Volume 19, Issue 4

This paper mainly presents a theoretical analysis for the characteristics of quantum dot infrared photodetectors (QDIPs) and quantum wire infrared photodetectors (QRIPs). The paper introduces a unique mathematical model of solving Poisson’s equations with the usage of Lambert W functions for infrared detectors’ structures based on quantum effects. Even though QRIPs and QDIPs have been the subject of extensive researches and development during the past decade, it is still essential to implement theoretical models allowing to estimate the ultimate performance of those detectors such as photocurrent and its figure-of-merit detectivity vs. various parameter conditions such as applied voltage, number of quantum wire layers, quantum dot layers, lateral characteristic size, doping density, operation temperature, and structural parameters of the quantum dots (QDs), and quantum wires (QRs). A comparison is made between the computed results of the implemented models and fine agreements are observed. It is concluded from the obtained results that the total detectivity of QDIPs can be significantly lower than that in the QRIPs and main features of the QRIPs such as large gap between the induced photocurrent and dark current of QRIP which allows for overcoming the problems in the QDIPs. This confirms what is evaluated before in the literature. It is evident that by increasing the QD/QR absorption volume in QDIPs/QRIPs as well as by separating the dark current and photocurrents, the specific detectivity can be improved and consequently the devices can operate at higher temperatures. It is an interesting result and it may be benefit to the development of QDIP and QRIP for infrared sensing applications.

The paper presents the application of non-modulation reflectance method for composition profiling of epitaxial AlxGa−xAs/GaAs structures. This non-destructive method is based on spectral measurements and theoretical reflectance spectrum matching. This is a very accurate and sensitive method of determining the Al composition in AlxGa1−xAs layers and structures with resolution down to 1 nm. In this work, the authors describe theoretic principles of this method and present experimental results of characterization of different AlGaAs structures to prove the potential of the worked out method.

The optical model of human joints synovial fluid is proposed. The statistic (statistic moments), correlation (autocorrelation function) and self-similar (Log-Log dependencies of power spectrum) structure of polarization two-dimensional distributions (polarization maps) of synovial fluid has been analyzed. It has been shown that differentiation of polarization maps of joint synovial fluid with different physiological state samples is expected of scale-discriminative analysis. To mark out of small-scale domain structure of synovial fluid polarization maps, the wavelet analysis has been used. The set of parameters, which characterize statistic, correlation and self-similar structure of wavelet coefficients’ distributions of different scales of polarization domains for diagnostics and differentiation of polycrystalline network transformation connected with the pathological processes, has been determined.

The photoluminescence (PL) of solar cells, based on Cu(In,Ga)Se2 and bare Cu(In,Ga)Se2 absorbers, has been studied. Shapes and intensity dependencies of the PL spectra in the junctions and in thin films are compared and discussed in terms of influence of the junction field. Measurements of the photoluminescence in the cells biased in the forward direction are employed in order to show straightforwardly how electric field changes the radiative recombination rate.

Increasing demand for growing high quality laser crystals puts a question about their most important parameters that one should concentrate on to get a desired product which will exhibit best properties in practical use. And by no means, this is a simple question. Apart of the usual lasing properties associated with a special dopant in the host material itself, one needs to consider another two lasing phenomena, namely second (SHG) and higher harmonic generation, and self-frequency doubling (SFD). Not necessarily all of these three can meet altogether in the same host material to yield in its best appearance in every case. We have made a review of basic properties of gadolinium oxoborate GdCa4O(BO3)3 (GdCOB) crystal and came to the conclusion that, currently, as a host material this is probably the best in all of its lasing applications. Although GdCOB has low thermal conductivity, which requires a suitable cooling, on the other hand it has got small thermo-optic coefficients which govern good operation in SHG and SFD experiments. Two inch dia. Nd-doped crystals were grown by the Czochralski technique. Since a large discrepancy in the literature exists on exact values of nonlinear coefficients, one is never sure about this whether theoretically predicted phase-matching angles (PMA) are those that are really optimal. Besides, none has yet measured the values of nonlinear coefficients as a function of doping concentration. Therefore we have not decided to cut numerous differently oriented samples for generation of different wavelengths in SHG and SFD, but rather tried to generate different wavelengths from the same samples. We have also not paid special attention to get highest possible conversion efficiencies. However, we have concentrated our attention on potential use of the core region in laser technique. Unlike in YAG crystals, when the core is by all means a parasitic structure, we discovered that the core region in GdCOB, that majority of investigators are even not aware of its presence in the crystal, can be also useful in laser technique. According to our best knowledge, a SHG of red light in this work is the second reported case in the world-wide literature.

We apply 8-band k.p model to study InAs/GaAs quantum dots (QDs). The strain was calculated using the valence force field (VFF) model which includes the four nearest-neighbour interactions. For the optical properties, we take into account both homogeneous and non-homogeneous broadening for the optical spectrum. Our simulation result is in good agreement with the experimental micro-photoluminescence (μ-PL) result which is from InAs/GaAs QD vertical cavity surface emitting lasers (VCSELs) structure wafer at room temperature. Accordingly, our simulation model is used to predict the QD emission from this QD-VCSELs structure wafer at different temperature ranging from 200–400 K. The simulation results show a decrease of 41 meV of QD ground state (GS) transition energy from 250–350 K. The changes of QDGS transition energy with different temperature indicate the possible detuning range for 1.3-μm wave band QD-VCSELs applications without temperature control. Furthermore, QD differential gain at 300 K is computed based on this model, which will be useful for predicting the intrinsic modulation characteristics of QD-VCSELs.

An important task for stereo vision is camera calibration, whose goal is to obtain the intrinsic and extrinsic parameters of each camera. This paper proposes a new accurate calibration method with multilevel process of camera parameters. In order to improve the calibration accuracy, a sub-pixel corner detection method is presented. We start with several views of a planar calibration to obtain some intrinsic camera parameters and to build an accurate model with lens distortion on a planar calibration target. Flexibly making use of geometry imaging theory, our algorithm obtains all the parameters through logical organization of solving order, accordingly avoids obtaining possible local optimized problem when solving the non-linear equation, gets over the relativity influence of every unknown parameters of traditional calibration way, and makes the error distributed among the constraint relation of parameters. Experiments with real images are carried out to verify the image correction effect and numerical robustness of our results. Compared with classical calibration techniques, that use expensive equipment and complicated mathematical computation, the proposed technique, which was verified by experiment, achieves high accuracy and reliable parameters.

The paper presents investigations concerning the design and realization of photonic structures with grating couplers. The first part of the paper deals with basic theoretical information on photonic structures with grating couplers and their application in optoelectronics. The further part presents the results of numerical investigations on photonic structures with grating couplers and shows the influence of geometrical parameters on the effectiveness of the input and output of optic power into and out of this photonic structure. The paper also provides the results of experimental investigations on a wideband gap semiconductor, viz. zinc oxide ZnO, as well as its application in planar waveguide structures and photonic structures with grating couplers.

The work presents the results of research on the systems formed from thin films of copper phthalocyanine (CuPc), N-N′-dimethylperylene-3,4,9,10-dicarboximide (MePTCDI), electrodes of ITO and Ag, and from buffer layers: MoO3 at ITO and BCP at Ag. We have observed the effect of each buffer layer on voltage dependence of dark current and photocurrent, and on open circuit voltage-light intensity relationship. The system with both buffer layers exhibited the highest values of open circuit voltage and fill factor. The buffer layers improve transport of charge carriers within near-electrode regions, reduce dissociation of excitons on electrodes and reveal processes of charge carrier generation and recombination within the CuPc/MePTCDI junction.

The work presents new way of extraction of charge carrier mobility from small signal spectra of admittance. It can be a useful method for thin organic layers in a sandwich arrangement. It is better than the version of small signal admittance currently applied for getting charge carrier mobility, since the final result is not charged with uncertainty of geometric capacitance and the upper limit of measurable charge carrier mobility is higher.

The optoelectronic method is one of the most promising concepts of biophysical program of the diagnostics of CIN and cervical cancer. Objectives of the work are evaluation of sensitivity and specificity of the optoelectronic method in the detection of CIN and cervical cancer. The paper shows correlation between the pNOR number and sensitivity/specificity of the optoelectronic method. The study included 293 patients with abnormal cervical cytology result and the following examinations: examination with the use of the optoelectronic method — Truscreen, colposcopic examination, and histopathologic biopsy. Specificity of the optoelectronic method for LGSIL was estimated at 65.70%, for HGSIL and squamous cell carcinoma of cervix amounted to 90.38%. Specificity of the optoelectronic method used to confirm lack of cervical pathology was estimated at 78.89%. The field under the ROC curve for the optoelectronic method was estimated at 0.88 (95% CI, 0.84–0.92) which shows high diagnostic value of the test in the detection of HGSIL and squamous cell carcinoma. The optoelectronic method is characterised by high usefulness in the detection of CIN, present in the squamous epithelium and squamous cell carcinoma of cervix.

A new concept of edge illuminated solar cells (EISC) based on silicon epitaxial technique has been proposed. In this kind of photovoltaic (PV) devices, sun-light illuminates directly a p-n junction through the edge of the structure which is perpendicular to junction surface. The main motivation of the presented work is preparation of a working model of an edge-illuminated silicon epitaxial solar cell sufficient to cooperation with a luminescent solar concentrator (LSC) consisted of a polymer foil doped with a luminescent material. The technological processes affecting the cell I–V characteristic and PV parameters are considered.

The paper describes comparison of laser generation of concentrated and SELG glasses developed at the General Physics Institute of Russian Academy of Sciences in Moscow and most recent EAT14 glass worked out by the CLaser Photonics Company in Shanghai. The laser generation was carried out using 976-nm pump wavelength in cw and quasi-cw regimes. Comparison of efficiencies and thresholds as well as of dissipative losses was made with a view to choose the best glass for “eye-safe” microchip laser range-finder. The generated wavelengths by each sample were measured.

Liquid crystal properties make them useful for the development of security devices in applications of authentication and detection of fakes. Induced orientation of liquid crystal molecules and birefringence are the two main properties used in security devices. Employing liquid crystal and dichroic colorants, we have developed devices that show, with the aid of a polarizer, multiple images on each side of the device. Rubbed polyimide is used as alignment layer on each substrate of the LC cell. By rubbing the polyimide in different directions in each substrate it is possible to create any kind of symbols, drawings or motifs with a greyscale; the more complex the created device is, the more difficult is to fake it. To identify the motifs it is necessary to use polarized light. Depending on whether the polarizer is located in front of the LC cell or behind it, different motifs from one or the other substrate are shown. The effect arises from the dopant colour dye added to the liquid crystal, the induced orientation and the twist structure. In practice, a grazing reflection on a dielectric surface is polarized enough to see the effect. Any LC flat panel display can obviously be used as backlight as well.