found to degrade the coherent contrast for non-monotonic group delay corrections. We subsequently present a new dispersion scheme and design a novel transmission grism-based stretcher optimized for LWS-20. The resulting temporal contrast of the amplified, compressed output pulses is improved by 2-4 orders of magnitude compared to the former design.

3D Rough Surface Topography Model of Fractal Interpolation Based on Wavelet Transform

With the development of computer technology, there are many kinds of instruments for obtaining the 3D surface topography such as confocal topography using optical principle, the scanning electron microscope, the transmission electron microscope and the probe contact topography. However, the topography or profile of the rough surface has scale correlation. The certain measurement deviation will be caused due to the limited resolution of the topographer when acquiring a 3D topography. In addition, the dimensions and attributes of the tested sample are strictly required and it is impossible to record the surface topography that changes in real time during friction and wear. In order to overcome the disadvantages of the above surface topography modeling methods, a method combining fractal interpolation and wavelet transform is used in this paper. The accuracy and the resolution of the 3D surface topography model can be controlled by the number of iterations and the selection of the reference data resolution.

An Image-based Laser Triangulation Width Model Applied in Sawn Lumber’s External Face Measurement

The yield of sawn lumber has been largely governed by the identification accuracy of the external face width. However, the traditional method cannot measure the external face width with high accuracy and low error. In view of this, an image-based laser-triangulation width measurement model was established to measure the width of sawn lumber’s external face in an effort to overcome the deficiency of the traditional method. A hypothesis was established from the theoretical model, as follows: when the laser line is cast on the external face and the reflected light is captured by the camera with a certain angle, the width resolution will be the least affected and will even depend on the resolution of the camera under precise conditions. Data from contrasting experiments suggested that a particular angle has a width-detection error 0.15% and accuracy 0.177 mm, which absolutely satisfies the need of wood industry detection online. Furthermore, this paper gives a theoretical proof of conjecture from the perspective of optical principles and mathematical analysis.

Large-scale tight-binding simulations of quantum transport in ballistic graphene

Graphene has proven to host outstanding mesoscopic effects involving massless Dirac quasiparticles travelling ballistically resulting in the current flow exhibiting light-like behaviour. A new branch of 2D electronics inspired by the standard principles of optics is rapidly evolving, calling for a deeper understanding of transport in large-scale devices at a quantum level. Here we perform large-scale quantum transport calculations based on a tight-binding model of graphene and the non-equilibrium Green’s function method and include the effects of p-n junctions of different shape, magnetic field, and absorptive regions acting as drains for current. We stress the importance of choosing absorbing boundary conditions in the calculations to correctly capture how current flows in the limit of infinite devices. As a specific application we present a fully quantum-mechanical framework for the ‘2D Dirac fermion microscope’ recently proposed by Bøggild et al (2017 Nat. Commun. 8 10.1038), tackling several key electron-optical effects therein predicted via semiclassical trajectory simulations, such as electron beam collimation, deflection and scattering off Veselago dots. Our results confirm that a semiclassical approach to a large extend is sufficient to capture the main transport features in the mesoscopic limit and the optical regime, but also that a richer electron-optical landscape is to be expected when coherence or other purely quantum effects are accounted for in the simulations.

Ionospheric Specification and Space Weather Forecasting With an HF Beacon Network in the Peruvian Sector

AbstractA network of high‐frequency (HF) transmitters and receivers used for ionospheric specification is being installed in Peru. The HF transmitters employ multiple frequencies and binary phase coding with pseudorandom noise, and the observables provided by the receivers include group delay, Doppler shift, amplitude, bearing (from interferometry), and polarization. Statistical inverse methods are used to estimate F region density in a volume from the data regionally. The method incorporates raytracing based on the principles of Hamiltonian optics in the forward model and involves an ionospheric parametrization in terms of Chapman functions in the vertical and bicubic B‐spline interpolation in the horizontal. Regularization is employed to minimize the global curvature of the reconstructions. HF beacon data for two nights in January 2018 are presented. We use the reconstructions to investigate why plasma irregularities associated with equatorial spread F formed on one occasion and not the other. The data indicate that the background ionospheric flow is not simply frozen in, that is, that longitude and local time variations cannot be equated, even at regional scales. This has ramifications for equatorial spread F forecasting strategies that assume equivalence.

Laser direct-writing lithography equipment system for rapid and μm-precision fabrication on curved surfaces with large sag heights.

A novel laser direct writing lithography equipment system was proposed to realize rapid and μm-precision fabrication on curved surfaces with large curvatures and large sag heights. Through detailed design, analysis, simulation, and measurement, it showed that the system was able to continuously, linearly and rapidly change the focus position in z coordinate. For demonstration, a concentric-circular photoresist grating with a sag height of 5.2 mm and a designed line width/space of 12.5 μm/25 μm was fabricated within 40 s on a convex K9 glass substrate surface with a curvature radius of 32.77 mm. When combining with the movement of the x-y-z stage, the system could fabricate the micropatterns on curved surfaces with larger dimensions. Further, the system possessed the general principles of optics, mechanics, and automation for μm-precision 3D microfabrication.

Imaging Through Fire Using Narrow-Spectrum Illumination.

This paper demonstrates a simple method to enhance visibility through clean-burning flames that allows new opportunities to perform qualitative and quantitative optical metrology in fire research. The method combines narrow-spectrum, blue illumination and matched optical filters to reduce the influence of optical emissions from a glowing hot target and a large natural gas diffusion flame. The paper describes how the required illumination strength and filtering can be estimated from basic combustion and optical principles. Compared to white light, the required illumination to detect objects 26 engulfed in flames with this method is reduced by a factor of 104. A series of experiments are conducted to determine the effectiveness of this method, successfully demonstrating the ability to take images of objects in natural gas fires up to 1000 kW using 200 W of illumination power.

Hazards Detection System Based on 3D Panorama for Tailings Dam in Mining

Tailings dam is a key facility for the mining process, which is also the major hazards for the surrounding environments. It could cause catastrophic accidents and severe personal injuries if the tailings dam failed. The occurrence of tailings dam accidents will greatly damage the life and property of the people in the surrounding areas and damage the ecological environment around the region. In recent years, Chinese government has introduced policies to step up investigation and management of mine tailings potential hazards and results in great achievements. However, a large part of the tailings dam still has prominent safety problems due to long-term site selection, design, system construction and management. Flood drainage system plays an important role both in the mining process and in the tailings dam safety. Through the analysis of the causes of tailings dam accidents, this paper discoveries that a number of accidents caused by the failure or damage of flood drainage facilities, and the risk in flood season is especially prominent. The safety hazards detection of the flood drainage is vital to secure the tailings dam safety. A safety hazards detection system based on 3D panorama technology has been achieved in this paper. It provided a new way to detect the safety hazards remotely on portable devices. Firstly, the 3D panorama data acquisition device was designed and developed. The functions and requirements of 3D panorama data acquisition device were investigated according to the actual environment of flood culvert. The structure and hardware of the device were calculated according to the target functions. Three-dimensional environment image data for rapid acquisition, and the use of feature matching and optical flow principle of the collected images were spliced to generate a 3D panoramic image of flood drainage of tailings dam in mining. The safety hazards detection system includes 3D panorama client and panorama images cloud database. It has five layers which are basic configuration layer, interface presentation layer, data management layer, function module layer and background management layer. The functional module layer has five functional modules, including mine personnel management module, tailings pond panoramic scene module, culvert potential danger detection module, interface menu navigation module and material information management module. It can help safety inspectors to detect and investigate potential safety hazards in flood drainage culverts, which would strengthen the safe operation of tailings dam and maintain the safe and sustainable production of mines. This system has been applied to the tailings dam of a mine to collect 3D environmental image data of the flood drainage culvert. The panoramic image is spliced to generate a panoramic view through the cloud platform. The results show that this system can be used in mine drainage culvert safety hazards detection.

Novel nanostructured indium tin oxide electrode for electrochemical immunosensors: Suitability for the detection of TNF-α

The need for new and innovative point of care (POC) systems providing a feasible alternative to costly and time consuming standard laboratory techniques is becoming more evident every day, particularly in the case of cardiovascular diseases. Coupling optical and electrochemical principles for highly specific and sensitive detection of biomarkers could boost the successful implementation of POC systems in biomedical environments. We suggest indium tin oxide (ITO) as a promising material for working electrodes in optoelectrochemical sensors, owing to the rare combination of high electrical conductivity and optical transparency it presents. Moreover, the nanostructured nature of the electrodes' surface is crucial for an eventual miniaturization of the POC system. In this work, we describe the construction and characterization of a nanostructured ITO electrode modified with aryl diazonium salt as transparent substrate for electrochemical immunosensors. The developed electrode was tested for the detection of tumour necrosis factor α (TNF-α), a cardiac biomarker playing an important role in the prevention of heart failure. Macro and microscopic evidences (gathered from electrochemical and spectral techniques) of covalent bonding and high surface coverage are provided. Specific interaction between antigen (TNF-α) and monoclonal antibody (Ab-TNF-α) was verified by fluorescence patterning, confirming the proper bio-recognition of the cytokine. As a proof-of-concept, results of electrochemical impedance spectroscopy (EIS) show stabilized semi-quantitative label-free detection of TNF-α at several concentrations (from 10 pg/mL to 100 pg/mL). These preliminary results demonstrate the feasibility of using transparent substrates for the detection of cytokines at low concentrations, and the consequent application in POC systems for the monitoring of cardiovascular diseases.

Development of a variable and broad speed range all-fiber laser vibration measurement technology

Abstract This paper realizes a variable and broad speed range all-fiber heterodyne laser vibration measurement system. The system employs a dual-parallel Mach-Zehnder modulator to generate a carrier-suppressed single-sideband signal and facilitates non-contact vibration measurements based on the optical Doppler shift principle. The maximum speed can be measured is much higher than the general vibrometer. This technology has the advantages of high precision, dynamically adjustable measuring range, full-frequency modulation etc. In this paper, a prototype has been built, and Hilbert Transform is used to extract the vibration signal from the frequency shift signal. Laboratory experiment result shows the ability of mutative and expansive measuring range.

Optical tweezers for trapping in a microfluidic environment.

Optical tweezers use the force from a light beam to implement a precise gripping tool. Based purely on an optical principle, it works without any bodily contact with the object. In this paper we describe an optical tweezers that targets an application within the framework of nuclear magnetic resonance (NMR) spectroscopy of small objects, which are embedded inside a microfluidic channel that will be integrated in a micro-NMR detector. In the project's final stages, the whole system will be installed within the wide bore of a superconducting magnet. The aim is to precisely maintain the position of the object to be measured, without the use of susceptibility disturbing materials or geometries. In this contribution we focus on the design and construction of the tweezers. For the optical force simulation of the system we used a geometrical optics approach, which we combined with a ray fan description of the output beam of an optical system. By embedding both techniques within an iterative design process, we were able to design efficient optical tweezers that met the numerous constraints. Based on details of the constraints and requirements given by the application, different system concepts were derived and studied. Next, a highly adapted and efficient optical trapping system was designed and manufactured. After the components were characterized using vertical scanning interferometry, the system was assembled to achieve a monolithic optical component. The proper function of the optical tweezers was successfully tested by optical trapping of fused silica particles.

Design and Fabrication of a Three-Dimensional Artificial Compound Eye Using Two-Photon Polymerization.

Microlens arrays have been widely used in the fields of micro-optics because of the advantages of their high diffraction efficiency, high fill factor, and wide operating band. However, the microlens array still has problems with its smaller field of view (FOV) and lower utilization of light energy. In this paper, a 3D compound eye system consisting of a microlens array and a pinhole array was designed according to the optical principle of insect compound eye. The artificial compound eye structure was processed in two-photon polymerization processing technology. Ray tracing and optical system simulation of the designed artificial compound eye structure were performed. The results showed that the artificial compound eye structure had a wider FOV and higher light energy utilization than a conventional 2D microlens array. This thesis may lay a theoretical foundation for the structural optimization design of microlens arrays.

Miniature fiber pressure sensor based on an in-fiber confocal cavity

A new type of miniature pressure sensor based on a hybrid Fabry-Perot (F-P) interferometer is proposed. The in-line air cavity of the sensor is a micro-confocal air cavity, which is formed by splicing together a single mode fiber (SMF) and a solid-core photonic crystal fiber (PCF) with the specific splicing parameters. The sensor is fabricated by simple steps involving only fusion splicing, cleaving and polishing. Optical interference principle of the sensor is analyzed and the parameters in sensor design are discussed. Due to low propagation loss, experiments show that the reflection spectrum of the sensor has a fringe contrast of more than 30 dB. By tracing the trough wavelength in the interference spectrum, the pressure can be demodulated. Within the pressure measurement range of 0–1 MPa, the sensitivity is −193 pm/MPa. The experimental results indicate that the deflection is consistent with the theoretical analysis and the sensor has a good linearity. Easy fabrication, low-cost and high-contrast make it appropriate for practical application.

Design and evaluation of an in-line system for gas sensing in flow-packed products

Abstract A method for the in-line application of Tunable Diode Laser Absorption Spectroscopy (TDLAS) for headspace oxygen sensing in flow-packed products is presented. This is one of the first automated, industrial application on food packaging samples of a well known spectroscopic technique.The developed instrument is discussed starting from its sensor design with details on the optical working principles to point out the peculiarities and application issues linked with this particular technique. A production line implementation of the sensor is then presented, based on a conveyor belt for automatic sampling. This device was also integrated with line automation in order to enable measurement on the full production. Both in-line and off-line instruments were validated against traditional, industry-standard invasive measurement techniques. The accuracy of the measurement applied to regular samples from production line was found better than 0.4% vol. O2.

Design of an Absolute Shaft Encoder Using Optically Modulated Binary Code

In order to avoid the fabrication of coding pattern over a shaft coupled disk of the binary coded absolute encoder, a new design concept has been presented in this paper. The proposed prototype can encode the binary information by optical modulation principle. Instead of lithographic fabrication, here the pattern code bits are implemented optically through a plurality of infra-red (IR) light emitting diodes (LED). Each LED transmits a bit of information as modulated optical signal and modulation is served by the principle of serial infra red control protocol. During the rotation of an object, a window position of the shaft coupled disk determines which bits’ information will be transmitted. Now, an IR detector of the receiver unit decodes this code by demodulating the transmitted signal. Finally, the absolute position of the object is evaluated from this code by searching a look-up table data. Thus, the receiver unit of the proposed encoder can sense the position of an object remotely without using any additional wireless device. Also, the sensing heads may not be damaged by the rotating disk vibration. The prototype has been tested by using De-Bruijn coding pattern and obtained promising results. Also, the proposed method is equally valid for any binary or gray pattern code.

Holographic Fabrication of 3D Nanostructures

AbstractIn this paper, the authors review the optical principles underlying the fabrication of 3D periodic nanostructures prepared using holographic lithography (HL) as well as their applications toward chemical sensors and energy storage devices using 3D functional nanomaterials. HL is potentially useful for the simple and rapid fabrication of defect‐free large‐area periodic nanostructures with various structural geometries. The use of optical elements, such as well‐designed prisms and diffraction gratings, improves the reproducibility of the manufacturing process by simplifying complicated optical setups. 3D functional nanostructures, including semiconductor and metallic nanomaterials, are useful in highly sensitive photonic crystals and plasmonic sensors, and high‐performance 3D electrodes for use in energy production and storage devices.

Optical Characteristics and Operational Principles of Hybrid Perovskite Solar Cells (Phys. Status Solidi A 12∕2018)

Perovskite Solar Cells The crystal structure of the CH3NH3PbI3 organic-inorganic hybrid perovskite with direct band gap formation in the crystal and the operating principle of a CH3NH3PbI3 solar cell are shown on the cover, referring to article number 1700730 by Hiroyuki Fujiwara and co-workers. In this article, the optical characteristics and operational principles of hybrid perovskite solar cells are reviewed. In particular, the unique optical properties of various hybrid perovskite materials, as revealed by experimental characterization and first-principles calculations, are described in detail. Moreover, from the photocurrent characterization results, the fundamental operating principles of the perovskite cells based on a simple p–n junction formation are discussed. The high short-circuit current observed in the solar cells is further interpreted by the suppressed parasitic light absorption and efficient optical confinement in the solar cells. This article provides renewed principles for the optical processes and operation of hybrid perovskite solar cells.