This PDF file contains the front matter associated with SPIE Proceedings Volume 10142, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Mid-infrared laser absorption spectroscopy (LAS) is useful for molecular trace gas concentration measurements in gas mixtures. While the gas chromatography-mass spectrometry is still the gold standard in gas analysis, LAS offers several advantages. It takes tens of minutes for a gas mixture to be separated in the capillary column precluding gas chromatography from real-time control of industrial processes, while LAS can measure the concentration of gas species in seconds. LAS can be used in a wide range of applications such as gas quality screening for regulation, metering and custody transfer,¹ purging gas pipes to avoid explosions,¹ monitoring combustion processes,² detection and quantification of gas leaks,³ by-products monitoring to provide feedback for the real-time control of processes in petrochemical industry,⁴ real-time control of inductively coupled plasma etch reactors,^{5, 6} and medical diagnostics by means of time-resolved volatile organic compound (VOC) analysis in exhaled breath.⁷ Apart from the concentration, it also permits us to determine the temperature, pressure, velocity and mass flux of the gas under observation. The selectivity and sensitivity of LAS is linked to a very high spectral resolution given by the linewidth of single-frequency lasers. Measurements are performed at reduced pressure where the collisional and Doppler broadenings are balanced. The sensitivity can be increased to ppb and sometimes to ppt ranges by increasing the interaction length in multi-pass gas cells or resonators and also by adopting modulation techniques.⁸

The propagation of optical pulses in dispersive nonlinear fibers is studied by using an adaptive split step Fourier method. Propagation of optical pulse is described by a generalized nonlinear Schrödinger equation. Various initial pulse shapes can be used, impact of group velocity dispersion up to the fourth-order dispersion, self phase modulation and their interplay are studied in connection with the dispersion and nonlinear length parameters. Properties of propagating field are analyzed in time and in frequency domain. For pulse propagation in telecommunication applications the results of implemented solutions are in good agreement with experiments.

Fluoride-type crystals (CaF₂, SrF₂) doped with neodymium Nd³⁺ and codoped with buffer ions for breaking clusters of active ions and increasing fluorescence efficiency, present interesting alternative as laser active media for the diode-pumped mode-locked lasers. In comparison with widely used materials as Nd:YAG or Nd:YVO₄, they have broad emission spectra as well as longer fluorescence lifetime, in comparison with Nd:glass, SrF₂ and CaF₂ have better thermal conductivity. In spite of the fact, that this thermal conductivity decreases with Nd³⁺ doping concentration, these crystals are alternative for the Nd:glass in subpicosecond mode-locked laser systems. In this paper we review the basic results reported recently on these active materials and in the second part we present our results achieved in low power diode pumped passively mode locked lasers with Nd,La:CaF₂ and Nd,Y:SrF₂ crystals. The pulses as short as 258 fs at wavelength of 1057 nm were obtained in the first case, while 5 ps long pulses at 1065 nm were generated from the second laser system.

Health services worldwide are seeking ways to improve patient care for amputees suffering from diabetes, and at the same time reduce costs. The monitoring of residual limb temperature, interface pressure and gait can be a useful indicator of tissue viability in lower limb amputees especially to predict the occurrence of pressure ulcers. This is further exacerbated by elevated temperatures and humid micro environment within the prosthesis which encourages the growth of bacteria and skin breakdown. Wearable systems for prosthetic users have to be designed such that the sensors are minimally obtrusive and reliable enough to faithfully record movement and physiological signals. A mobile sensor platform has been developed for use with the lower limb prosthetic users. This system uses an Arduino board that includes sensors for temperature, gait, orientation and pressure measurements. The platform transmits sensor data to a central health authority database server infrastructure through the Bluetooth protocol at a suitable sampling rate. The data-sets recorded using these systems are then processed using machine learning algorithms to extract clinically relevant information from the data. Where a sensor threshold is reached a warning signal can be sent wirelessly together with the relevant data to the patient and appropriate medical personnel. This knowledge is also useful in establishing biomarkers related to a possible deterioration in a patient’s health or for assessing the impact of clinical interventions.

We consider a microscopic system in which the focused Gaussian beam with the embedded vortex illuminates the sample. The vortex beam is very sensitive to any imperfections introduced into it. Small defects introduced into the dark area of the vortex beam causes the change in its internal structure. We investigate theoretically and experimentally how the small rectangular groove introduced into the beam at the critical plane influence the phase structure of the beam. The analytical model of the setup is provided and following it the scheme for recovering the information about the sample is proposed.

In this paper we apply the terahertz time-domain spectroscopy (THz-TDS) to obtain optical function spectra in the range from 0.06 to 3 THz. Polarization sensitivity is obtained using azimuth-controlled wire-grid polarizers. We demonstrate general methods on characterization of plasmonic semiconductors. Detail characterization of optical and magneto-optical material properties is also motivated by a need of optical isolator in THz spectral range. The technique is applied to III-V semiconductors. The typical material is a single crystal undoped InSb having the plasma frequency in the range of interest. With appropriate magnetic field (in our case 0.4 T) we observed coupling of plasma and cyclotron behavior of free electrons with gigantic magneto-optic effect in the THz spectral range.

Polymer based photonics brings simple and cheap solutions often with interesting results. We present capabilities of some siloxanes focusing on polydimethylsiloxane (PDMS) with unique mechanical and optical properties. In combination of laser lithography technologies with siloxane embossing we fabricate different grating structures with one- and two-dimensional symmetry. Concept of PDMS based thin membranes with patterned surface as an effective diffraction element for modification of radiation pattern diagram of light emitting diodes is here shown. Also the PDMS was used as an alternative material for fabrication of complicated waveguide with implemented Bragg grating. For lab-on-chip applications, we patterned PDMS microstructures for microfluidic and micro-optic devices.

Fringe pattern processing and analysis is an important task of full-field optical measurement techniques like interferometry, digital holography, structural illumination and moiré. In this contribution we present several adaptive automatic data analysis solutions based on the notion of Hilbert-Huang transform for measurand retrieval via fringe pattern phase and amplitude demodulation. The Hilbert-Huang transform consists of 2D empirical mode decomposition algorithm and Hilbert spiral transform analysis. Empirical mode decomposition adaptively dissects a meaningful number of same-scale subimages from the analyzed pattern - it is a data-driven method. Appropriately managing this set of unique subimages results in a very powerful fringe pre-filtering tool. Phase/amplitude demodulation is performed using Hilbert spiral transform aided by the local fringe orientation estimator. We describe several optical measurement techniques for technical and biological objects characterization basing on the especially tailored Hilbert-Huang algorithm modifications for fringe pattern denoising, detrending and amplitude/phase demodulation.

Enzymes are highly versatile and ubiquitous biological catalysts. They can greatly accelerate large variety of reactions, while ensuring appropriate catalytic activity and high selectivity. These properties make enzymes attractive biocatalysts for a wide range of industrial and biomedical applications. Over the last two decades, directed evolution of enzymes has transformed the field of protein engineering. We have devised microfluidic systems for directed evolution of haloalkane dehalogenases in emulsion droplets. In such a device, individual bacterial cells producing mutated variants of the same enzyme are encapsulated in microdroplets and supplied with a substrate. The conversion of a substrate by the enzyme produced by a single bacterium changes the pH in the droplet which is signalized by pH dependent fluorescence probe. The droplets with the highest enzymatic activity can be separated directly on the chip by dielectrophoresis and the resultant cell lineage can be used for enzyme production or for further rounds of directed evolution. This platform is applicable for fast screening of large libraries in directed evolution experiments requiring mutagenesis at multiple sites of a protein structure.

A biomass of yeast strains has been studied using Raman spectroscopy due to their potential applications in the field of biofuel generation, food industry and biotechnological applications. In order to utilize biomass for efficient industrial/biotechnological production, the optimal cultivation parameters have to be determined which in turn lead to high production of desired substances such as oil, carotenoids, and pigments in the selected cell line of yeast. Therefore, we focused on different cultivation conditions (the effects of temperature regime and medium composition) and their influence on microorganisms growth and metabolic changes.

Design and fabrication of appropriate biocompatible microstructures that ensure fixation and control of experimental conditions for live cell and bacteria observations is an important prerequisite for number of real time experiments. Our approach is to design engineered microfabricated 3D structures for growth of cells in culture without significant modification of their metabolic state. Presented approach is aimed at evaluation of the potential applicability of biocompatible constructs in the biomedical field and thus live cell monitoring in controlled conditions. Design and evaluation of properties of materials and structures with mesoscopic arrangement and their interaction with biological objects is a prerequisite for establishment of physiologically relevant in vitro models of pathologies as well as for development of a new generation of nano / micro / bio-sensors.

We proposed the improved control software for the holographic optical tweezers (HOT) proper for simple semi-automated sorting. The controller receives data from both the human interface sensors and the HOT microscope camera and processes them. As a result, the new positions of active laser traps are calculated, packed into the network format and sent to the remote HOT. Using the photo-polymerization technique, we created a sorting container consisting of two parallel horizontal walls where one wall contains “gates” representing a place where the trapped particle enters into the container. The positions of particles and gates are obtained by image analysis technique which can be exploited to achieve the higher level of automation. Sorting is documented on computer game simulation and the real experiment.

We report on the frequency noise investigation of a linewidth-suppressed Extended Cavity Diode Laser (ECDL), working at 729 nm. Since the ECDL is intended as an excitation laser for the forbidden transition in a trapped and laser cooled ⁴⁰Ca⁺ ion, an Hz-level linewidth is required. We present the experimental design that comprises a two-stage linewidth narrowing and a facility for frequency and noise analysis. The linewidth is first narrowed with a phase lock loop of the ECDL onto a selected component of an optical frequency comb where the frequency noise was suppressed with a fast electronic servo-loop controller that drives the laser injection current with a high bandwidth. The second stage comprises locking the laser onto a selected mode of a high-finesse passive optical cavity. The frequency analysis used an unbalanced Mach-Zehnder interferometer with a fiber spool inserted in the reference arm in order to give a general insight into the signal properties by mixing two separated beams, one of them delayed by the spool, and processing it with a spectral analyzer. Such a frequency noise analysis reveals what are the most significant noises contributions to the laser linewidth, which is a crucial information in field of ion trapping and cooling. The presented experimental results show the effect of the linewidth narrowing with the first stage, where the linewidth of ECDL was narrowed down to a kHz level.

Emulsion droplets of liquid crystals (LC) suspended in water and labeled with a suitable fluorescent dye can serve as active optofluidic microcavities, since the contrast of refractive index between the LC droplets and the surrounding aqueous medium allows excitation of whispering gallery modes (WGMs) in the droplets. In addition, such emulsion droplets can be also stably trapped in three-dimensions using optical tweezers which stabilizes the droplets while investigating their spectral characteristics. We explore various combinations of fluorescently dyed LC droplets and host liquid - surfactant systems and show that the WGM emission spectrum of an optically trapped LC droplet-based cavity can be largely and (almost) reversibly tuned by controlled changes of the ambient temperature that induce phase transitions in the LC droplets. Our results indicate feasibility of this approach for creating miniature tunable sources of coherent light.

High-power Tm-doped fiber lasers are greatly suitable for various applications, such as material processing, medicine, environmental monitoring and topography. In this work we present an all-fiber narrowband CW laser in near fundamental mode operation based on a Tm-doped double-clad active fiber pumped by 793 nm laser diodes with a central wavelength stabilized at 2039 nm by a fiber Bragg grating. The achieved output power is 60 W with a slope efficiency of 46%. The measured beam quality factor is less than 1.4. Further increasing of the output power is possible using various power scaling techniques, for example, coherent combination of several Tm-doped fiber lasers. The developed fiber laser could be employed for welding, cutting and marking of thermoplastics in industry, minimally invasive surgery in medicine or sensors in lidar systems. Future improvements of thulium fiber lasers are possible due to the extremely wide gain-bandwidth of the active medium and the rapid growth of 2-μm fiber components production.

Several schemes of side-pumping by novel, high brightness, 2D laser diode stacks were analyzed. The three most promising schemes were chosen, for which the optical set-ups have been designed, manufactured and preliminary characterized. The special, robust, compact cavity with high tolerances to misalignments, mechanical disturbances and shocks was designed. The analysis of temperature sensitivity of pump unit and laser was performed. In preliminary characterization 180 mJ of output energy with 2-mrad full divergence angle (parameter M² ~ 5) in free running mode for 0.8-J of incident pump energy was demonstrated in such a compact cavity with 80% transmission of integrated output coupler. The main drawbacks in such design found in preliminary experiments are: low threshold of self-lasing due to high gain density and inhomogeneities in transverse beam profile. The strategy of mitigation of these drawbacks was discussed.

In this work we analyze two aspects of our research towards a laser-based setup for open-path hydrogen sulfide detection. We demonstrate a compact and portable electronic part of the sensing system that can be constructed solely with commercially available, off-the-shelf components. Comparison with the setup that uses benchtop lock-in amplifier for signal demodulation is presented. We also discuss challenges in spectral modelling of H₂S transitions in the near-IR spectral region using the data available in HITRAN base. We show that in order to perform correct spectral simulations (for both direct absorption spectroscopy and wavelength modulation spectroscopy) appropriate corrections to the data available in the database have to be applied.

Two-photon photopolymerization is used to create structures with sub-micron details or tiny particles by solidifying monomer liquid in pre-defined locations with focused laser beam. The process is time consuming, especially when high volumes are processed, because the building blocks are typically 200 nm in diameter. Possible way how to speed up the technique is to use multiple focal points created by dynamically generated hologram. Corrections of the focal spot shape and even distribution the laser beam intensity is described together with examples of structures created with this method.

In this work we investigate the regime of amplitude bistability in the driven dissipative Jaynes-Cummings (JC) model. We study the semiclassical equation dynamics in contrast to entangled cavity-photon and qubit quantum trajectories, discussing our results in the context of an out-of-equilibrium first order quantum dissipative phase transition for a single JC resonator. Finally, we compare the switching process between metastable states for the two system degrees of freedom by examining a single realization of the random qubit vector in the Bloch sphere next to the intracavity amplitude quasi distributions at given time instants.

The noise-to-signal transitions are considered as interesting processes in physics as they might transform environmental noise to useful mechanical effects. Previously, we theoretically analyzed stochastic noise-to-signal transition, first passage times, and other stochastic quantities of overdamped Brownian motion of a nanoparticle in the cubic potential. Here we present a feasibility study showing that the cubic potential can be successfully obtained in a pair of overlapping optical tweezers even in the case of a dielectric microparticle having radius comparable to the trapping wavelength.

Optical fibre links for distributing optical frequencies and time stamps were researched and experimentally tested in the past fifteen years. They have been used mainly for stability comparison of experimental optical clocks. But recent development puts demands on a technology transfer from laboratory experiments to the real industry. The remote calibration of interrogators of Fibre Bragg Grating strain sensory networks is one of important examples. The first step of the adoption the time and frequency broadcasting should be the drop-out free long-term operation of this technology between research laboratories connected via long-haul fibre links. We present a 306 km long-haul optical fibre link between the cities of Prague and Brno in the Czech Republic where a coherent transfer of stable optical frequency and a stable time signal has been firstly demonstrated. The link between ISI CAS Brno and CESNET Prague uses an internet communication fibre where a window of 1540-1546 nm is dedicated for the coherent transfer and 1PPS signal. The link is equipped with 6 bidirectional EDFA amplifiers. The optical frequency standard based on the highly-coherent laser Koheras Adjustik working at 1540.5 nm and stabilized with a saturation absorption spectroscopy technique was used for the coherent wave transfer. The suppression of the Doppler shift induced by the optical fibre was based on an accoustooptical modulator with a servo-loop including a fast PID controller processing the beat-note frequency given by mixing of the Adjustik laser (Brno) and the reflected frequency of this laser from the far end of 306 km long-haul fibre link (Prague). We verified the Doppler shift suppression for the coherent wave with a measuring method analysing the transport delay of the 1PPS signal.

In recent years, optical microscopy has been enriched by a wide range of modern techniques enabling exploration of volume samples. One of the preferred ways for reaching a depth estimation required in three-dimensional (3D) imaging is based on utilization of optical systems working with a point spread function (PSF) that rotates under defocusing. Here, the method of axial localization of microparticles is examined that is based on the evaluation of the PSF rotation caused by interference of the vortex nondiffracting beams (VNBs). For generation of the VNBs, a special complex mask is used, modulating both amplitude and phase of the spatial spectrum of the specimen. The main attention is focused on examination of the optical performance of the method and analysis of the effects that occur, when the mask is implemented using a spatial light modulator (SLM).

This paper presents a contactless method for gauge blocks calibration combining laser interferometry and low-coherence interferometry. In the presented system, the contactless measurement of the absolute gauge block length is done as a single-step operation without any change in optical setup during measurement, giving complete information about the gauge block length. The paper also presents a set of optimization steps which have been done in order to transform the original experimental setup into the automatic system which meets legal length metrology requirements. To prove the measurement traceability, we conducted a set of gauge block length measurement comparing data from the optimized system and the established reference systems TESA NPL A.G.I. 300 and TESA–UPC operated in Czech Metrology Institute laboratory.

Polymeric slot waveguide for photonics sensing was designed, simulated and studied in this work. The polymeric slot waveguide was designed on commercial Ormocer polymer platform and operates at visible 632.8 nm wavelength. Designed polymeric slot waveguide detects the refractive index change of the ambient material by evanescent field label-free techniques. The motivation for the reported work was to design a low-cost polymeric slot waveguide for sensing arms of integrated Mach-Zehnder interferometer optical sensor with reduced temperature dependency. The minimal dimensions of advanced sensing slot waveguide structure were designed for researcher direct laser writing fabrication by nonlinear two-photon polymerization. The normalized effective refractive index changes of TE and TM fundamental modes in polymeric slot waveguide and slab waveguides were compared. The sensitivity of the normalized effective refractive index changes of TE and TM fundamental modes on refractive index changes of the ambient material was investigated by glucose-water solutions.

Optical binding of polystyrene microparticle pairs in retro-reflected wide Gaussian beam, called "tractor beam", is studied experimentally and the results are compared with the numerical calculations based on the multiple-particle Mie scattering theory. To investigate the dynamics of optically bound particle pairs in three dimensions we employ holographic video microscopy technique. We show that the particle pair motion is strongly dependent on the relative distances of the particles and the switching between applying pushing and pulling force on particle pairs can be achieved only by changing their configuration even though the "tractor-beam" parameters remain unchanged.

Biological tissue is a very complex, yet important material to describe and analyze. Its properties are affected by chemical processes too numerous to easily understand and describe. By simplifying and grouping some aspects together we are able to create a model for simulating behavior of a photon inside of a biological sample. Using the Monte Carlo method an algorithm for calculating photon propagation through the tissue based on several optical parameters, like absorption and scattering coefficients, refractive indices and optical anisotropy, can be created. Based on some of the results of the simulation a comparative measurement on a muscle sample was performed to prove the usefulness of such model and to describe changes in the tissue sample based on the aforementioned optical parameters in both real life and the simulation.

We present system of structure health measurement by optical fiber sensors based on fiber Bragg gratings. Our system is focused to additionally install to existing buildings. We prepared first set-up of the system to monitoring of the nuclear power plant containment shape deformation. The presented system can measure up to several tens of sensors simultaneously. Each sensor contains optical fiber grating to measurement of change of length and the other independed fiber grating to monitor the temperature and the other ineligible effects.

We report on the length measuring instrument with the absolute scale that was based on the combination of an optical frequency comb and a passive optical cavity. The time spacing of short femtosecond pulses, generated by the optical frequency comb, is optically phase locked onto the cavity free spectral range with a derivative spectroscopy technique so that the value of the repetition frequency of the femtosecond laser is tied to and determines the measured displacement. The instantaneous value of the femtosecond pulse train frequency is counted by a frequency counter. This counted value corresponds to the length given by the spacing between the two mirrors of the passive cavity. The phase lock between the femtosecond pulsed beam and the passive cavity is possible due to the low-dispersion of the cavity mirrors, where the silver coating on the mirrors was used to provide the low dispersion for the broadband radiation of the comb. Every reflection on the output mirror feeds a portion of the beam back to the cavity so that the output beam is a result of multiple interfering components. The parameters of the output beam are given not only by the parameters of the mirrors but mainly by the absolute distance between the mirror surfaces. Thus, one cavity mirror can be considered as the reference starting point of the distance to be measured and the other mirror is the measuring probe surveying the unknown distance. The measuring mirror of the experimental setup of the low-dispersion cavity is mounted on a piezoelectric actuator which provides small changes in the cavity length we used to test the length measurement method. For the verification of the measurement accuracy a reference incremental interferometer was integrated into our system so that the displacement of the piezoelectric actuator could be obtained with both measuring methods simultaneously.

The search for alternative sources of renewable energy, including novel photovoltaics structures, is one of the principal tasks of 21th century development. In the field of photovoltaics there are three generations of solar cells of different structures going from monocrystalline silicon through thin-films to hybrid and organic cells, moreover using nanostructure details. Due to the diversity of these structures, their complex study requires the multiscale interpretations which common core includes an integrated approach bridging not only the length scales from macroscale to the atomistic, but also multispectral investigation under different working temperatures. The multiscale study is generally applied to theoretical aspects, but is also applied to experimental characterization. We investigate multiscale aspects of electrical, optical and thermal properties of solar cells under illumination and in dark conditions when an external bias is applied. We present the results of a research of the micron and sub-micron defects in a crystalline solar cell structure utilizing scanning probe microscopy and electric noise measurement.

We describe our investigations aiming at the detection of the Bloch–Siegert effect (BSE) with nonlinear magneto– optical effects. Although theoretical aspects of the BSE were thoroughly investigated, there are still open questions concerning experimental demonstration of the effect. The most recent BSE experiment was performed in alkali–metal vapor, where atoms were pumped by electron collisions, but the results of those investigations were rather inconclusive. Here we propose to search for the BSE with optically pumped magnetometers (OPMs) and describe the preparation of a dedicated setup providing improved capabilities for observation of the effect in atomic vapor. As the main difficulty is the weakness of the effect and presence of other competing processes, we concentrate on identification and assessment of various systematic effects that may imitate and/or perturb the investigated effect.

A big challenge for standard interferogram analysis methods such as Temporal Phase Shifting or Fourier Transform is a parasitic set of fringes which might occur in the analyzed fringe pattern intensity distribution. It is encountered, for example, when transparent glass plates with quasi-parallel surfaces are tested in Fizeau or Twyman-Green interferometers. Besides the beams reflected from the plate front surface and the interferometer reference the beam reflected from the plate rear surface also plays important role; its amplitude is comparable with the amplitude of other beams. In result we face three families of fringes of high contrast which cannot be easily separated. Earlier we proposed a competitive solution for flatness measurements which relies on eliminating one of those fringe sets from the three-beam interferogram and separating two remaining ones with the use of 2D Continuous Wavelet Transform. In this work we cover the case when the intensity of the reference beam is significantly higher than the intensities of two object beams. The main advantage of differentiating beam intensities is the change in contrast of individual fringe families. Processing of such three-beam interferograms is modified but also takes advantage of 2D CWT. We show how to implement this method in Twyman-Green and Fizeau setups and compare this processing path and measurement procedures with previously proposed solutions.

We present a comprehensive analysis of grating three-beam interference to discover a broad range of the ratio of amplitudes A of +/-1 diffraction orders and the zero order amplitude C providing phase edge dislocations. We derive a condition A/C > 0.5 for the occurrence of phase edge dislocations in three-beam interference self-image planes. In the boundary case A/C = 0.5 singularity conditions are met in those planes (once per interference field period), but the zero amplitude condition is not accompanied by an abrupt phase change. For A/C > 0.5 two adjacent singularities in a single field period show opposite sign topological charges. The occurrence of edge dislocations for selected values of A/C was verified by processing fork fringes obtained by introducing the fourth beam in the plane perpendicular to the one containing three coplanar diffraction orders. Two fork pattern processing methods are described, 2D CWT (two-dimensional continuous wavelet transform) and 2D spatial differentiation.

White-light interferometry is an established method for the measurement of the shape of objects. Unlike to the classical interferometry, white-light interferometry can measure the shape of objects with rough surface. A major disadvantage of white-light interferometry is the low scanning speed and thus the long measurement time. This disadvantage can be overcome by a strong undersampling and Hilbert transform evaluation. We propose a system that measures the shape of objects with rough surface with the scanning speed of more than 100 μm/s with the standard frame rate of 25 fps. The measurement uncertainty is comparable with that obtained with standard design.

The homodyne detection with only a single detector represents a promising approach in the interferometric application which enables a significant reduction of the optical system complexity while preserving the fundamental resolution and dynamic range of the single frequency laser interferometers. We present the design, implementation and analysis of algorithmic methods for computational processing of the single-detector interference signal based on parallel pipelined processing suitable for real time implementation on a programmable hardware platform (e.g. the FPGA - Field Programmable Gate Arrays or the SoC - System on Chip). The algorithmic methods incorporate (a) the single detector signal (sine) scaling, filtering, demodulations and mixing necessary for the second (cosine) quadrature signal reconstruction followed by a conic section projection in Cartesian plane as well as (a) the phase unwrapping together with the goniometric and linear transformations needed for the scale linearization and periodic error correction. The digital computing scheme was designed for bandwidths up to tens of megahertz which would allow to measure the displacements at the velocities around half metre per second. The algorithmic methods were tested in real-time operation with a PC-based reference implementation that employed the advantage pipelined processing by balancing the computational load among multiple processor cores. The results indicate that the algorithmic methods are suitable for a wide range of applications [3] and that they are bringing the fringe counting interferometry closer to the industrial applications due to their optical setup simplicity and robustness, computational stability, scalability and also a cost-effectiveness.

Contemporary, attention is paid to photonic crystals, which can strongly modify light propagation through them and enable a controllable light manipulation.

The contribution is focused on a sub-wavelength 2D structure formed by Al₂O₃ layer on silicon substrate, patterned with periodic hexagonal lattice of deep air holes. Using various laser sources of light at single wavelength, azimuthal angle dependence of the mirror-like reflected light intensity was recorded photo-electrically.

The results obtained can be used to sample the band-structure of leaky modes of the photonic crystal more reliably and help us to map the photonic dispersion diagram.

We demonstrate the model specification of the MO-SPR coupling-prism system consisting of the Ag film deposited between two garnet layers; the water is supposed as an analyte. The bismuth-doped gallium-gadolinium iron garnet offers low optical losses as well as strong MO response from visible to near infrared optical region. We apply two different response functions that detect a change of analyte refractive index that operate either directly with reflectance change at appropriate incidence angle or with the magneto-optically highlighted SP resonance dip shift. Suggested sensitivity criteria lead to the sensitivity about 120 1/RIU or 75 deg/RIU with the resolution of the order 10^-5 RIU by experimentally acceptable variation of response factors.

A two-step spectral interferometric technique to detect the spectral phase shift of surface plasmon resonance (SPR) in the Kretschmann configuration is proposed and demonstrated. The technique utilizes a polarimetry setup to record two channeled spectra, one including reflection of p- and s-polarized waves from an SPR structure for air when the SPR phenomenon does not occur, and the other one for an analyte when the SPR phenomenon occurs. The channeled spectra are used to detect the SPR spectral phase shift and first, an SF10 glass prism and a gold coated SF10 slide with a chromium adhesion layer is used to measure the SPR phase shift for aqueous solutions of ethanol. In addition, the position of a sharp maximum in the spectral derivative of the SPR phase shift is measured as a function of the analyte parameter. Second, the setup with a gold coated SF10 glass prism is used to measure the SPR phase shift for the same analyte. It is revealed that the detection accuracy of the measurement of the spectral derivative of the SPR phase shift in the second setup is lower than that in the first setup. For the first case, the measurements are accompanied by theoretical modeling of the SPR responses using the material dispersion characteristics.

Grating couplers are one of the most used elements for coupling of light between optical fibers and photonic integrated components. Silicon–on–insulator platform provides strong confinement of light and allows high integration. In this work, using simulations we have designed a broadband silicon nitride surface grating coupler. The Fourier–eigenmode expansion and finite difference time domain methods are utilized in design optimization of grating coupler structure. The fully, single etch step grating coupler is based on a standard silicon–on–insulator wafer with 0.55 μm waveguide Si3N4 layer. The optimized structure at 1550 nm wavelength yields a peak coupling efficiency –2.6635 dB (54.16%) with a 1–dB bandwidth up to 80 nm. It is promising way for low-cost fabrication using complementary metal–oxide– semiconductor fabrication process.

The automotive industry has been always a driving force for all economies. Despite of its beneficial meaning to every society it brings also many issues including wide area of road safety. The latter has been enforced by the increasing number of cars and the dynamic development of the traffic as a whole. Road signs and traffic lights are crucial in context of good traffic arrangement and its fluency.

Traffic designers are used to treat horizontal road signs independently of vertical signs. However, modern light sources and growing flexibility in shaping optical systems create opportunity to design more advanced and smart solutions. In this paper we present an innovative, multidisciplinary approach that consists in tight interdependence of different traffic signals. We describe new optical systems together with their influence on the perception of the road user. The analysis includes maintenance and visibility in different weather conditions. A special attention has been focused on intersections of complex geometry.

In this paper we present preparation process of ring resonator in racetrack configuration based on polydimethylsiloxane (PDMS). 3D laser lithography in combination with imprinting technique was used to pattern photoresist layer as a master for imprinting process. In the next step, PDMS ring resonator was imprinted and filled with core PDMS. Finally, morphological properties of prepared device were investigated by scanning electron microscope (SEM) and confocal microscope and transmission spectrum measurements were performed.

Emission of photon pairs has been numerically investigated in both the volume and at the boundaries of layered Gallium-Nitride/Aluminium-Nitride (GaN/AlN) structures that occurs in the process of spontaneous parametric down conversion (SPDC). The developed model of SPDC is one dimensional and exploits the quantization of momentum of an electromagnetic field (EM field). Nonlinear boundary conditions for the quantized EM field between the linear (AlN) and nonlinear (GaN) layers are treated by the transfer-matrix formalism. The developed theory describes both the volume and interface emissions of photon pairs and it also allows for their separation. The emission of photon pairs from interfaces contributes by 9.7 % of total number of emitted photon pairs. In the spectral regions with low volume emission, the spectral joint photon number density for interface emitted photon pairs reaches up to 40 % of the quantity characterizing the photon pairs emitted in the volume.

A new special second-generation computer-controlled device has been developed for measuring biomechanical characteristics of the lower part of the spine vertebras L1–L5 [1]. During straining and measurement of the rigidity of the sample as a whole it is also necessary to observe the movement of individual parts of the sample and to measure their mechanical resistances. The measurement of displacement and rotation of individual parts of the studied model was evaluated by optical methods based on the principle of moiré interferometry and fast Fourier transform [2]. During this device development and its verification the lumbar samples were replaced with a system of wooden rollers with system discrete rubber pads. The new computer-controlled device containing four stepper motors, four strain gauges and two CCD cameras.

Nowadays, aging of the optical components is a very current topic. Therefore, some investigations are focused on this area, so that the aging of the optical components is accelerated by thermal, high power and gamma load. This paper deals by findings of the influence of the load by laser with high optical power on the transmission parameters of the optical coupler. The investigated coupler has one input and eight outputs (1x8). Load by laser with high optical power is realized using a fiber laser with a cascade configuration EDFA amplifiers. The output power of the amplifier is approximately 250 mW. Duration of the load is moving from 104 hours to 139 hours. After each load, input power and output powers of all branches are measured. Following parameters of the optical coupler are calculated using formulas: the insertion losses of the individual branches, split ratio, total losses, homogeneity of the losses and cross-talk between different branches. All measurements are performed at wavelengths 1310 nm and 1550 nm. Individual optical powers are measured 20 times, due to the exclusion of statistical error of the measurement. After measuring, the coupler is connected to the amplifier for next cycle of the load. The paper contains an evaluation of the results of the coupler before and after four cycles of the burden.

In optical lens imaging, the main attention has traditionally been paid to the lateral resolution roughly estimated by a two-dimensional point spread function (PSF) describing sharp image of a point object. In three-dimensional (3D) imaging and methods based on depth information, an axial profile of the PSF becomes of particular importance. In studies on the 3D PSF, the axial image asymmetry and shift of the intensity maximum out of the focal plane were revealed for optical systems characterized by low Fresnel numbers. In this paper, the 3D PSF is examined in terms of digital imaging, where a point object is recorded optically and its image reconstructed numerically. The analysis includes methods of digital holography, in which the axial image asymmetry is examined in relation to different geometries of coherent recording waves. Attention is also devoted to the Fresnel incoherent correlation imaging that enables recording of 3D objects in spatially incoherent light.

Today interferometric sensors are among the most accurate available thanks to their inherent high sensitivity. These highly versatile sensors may be used to measure phenomena such as temperature, strain, fluid level, flow, vibration, stress, etc. This article concentrates on the composition of fiber-optic interferometers, in particular the Mach-Zehnder type. The Mach-Zehnder type is composed of two arms, one for measurement and a second serving as a reference. When light enters the interferometer, ideally the phase of the light is shifted only in the measurement arm while the phase in the second arm remains unchanged. Interference occurs when the light recombining at the output and the resulting light intensity is proportional to the measurand. A major issue in the application of fiber based sensors is laying and fixing the fibers effectively in real life environments. Different approaches are necessary for both arms. The reference arm should as far as possible be isolated from the measurand. In this paper, various isolating materials are considered, however there are almost unlimited materials that may be used for isolation purposes. Conventional construction methods and materials were used such as aluminum tubing, flexible PVC tubing, double sided tape, steel clinches, superglue, PVC strips and PVC strips filled by silicon.

This paper reports on optical measurements of GaP nanowire (NW) arrays with thin nanocrystalline ZnO layer. The GaP core was prepared by metal organic vapor phase epitaxy (MOVPE) and the ZnO shell by RF sputtering by different sputtering conditions. The NWs were grown from Au seeds created from very thin Au layer deposited on top of GaP substrate. Reflectance of different NWs structures covered by ZnO coating was measured in angular dependence in wide range of angles and compared. We experimentally show the reflectance suppression of the ZnO coated NWs in the wide range of angles.

Nowadays, lab on a chip (LOC) applications are very popular in the field of biomedicine. LOC device works with biological materials and enables to arrange conventional laboratory operations on a small chip. Philosophy of LOC applications stands on quick and precise diagnostics process and technology, which uses cheap materials with possibility of rapid prototyping. LOC, as a time saving application, works with small volume of samples and reagents and enables better control over the sample.

We present fabrication method of functional LOC chip for different biomedical microfluidic applications based on direct laser writing (DLW) lithography. We present fabrication of few types of microfluidic and micro-optic structures with different capabilities created by DLW system. The combination of DLW lithography in photoresist layer deposited on glass substrate and polydimethylsiloxane (PDMS) replica molding process were used for patterning of designed microstructures. Prepared microfluidic and micro-optic structures were observed by confocal microscope and microfluidic flow observations were investigated by conventional optical microscope and CCD camera.

In this paper we have investigated Bragg fibers for the 1.94 μm laser- radiation delivery generated by a thulium fiber laser with a maximal continuous output power 50W. For such investigation laboratory-designed and fabricated hollow-core Bragg fibers have been employed with different diameters of 5, 40, 56 and 73 μm surrounded by three pairs of circular Bragg layers. Fundamental optical characteristics such as overall transmittance, attenuation coefficient, bending losses, and delivered spatial beam profiles at the wavelength of 1.94 μm for all tested fibers are reported and summarized in this contribution. In the case of laser radiation delivery with the intensity of 65 kW/cm², the lowest attenuation coefficient of 1.278 dB/m was determined for the Bragg fiber with the inner air-core diameter of 56 μm. Moreover, the bending losses for a small bend diameter of 15 mm reached 0.177 dB only. However delivered laser radiation was highly multimode character.

In this paper the optimization of a continuously diode-pumped Nd:GdVO₄ laser oscillator in bounce geometry passively mode-locked using semiconductor saturable absorber mirror is presented. In the previous results the Nd:GdVO₄ laser system generating 30 ps pulses with the average output power of 6.9 W at the repetition rate of 200 MHz at the wavelength of 1063 nm was reported. Now we are demonstrating up to three times increase of peak power due to the optimization of mode-matching in the laser resonator. Depending on the oscillator configuration we obtained the stable continuously mode-locked operation with pulses having selectable duration from 15 ps to 70 ps with the average output power of 7 W and the repetition rate of 150 MHz.

In this paper we demonstrate possibilities of three-dimensional (3D) printing technology based on two photon polymerization. We used three-dimensional dip-in direct-laser-writing (DLW) optical lithography to fabricate 2D and 3D optical structures for optoelectronics and for optical sensing applications. DLW lithography allows us use a non conventional way how to couple light into the waveguide structure. We prepared ring resonator and we investigated its transmission spectral characteristic. We present 3D inverse opal structure from its design to printing and scanning electron microscope (SEM) imaging. Finally, SEM images of some prepared photonic crystal structures were performed.

In this paper we present fabrication process of waveguides with surface relief Bragg grating (SR-BG) embossed in poly dimethyl diphenyl siloxane (PDMDPS). Generally, the Bragg grating causes spectral selectivity of propagated light in optical fibers and optical waveguides. We prepared the original concept of fabrication of novel optical waveguides with SR-BG using the laser interference lithography in combination with embossing process of liquid polymer. We used laser interference lithography in Mach-Zehnder configuration to create a grating with period of 21 μm in thin photoresist layer. In this manner, we created an array of D-shaped waveguides of 10 μm wide and app. 2.5 μm high. SR-BG was created in the next step, where the one dimensional surface Bragg grating with period 1.64 μm was prepared by interference lithography. This period was designed to reflect narrow spectral band close the telecommunication wavelength of 1.55 μm. Quality of the prepared waveguides and SR-BG was confirmed from atomic force microscope analysis. Transmission and coupling properties of the prepared SR-BG waveguides were finally measured by spectral measurements in infrared spectral region.

Design of a model of a sensor based on the Shape from focus method is presented. The model uses polychromatic point spread functions of a generalized aperture function of lens and their convolution with an ideal image. The model approaches the reality and allows one to employ parameters of real components of the corresponding sensor, e.g. a spectrum of a light source, a dispersion function of a real imaging optical system and spectral sensitivity of a real light sensitive sensor. The model enables to study accuracy and reliability of the determination of the object’s surface topography by means of the Shape from focus method.

This research deals with preparation of an optical frequency references based on hollow-core photonic crystal fibers (HC-PCF). This fiber-based type of absorption cells represents a effiecient way how to replace classic bulky and fragile glass made tubes references with low-weight and low-volume optical fibers. This approach allows not only to increase possible interaction length between incident light and absorption media but it also carries a possibility of manufacturing of easy-operable reference which is set up just by plugging-in of optical connectors into the optical setup. We present the results of preparation, manufacturing and filling of a set of fiber-based cells intended for lasers frequency stabilization. The work deals with setting and optimalization of HC-PCF splicing processes, minimalization of optical losses between HC-PCF and SMF fiber transitions and finishing of HC-PCF spliced ends with special care for optimal closing of hollow-core structure needed for avoiding of absorption media leakage.

The absorption cells represent an unique tool for the laser frequency stabilization. They serve as irreplaceable optical frequency references in realization of high-stable laser standards and laser sources for different brands of optical measurements, including the most precise frequency and dimensional measurement systems. One of the most often used absorption media covering visible and near IR spectral range is molecular iodine. It offers rich atlas of very strong and narrow spectral transitions which allow realization of laser systems with ultimate frequency stabilities in or below 10^-14 order level. One of the most often disccussed disadvantage of the iodine cells is iodine’s corrosivity and sensitivity to presence of foreign substances. The impurities react with absorption media and cause spectral shifts of absorption spectra, spectral broadening of the transitions and decrease achievable signal-to-noise ratio of the detected spectra. All of these unwanted effects directly influence frequency stability of the realized laser standard and due to this fact, the quality of iodine cells must be precisely controlled. We present a comparison of traditionally used method of laser induced fluorescence (LIF) with novel technique based on hyperfine transitions linewidths measurement. The results summarize advantages and drawbacks of these techniques and give a recommendation for their practical usage.

We prepared and demonstrated a compact, simple-to-fabricate, air microcavity in polydimethylsiloxane (PDMS), placed at the end of a single-mode optical fiber. The air microcavity creates a Fabry-Perot interferometer. The length of microcavity changes with change of temperature. So the wavelength shift of reference minima (maxima) of interference pattern corresponds to temperature change. For the operation of the sensor broadband light source and low-resolution optical spectral analyzer can be used. The sensor response for change of temperature is fast and occurs within a few seconds. The temperature sensitivity is 6.1 nm/°C. For optical spectral analyzer resolution 0.1 nm the smallest temperature difference possible to determine is 0.017 °C.

We propose two parameters which are mutually related to the fidelity between two states^1-4 and mean number of photons. We discuss them for situations corresponding to the regular and chaotic behavior of the classical counterpart of Kerr-like quantum system, showing that proposed parameters could be applied as indicators of quantum chaos.

During track maintenance operations, the early detection of oncoming rail vehicles is critical for the safety of maintenance personnel. In addition, the detection system should be simple to install at the trackside by minimally qualified personnel. Fibre optic based sensor systems have the inherent advantages of being passive, unaffected by radio frequency interference (RFI) and suffering very low signal attenuation. Such a system therefore represents a good alternative to conventional approaches such as ultrasonic based sensor systems. The proposed system consists of one or more passive fibre trackside sensors and an x86 processing unit located at the work site. The solid fibre connection between sensors and processing unit eliminates the risk of RFI. In addition, the detection system sensors are easy to install with no requirement for electrical power at the sensor site. The system was tested on a tram line in Ostrava with the results obtained indicating the successful detection of all the trams in the monitoring windows using a single sensor. However, the platform allows flexibility in configuring multiple sensors where required by system users.

The word soliton refers to a special kind of wave packets that can propagate undistorted over long distances. As a source for generating soliton pulses in 1990 erbium doped lasers were used. Soliton transmission systems have been the subject of interest for years. It is known that interaction and the balance between the dispersion and nonlinear effects in optical fibers can lead to a special pulse behavior. Soliton pulses can propagate without any changes of the amplitude and the shape via long transmission systems. Due to this advantage they are of interest in long haul communication systems. Here we describe how the random change of input pulse chirp in optical fibers can affect the soliton propagation and interaction between two or more solitons. We have focused on describing some numerical approaches to solve the coupled nonlinear Schrödinger equations, which are useful by solving this kind of problem. Most of laser sources can be approximated by Gaussian distribution or in special cases the second hyperbolic pulses are generated to produce a soliton shaped pulse. The effect of pulse chirp can generate new frequencies due to the frequency chirp. In high bitratetransmission systems this chirp is very important to reduce, because of this new frequency can influence the neighbor channels and lead to BER increasing.

This paper deals with problematic of Free Space Optical (FSO) Links. The theoretical part describes the effects of atmospheric transmission environment on these FSO connections. The practical part is focused on the creation of an appropriate experimental workplace for turbulences simulation (mechanical and thermal turbulences), fog effects and subsequent measurement of these effects. For definition how big impact these effects on the FSO system have is used the statistical analysis and simulation software Optiwave. Overall there were tested three optical light sources operating at wavelengths of 632.8 nm, 850 nm and 1550 nm respectively. Influences of simulated atmospheric effects on the signal attenuation were observed. Within the frame of simulation in Optiwave software there were studied influences of attenuation on given wavelengths in form of FSO link transmission parameters degradation. Also for the purposes of real measurements it was necessary to fabricate an experimental box. This box was constructed with sizes of 2.5 and 5 meters and was used for simulation of atmospheric environment.

This contribution presents implementation of one dimensional Fresnel structure in surface emitting part of the AlGaAs/GaAs multi-quantum well light emitting diode (LED).The structure consists in drilled lines distributed with square root of distance in order to obtain structures with different foci. First structure was prepared by electron beam lithography and etched directly in the emitting surface using reactive-ion etching. Second structure was prepared in the surface of thin PDMS membrane that can be stack directly on the emitting surface. The membrane is fabricated using dip in laser lithography combined with PDMS embossing. Implementation of such Fresnel structures leads in modification of LED far-field what was proved by goniophotometer measurements.

The paper concerns the development of an optical emission spectrometer with a helium microwave rotating plasma as the excitation source which is an alternative to ICP spectrometers. In the new solution helium is used as the plasma and carrier gases, which helps to determine elements such as halogens and some non-metals. The new system should demonstrate decreased operating costs i.e. the flow of 1L He/min compared to about 15L Ar/min for ICP. Its spectral range is within 165 nm - 840 nm, sensitivity at the level of ppb and spectral resolution is equal to 0.01 nm. The system uses a set of two photomultipliers for VIS and UV regions. The entire spectrum is collected during a single rotation of the diffraction gratings. The paper describes the collection of algorithms developed to decrease noise and smooth spectral data.

The family of VAWI techniques (for transmitted and reflected light) is especially efficient for characterizing objects, when in the interference system the optical path difference exceeds a few wavelengths. The classical approach that consists in measuring the deflection of interference fringes fails because of strong edge effects. Broken continuity of interference fringes prevents from correct identification of the zero order fringe, which leads to significant errors. The family of these methods has been proposed originally by Professor Pluta in the 1980s but that time image processing facilities and computers were hardly available. Automated devices unfold a completely new approach to the classical measurement procedures. The Institute team has taken that new opportunity and transformed the technique into fully automated measurement devices offering commercial readiness of industry-grade quality. The method itself has been modified and new solutions and algorithms simultaneously have extended the field of application. This has concerned both construction aspects of the systems and software development in context of creating computerized instruments. The VAWI collection of instruments constitutes now the core of the Institute commercial offer. It is now practically applicable in industrial environment for measuring textile and optical fibers, strips of thin films, testing of wave plates and nonlinear affects in different materials. This paper describes new algorithms for identifying the zero order fringe, which increases the performance of the system as a whole and presents some examples of measurements of optical elements.

The polysiloxane fibres made of polysiloxanes such as polydimethylsiloxane (PDMS) and poly(dimethyl)(diphenil)siloxane (PDMDPS) can be attractive for different fibre applications and fibre structures. In this paper we describe the fabrication technological process of polysiloxane fibres and fibre structures integrated with conventional single-mode optical fibres. We present two-modes interferometer prepared from PDMS biconical optical fibre taper, PDMDPS optical fibre microloop interferometer and liquid microdroplet optical fibre interferometer. We achieved interesting optical properties all these fibre structures as was confirmed from the transmission characteristics what may be attractive for utilisation in various types of optical fibre sensors.

In network communication field, routing protocols have got a significant role which are not only used in networks to handle the user data but also to monitor the different network environments. Dynamic routing protocols such as OSPF, EIGRP and RIP are used for forwarding user data to its destination by instantly detecting the dynamic changes across the network. The dynamic changes in the network can be in the form of topological changes, congestions, links failure etc. Therefore, it becomes a challenge to develop and implement dynamic routing protocols that fulfills the network requirements. Hence, each routing protocol has its own characteristics such as convergence activity, routing metric, routing table etc. and will perform differently in various network environments. This paper presents a comprehensive study of static and dynamic routing, along with dynamic routing protocols. Experiments that are conducted under various network limitations are presented using the OPNET tool. The performance of each of dynamic routing protocols are monitored and explained in the form of simulated results using network parameters. The results are analyzed, in order to provide a clear understanding of each protocol performance for the selection of the proper protocol for a given network environment.

Spectral interferometric techniques utilizing the interference of polarization modes in a highly birefringent (HB) elliptical-core fiber to measure temperature are analyzed experimentally. First, an experimental setup comprising a white-light source, a polarizer, a sensing birefringent fiber, an analyzer and a spectrometer is considered. Temperature sensing by this method is based on the wavelength interrogation. Second, the above setup is extended by a birefringent quartz crystal to increase the sensitivity of the temperature sensing. Third, the above setup is extended by an analyzer, and the combination of a polarizer, a birefringent quartz crystal and an analyzer represents another interferometer, which is used to increase the sensitivity of the temperature sensing. In this case the Vernier effect is present and the resultant spectrum is with an envelope, which is utilized in temperature sensing. We reached a sensitivity of 0.56 nm/K in the third setup, compared to -0.12 nm/K and -0.19 nm/K in the first and the second setup, respectively.

The magneto-plasmonic response in planar multilayer with prism coupling composed from Fe and Au bilayer supplied by photonic crystal (Ta₂O₅ / SiO₂) is studied. Modeled structure is intended as a sensor unit combining magneto-optical (MO) and surface-plasmon-resonance (SPR) effects. The sensitivity of MO-SPR system by small variations of analyte refractive index is tested to obtain optimal resolution ability.

This article is focused on the design of an all-fiber laser that was supposed to be used for simulating power load similar to the power load in backbone networks. The first part of the article is a brief introduction to the topic of lasers and erbium doped fiber amplifiers. The following parts present design of a fiber laser with ring cavity, and measuring the ideal length of a doped fiber and the split ratio of the output coupler. After proposing the first stage –a laser– we focused on the construction of the two following stages –EDFA preamplifier and EDFA amplifier. There were used fibers with various levels of erbium ion density, namely ISO-GAIN I6, and Liekki ER110-4/125. The resulting output power of the whole system was 320 mW. This value is sufficient when we take into account that we used only single-mode fibers with energy pumped directly to the fiber core. The output wavelength of the whole laser system was 1559 nm.

This paper is dedicated to laser engraving and drilling process of the alumina ceramics. Both processes are characterized by exquisite features in comparison with conventional ones. The main benefits are high speed, high precision and good quality along with flexibility. Moreover ceramics are hardly processed by conventional methods due to their high hardness and brittleness. Analysis of Nd:YLF laser engraving alumina ceramics concerning the influence of parameters like output power, processing speed and number of runs on various mark characteristics was carried out. Mark width, mark depth and contrast were evaluated and it was found out that output power determines both mark depth and width. Higher power caused generation of deeper and wider marks characterized by high contrast. Processing speed controls the overlapping of spots and the laser-material interaction time, thus having impact on the mark depth and contrast. Laser drilling was examined in dependence of output power that had crucial effect on the hole depth not on diameter. The research clarified that high output powers are necessary for producing deep holes so as high output powers together with low processing speeds are the optimal parameters to get maximal mark width and depth with satisfactory quality during engraving. Samples were analyzed using confocal microscope and contact profilometer.

We present a new self-referenced interferometer for the form measurement of hollow cylindrical tubes that provides the accuracy in the micrometer range. It is based on a simple and robust setup where the reference and object waves are represented by the central and peripheral parts, respectively, of the conical wave generated by a single axicon. The inteferogram is characterized by a closed-fringe pattern with a circular carrier which allows for the interference phase demodulation using spatial synchronous detection. The misalignment aberrations are corrected by an iterative computational procedure. The measurement capabilities of the interferometer are experimentally tested for the glass and stainless steel tubes with lengths from 220 mm to 600 mm.

Although nonlinear fiber Bragg gratings (FBGs) are well known devices more than three decades their using as all-optical switching elements is still investigated. Current research is focused on optimization their properties for their using in future all-optical networks. The main problem is minimizing of switching intensities needed for achieving the changes of transmission state. Switching intensities were over several years reduced from hundreds of GW/cm² to tens of MW/cm². Reduction of switching intensities can be achieved by selecting appropriate gratings and signal parameters or using suitable materials. This contribution is focused on nonlinear FBGs based on chalcogenide glasses which are very often used in various applications. Chalcogenide glasses thanks to their high nonlinear parameters are suitable candidates for reducing switching intensities of nonlinear FBGs.

Nonlinear crystals are typically used when interaction of different frequencies of light is requested. In classical optics these nonlinear phenomena are used for second-harmonic generation, sum-frequency generation, optical parametric amplification and many other effects. In quantum optics, dealing with optical interaction on the level of individual photons, the most prominent process is spontaneous parametric down-conversion (SPDC),¹ where the crystal is pumped by intensive laser light and the crystal can mediate the splitting of a pump photon to a photon pair. The two generated photons are typically called signal and idler.

Influence of magnetic field on these nonlinear processes was not thoroughly tested yet. This topic deserves intensive study both from theoretical and experimental point of view, because the magnetic field can decrease the symmetry of the nonlinear crystal and so it may allow to use new types of phase-matching conditions. We started to test the SPDC process in BBO crystals. Nonlinear magneto-optic tensor of this material is not known and we can hardly predict it. According to our first theoretical derivations the efficiency of the nonlinear processes has to oscillate when rotating the magnetic-field orientation.

The photonic crystals (PhCs) and photonic quasi-crystals (PQCs) have the considerable effect on enhancement of extraction efficiency and radiation pattern of light emitting diodes (LEDs). We present thin polymer membranes based on polydimethylsiloxane (PDMS) with PhC and PQC patterned surface for direct application on the LED chip. The patterned PDMS surface was achieved by embossing of liquid PDMS (Sylgard 184) on structured photoresist surface prepared by interference lithography. The patterned PhC and PQC modify the Lambertian radiation diagram of conventional LEDs. Radiation properties of LEDs were documented from far-field emission by goniophotometer measurements. Structure quality and symmetry was examined by atomic force microscope and related to the measured diffraction pattern of the PhC and PQC LEDs. The emitting LEDs were also investigated in the near field using the near-field scanning optical microscope. Presented results favor patterned PDMS membranes for the employment in LED emission improvement and with considerable effect on light diffraction.

We created a record of an interference field of reference plane wave and convergent wave in a self-developing photopolymer film using a He-Ne laser and Mach-Zehnder interferometer. Due to Bragg reflections the record acts as holographic lens and transforms the reference plane wave onto a convergent one. To achieve the best performance of the lens the response of the photopolymer film is found and proper conditions for recording are determined. After successful recording the optical parameters of the lens – focal length and diffraction efficiency are measured and compared with values following from the theory. The formed holographic lens has focal length f = 160 mm and reaches diffraction efficiency of 78% at Bragg angle. The used photopolymer meets criteria for the purpose of creating various holographic optical elements.

Free Space Optics (FSO) is a license free Line of Sight (LOS) telecommunication technology which offers full duplex connectivity. FSO uses infrared beams of light to provide optical broadband connection and it can be installed literally in a few hours. Data rates go through from several hundreds of Mb/s to several Gb/s and range is from several 100 m up to several km. FSO link advantages: Easy connection establishment, License free communication, No excavation are needed, Highly secure and safe, Allows through window connectivity and single customer service and Compliments fiber by accelerating the first and last mile. FSO link disadvantages: Transmission media is air, Weather and climate dependence, Attenuation due to rain, snow and fog, Scattering of laser beam, Absorption of laser beam, Building motion and Air pollution. In this paper FSO availability evaluation is based on long term measured data from Fog sensor developed and installed at TUKE experimental FSO network in TUKE campus, Košice, Slovakia. Our FSO experimental network has three links with different physical distances between each FSO heads. Weather conditions have a tremendous impact on FSO operation in terms of FSO availability. FSO link availability is the percentage of time over a year that the FSO link will be operational. It is necessary to evaluate the climate and weather at the actual geographical location where FSO link is going to be mounted. It is important to determine the impact of a light scattering, absorption, turbulence and receiving optical power at the particular FSO link. Visibility has one of the most critical influences on the quality of an FSO optical transmission channel. FSO link availability is usually estimated using visibility information collected from nearby airport weather stations. Raw data from fog sensor (Fog Density, Relative Humidity, Temperature measured at each ms) are collected and processed by FSO Simulator software package developed at our Department. Based on FSO link data the FSO link and experimental FSO network availability was estimated for years from 2007 up to 2015. The average FSO network availability up to 98,3378 % was measured (for the BER 10^-9). From the experimental data also Hybrid RF/FSO link availability was evaluated. As the weather conditions for FSO and RF link are complementary (FSO works well in rain and RF works well in fog) Hybrid FSO/RF system long time average availability was much better up to 99,9986 %.

This paper deals with the aging of optical fibers influenced by temperature and radiation. There are analyzed changes in the structure of the optical fiber, related to the propagation of light in the fiber structure. In this case for numerical aperture. For experimental measurement was used MM fiber OM1 with core diameter 62.5 μm, cladding diameter 125 μm in 2.8 mm secondary coating. Aging of the optical fiber was achieved with dry heat and radiation. For this purpose, we were using a temperature chamber with a stable temperature of 105 °C where the cables after two months. Cables were then irradiated with gamma radiation ⁶⁰Co in doses of 1.5 kGy and then 60 kGy. These conditions simulated 50 years aging process of optical cables. According to European Standard EN 60793-1-43:2015 was created the automatic device for angular scan working with LabVIEW software interface. Numerical aperture was tested at a wavelength of 850 nm, with an output power 1 mW. Scanning angle was set to 50° with step 0.25°. Numerical aperture was calculated from the position where power has fallen from maximal power at e² power. The measurement of each sample was performed 10 hours after thermal and radiation aging. The samples were subsequently tested after six months from the last irradiation. In conclusion, the results of the experiment were analyzed and compared.

Theoretical studies on Stokes polarimeter made of one twisted nematic crystal (TNLC) and one linear polarizer were carried out. Approaching the description of the TNLC theoretically, a model of Stokes polarimeter was created and its behavior was investigated in a numerical way. The minimization criterion of the condition number of the matrix describing the setup’s behavior was applied leading to the conclusion concerning the extension of the introduced by TNLC phase difference range up to 4π.

The concept of system for intracavity interferometry based on the beat note detection in subharmonic synchronously intracavity pumped optical parametrical oscillator (OPO) is presented. The system consisted of SESAM-modelocked, picosecond, diode pumped Nd:YVO₄ laser, operating at wavelength 1.06 μm and tunable linear intracavity pumped OPO based on MgO:PPLN crystal, widely tunable in 1.5 μm able to deliver two independent trains of picosecond pulses. The optical length of the OPO cavity was set to be exactly twice the pumping cavity length. In this configuration the OPO produces signal pulses with the same repetition frequency as the pump laser but the signal consists of two completely independent pulse trains. For purpose of pump probe measurements the setup signal with half repetition rate and scalable amplitude was derived from the OPO signal using RF signal divider, electropotical modulator and fiber amplifier. The impact of one pump beam on the sample is detected by one probing OPO train, the other OPO train is used as a reference. The beat note measured using the intracavity interferometer is proportional to phase modulation caused by the pump beam. The bandwidth of observed beat-note was less than 1 Hz (FWHM), it corresponds to a phase shift measurement error of less than 1.5 × 10^-7 rad without any active stabilization. Such compact low-cost system could be used for ultra-sensitive phase-difference measurements (e.g. nonlinear refractive index measurement) for wide range of material especially in spectral range important for telecom applications.