Optical Principles Research Articles

DEVELOPMENT TRENDS IN OPTICAL TECHNOLOGY OF MIRROR ANASTIGMATIC SYSTEMS

The results of the analysis of the design features of mirror anastigmatic systems were given in this article. Such systems can correct three third-order aberrations; they provide a convenient placement of the image plane, protected from stray light by special hoods. Mirror anastigmatic systems make it possible to find research areas of schematic solutions, archiving systems with an increased field of view and a high luminosity, qualities required for registering the radiation of weak and rather extended objects. We established perspective options, with aligned vertices of even and odd mirrors; additionally, identified a group of systems based on the two-stage optic principle. We notice the development trends of compact systems, with a monoblock of two mirrors, including three-mirror schemes with double reflection from the first mirror, and schemes with a monolith of the first and fourth mirrors, they are more technologically advanced than staggered vertex designs. The small aberration values obtained and the presence of high resolution opens up wide possibilities for the use of mirror anastigmatic systems. They can be used in optical devices operating in a wide range of the spectrum: in satellite scanning systems (photographing) of the earth's surface and thermal scanning systems. The variety of application is limited by the range sensitivity of the photodetector and the operation range, of reflective optical coatings. The disadvantages of anastigmatic mirror systems can be large dimensions and technological difficulties in complex aspherical surface manufacturing, besides a significant central obstruction and vignetting when increasing the field of view. The recent works on the calculation of mirror systems show that some traditional theoretical concepts are insufficient for solving modern optical engineering problems. Therefore, research in the mirror anastigmatic systems field of varying degrees of complexity; in the first place, systems with more than three mirrors, the search for original off-axis schemes that improve optical characteristics have received a significant place in the computational optics.

Ultrasensitive Materials for Electrochemical Biosensor Labels.

Since the fabrication of the first electrochemical biosensor by Leland C. Clark in 1956, various labeled and label-free sensors have been reported for the detection of biomolecules. Labels such as nanoparticles, enzymes, Quantum dots, redox-active molecules, low dimensional carbon materials, etc. have been employed for the detection of biomolecules. Because of the absence of cross-reaction and highly selective detection, labeled biosensors are advantageous and preferred over label-free biosensors. The biosensors with labels depend mainly on optical, magnetic, electrical, and mechanical principles. Labels combined with electrochemical techniques resulted in the selective and sensitive determination of biomolecules. The present review focuses on categorizing the advancement and advantages of different labeling methods applied simultaneously with the electrochemical techniques in the past few decades.

Launcher of high-order Bessel vortex beam carrying orbital angular momentum by designing anisotropic holographic metasurface

In this paper, an ultra-low profile anisotropic holographic metasurface is proposed to generate a linearly polarized high-order Bessel vortex beam carrying orbital angular momentum with predesigned topological charge. Based on the leaky-wave theory and optical holographic principle, the anisotropic impedance pattern can be properly mapped by shaping the quasi-periodic metasurface with different meta-atom sizes. Compared with the prevalent spatial wave-modulated metasurface, this surface wave-modulated holographic metasurface effectively transforms a reference wave excited by a feeding source in a single point at the center of the antenna to a leaky high-order Bessel vortex beam without any extra air feeding, which enables a unique characteristic of error-free alignment between the air feeding and designed metasurface. The good agreement between the numerical simulation and the measured result demonstrates that the proposed approach can be employed to launch a linearly polarized high-order Bessel vortex beam with an arbitrary topological mode of interest.

Growth of sillenite Bi12FeO20 single crystals: structural, thermal, optical, photocatalytic features and first principle calculations

Ideal sillenite type Bi12FeO20 (BFO) micron sized single crystals have been successfully grown via inexpensive hydrothermal method. The refined single crystal X-ray diffraction data reveals cubic Bi12FeO20 structure with single crystal parameters. Occurrence of rare Fe4+ state is identified via X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The lattice parameter (a) and corresponding molar volume (Vm) of Bi12FeO20 have been measured in the temperature range of 30–700 °C by the X-ray diffraction method. The thermal expansion coefficient (α) 3.93 × 10–5 K−1 was calculated from the measured values of the parameters. Electronic structure and density of states are investigated by first principle calculations. Photoelectrochemical measurements on single crystals with bandgap of 2 eV reveal significant photo response. The photoactivity of as grown crystals were further investigated by degrading organic effluents such as Methylene blue (MB) and Congo red (CR) under natural sunlight. BFO showed photodegradation efficiency about 74.23% and 32.10% for degrading MB and CR respectively. Interesting morphology and microstructure of pointed spearhead like BFO crystals provide a new insight in designing and synthesizing multifunctional single crystals.

Non-Destructive Testing of Aircraft Structures Using Microwire-Based Tensile Stress Sensor

The development of non-destructive methods for material testing and diagnostics has been, in the last few decades, focused mainly on optical, infrared, thermography, ultrasonic, acoustic or X-ray principles. This article deals with the possibility of adaptation of magnetic sensors for the diagnostics of aircraft structures. The developed sensors are based on the enhanced induction method, allowing contactless diagnostics of the material structure. In the role of the sensing element, amorphous magnetic microwires were used. Thanks to their dimensions, microwires can either be placed on the material surface or be embedded directly into the composite material without structural violations. In the article, the measurement principles of the developed microwire-based tensile stress sensors, together with the experimental measurements with the sensors originally tested in the aircraft wing, are presented.

Multimodal Microscopy: Fast Acquisition of Quantitative Phase and Fluorescence Imaging in 3D Space

Multimodal optical microscopy combines different optical and physiological principles working together to obtain rich perspectives from a single biological event. In this paper, the recent advances in multimodal microscopy systems based on off-axis digital holography and transport-of-intensity equation are reviewed. Both methods used the common-path configuration, and realized simultaneous quantitative phase and fluorescence imaging in 3D space. Feasibility checks with fluorescent micro-beads and live plant cells are presented. The results show that both methods are capable of fast acquisition of the quantitative phase and fluorescence information with digital refocusing ability.

The Optical Design Principle of Twisted-Vertically Aligned Mode LCD

Compared with normal VA mode LCD, twisted-vertically aligned (TVA) mode LCD gained more and more attention due to its high transmittance as well as high contrast ratio (CR). To realize the optimized electro-optical performance and low cost, this work revealed the optical design principle of TVA mode LCD by Jones Matrix and Computer simulations. Subsequently, the TVA mode sample with high transmittance under orthogonal polarizers was obtained by optimizing the design of the pixel electrode pattern and parameters of chiral LC materials.

Asymmetric Scattering and Reciprocity in a Plasmonic Dimer

We study the scattering of polarized light by two equal corner stacked Au nanorods that exhibit strong electromagnetic coupling. In the far field, this plasmonic dimer manifests very prominent asymmetric scattering in the transverse direction. Calculations based on a system of two coupled oscillators, as well as simulations based on the boundary element method, show that, while in one configuration both vertical and horizontal polarization states are scattered to the detector, when we interchange the source and the detector, the scattered intensity of the horizontal polarization drops to zero. Following Perrin’s criterion, it can be shown that this system, as well as any other linear system not involving magneto-optical effects, obeys the optical reciprocity principle. We show that the optical response of the plasmonic dimer, while preserving electromagnetic reciprocity, can be used for the non-reciprocal transfer of signals at a subwavelength scale.

Spatially modulated snapshot imaging polarimeter using two Savart polariscopes.

We present a spatially modulated snapshot imaging polarimeter using two Savart polariscopes (SMSIPTS). Not only can it avoid alignment angle errors and additional phase errors of a half-wave plate (HWP), it can also avoid changing the HWP frequently when we want the target polarization state at different wavelengths and can increase some channel bandwidth to improve image quality, compared with a spatially modulated snapshot imaging polarimeter (SMSIP). The alignment angle error and additional phase errors of SMSIP and the optical layout and principle of SMSIPTS are derived first. The full Stokes polarization images can be obtained by processing the interferogram. Based on SMSIPTS, we determine the filtering method by simulation. We proved the feasibility of SMSIPTS, and the effect of SMSIPTS and SMSIP on reconstruction is compared by simulation. Last, we experimentally verified the feasibility of the theory of SMSIPTS.

Electrostatic sensors – Their principles and applications

Over the past three decades electrostatic sensors have been proposed, developed and utilised for the continuous monitoring and measurement of a range of industrial processes, mechanical systems and clinical environments. Electrostatic sensors enjoy simplicity in structure, cost-effectiveness and suitability for a wide range of installation conditions. They either provide unique solutions to some measurement challenges or offer more cost-effective options to the more established sensors such as those based on acoustic, capacitive, optical and electromagnetic principles. The established or potential applications of electrostatic sensors appear wide ranging, but the underlining sensing principle and resultant system characteristics are very similar. This paper presents a comprehensive review of the electrostatic sensors and sensing systems that have been developed for the measurement and monitoring of a range of process variables and conditions. These include the flow measurement of pneumatically conveyed solids, measurement of particulate emissions, monitoring of fluidised beds, on-line particle sizing, burner flame monitoring, speed and radial vibration measurement of mechanical systems, and condition monitoring of power transmission belts, mechanical wear, and human activities. The fundamental sensing principles together with the advantages and limitations of electrostatic sensors for a given area of applications are also introduced. The technology readiness level for each area of applications is identified and commented. Trends and future development of electrostatic sensors, their signal conditioning electronics, signal processing methods as well as possible new applications are also discussed.

Non-Linear Image Distortions in Flexible Fiberoptic Endoscopes and their Effects on Calibrated Horizontal Measurements Using High-Speed Videoendoscopy

Laryngeal images obtained via high-speed videoendoscopy are an invaluable source of information for the advancement of voice science because they can capture the true cycle-to-cycle vibratory characteristics of the vocal folds in addition to the transient behaviors of the phonatory mechanism, such as onset, offset, and breaks. This information is obtained through relating the spatial and temporal features from acquired images using objective measurements or subjective assessments. While these images are calibrated temporally, a great challenge is the lack of spatial calibration. Recently, a laser-projection system allowing for spatial calibration was developed. However, various sources of optical distortions deviate the images from reflecting the reality. The main purpose of this study was to evaluate the effect of the fiberoptic flexible endoscope distortions on the calibration of images acquired by the laser-projection system. Specifically, it is shown that two sources of nonlinear distortions could deviate captured images from reality. The first distortion stems from the wide-angle lens used in flexible endoscopes. It is shown that endoscopic images have a significantly higher spatial resolution in the center of the field of view than in its periphery. The difference between the two could lead to as high as 26.4% error in calibrated horizontal measurements. The second distortion stems from variation in the imaging angle. It is shown that the disparity between spatial resolution in the center and periphery of endoscopic images increases as the imaging angle deviates from the perpendicular position. Furthermore, it is shown that when the imaging angle varies, the symmetry of the distortion is also affected significantly. The combined distortions could lead to calibrated horizontal measurement errors as high as 65.7%. The implications of the findings on objective measurements and subjective visual assessments are discussed. These findings can contribute to the refinement of the methods for clinical assessment of voice disorders. Considering that the studied phenomena are due to optical principles, the findings of this study, especially those related to the effects of the imaging angle, can provide further insights regarding other endoscopic instruments (eg, distal-chip and rigid endoscopes) and procedures (eg, gastroendoscopy and colonoscopy).

X-ray Spectral Imaging Program: XSIP.

Spectral K-edge subtraction imaging and wide-field energy-dispersive X-ray absorption spectroscopy imaging are novel, related, synchrotron imaging techniques for element absorption contrast imaging and element speciation imaging, respectively. These two techniques serve different goals but share the same X-ray optics principles with a bent Laue type monochromator and the same data processing algorithms. As there is a growing interest to implement these novel techniques in synchrotron facilities, Python-based software has been developed to automate the data processing procedures for both techniques. In this paper, the concept of the essential data processing algorithms are explained, the workflow of the software is described, and the main features and some related utilities are introduced.

Optomechanical Modeling and Validation of a Distributed Bragg Reflector Force Sensor With Drift and Temperature Compensation

Distributed Bragg reflector fiber laser with the dual-polarization mode is commonly used as a sensing element in optical sensors. Lateral force on such a fiber induces birefringence and results in beating frequency generation in it. Also, the change in the magnitude of the lateral force is correlated to the shift in the beating frequency. This article presents a multi-physics optomechanical model for a fiber laser force sensor based on the birefringence phenomenon. To this end, a theoretical model for the sensing principle was developed through employing the elastic beam theory, Hertzian contact mechanics, and optical birefringence principle. Based on the linearity of the developed optomechanical model to the lateral force and ambient temperature variation, a multi-linear regression calibration for the force sensor was proposed and experimentally validated. Also, the temperature-induced drift in the beating frequency was compensated through exponential adjustment. Moreover, the calibration results showed a relatively small sensitivity for temperature sensing with respect to the external force (cross-talk). This phenomenon was predicted with the theoretical model. Verification of the calibration revealed a root-mean-square error of 0.12°C and 0.04 N for temperature and force sensing, respectively. Furthermore, the validation study showed a root-mean-square error of 0.04± 0.03 N and zero hysteresis for the developed sensor. Moreover, the theoretical sensitivity to external force was similar to the experimental results. For future applications, the compliance of the sensor specifications with the requirements of three surgical procedures was confirmed through comparison with the available literature.

An Innovative Method for Locating the Welded Circular Seam on the Inner Surface of Cylinder Pipeline to Inspector Robot

Locating the welded seam on the inner surface of a pipeline from the frame image captured by the monocular optical camera is a key and challenging problem in intelligentizing the defect inspection robot. Due to the lack of feature points and feature straight lines on the image of the welded seam, the existing visual odometry method cannot be used to locate the welded seam relative to the inspector robot. In this paper, an innovative method is proposed for locating the welded circular seam on the inner surface cylinder pipeline to inspector robot. In this method, the whole shape of the welded seam is retrieved from the frame captured by the monocular camera of the robot and is used as the feature for the location. Through combining the retried shape features and the moving velocity of the robot, the distance from the robot to the welded seam can be calculated quickly based on the optical imaging principle. Experiments show that our method can effectively locate the welded seam. Our method can used in intelligent pipeline inspector robot to locate the welded seam to defect test.

Channel Estimation of MIMO-OFDM through Wavelet Transform to Improve the Spectral Efficiency and Data Transmission Rate

We define a new wavelet transform that is based on a recently defined family of scaling functions: the fractional B-splines. The interest of this family is that they interpolate between the integer degrees of polynomial B- splines and that they allow a fractional order of approximation. The approximation can determine noise in communication signals and help in signal reconstruction and channel estimation in MIMO receiver system. In free space optical communication links, the turbulent atmospheric channel causes fluctuations in both intensity and phase of the transmitted optical signal which degrades their performance. In order to make free space optical communications commercially viable, there is a need for characterizing the atmospheric effects on the received signal statistics, and possibly correcting for the signal degradation using physical optics principles and advanced real-time signal processing techniques. As part of this work, we have constructed an experimental free space optical link over 100 meters so as to characterize the effects of inner-scale and outer-scale turbulence effects, and used it as the platform for carrying out the above objectives. Through these techniques, we have demonstrated bit error rate (BER) reduction and propose to estimate channel accurately.

An Innovative Dual-Axis Precision Level Based on Light Transmission and Refraction for Angle Measurement

Currently, the widely used pendulum-type precision level cannot be miniaturized because reducing the size of the pendulum will reduce its displacement so as to decrease the measurement accuracy and resolution. Moreover, the commercial pendulum-type level can only sense one direction. In this paper, an innovative compact and high-accuracy dual-axis precision level is proposed. Based on the optical principle of light refraction and the reference of the invariant liquid level, the pendulum is no more needed. In addition, based on the light transmission design, there is no reflection signal to interfere with the true signal. Therefore, the level can achieve a high accuracy and small-sized design. The calibration result shows the error of the proposed precision level is better than ±0.6 arc-sec in the measurement range of ±100 arc-sec, and better than ±5 arc-sec in the full measurement range of ±800 arc-sec.

Laser fluorescence as an alternative for digital radiography in detecting caries lesions

Diagnosis of caries lesions consists of visual/tactile methods following the International Caries Detection and Assessment System (ICDAS) and radiographic methods (BW), however these methods have limitations for detecting caries at different depths and locations and is usually influenced by the examiner’s experience. New technologies have emerged to improve caries diagnosis methods, among these are methods that use optical principles to quantify differences between healthy and demineralized tissues, for example: quantitative light- -induced fluorescence (QLF), the “DIAGNOdent” caries detection pen, and VistaProof (fluorescence camera). This literature review aims to provide up-to-date information on the applicability of fluorescence-based methods in the diagnosis of caries. The results show that DIAGNOdent pen was the most effective method for diagnosing caries, wherein some authors indicate that it can be used as the only diagnostic method, but most recommend using it as a complementary method to ICDAS and BW. LFpen must be used in association with ICDAS and 2 articles indicate near-infrared light transillumination (NILT) as a substitute for BW, however there is still a need for further studies to reach a concrete decision. In conclusion, digital methods for the diagnosis of caries are efficient, but they do not replace visual/tactile methods and bitewing radiographs. Therefore, they should be used as a complementary diagnostic method to those already known and widely used and studied.

Sliding on ice: Real contact area, melted film thickness, and friction force

It is easy to slide on ice because of water films arising as a consequence of frictional melting. Although the friction force of ice and a slider critically depends on the area and thickness of the liquid film as well as the sliding speed, direct experimental visualization and quantification of temporal evolutions of the contact area, film thickness, and the resulting friction force have been scarce to date. Here we develop an experimental technique to visualize the contact area of ice asperities and a high-speed sliding surface in situ based on the optical principle of total internal reflection. We construct a hydrodynamic model to predict the contact area, liquid film thickness and friction force of a model system of hemispherical ice on a flat solid surface. Upon showing good agreement between theory and experiment, we briefly discuss how the fundamental understanding of the friction behavior of a single ice bump can be extended to understand the friction behavior of flat ice surfaces.

Effects of Voltage and Current Waveforms on Pulse Discharge Energy Transfer to Underwater Shock Waves for Medical Applications

The effects of voltage and current pulse durations of underwater discharge on shock wave generation are reported. In this article, underwater discharges were generated by using a magnetic pulse compression (MPC) circuit. The compression number of the MPC circuit was varied from two compressions to one and no compression; also the capacitance of an output peaking capacitor connected in parallel to discharge electrodes (load) was varied from 10 to 6 and 2 nF. As a result, electric pulses with different rise time/duration and variable peak voltages and currents were obtained and applied to generate shock waves. The shock waves were quantitatively measured with optical principles using a fiber optic probe hydrophone (FOPH) pressure transducer. By reflecting the generated shock waves from a reflector, uniform shock waves were produced, which made it possible to accurately measure the shock waves. The maximum pressure of the generated shock wave after the reflection was in the range of 40 MPa. The energies of the output shock waves were calculated from the pressure histories and the electrical to shock wave energy conversion efficiency was calculated from the electrical energy used to generate the shock waves. The results indicated that the rise time of voltage and current significantly affects the electrical energy that can be delivered to generate the shock waves. For the range of the electric pulse durations of 100 to 500 ns of this article, the shock waves pressures were independent of the pulse duration for the same input energy consumed during the rise and full width at half maximum times of the current. The method presented here gives possibility to select the shock wave profile, which would be crucial for successful medial applications.

The Outlook for Gyroscopy

Modern gyroscopy is characterized by a great diversity of gyroscopes that have been and are being developed. Dominant positions belong to wave optic gyroscopes implementing the relativistic Sagnac effect, and micromechanical vibratory gyroscopes the operating principle of which is based on Coriolis effect. At the same time, high-precision rotor mechanical gyroscopes based on the principles of rotating solid body dynamics partially retain their position; also, the research of gyroscopes developed on the principles of nuclear physics and quantum optics is progressing successfully. Current state and the prospects of gyroscopes development are discussed in this paper.