Proceedings Volume 8306

Photonics, Devices, and Systems V

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Proceedings Volume 8306

Photonics, Devices, and Systems V

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Volume Details

Date Published: 11 October 2011
Contents: 12 Sessions, 62 Papers, 0 Presentations
Conference: Photonics Prague 2011 2011
Volume Number: 8306

Table of Contents

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Table of Contents

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  • Front Matter: Volume 8306
  • Plenary Presentations
  • Lasers and Photodetectors in Industry, Imaging, and Sensors
  • Biophotonics
  • Design and Simulation of Photonic Devices
  • Diffractive Photonic Devices
  • Guided Wave Photonics
  • Organic Photonic Materials and Devices
  • Non-Linear Materials, Devices, and Applications
  • Nanophotonics + Nanooptics
  • Solid State Lighting + LED, LD, OLED, Solar Cells
  • Photonics: Education and Multimedia
Front Matter: Volume 8306
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Front Matter: Volume 8306
This PDF file contains the front matter associated with SPIE Proceedings Volume 8306, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Plenary Presentations
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Towards green high capacity optical networks
I. Glesk, M. N. Mohd Warip, S. K. Idris, et al.
The demand for fast, secure, energy efficient high capacity networks is growing. It is fuelled by transmission bandwidth needs which will support among other things the rapid penetration of multimedia applications empowering smart consumer electronics and E-businesses. All the above trigger unparallel needs for networking solutions which must offer not only high-speed low-cost "on demand" mobile connectivity but should be ecologically friendly and have low carbon footprint. The first answer to address the bandwidth needs was deployment of fibre optic technologies into transport networks. After this it became quickly obvious that the inferior electronic bandwidth (if compared to optical fiber) will further keep its upper hand on maximum implementable serial data rates. A new solution was found by introducing parallelism into data transport in the form of Wavelength Division Multiplexing (WDM) which has helped dramatically to improve aggregate throughput of optical networks. However with these advancements a new bottleneck has emerged at fibre endpoints where data routers must process the incoming and outgoing traffic. Here, even with the massive and power hungry electronic parallelism routers today (still relying upon bandwidth limiting electronics) do not offer needed processing speeds networks demands. In this paper we will discuss some novel unconventional approaches to address network scalability leading to energy savings via advance optical signal processing. We will also investigate energy savings based on advanced network management through nodes hibernation proposed for Optical IP networks. The hibernation reduces the network overall power consumption by forming virtual network reconfigurations through selective nodes groupings and by links segmentations and partitionings.
The physics in applications of ultrafast lasers
Dirk Wortmann, Martin Reininghaus, Johannes Finger, et al.
High precision and high throughput material processing using ultrashort pulsed laser radiation of high average power requires a detailed understanding of the laser matter interaction on ultrafast time scales. In this paper, we will focus on energy transport mechanisms based on the two-temperature-model and the resulting ablation regimes for single pulses. Heat accumulation at high pulse repetition rates and spatial pulse overlap will be discussed. Additional, a novel nonthermal ablation mechanism for graphite and corresponding materials will be presented.
Light: the physics of the photon
A unified description of the physics of the photon based on the transverse vector potential is presented. The description covers subjects from microscopic quantum electrodynamics (QED) to eikonal theory in curved space-time. The link between photon wave mechanics and QED is emphasized. Localized transverse single-photon states in direct space are introduced via a new mean position state in Hilbert space. It is shown that the related correlation matrix is proportional to the transverse subspace part of the Feynman photon propagator. It is argued that a transverse photon acquires an effective rest mass in its interaction with charged massive particles. Starting from the Lorenz gauge four-potential form of the Maxwell-Lorentz equations in General Relativity, the eikonal theory for transverse (unlocalized) light particles is discussed. Contact to the geodesic equation for light rays is made.
Lasers and Photodetectors in Industry, Imaging, and Sensors
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Preparation of spherical optical microresonators and their resonance spectra in air and gaseous acetone
Vlastimil Matějec, Filip Todorov, Michal Jelínek, et al.
This paper deals with the preparation of spherical silica whispering-gallery-mode (WGM) microresonators and with their resonance spectra measured in air and in acetone vapors. Spherical microresonators with a diameter ranging from 320 to 360 micrometers have been prepared by heating the tip of a silica fiber by a hydrogen-oxygen burner. Details of this preparation are shown on spherical and spheroidal microresonators. The prepared microspheres were excited by a fiber taper and their resonance spectra were measured and Q factors estimated. Changes in the resonance spectra of the microspheres due to their contact with acetone vapor heated to 55 °C or with liquid acetone have been observed. These changes are explained by interaction of acetone with silica and by temperature changes of the microspheres.
A discussion of sources of error in laser-speckle based systems
Bernhard G. Zagar, Johannes Lettner
Applying laser-speckle techniques in the material sciences as well as in methods to characterize surface conditions of specimen has become the method of choice especially if a non-contacting principle is sought. This is almost always the case for specimen that are small in at least one dimension as for example in the material testing of foils, fibres or micromaterials and certainly also if elevated test-temperatures are preventing standard gauges. In this paper some widely overlooked sources of errors that - if unavoidable - increase measurement uncertainty beyond the theoretical limit attainable are discussed and the magnitude of their influence is detailed. In particular the following effects are considered: The laser-source wavelength stability as well as its pointing stability, the effects caused by so-called schlieren occuring along the optical path as well as temperature effects causing changes in the systems geometry, thermally influencing the optical parameters of the imaging optics as well as the often overlooked and in most illumination systems unknown radius of curvature of the laser wavefronts used to illuminate the specimen. Small though as these influences seem, they might contribute significant uncertainties especially in material testing applications where the strain ε = ▵l/l is to be determined out of consecutive measurements of usually small changes in overall length l of the specimens geometry parameter. Typical values of ε are bounded by ±2000 ppm (the typical range of Hooke's law for steel). So values of ▵l on the order of tenth of micrometers for typical gauge lenghts around 50 mm yield ppm resolutions for ε. Analyzing the above mentioned error sources one can quickly see that all of them, if not taken care of appropriately, carry the potential to cause significantly larger deviations than the resolution sought after demands.
Position measurement in standing wave interferometer for metrology of length
We present techniques oriented to improvement of precision in incremental interferometric measurements of displacements over a limited displacement range. The wavelength of the coherent laser source is here directly stabilized to a mechanical reference and not to a reference of any optical frequency. This may represent a reduction of uncertainty linking the laser wavelength not to indirectly evaluated refractive index but to the setup mechanics which cannot be completely eliminated. Here we suggest an approach where the traditional interferometers are replaced by a passive Fabry-Perot cavity with position sensing using an intracavity transparent photodetector.
Preparation and characterization of highly thulium- and alumina-doped optical fibers for single-frequency fiber lasers
Pavel Honzatko, Anirban Dhar, Ivan Kasik, et al.
Thulium-doped fibers suitable for core-pumped single-frequency lasers were fabricated by the modified chemical vapor deposition (MCVD) method. Refractive index profile, doping profile and spectral absorption was measured. High doping concentration of thulium ions should be achieved to allow for high absorption of light at a pump wavelength while the thulium ions clustering should be avoided to prevent the cooperative upconversion and quenching processes. The fabricated fibers featured pump absorption up to 70dB/m at a pump wavelength of 1611nm. The single-frequency master oscillator with a resonator composed of a pair of fiber Bragg gratings and a thulium-doped fiber was demonstrated with predominantly single ended operation. We achieved a slope efficiency of 22\% and a threshold of 22mW at a lasing wavelength of 1944nm.
Optical loop memory based on controlling the lasing of optical fiber loop amplifiers using a wavelength-tunable add/drop filter
We demonstrated that the wavelength range of lasing generated in optical loop amplifiers can be controlled by varying the reflection wavelength range of an add/drop filter. Controlling the lasing wavelength range enabled the gain to be precisely controlled relative to the input wavelength. The ring-down pulse waveform exhibits similar behavior to an optical memory when the lasing region is close to the input wavelength and it is exponentially attenuated when the region is far from the input. When the optical loop memory effect is optimized, a 200 ns optical pulse can be retained in the memory for 20 μs.
Measurement of vibrations at different sections of rail through fiber optic sensors
A. Barreda, T. Molina-Jiménez, E. Valero, et al.
This paper presents the results of an investigation about how the vibration of railway vehicles affects nearby buildings. The overall objective is to study the vibration generated in urban environments by tram, train and subway, its transmission to the ground and how the buildings and constructions of the environment receive them.
Silicon micro sensors as integrated readout platform for colorimetric and fluorescence based opto-chemical transducers
Matthias Will, Tomas Martan, Olaf Brodersen
Opto-chemical transducer almost offers unlimited possibilities for detection of physical quantities. New technologies and research show a steady increasing of publications in the area of sensoric principles. For transfer to real world applications the optical response has to be converted into an electrical signal. An exceptional opto chemical transducer loses the attraction if complex and expensive instruments for analysis are requires. Therefore, the readout system must be very compact and producible for low cost. In this presentation, the technology platform as a solution for these problems will be presented. We combine micro structuring of silicon, photodiode fabrication, chip in chip mounting and novel assembly technologies for creation of a flexible sensor platform. This flexible combination of technologies allows fabricating a family of planar optical remission sensors. With variation of design and modifications, we are able to detect colorimetric, fluorescent properties of an sensitive layer attached on the sensor surface. In our sensor with typical size of 6mm x 6mm x 1mm different emitting sources based on LED's or laser diodes, multiple detection cannels for the remitted light and also measurement of temperature are included. Based on these sensors we proof the concept by demonstrating sensors for oxygen, carbon dioxide and ammonia based on colorimetric and fluorescent changes in the transducer layer. In both configurations, LED's irradiated the sensitive polymer layer through a transparent substrate. The absorption or fluorescence properties of dyed polymer are changed by the chemical reaction and light response is detected by PIN diodes. The signal shift is analyzed by using a computer controlled evaluation board of own construction. Accuracy and reliability of the remission sensor system were verified and the whole sensor system was experimentally tested in the range of concentrations from 50 ppm up to 100 000 ppm for CO2 and O2 Furthermore, we develop concepts to use the sensor also for interferometric detection of layer properties and the combination with capacitive structures on the surface. This allows detecting of thickness or refractive index variation of layers in future.
Deformation measurement along two directions of a continuously deforming object by using two lasers and one color camera
In order to extract accurate phase changes due to deformation, the phase-shifting methods have been extensively investigated and applied to many practical measurements because of its simplicity and high resolution. But it requires that several specklegrams be captured in the static, non-deforming, condition of an object, making it unsuitable for measuring continuously deforming objects. Then we developed the method which does not require specklegram in static condition and can measure a large continuous-deformation with high accuracy. But this method was applied to deformation measurement of only one direction. We have improved this method and have obtained the new method which can measure deformation along two directions by using two lasers and one color camera. In addition, the method has potential to measure deformation along three directions: two in-planes and one out-of-plane.
Performance evaluation of fast, high precision laser rangefinder electronics with a pulsed laser
David Vyhlídal, Michal Jelínek, Miroslav Čech, et al.
A laser rangefinder system based on a pulsed time of flight distance measurement technique was constructed and tested. The system is composed of a receiver channel connected to a leading edge timing discriminator and time interval measurement electronics. The receiver channel consists of a wide bandwidth InGaAs photodiode with a typical rise time of 35 ps. A timing discriminator has 8 GHz equivalent input rise time bandwidth and a programmable threshold. It is capable of processing electrical pulses as short as 80 ps and is constructed using commercially available components. The time interval measurement electronics is highly programmable system. The measurement method is based on an interpolation principle where the time interval is roughly digitized by a coarse counter driven by a high stability reference clocks and the fractions between the clock periods are measured by two time-to-digital converter chips. The system has two reference clock inputs and two independent channels for measuring start and stop events. Only one 40 MHz reference is required for the measurement. The system can achieve a timing resolution better than 15 ps rms with up to 90 kHz repetition rate. The measurement range is from 0 ps up to 1 second. The performance of the system was evaluated at short distances with a pulsed laboratory constructed laser. It is a mode-locked Nd:YAG laser generating 20 ps output pulses at the wavelength of 1064 nm with a repetition rate up to 100 Hz. The system is capable of measuring distances down to 0 m. The overall measurement accuracy is estimated to be 5 mm and will be verified by the experiment.
Light source for low-coherence interferometry combining LED and single mode optical fiber
This paper describes a pilot experiment of optimization of a white-light source for a low-coherence interferometry. The white-light source combines the light beams generated with colour LEDs. By modelling of the white light spectra, a contrast of a white light interference fringe could be changed and set to the maximal value. Hereafter, a concept of the light source for the low-coherence interferometry based on high-luminescent LED and single mode optical fibres is presented.The design comes out form a requirement to have an output beam combining a white-light beam and a laser beam. In the case of coaxial white-light and laser beam, the white-light interferometer is precisely combined with an incremental laser interferometer. This combination allows doing online surface diagnostics with high precision. The optimized white light source is designed to be a crucial part of an experimental setup for the surface diagnostics and automatic calibration of gauge blocks.
Stabilization of DFB laser diodes with 760nm and 1541nm wavelength
The linewidth of the emission spectrum and the mode-hop free tuning range of the wavelength are crucial parameters for laser sources in laser interferometry, especially absolute laser interferometry. At present time the DFB laser diodes are the most suitable laser sources from semiconductor laser sources for using in laser interferometry. We present our set-up of the optical fiber based laser interferometer where these laser diodes can be used. The measurement probe is realized by standard optical fiber with reflection coated fiber optical connector. First we used VCSEL laser diode to measurement with our fiber interferometer. The frequency linewidth, the mode hop free tuning range and the optical power is not sufficient for practical measurement outside of laboratory. The DFB laser diode has narrower frequency linewidth, wider mode hop free tuning range and more optical power. In addition to the opposite of VCSEL laser diodes are available in the package with optical fiber at the output and the DFB laser diodes with 1541 nm wavelength has optical isolator inside package. One of the main problems in using of the DFB laser diodes with 760 nm wavelength is a back reflection from the fiber connections at the output. We present our experience with adaptation of both types of the DFB laser diodes to laser interferometer and methods to decrease back reflections from the connections of optical fibers. We used stabilization by frequency lock to F-P (Fabry - Perot) resonator for VCSEL laser diode. The absorption in Krypton and Acetylen (760 nm, 1542 nm, 1552 nm) is used for the frequency stabilization of the DFB laser diodes. We present comparison of our first measurement with frequency stabilization of these laser diodes with 760 nm and 1541 nm wavelength using absorption in Acetylene and Krypton and adaptation of these diodes to our laser interferometer.
Diamond Raman laser in eye safe region
Helena Jelinková, Ondřej Kitzler, Michal Jelínek, et al.
The goal of this work was the external cavity CVD diamond Raman laser generating at wavelength of 1.63 μm which belongs to an eye safe region. As the Raman medium a sample of CVD grown single diamond crystal was used. The crystal was grown in the [100] direction and after cutting, the sample sides were formed by {110} planes. The diamond crystal sample dimensions were 5 mm × 5 mm × 2 mm and it had no anti-reflection coatings. As a pumping radiation source the compact Q-switched Nd:YAP laser operating at the wavelength 1.34 μm was used. The pulse duration was 12 ns. This pumping radiation was focused by the lens (f = 250 mm) perpendicularly on the diamond crystal face. The beam radius inside the crystal was 180 μm. The 15 mm long Raman laser resonator was formed by a pumping mirror (HR @ 1.63 μm and T = 97 % @ 1.34 μm) and an output coupler (R = 95 % @ 1.63 μm, r = 500 mm). The maximum generated laser output energy was 18 μJ @ 1.63 μm for the pumping energy of 3.35 mJ corresponding to the conversion efficiency of 0.5 %. The output spatial beam profile corresponds to the fundamental Gaussian beam in both axes.
Biophotonics
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Laser evaporation of models of normal and tumoral biological tissues
V. A. Ulyanov, A. K. Dmitriev, A. N. Konovalov, et al.
For study of the dynamics of laser evaporation of model normal and tumoral biotissues the method autodyne detection (self-mixing on laser resonator) of back scattered light from the irradiated zone was used. Biomodels of tumors using of laboratory animals and gelatin models were used. These biomaterials were irradiated by focused beam of CO2 laser 5-10 Watts power with concurrent recording autodyne signal. The level of autodyne signal at laser cutting of multi-layer gelatinous models varies from 1.5 to 3 times at difference of water content in layers from 10 to 30% respectively. The level of autodyne signal as the average power spectrum of this signal varies in different degrees depending on the type of normal and tumoral biotissues at its laser evaporation.
Metamaterial resonator arrays for organic and inorganic compound sensing
In this paper, an electromagnetic metamaterial resonator operating in the terahertz frequency range is presented. By arranging the resonator in a planar array, it is possible to use the structure as a sensing device for organic and inorganic compounds. The sensor is designed to detect the presence of a biological compound by permittivity or absorption measurements. The presence of the biological matter modifies the effective permittivity and, thus, the resonant frequency significantly varies. In addition, biological compounds typically exhibit absorption characteristics that depend on the corresponding molecular structure. Therefore, it is necessary to illuminate the material selectively. We show that by employing the "selective" properties of the metamaterial resonator proposed, it is possible to enhance the sensing performances. The proposed design is suitable to sense the presence of healthy and malignant tissues, with possible applications in food and medical diagnostics. The operation of the sensing device has been demonstrated through proper full-wave simulations.
Detecting positive surgical margins of prostate tissues using elastic light single-scattering spectroscopy
Murat Canpolat, Tuba Denkçeken, İbrahim Başsorgun, et al.
Elastic light single-scattering spectroscopy (ELSSS) system with a single optical fiber probe was employed to differentiate cancerous prostate tissue from non-cancerous prostate tissue ex-vivo just after radical prostatectomy. First, ELSSS spectra were acquired from cancerous prostate tissue to define its spectral features. Then, spectra were acquired from surgical margins of excised prostate tissue to detect positive surgical margins based on the spectral features of the spectra taken from cancerous prostate tissues. Of the total 128 tissue samples were evaluated from 18 patients by ELSSS system. Comparing of histopathology results and ELSSS measurements revealed that sign of the spectral slopes of cancerous prostate tissue is negative and non-cancerous tissue is positive in the wavelength range from 450 to 750 nm. Sign of the spectral slopes were used as a discrimination parameter between cancerous and non-cancerous prostate tissues. Based on the correlation between histopathology results and sign of the spectral slopes, ELSSS system differentiates cancerous prostate tissue from non-cancerous with a sensitivity of 0.97 and a specificity of 0.87.
Photosensitizer fluorescence emission during photodynamic therapy applied to dermatological diseases
I. Salas-García, F. Fanjul-Vélez, N. Ortega-Quijano, et al.
We present a first approach to predict the photosensitizer fluorescence dependence with depth during the Photodynamic Therapy applied to a skin disease commonly treated in the dermatological clinical practice. The obtained results permit us to know the photosensitizer temporal fluorescence evolution in different points of the tumor sample during the photochemical reactions involved in PDT with a predictive purpose related to the treatment evolution. The model presented also takes into account the distribution of a topical photosensitizer, the propagation of light in a biological media and the subsequent photochemical interactions between light and tissue. This implies that different parameters related with the photosensitizer distribution or the optical source characteristics could be adjusted to provide a specific treatment to a particular pathology.
Raman microspectroscopy of algal lipid bodies: β-carotene as a volume sensor
Zdenek Pilát, Silvie Bernatová, Jan Ježek, et al.
Advanced optical instruments are useful for analysis and manipulation of individual living cells and their internal structures. We have employed Raman microspectroscopic analysis for assessment of algal lipid body (LB) volume in vivo. Some algae contain β-carotene in high amounts in their LBs, including strains which are considered useful in biotechnology for lipid and pigment production. We have detected proportionality between the Raman vibrations of β-carotene and the LB volume. This finding may allow fast acquisition of LB volume approximation valuable e.g. for Raman microspectroscopy assisted cell sorting. We combine optical manipulation and analysis on a microfluidic platform in order to achieve fast, effective, and non-invasive sorting based on spectroscopic features of the individual living cells. The resultant apparatus could find its use in demanding biotechnological applications such as selection of rare natural mutants or artificially modified cells resulting from genetic manipulations.
Accommodation and vergence infrared measurement using hologram stimulus
T. Jindra, J. Dušek, M. Dostálek, et al.
Diagnostics of the visual system disorders belongs to the common examination in infancy. Especially important is diagnostics of refractive and oculomotor disorders that could negatively affect development of the infants' visual system and rapidly decrease quality of life. This work describes application of hologram stimulation and infrared videometrics in measuring of the dynamics of the human accommodation and vergence. Virtual hologram stimulation rapidly decreases diameters of the system and allows its compact construction. Data about dynamic changes of accommodation and vergence were not yet available so far in the clinical practice. This data could be helpful tool for early diagnostics of the visual system disorders as the strabismus.
THz spectroscopy and molecular modeling of bovine serum albumin under various hydration conditions
Maria Mernea, Octavian Calborean, Livia Petrescu, et al.
Bovine serum albumin (BSA) is the most abundant protein in bovine plasma; its three dimensional structure is yet unknown. We investigated the structure and dynamics of BSA in lyophilized samples, in 10% w/w and 50% w/w BSA aqueous solutions using THz spectroscopy and molecular modeling. THz spectra were recorded with a spectral resolution of 7.4 GHz. Theoretical spectra were simulated using a structural model of BSA based on the homology with the known structure of human serum albumin (HSA). The agreement between simulated THz spectra and THz spectra recorded experimentally allowed us to validate the BSA model and the solution models. Based on these models we investigated the flexibility of dry BSA and of BSA with one hydration layer. The hydrated structure of BSA is less flexible than the structure free of water molecules, except for residues 54 - 104 that are more mobile in the hydrated structure. We also investigated the fluctuations of the water molecules within the first hydration layer and identified two groups of water molecules: one that exhibits small fluctuations and one of highly mobile water molecules. These molecules are associated to highly mobile regions from the proteins and move in positive correlation with the neighboring protein regions. We also propose a BSA dimerization model in which the molecules strongly interact. The fluctuations of the BSA monomers and of their first hydration layer were investigated. The two molecules display similar fluctuation patterns, but one of them is slightly more flexible.
Polarization of scattered light in biological tissue
Hamed Mohamed Abubaker, Pavel Tománek
The real-time nondestructive inspection of biological tissues begins to be one of important tools which could contribute to better human life not only in medical diagnosis but also in everyday mankind activities. A biological tissue is considered as a turbid medium in which light is scattered. Although single or multiple scattering in tissue multiple randomizes polarization states of incident light, linear, circular and elliptical polarization states in the medium are considered, and there are circumstances when appreciable degree of polarization can be observed in diffusive scattering. Our work shows that with a sufficient degree of sensitivity is possible to detect structural changes due to the aging of processed meat by using Mueller matrix polarimeter. Moreover, it demonstrated that the degree of polarization of the backscattered light is sensitive to the optical properties of specimen material and to its thickness.
Design and Simulation of Photonic Devices
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The cavity resonator design: stochastic optimization of the transmission line method
Stanislav Jurečka, Jarmila Müllerová, Milan Dado
Stable cavity resonators provide an ideal solution for high quality applications in telecommunications, laser sources, sensors, oscillators and filters, instrumentation and other large area of applications. For the determination of the electromagnetic field (EMF) properties in a cavity resonator several numerical methods are widely used. In our approach we used the transmission line modeling method (TLM). It is a wide-band time-domain numerical method suitable for solution of the electromagnetic field in a studied region. TLM method is based on the isomorphism between the theory of passive electrical network and the wave equation describing the properties of the EMF. TLM method offers two important advantages over the time-domain techniques such as the finite-difference time domain methods. The electric and magnetic field are resolved synchronously in time and space and TLM in implicitly stable method due to the mapping to electrical circuits. The EMF in the rectangular cavity is in our approach determined by the TLM method and the frequency spectrum is computed by the Fourier transform of the time signal. The theoretical model of the cavity EMF power spectral density function contains information about the geometrical configuration of the resonator. In our work we use the genetic algorithm for the determination of optimal dimensions of the cavity resonator expected for the proposed output resonant frequency. The stochastic modification of the theoretical model parameters is controlled by the genetic operators of mutation, crossover and selection, leading to overall improvement of the theoretical model estimation during the optimization process.
Preparation and characterization of bottle optical microresonators with circular and hexagonal cross-sections
Whispering-Gallery-Mode (WGM) optical microresonators have attracted growing attention because of their big potential for chemical and biological sensing. Recently, optical bottle microresonators have been fabricated from short sections of optical fibers. These double-neck bottle-shaped microresonators have some features distinguishing them from spherical microresonators. They support non-degenerate whispering-gallery modes that exhibit two well-separated spatial regions with enhanced field strength. The free spectral range (FSR) of such microresonators is about one order of magnitude smaller than that of microsphere resonators of equal diameters. It means that these microresonators have much longer optical path-lengths and can be employed for highly sensitive detection. The paper deals with the preparation and characterization of bottle optical microresonators fabricated from silica optical fibers. A simple 2D numerical modelling has been used to investigate basic spectral characteristics of microresonators with hexagonal cross-sections. Cylindrical bottle microresonators are prepared from optical fiber Corning SMF-28, while microresonators with hexagonal cross-section are prepared from an experimental hexagonal silica fiber. This novel type of bottle microresonators is expected to have much simpler mode structure than cylindrical bottle microresonators. There are compared two methods for the preparation of bottle microresonators in this paper. The first method is based on a combination of controlled local heating and tapering the fiber by the use of carbon dioxide laser Coherent GEM SELECT 50. The second method is based on weak tapering of the silica optical fiber with glass processing unit Vytran GPX-3400.
Light polarization state analyzer based on two spatial carrier frequencies method
Sławomir Drobczyński, Władysław A. Woźniak, Piotr Kurzynowski
The device for the measurements of light polarization state parameters distributions has been presented. It consists of two Wollaston like prisms (acting as spatial frequency generators), a linear analyzer, a CCD camera and a computer with the specific software. The 2D Fourier transform of the recorded output intensity distribution contains two nonzero carrier frequencies. The areas around these frequencies carry the information about the azimuth and the ellipticity angles distributions of the examined light assuming that the variations of these parameters are with the frequency much lower than the analyzer's carrier frequencies. Applying the Fourier transform methods of masking, shifting and inverse Fourier transform with regard to these two areas, one can receive the wanted light polarization state distributions. The main merits of this technique are: (1) the reconstruction of the polarization parameters distributions from one recorded output image only, (2) the setup's compactness and no movable or electronically driven components. The paper presents the setup details, critical points of adjusting setup procedure and numerical analysis, as well as the theoretical and experimental results for uniform and non-uniform examined waves. The accuracy of the tests was estimated as λ/100.
Application of infrared ATR ellipsometry for measurement of solid samples: calibration procedure
Zuzana Mrázková, David Hrabovský, Kamil Postava, et al.
Attenuated total reflection (ATR) is widely used in infrared spectral range for measurement of surface properties of solid samples, powders, and liquids. In this paper we use a commercial Fourier-transform infrared (FTIR) spectrometer Vertex 70v from Bruker company equipped with the ATR Golden Gate accessory from Specac. To increase sensitivity of the method we included infrared polarizer and analyzer, which enable measurement of the reflected amplitudes ratio and the phase differences between p- and s-polarizations in the frame of the ATR ellipsometry. Procedure of ellipsometric angles measurement is proposed using data acquisition at several azimuthal angles of polarizers. Spectral dependence of real polarizer extinction ratio, partial polarization of beam coming from the interferometer and polarization sensitivity of infrared detector are presented.
WDM hybrid microoptical transceiver with Bragg volume grating
Vitezslav Jeřábek, Julio Armas, David Mareš, et al.
This paper presents the design results, simulation and construction of WDM wavelength division multiplexer-bidirectional transceiver module (WDM-Transceiver) for the passive optical network (PON) of a fiber to the home FTTH topology. WDM transceiver uses a microoptics hybrid integration technology with volume holographic Bragg grating triplex filter (VHGT) and a collimation lenses for wavelength multiplexing/ demultiplexing.
Multimode fiber-based transmitter for free space optical communications
Félix Fanjul-Vélez, Otakar Wilfert, Martin Hampl, et al.
The importance of free space optical links is increasing. The influence of the atmosphere on the optical beam is one of the most relevant issues to be considered for the quality of the link. In this work we deal with optical wave distribution in a multimode fiber, which can be applied as a primary optical beam source in a transmitter for a free space optical link. The utilization of the fiber instead of a laser diode as the primary source of the optical beam presents certain advantages, the beam spot is circularly symmetrical and can be made optimal by a particular excitation of the fiber, and the head of the link can be based on a completely photonic concept. The optical intensity distribution and the complex degree of coherence at the end of the fiber are modeled. The results show that the optimal beam shape can be obtained in the transmitting fiber.
Diffractive Photonic Devices
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Synthesis of diffractive structures
Libor Kotacka, Petr Vizdal, Tomas Behounek
Our paper deals with advanced approaches exploiting electron-beam lithography origination technologies in order to produce the so-called DOVIDs offering new visual features, though based on subwavelength origination. Synthesized security elements are recorded with a resolution reaching even 2,500.000 dpi and are specially developed for the security measures of the most important state valuable documents. We shall mention some principal features, where the ultra-precise recording of diffractive elements is requested.
Optoelectronic systems with delayed acousto-optic feedback
Vladimir I. Balakshy, Yury I. Kuznetsov
The paper represents a brief overview on theoretical and experimental investigations of feedback acousto-optic systems carried out in Moscow State University in recent years. These systems are of great interest by reason of their complicated and intriguing behavior as well as in view of new applications in optical information processing. Various regimes of operation of acousto-optic systems with amplitude and frequency feedback are analyzed. The application of these systems for optical beam intensity and direction stabilization are considered. An original scheme of acousto-optic generator based on the effect of optical heterodyning is proposed and examined theoretically and experimentally.
Designing of binary diffractive optical elements for beams performing
At present, the progress in optics is associated with wide use of diffractive optical elements (DOEs). In this paper we present a DOE design method, which not use computer iterative methods. Starting from the knowledge of the expression of the propagated field on image plane, we use simple formulas to obtain the entire information necessary to characterize the desired DOE. The DOE designed with the proposed method can equate an arbitrary complex amplitude transmission T(r) and has higher imaging accuracy than other DOEs. Even if it is possible studying any level combination, the aim of this paper is to summarize the results of simulation experiments which were carried out only to test the binary level diffractive optical elements (DOEs).
Guided Wave Photonics
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Comparison of 2D and 3D Fourier modal methods for modeling subwavelength-structured silicon waveguides
Frequency-domain Fourier modal methods have recently evolved into efficient tools for rigorous numerical modeling of a wide class of photonic and plasmonic structures and devices. In this contribution we describe the application of our 2D and 3D in-house tools, namely aperiodic rigorous coupled wave analysis (aRCWA) and bi-directional mode expansion propagation method using harmonic expansion (BEXX), on a recently described novel type of subwavelength grating (SWG) waveguides. They are created by means of periodically interlacing silicon segments with a superstrate material with a lower refractive index. It has been shown recently, both theoretically and experimentally, that for a suitable choice of SWG parameters such as grating period and duty cycle, the structure can support low-loss guided (Bloch) mode. Its effective index, mode profile and dispersion characteristics can thus be tailored to specific needs without the necessity of changing material composition. In our methods, either complex coordinate transformation or uniaxial anisotropic perfectly matched layers have been applied as efficient absorption boundary conditions. In order to reduce the number of expansion terms needed to reach required accuracy, the adaptive spatial resolution technique has been implemented. Structural symmetries of the devices can be fully utilized to this aim, too. Propagation constants of Bloch modes are also compared with those obtained with a full-vector film mode matching (FiMM) mode solver using the very simple effective medium theory (EMT).
Broadband dispersion compensating photonic crystal fiber
Michal Lucki, Richard Zeleny
Presented work is a study of dispersion properties of photonic crystal fibers. The main objective is to design photonic crystal fibers suitable for potential compensation of group velocity dispersion of optical signals. New fiber structures are proposed, for example, a flattened-dispersion compensating photonic crystal fiber for broadband utilization in high-speed transmission systems is presented. The structure shows flattened negative value of dispersion over the O, C, and L bands. The fiber can eventually get applied in broadband optical signal recovery in systems with wavelength division multiplexing. Last but not least, a dual-core compensating microstructured fiber is optimized in order to achieve low dispersion and low loss at the C-band. Results presented in this work are obtained by using the FDFD method.
Dynamical properties of a coupled nonlinear dielectric waveguide - surface-plasmon system as another type of Josephson junction
We demonstrate that a weakly-coupled nonlinear dielectric waveguide surface-plasmon (DWSP-JJ) system can be formulated in analogy to bosonic Josephson junction of atomic condensates at very low temperatures, yet it exhibits different dynamical features. Such a system can be realized along a metal - dielectric interface where the dielectric medium hosts a nonlinear waveguide (e.g. fiber) for soliton propagation. The inherently dynamic coupling parameter generates novel features in the phase space.
Study of thin films of LiNbO3 using FTIR and Raman spectroscopy
Marketa Zezulová, Miroslav Jelínek, Vladimír Železný, et al.
Lithium niobate (LiNbO3) is a material which can be used in many applications. LiNbO3 thin films were studied for the development of doped planar waveguides using Pulsed Laser Deposition (PLD) method from two targets. The films were deposited by PLD on SiO2/Si and (0001) sapphire substrates at temperatures 650°C, 700°C, 750°C, from one crystalline and two sintered LiNbO3 targets using KrF excimer laser. The film thickness was ~680 nanometers. Two techniques - Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy - are used to characterize the dependence of the deposited thin films on the deposition conditions. These methods characterize the materials by monitoring their phonons whose spectra are sensitive to film deposition parameters. Bulk LiNbO3 has rhombohedral crystal structure with two chemical units per primitive cell, it means, that 30 degrees of freedom are distributed between A1 and E irreducible representations. The precise assignment of phonon modes, however, has not been unambiguously established. So, we use the spectra for qualitative comparison of the conditions of deposition. The spectra on SiO2/Si substrates of the same temperatures are essentially the same, indicating good reproducibility of the deposition process, but the spectra are shifted in case of different targets. The spectra of the samples deposited from the powder target or magnetron target are shifted to lower wavenumbers. This implies that different targets have an impact on the film growth. The deposition temperature also influences the spectra. The same is valid for films prepared on (0001) sapphire substrates. The bands shift with increasing temperature.
Modeling of a fiber-optic sensor based on surface plasmon resonance including the dispersion of the analyte
Dalibor Ciprian, Petr Hlubina
A model of surface plasmon resonance fiber-optic sensor based on the theory of attenuated total internal reflection is presented. Because of the mathematical complications related to rigorous theory of cylindrical optical waveguides, the analysis is carried out in frame of optics of multilayered media. The sensing scheme uses a wavelength interrogation method and the calculations are performed over a broad spectral range. The influence of the dispersion of the analyte on the sensor performance is considered and discussed. Model computations are performed for two mostly used types of excitation conditions. In the first case, the usage of a focused beam from the collimated light source is considered. The second case is related to the excitation of the fiber by a diffusive source. According to the excitation conditions, the contribution of meridional rays, or skew and meridional rays has to be taken into account. The calculation of optical power transmitted through the multimode sensing fiber is carried out. The effects of the layered structure thicknesses on surface plasmon resonance as well as the influence of the parameters describing the considered fiber are discussed. The influence of the analyte dispersion on the sensitivity, detection accuracy and signal to noise ratio is discussed.
Organic Photonic Materials and Devices
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High performance low refractive index materials for photonics I: preliminary characterization
Anna B. Wojcik, Łukasz John, Sławomir Szafert
The series of inorganic-organic hybrid materials were prepared from silane precursors by the sol-gel process. The resulted perfluorinated organosilicate liquid oligomers were applied on glass substrates and cured by heat yielding hard, clear and well adhering films. The films porosity, water contact angle, refractive index, and absorption in UV-Vis and IR were measured to characterize optical and physicochemical properties of the prepared films. The perfluorinated organosilicate films exhibited excellent optical transparency, low refractive indices, low porosity as well as non-wetting, hydrophobic behavior.
Investigation of nonlinear chalcogenide fiber Bragg gratings as a promising tool for all-optical switching
Eliška Jurisová, Jarmila Müllerová, Marcela Koščová
The theoretical analysis is presented to search for the nonlinear phenomenon of the optical bistability in the fiber Bragg gratings (FBGs).We investigate the continuous wave nonlinear transmission characteristics of chalcogenide FBGs where chalcogenide glass is based on the chalcogen element Te. Simulations based on the nonlinear coupled mode theory considering forward and backward light waves are used to search numerically for the relationships between the input light fields and the transmissivity of FBGs. Material properties of photosensitive chalcogenide glasses, grating parameters, such as grating length and index modulation of grating on the transmission characteristics and the impact of the change of the Bragg wavelength are studied.
Novel ene-yne compounds as quadratic nonlinear optical materials
Daniel Lumpi, Ernst Horkel, Berthold Stoeger, et al.
We present a reliable strategy towards title compounds as a novel scaffold for highly nonlinear optical chromophores, using the selective ring fragmentation of thiophenes as a key step. This methodology selectively leads to the Z-isomer of ene-yne substrates, which are subsequently modified by a Huisgen-type cycloaddition yielding the target compounds. To prove the reliability of the developed synthetic route, one target compound was successfully prepared. This material crystallizes in an enantiomorphic space group, despite of being a flexible non-chiral molecule. A detailed discussion regarding the synthetic approach towards title compounds, a determination of material characteristics, including the investigation of the second order nonlinear susceptibility as well as a systematic variation of substituents in order to examine the resulting effects on NLO properties are subject of this presentation.
Non-Linear Materials, Devices, and Applications
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Dual pulse operation of 1.5 um picosecond intracavity synchronously pumped optical parametric oscillator
Alena Zavadilová, Václav Kubeček, Jean-Claude Diels, et al.
Singly resonant optical parametric oscillators (OPO) are most promising approach to sensors in which two pulses circulate independently in a cavity. The OPO should be pumped intracavity, not only to access the high intracavity power of the pump laser, but also because the two signal pulses share the same mode. The first synchronously pumped OPO were pumped intracavity by a mode-locked dye laser. Subsequent implementation with solid-state pump lasers has been plagued by a tendency to Q-switching, as well as competition between the two pulses generated in the signal cavity. In this contribution we report the improved and optimized experimental setup of an intracavity synchronously pumped OPO based on a periodically poled LiNbO3 crystal (PPLN) and of the pumping resonator of passively mode locked Nd:YVO4 laser from the point of view of achievability of stable mode-locking and compensation of the astigmatism caused by Brewster angle cut PPLN. This resulted in higher conversion efficiency due to the good overlap of pump and signal beam.
Peculiarities of As-S glass structure doped with ytterbium
Alexandr P. Paiuk, Alexander V. Stronski, Miroslav Vlček, et al.
Chalcogenide glasses As2S3 doped with ytterbium were investigated by Raman spectroscopy in order study the structural changes accompanying the incorporation of impurity metal ions in the host glass structure. Doping of As2S3 glasses with small amount of Yb ions, up to 1 % wt., only slightly affect the short-range order structure of the host matrix. For Yb concentration more than 1 % wt. the sharp increase of presence of the additional bands characteristic for the vibrations non-stoichiometric molecular fragments which contain homopolar S-S and As-As bonds was observed. Such changes correlate with data on the thermal properties of such glasses where Tg values were sharply decreased if Yb concentration was more than 1 % wt. No additional bands besides characteristic for As2S3 stoichiometric and non-stoichiometric structural units were found. The main observed effect under the introduction of ytterbium into As2S3 is the change of relative concentration of the main and non-stoichiometric structural units characteristic for As2S3 glasses.
Influence of deposition conditions of ZnO thin films on their photonic properties
Marie Netrvalová, Lucie Prušáková, Petr Novák, et al.
The effects of deposition conditions (especially lateral position against target during deposition and deposition temperature) on optical properties and structure are presented. The X-ray diffraction (XRD) analysis showed that all the films were polycrystalline with hexagonal structure and preferred orientation in [001] direction perpendicular to the substrate surface. Micro-structure properties as crystallite size and micro-strains were not too influenced by deposition conditions and values of crystallites were evaluated in tens of nanometers and micro-strains were about 10-2. Film thicknesses obtained from transmittance spectra decreased more than two times with increased lateral position of the samples against the target. Dispersion of the spectral refractive index was observed depending on the sample position in deposition chamber. Smaller dispersion was observed in series containing more redundant oxygen in their structure.
Local laser-induced crystallization of lanthanum boron germanate glass near LaBGeO5 composition
S. V. Lotarev, T. O. Gelmanova, Yu. S. Priseko, et al.
Local crystallization of glasses induced by laser irradiation is an efficient technique of fabricating regular structures (arrays of dots, lines, gratings) which can be used as waveguides and other elements in the novel glass-based devices of integrated optics and photonics. One of the most important cases is local laser-induced crystallization of nonlinear optical crystals which can form a base for integrated active elements for optical frequency conversion or electrooptical modulation. We report a comparative study on laser-induced crystallization of lanthanum borogermanate glasses with different additives using different types of lasers. A stillwellite-like crystalline LaBGeO5 phase possessing ferroelectric and nonlinear optical properties or its solid solutions with partial substitution of La by Nd or Sm depending on the additive are shown to precipitate as well-formed crystals a few microns in size near the glass surface under radiation of the continuous wave Nd:YAG laser (1064 nm), the continuous wave copper vapor laser (510,6 nm and 578,2 nm). To enhance optical absorption of the basic glass we added Sm2O3 oxide for irradiation at 1064 nm and Nd2O3 for irradiation at 510,6 nm and 578,2 nm whereas pure glass was subjected to KrF laser irradiation due to high native absorption at 248 nm. A copper vapor laser which almost has not been applied to this technique before is shown to be an effective tool for laser-induced crystallization providing short times of crystal growth and high speed of laser writing.
Photosensitive polyurethanes for optical record
The method of synthesis of photosensitive polyurethanes polymers on glycerine, toluenediisocyanate and Disperse Red 1 base has been described. Two types of polymers with different amount of Disperse Red 1 fragments in macromolecules were compared. Films of the polymers were obtained from solutions in organic solvents on glass substrate. The dry film thickness was in the range of 3,5 - 4.5 μm. The transmission spectrums of the films were studied. Possibility of formation of side product in the process of synthesis was observed. The photobirefringence measurements of polymers films were performed. Surface relief grating (SRG) formation was observed during polarization holographic recording process. A profile of SRG was studied by AFM.
Nanophotonics + Nanooptics
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All-optical multi-dimensional imaging of energy-materials beyond the diffraction limit
Steve Smith, D. J. Dagel, L. Zhong, et al.
Efficient, environmentally-friendly, harvesting, storage, transport and conversion of energy are some of the foremost challenges now facing mankind. An important facet of this challenge is the development of new materials with improved electronic and photonic properties. Nano-scale metrology will be important in developing these materials, and optical methods have many advantages over electrons or proximal probes. To surpass the diffraction limit, near-field methods can be used. Alternatively, the concept of imaging in a multi-dimensional space is employed, where, in addition to spatial dimensions, the added dimensions of energy and time allow to distinguish objects which are closely spaced, and in effect increase the achievable resolution of optical microscopy towards the molecular level. We have employed these methods towards the study of materials relevant to renewable energy processes. Specifically, we image the position and orientation of single carbohydrate binding modules and visualize their interaction with cellulose with ~ 10nm resolution, an important step in identifying the molecular underpinnings of bio-processing and the development of low-cost alternative fuels, and describe our current work implementing these concepts towards characterizing the ultrafast carrier dynamics (~ 100fs) in a new class of nano-structured solar cells, predicted to have theoretical efficiencies exceeding 60%, using femtosecond laser spectroscopy.
Partial polarization of pulsed light beams
Timo Voipio, Tero Setälä, Ari T. Friberg
We introduce a formalism for characterizing partial polarization in random pulsed electromagnetic beams in time and frequency domains. The connection between the temporal and spectral polarization properties is analyzed, and compared to the analogous relationship in the context of stationary beams. The formalism is demonstrated using as an example a beam whose orthogonal components are delayed copies of the same Gaussian-shaped and Gaussian-correlated linearly polarized pulse. The results show that the temporal and spectral polarization properties are quite different, and the time-dependent polarization behavior of the beam may be tailored by changing the delay between the orthogonal components and their coherence time.
Advanced optical manipulation with tailored counter-propagating laser beams
We present an advanced configuration for optical manipulation of micro- and nano-objects employing adaptive optical element to control properties of more counter-propagating beams overlapping in a sample chamber. This system can eliminate optical aberrations in both pathways, online re-align the system remotely from a computer interface, arbitrarily switch in real time between various beams types (vortex, Gauss, Bessel etc.) and their spatial intensity distributions (beam width, vorticity etc.). We demonstrate variety of applications of this set-up ranging from formation of spatial solitons, longitudinal optically bound 1D, 2D, and 3D colloidal structures, precise particle delivery via optical conveyor belt, stable confinement of low-index particles or nanoparticles, controlled rotation or swing of heterogeneous living microorganisms.
Theoretical study of photon emission related to evanescent fields
Dann S. Olesen, Ole Keller
We present a theoretical study of the transverse and longitudinal parts of the evanescent electric field from a current density sheet (quantum well). The aim is to identify the part of the evanescent field which upon quantization belongs to the transverse photons. An examination of the field momentum shows that the transverse field is prevented from escaping the evanescent tail by its coupling to the longitudinal field momentum attached to the sheet particles. In the perspective of the four-potential the field-matter interaction is spread over the entire evanescent regime, and in QED this corresponds to an interaction between transverse photons and longitudinal and scalar photons.
Magneto-optical effects in nanostructures with reduced symmetry
Using Yeh's matrix formalism, the approximate formulas for the magneto-optical effects in reflection from semi-infinite orthorhombic crystal with symmetry axes parallel to the Cartesian axes are derived for a general orientation of the magnetization vector. The magneto-optical (MO) effects in such structures are usually calculated numerically, but theoretical formulas give us physical insight into these effects and an good understanding of their symmetry properties. The near normal incidence approximation allows to study effects, which appear in the case of small angle of incidence in the contrast to the normal incidence. Different dependencies of these effects on the sample rotation allow us to distinguish between trigonal, tertragonal and hexagonal structures including and missing two-fold in-plane symmetry axis. The theoretical description of the magneto-optical effects can be applied to the magneto-optical ellipsometry, which is very sensitive nondestructive methods suitable for study of magnetic anisotropy, magnetization reversal properties of nanostructures, and exchange coupling.
Synthesis of ZnO nanostructures with different morphologies by a direct melt oxidation of Al-Zn mixture
ZnO nanostructures with different morphologies were synthesized through a direct melt oxidation of source materials mixed with Al and Zn in air at atmospheric pressure. When Al-Zn mixture was used as a source material, tetrapod-shaped ZnO nanostructures were formed. ZnO nanostructures with bottle and tubular shape were fabricated when Al-Zn source material contained Au. The morphology depended on the Au content in Al-Zn source material. In addition, when carbon was contained in Al-Zn source material, ZnO nanostructures with comb shape were observed after the oxidation of the source material. All the ZnO nanostructures showed a hexagonal wurtzite crystallographic structure and were grown along the [0001] direction. On the other hand, the green emission centered at 510 nm was detected for all the ZnO nanostructures. This suggests that the ZnO nanostructures had high density of oxygen vacancies, which is supposed to be ascribed from high density of surface and subsurface oxygen vacancies in the nanostructures.
Solid State Lighting + LED, LD, OLED, Solar Cells
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Local measurement of solar cell emission characteristics
Pavel Škarvada, Pavel Tománek, Lubomír Grmela
Light emission inspection technique are generally used for the localization of defects. In this paper, the emission comes from reverse biased mono-crystalline solar cells. Firstly, it is demonstrated that light emission of reverse biased solar cells is observable with our system. Experimental data of light emission from cracks, bulk defects, and borders of the cell are presented. Following these measurements, a few scratches were wittingly made on the top side of the solar cell sample and light emission was measured again for the same reverse voltage value. A method for distinguishing micro-crack and scratches from recombination centers is also presented. This method is based on detecting light emission intensity while varying the sample temperature, holding the reverse bias level fixed. The light emission data are then correlated with laser beam induced current maps. It is found that there is a different light emission temperature behavior in the case of bulk recombination defects and artificial damage defects. Finally, the scratched areas are inspected as sites of local structure damage.
Investigation of the photon emission from p-n junction of silicon solar cells studied by electro-optical methods
Roberrt Macku, Pavel Koktavy, Pavel Tomanek
We investigate localized defects of silicon solar cells. These imperfections represent real problem because of solar cell long-term degradation and decreasing conversion efficiency. To solve this issue, this paper does systematic research about optical investigation of local defect spots and correlation with rectangular microplasma fluctuation. Sensitive CCD camera has been used for mapping of surface photon emission. The operation point of the samples has been set to reverse bias mode and the different electric field intensity was applied. It turns out, that some solar cells exhibit an imperfection in the bulk and close to the edges. Nevertheless, we confine ourselves to bulk defects of potential barrier. We managed to get interesting information using combination of optical investigations and electrical noise measurement in the time and spectral domain. It will be revealed that a direct correlation between noise and photon emission exists and the results related to several defect spots are presented in this paper in detail.
Studies of active Nd-doped silicon rich silicon oxide waveguides
Parastesh Pirasteh, Joël Charrier, Yannick Dumeige, et al.
The Nd3+-doped Silicon Rich Silicon Oxide (SRSO) layers were elaborated by reactive magnetron cosputtering. We report on refractive index measurements of Nd3+-doped SRSO layers obtained by both m-lines method and reflectance spectroscopy. From these measurements, the Si volume fraction and also the Nd3+-doped SRSO index dispersion were deduced by using the Bruggeman model. At 1.06 μm, work wavelength, Nd3+-doped SRSO refractive index was equal to 1.543 corresponding to a Si volume fraction of 6.5%. Optical losses measurements were performed on these waveguides at different wavelengths and were about 0.3 dB/cm at 1.55 μm and 1 dB/cm at 1.06 μm. Measurements are confirmed by theoretical models showing that the losses are essentially attributed to surface scattering. Guided fluorescence by top pumping at 488 nm on planar waveguides was studied as a function of the distance between the excitation area and the output of the waveguide and also as a function of the pump power. The guided fluorescence at 945 and 1100 nm was observed until 4mm of the output of the waveguide and, of course, decreased when the excitation area moved away from the output. The fluorescence intensity increased linearly for low pump power and this linear increasing of the guided fluorescence of Nd3+ excited by a non resonant excitation at 488 nm confirms the strong coupling between the Si- nanoparticles and rare earth ions.
Investigation of optical properties of SiC/(SiC)1-x(AlN)x heterostructures
G. Safaraliev, B. Bilalov, D. Dallaeva, et al.
In this study the optical properties of SiC/(SiC)1-x(AlN)x heterostructures were investigated. The photoluminescence spectrum of (SiC)1-x(AlN)x samples at different temperatures and also the dependence of photoluminescence on wavelength of exciting light were studied. Absorption factor is defined using measured values of transmitting efficiency. The results of study of morphology and composition of obtained samples confirm growth regularity in single-crystal phase. It was observed that n-SiC/p-(SiC)1-x(AlN)x begins to shine at reverse voltage that a little exceed the voltage of irreversible breakdown.
Photoluminescent properties of rare-earth ions in TeO2-WO3-PbO-La2O3 glasses
Z. Mazurak, B. Burtan, J. Cisowski, et al.
The tellurite-tungstate glasses containing small amounts of rare-earth ions have been studied experimentally at 77 and 293 K using spectroscopic methods. The photoluminescence (PL) studies reveal the emission of efficient green-yellow light from Tb3+ ions and red light from Eu3+ ions. The Judd-Ofelt intensity parameters have been derived for Nd3+ and Er3+ ions from the absorption spectra and they have used to calculate the radiative lifetimes and branching ratios. The quantum efficiency η = 0.95 of the 4F3/2 level of Nd3+ ion is higher than the typical value of other tellurite-based glasses. For Er3+ ions, PL originating from the 4S3/2,4I11/2 and 4I13/2 levels has been observed and the luminescence decay of the first two levels has been found to be governed by radiative transitions and multiphonon relaxation involving the highest energy of Te-O vibrations.
Photoluminescence properties of polynaphthalisoimides and polynapththalimides in solutions and thin layers
Andrzej Wanic, Zbigniew Mazurak, Jan Cisowski
A series of polynaphthalsoimides and polynaphthalimides from 1,4,5,8-naphthalene dianhydride and 4,4'-methylene-bis(2,6-diisopropylaniline) or its hydrochloride in HMPA were synthesized in one-step high temperature polycondensation process. The different temperatures of the reaction from 125°C to 180°C were applied. The products were investigated using PL techniques in both solutions and thin layers. The observed changes in all investigated spectra and photochemical properties were presented. The remarkable changes in emission wavelength in photoluminescence was observed together with the increase of the reaction temperature. This work presents novel approach to the class of polymers well known to literature worldwide trying to explain of some surprising aspects of photoluminescence of these compounds. When investigated in solution, the polymer synthesized at 125°C exhibit almost no photoluminescence. The increase of the temperature to 150°C causes the strong increase in the photoluminescence intensity at 545 nm. When the reaction temperature increase to 180°C the intensity of photoluminescence exhibits moderate increase at 546.5 nm, however, remarkable increase was observed for 476.5 nm and 440 nm. The photoluminescence analysis of the polymers synthesized shows that depending on reaction temperature products emitting at different wavelengths may be obtained. Investigations were repeated for thin layers of the polymers. The obtained results and their comparison with the results in solution were also presented and discussed.
LED applications in road and railway signals: is it possible to fit specifications?
In recent times, the transportation industry has generated a number of developments involving new technology in signaling. Important developments have involved the production of light by means of light emitting diode (LED). Since the heat from the junction must be dissipated into the ambient somehow, changing the ambient temperature affects the junction temperature and hence the emitted light. When the LEDs have been used in the railway or traffic signals, the optical proprieties of these have to maintain more rigorous specifications. The junction temperature of the power LEDs affects the device's luminous flux of the device. In this paper, we describe problems of the temperature dependent changes of LED intensity. Besides we will introduce an innovative technical to allow the use of the LEDs in applications with rigorous specifications.
Photonics: Education and Multimedia
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Holographic grating: a useful tool
Dagmar Senderáková, Milan Drzik, Anton Strba, et al.
Holography enables us to create various optical elements, in a simply way. They can be used for any purpose that conventional optical elements can be used for. Especially holographic gratings can demonstrate the advantage of such an approach. To make the dense line structure of a grating classically, a special ruling engine had to be used. Instead mechanically ruled grating grooves a hologram of a plane wave with plane reference wave can be recorded. The interference pattern has the form of regular parallel strips - intensity maxims and the grating interval can be changed very simply, by choosing a proper angle between the interfering waves. Exposition allows us to form the grating profile. The contribution is to present some of our results, applicable during educational process (master study - Optics, lasers and optical spectroscopy), too. A holographic grating may become a simple and useful tool to reveal real temporal coherence properties of widely used laser diode modules and determine frequency spacing ▵ν when more longitudinal modes are generated. Moreover, when choosing a proper angle between two interfering waves creating the grating, the grating interval Λ may become less than the wavelength λ, and a sub-wavelength structure can be created in a simply way if a proper recording medium is accessible. That enables us to model light spreading phenomena when approaching sub-wavelength structures.
CCD noise influence on JPEG2000 compression of astronomical images
Compression of astronomical images is still current task. In most applications, lossless approaches are used that do no damage to the compressed data. These algorithms, however, have lower compression ratios and are not as effective. It is therefore important to deal with more efficient lossy compression techniques. For them it is necessary to define quality criteria and level of acceptable distortion of image data. The usual multimedia approach is not possible to use for the scientific image data. They are optimized for human vision. This work deals with the influence of noise generated in the CCD structure to the defined quality criteria. It will also be shown the impact of the lossy standard JPEG2000 on quality of image data in astronomy.
Wavelet transform for processing of video from MAIA system
Elena Anisimova, Petr Páta, Martin Blazek, et al.
This article will present the use of wavelet transforms for image processing system of MAIA (Meteor Automatic Imager and Analyser). The main objective of these algorithms is the object detection with a high proportion of background noise and complicated imaging function. This noise is generated high brightness of the sky, an image intensifier and CCD sensor used. Analyzed images contain a large number of objects, which have dimensions of only a few pixels. In such cases, it is very difficult to use conventional methods of analysis images that are failing. Application of wavelet transform allows the use of specific features of image function and effectively detect objects.