Numerical modeling Optical Coherence Tomography (OCT) systems is needed for optical setup optimization, development of new signal processing methods and assessment of impact of different physical phenomena inside the sample on OCT signal. The Monte Carlo method has been often used for modeling Optical Coherence Tomography, as it is a well established tool for simulating light propagation in scattering media. However, in this method light is modeled as a set of energy packets traveling along straight lines. This reduces accuracy of Monte Carlo calculations in case of simulating propagation of dopeds. Since such beams are commonly used in OCT systems, classical Monte Carlo algorithm need to be modified. In presented research, we have developed model of SD-OCT systems using combination of Monte Carlo and analytical methods. Our model includes properties of optical setup of OCT system, which is often omitted in other research. We present applied algorithms and comparison of simulation results with SD-OCT scans of optical phantoms. We have found that our model can be used for determination of level of OCT signal coming from scattering particles inside turbid media placed in different positions relatively to focal point of incident light beam. It may improve accuracy of simulating OCT systems.
In this paper we present construction of an optical coherence tomography system capable to measure birefringeant properties of the materials. Radiation in this measuring system propagates in the free space with polarization state preservation. Balanced detection has been used to improve noise properties of a system. Preliminary measurements are presented.
Dispersion of optical elements and sample in optical coherence tomography (OCT) system introduce a wavelength dependent phase distortion to the light beam propagating in OCT system. This causes blurring of the image in high resolution OCT using broadband light sources. Also decreased resolution with the depth of a sample is observed. To avoid this, the overall dispersion of the system can be compensated using a dispersive material in the reference arm of a system. Unfortunately, the dispersion is changed in the system with the probing depth. Overcome to this problem is numerical dispersion compensation technique. Calculations can be made after the measurements have been taken to provide depth dependent compensation. Various techniques and their possibilities are presented.
Optical Coherence Tomography (OCT) is a novel optical measurement technique for high resolution, high sensitivity 2D and 3D visualization of material inner structure. With the aid of OCT one can analyze a wide range of biological and technical materials in non-contact and non-destructive way. In our research we concentrate on possibilities of using OCT systems for characterization of polarization properties of investigated materials. We present a short review of polarization sensitive OCT topologies and principle of polarization state measurement.
The spectral shape of a light source in optical coherence tomography imaging is of prime importance because it determines resolution and quality of the image. Spectra and axial point spread function of photonic crystal fiber light source TB-1550 from Menlosystems GmbH before and after optical spectral shaping are presented. Low-pass and high-pass filters are simulated to shape the irregularities in light spectra of the source. Full-spectrum shaping results with use of spectral processor are calculated. Results show that shaping of a light source improves meaningly axial resolution and inhibits sidelobes of the point spread function.
An Optical Low-Coherence Tomography (OCT) is a novel optical measurement technique, which enables non-destructive and non-contact investigation of multilayer structures. Nowadays, this method is highly applied in medical diagnostics. Despite of great progress in optoelectronics and optical measurement methods there is lack of studies on the OCT for non-medical application. In this paper authors present a laboratory OCT system for surface and subsurface investigation of scattering technical objects such as polymer layers. Preliminary test results on subsurface technical objects investigation using OCT system have been presented and discussed.
Fiber-optic low-coherence tomography system with low-coherent reflectometry has been used to non-destructive characterization of ceramics. We presents experimental results showing that the measurements of ceramics internal structure can be done with suitable resolution.
The influence of low-coherence source parameters on the optical coherence tomography imaging has been studied. Experimentally and theoretically it is demonstrated, that by summing autocorrelation function of two superluminescent diodes with different wavelength, the effective coherent length of the source and signal-to-noise ratio required to identify the central fringe position can be greatly reduced.
The operation of optical fiber sensors using optical time-domain reflectometers (OTDRs) is outlined. Limitations introduced by telecommunication OTDRs used in these sensors are discussed. Other approaches based on specialized short-range OTDRs are presented. Finally, OTDRs based on sub-picosecond fiber laser sources and fast detection and acquisition systems.
The base of time-of-flight fiber optic sensors using short laser pulses was presented. This kind of sensors can work in the transmission mode or in the reflection mode. Because attenuation of these sensors is small, they may be operated in sensor networks having tens or hundreds measuring points. The example of a time-of-flight fiber optic sensor is a segment of a singlemode optical fiber that is affected by temperature or longitudinal stress. The changes of temperature or strain applied to the fiber change the propagation time of light in the fiber. In the paper a time-of-flight sensor is presented. Using a picosecond semiconductor laser source and a photon avalanche photodiode detector, the system iscapable of measuring of temperature and force acting on the fiber. The performance of such sensor was tested for temperature in 20÷110 °C range or stress force in 0÷8 N range.
Interferometric sensors exhibit very high measurement resolution. In order to attain high accuracy, these sensors are often implemented as polarization interferometers, in which stable and well-defined states of polarization are maintained. By using correction techniques originally developed for metrology and outlined in this paper, accuracy of discussed sensors can be further increased by adjusting gains and offsets in detection setup. Sensors that can use this technique are presented and problems arising in implementation of polarization interferometric sensors are discussed.
The use of Single Mode Polarization-Maintaining Side-Hole (SMPM-SH) fibers for direct measurement of transverse force has been studied theoretically and experimentally. Based on results of Finite Element modeling reported elsewhere it was known that certain SMPM-SH fibers exhibit higher sensitivity to transverse force than a standard SMPM fiber. In order to verify these predictions, an experiment was performed. Measurement results agreed well with theoretical predictions. However, more systematic research is needed to determine the relationship between the sensitivity, dimensions and geometry of the holes.
The influence of splicing inaccuracy of fiber segments of polarimetric sensors on visibility of polarization modes interfering at the sensor output was investigated. Two types of sensors were analyzed using Jones matrix formalism: one with single and one with double temperature compensation.
A method for modeling of multiply purturbed fibers was developed as an extension to the modified coupled-mode method. Being based on numerical solution of coupled mode equations, the method is not limited in the scope of its applications to the cases in which coupling coefficients are constant along the fiber. Short computation time was achieved as a result of modification to the solved coupled-mode equations. Presented method was developed as a design tool for polarimetric optical fiber sensors. The use of the method is demonstrated on an example of a twisted single-mode elliptic-core fiber subjected to pure bending. Moreover, it was shown that the presented method can be also applied to visibility calculation in polarimetric sensors using polychromatic sources.
Optical fiber force sensors using Michelson interferometer and a tunable external cavity semiconductor lase rsource are investigated in order to develop a sensor whose operating point is actively stabilized by the change of the source wavelength. Two configurations of such sensros are briefly discussed, and their advantages are compared. Based on presented results a sensor was built and tested. The sensor employs an indirect force transducer in which the force acting on it is converted into hydrostatic pressure which is subsequently measured. The sensor exhibits good linearity. Its bandwidth is currently limited by the tuning speed of the laser and can be extended by increasing the tuning speed of the laser.
Nowadays, the car driver are faced with a rapidly increasing flood of information. In addition to established information systems (car radio, vehicle monitoring, mobile phones), high class vehicles feature navigation systems almost as standard. In the current decade, driver assistance and collision avoidance systems will appear in vehicles. Hence, there is an increasing demand for supplying the driver with more information that help him to drive safer and more economical. The price decline in the computer market and the availability of powerful graphic hard- and software concepts make it possible to enhance the classical functions of the instrument board to an interactive multifunctional information panel - an interface between information systems of the car and the driver. Therefore, the question of additional visual and cognitive stress, and a possible distraction of the driver by the large amount of information, and its complexity becomes predominant. Reconfigurable instruments, based on a microprocessor controlled active matrix color display, provide a powerful alternative to the usual mechanical/electromechanical instrument clusters in vehicles. They will help to strengthen passive safety, they adapt to user and situation requirements, and they are easy to install, to configure, and to maintain. Reconfigurable instruments in future cars will have a high impact on traffic since they can provide the driver with much more information, presenting it in a way that is flexibly matched to the importance of particular data and to the ergonomic properties of the driver. The functions are manifold and span from classical driver information like speed to navigation prompts and ultimately to video and multimedia access.
The development of information techniques, using new technologies, physical phenomena and coding schemes, enables new application areas to be benefited form the introduction of displays. The full utilization of the visual perception of a human operator, requires the color coding process to be implemented. The evolution of displays, from achromatic (B&W) and monochromatic, to multicolor and full-color, enhances the possibilities of information coding, creating however a need for the quantitative methods of display parameter assessment. Quantitative assessment of color displays, restricted to photometric measurements of their parameters, is an estimate leading to considerable errors. Therefore, the measurements of a display's color properties have to be based on spectral measurements of the display and its elements. The quantitative assessment of the display system parameters should be made using colorimetric systems like CIE1931, CIE1976 LAB or LUV. In the paper, the constraints on the measurement method selection for the color display evaluation are discussed and the relations between their qualitative assessment and the ergonomic conditions of their application are also presented. The paper presents the examples of using LUV colorimetric system and color difference (Delta) E in the optimization of color liquid crystal displays.
An interferometric optical fiber sensor intended for use in Weigh-in-Motion systems is presented. The sensor uses a modified Michelson interferometer configuration with two sensing arms. To avoid polarization induced fading the force acting on the sensor is measured indirectly, using modulators which convert it to pressure. Operation of such modulators was verified by experiment and based on its results a laboratory model of a sensor was built and tested.
The requirements for design and construction of fiber optic measuring heads (probes) based on an imaging rigid fiber optic bundle and on flexible fiber optic bundles are presented. The models of the probes and their application in a spectrophotometric measurement system for a medical application are described and discussed. The performed experiments confirmed their usefulness.
Stress sensors dedicated for Weigh-in-Motion of road vehicles should exhibit high dynamic range, good accuracy and repeatability, as well as long service life. One of the most promising group of sensors for this application are polarimetric sensors, due to their simplicity and high sensitivity. Preliminary measurements of the optical fiber properties in this application resulted in significant hysteresis being observed even for relatively low stress, which is probably caused by the cladding properties or by the construction of the modulator used in the measurement.
The subject of this paper is an optical fiber temperature sensor using the techniques of optical time domain reflectometry. The sensor uses the dependence between the refractive index of epoxy resins and temperature and allows us to develop sensors working in transmission as well as in reflective mode.
The advancement of the liquid crystal display (LCD) technology, and improvements of the optical and electro-optical properties, have enabled the broad expansion of LCDs application field. The rapid development of the multimedia techniques, new applications in automotive, office, medical domain, forced the demand for the color displays--for the information presentation with the color code. The necessity to fulfil many contradictory and extreme conditions caused the development of the optimization procedures of the color LC displays to be a big problem. Most of the LCDs used nowadays are the twisted nematic, super twisted nematic, and active matrix thin film transistor LCD. The characterization of the achromatic black/white LCDs is made by means of photometric measuring methods, and quantitative measures are used: luminance, reflectance, contrast, contrast ration; as a function of a driving voltage, viewing angle, temperature, etc. The characterization of the color LCD is based on the spectral distributions of the transmittance or reflectance. Quantitative measures are chromatic coordinates and luminance factors are defined according to the colorimetric systems--CIE 1931, CIE 1976, CIELUV, CIELAB. The color difference (Delta) E in the CIELUV system is applied as a optimization parameter for the color display module. The spectral properties of all optical elements of the display module are analyzed and their influence on the set of the optical factors of LCD is evaluated. The correlation between technological parameters and optical characteristics of the LCD has been investigated. The choice of the optimization criterion is discussed and the optimization algorithm is proposed. Results of the color displays evaluation for some examples with different preconditions are presented.
The subject of this paper is modelling and optimization of fiber optic refractometric sensors that based on the principle of attenuation caused by bends of the optical fiber. Sensors of this type are meant to measure the refractive index of fluids and, after some modifications, to measure temperature. The model designed allows us to optimize the construction of this type of sensors in order to obtain the highest possible sensitivity and linearity of characteristics in the assumed range of changes of the measured refractive index.
The strong increase of applications of liquid crystal displays in various areas (measuring, medical equipment, automotive, telecommunication, office, etc.) has forced the demand for the adequate specification of the LCDs performances. The optical, electro-optical and spectral properties of LCDs are strongly dependent on viewing direction, electrical driving conditions, illumination and temperature. All these quantities have to be precisely controlled, when one of them is varied, the resulting optical response of the object is recorded. In this paper we present measuring methods proposed for LCD panels and the computer controlled measuring system (DMS) for their evaluation.
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