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

The paper describes an injection seeder driver (prototype) for a directly modulated semiconductor laser diode. The device provides adjustable pulse duration and repetition frequency to shape an output signal. A temperature controller stabilizes a laser diode spectrum. Additionally, to avoid a back oscillation, redundant power supply holds a generation until next stages shut down. Low EMI design and ESD protection guarantee stable operation even in a noisy environment. The controller is connected to the PC via USB and parameters of the pulse are digitally controlled through a graphical interface. The injection seeder controller can be used with a majority of commercially available laser diodes. In the experimental setup a telecommunication DFB laser with 4 GHz bandwidth was used. It allows achieving subnanosecond pulses generated at the repetition rate ranging from 1 kHz to 50 MHz. The developed injection seeder controller with a proper laser diode can be used in many scientific, industrial and medical applications.

In this paper, a practical model of a thin disk regenerative amplifier has been developed based on an analytical approach, in which Drew A. Copeland ^[1] had evaluated the loss rate of the upper state laser level due to ASE and derived the analytical expression of the effective life-time of the upper-state laser level by taking the Lorentzian stimulated emission line-shape and total internal reflection into account. By adopting the analytical expression of effective life-time in the rate equations, we have developed a less numerically intensive model for predicting and analyzing the performance of a thin disk regenerative amplifier. Thanks to the model, optimized combination of various parameters can be obtained to avoid saturation, period-doubling bifurcation or first pulse suppression prior to experiments. The effective life-time due to ASE is also analyzed against various parameters. The simulated results fit well with experimental data. By fitting more experimental results with numerical model, we can improve the parameters of the model, such as reflective factor which is used to determine the weight of boundary reflection within the influence of ASE. This practical model will be used to explore the scaling limits imposed by ASE of the thin disk regenerative amplifier being developed in HiLASE Centre.

Time resolved experimental investigation of laser produced plasma-induced shockwaves has been carried out in the presence of confining walls placed along the lateral directions using a Mach Zehnder interferometer in air ambient. Copper was used as target material. The primary and the reflected shock waves and their effects on the evolution of medium density and the plasma density have been studied. The reflected shock wave has been seen to be affecting the shape and density of the plasma plume in the confined geometry. The same experiments were performed with water and isopropyl alcohol as the ambient liquids and the produced nanoparticles were characterised for size and size distribution. Significant differences in the size and size distribution are seen in case of the nanoparticles produced from the ablation of the targets with and without confining boundary. The observed trend has been attributed to the presence of confining boundary and the way it affects the thermalisation time of the plasma plume. The experiments also show the effect of medium density on the mean size of the copper nanoparticles produced.

In this work the temperature dependence of spectroscopic and laser properties of new ac- tive medium Tm:SBN (Strontium-Barium Niobate, Sr_xBa_1−xNb₂O_6, x = 0.61). The tested sample of Tm:SBN (2 wt. % of Tm₂O₃) appropriate for generation of laser radiation at 1.88 μm had plan-parallel polished faces without anti-reflection (thickness 6.65 mm). During spectroscopy and laser experiments the Tm:SBN was at- tached to temperature-controlled copper holder and was placed in a vacuum chamber. The transmission and emission spectra of Tm:SBN and the fluorescence decay time were measured depending on temperature range 80 - 350 K. The fluorescence decay time was measured to be 3.5 ms and 2.8 ms at 80 and 350 K, respectively. Longitudinal excitation of Tm:SBN was carried out by a fibre-coupled laser diode (pulse duration 10 ms, rep- etition rate 10 Hz, pump wavelength 793 nm). The laser resonator was hemispherical, 146 mm long, with flat pumping mirror (HR @1.8 - 2.1 μm) and spherical output coupler (r = 150 mm, R = 97.5 % @1.8 - 2.1 μm). The Tm:SBN laser properties were investigated at temperature range 80 - 300 K. The highest slope efficiency with respect to absorbed pumped power was 3 % at 80 K. The maximum output peak amplitude power was 0.12 W at 80 K, i.e. 3.2 times higher than it was measured at 200 K. Tunability of laser wavelength at 80 K in the range of 1827 - 1962 nm was obtained by using SiO₂ birefringent filter. At 300 K, wavelength tunability reached 1859 - 1970 nm. Thus, the new Tm:SBN crystal can be an useful laser material in the region of 2 μm.

We report recent progress in design and testing of a distribution system for high-power laser beam delivery developed within the HiLASE project of the IOP in the Czech Republic. Laser beam distribution system is a technical system allowing safe and precise distribution of different laser beams from laboratories to several experimental stations. The unique nature of HiLASE lasers requires new approach, which makes design of the distribution system a state-of-the-art challenge.

Q-switched microchip laser emitting radiation at wavelength 1338nm was tested as a radiation source for laser induced breakdown spectroscopy (LIBS). This laser used sandwich crystal which combined in one piece the cooling part (undoped YAG crystal 4mm long), the active laser part (Nd:YAG crystal 12mm long), and the saturable absorber (V:YAG crystal 0.7mm long). The diameter of this crystal was 5 mm. The microchip resonator consisted of dielectric mirrors directly deposited on the monolith crystal surfaces. The pump mirror (HT @ 808 nm, HR @ 1.3 ¹m) was placed on the undoped YAG part. The output coupler (R = 90% @ 1338 nm) was placed on the V:YAG part. The fibre-coupled 808nm pumping laser diode was operating in pulsed regime (rep. rate 250 Hz, pulse width 300 ¹s, pulse energy 6 mJ). Using this pumping, stable and high reproducible Q-switched pulses were generated at wavelength 1338 nm. Pulse length was 6.2 ns (FWHM) and the mean output power was 33mW. The single pulse energy and peak power was 0.13mJ and 21kW, respectively. Laser was operating in fundamental TEM₀₀ mode. The laser radiation was focused on a tested sample using single plano-convex lens (focal length 75 mm). The focal spot radius was 40 ¹m. The corresponding peak-power density was 0.83GW/cm². The laser induced break-down was successfully reached and corresponding laser-induced plasma spectra were recorded for set of metallic elements (Cu, Ag, Au, In, Zn, Al, Fe, Ni, Cr) and alloys (Sn-Pb solder, duralumin, stainless-steel, brass). To record the spectra, StellarNet BLACK-Comet concave grating CCD-based spectrometer was used without any special collimation optics. Thanks to used laser wavelength far from the detector sensitivity, no special filtering was needed to overcome the CCD dazzling. The constructed laser could significantly improve repletion-rate of up-to-date LIBS devices.

A CW operating, compact, high-power, high-efficient diode pumped 1064nm laser, based on Nd:YAG active medium, was developed for optical surface scanning and mapping applications. To enhance the output beam quality, laser stability, and compactness, a microchip configuration was used. In this arrangement the resonator mirrors were deposited directly on to the laser crystal faces. The Nd-doping concentration was 1 at.% Nd/Y. The Nd:YAG crystal was 5mm long. The laser resonator without pumping radiation recuperation was investigated {the output coupler was transparent for pumping radiation. For the generated laser radiation the output coupler reflectivity was 95%@1064 nm. The diameter of the samples was 5 mm. For the laser pumping two arrangements were investigated. Firstly, a fibre coupled laser diode operating at wavelength 808nm was used in CW mode. The 400 ¹m fiber was delivering up to 14W of pump power amplitude to the microchip laser. The maximum CW output power of 7.2W @ 1064nm in close to TEM00 beam was obtained for incident pumping power 13.7W @ 808 nm. The differential efficiency in respect to the incident pump power reached 56 %. Secondly, a single-emitter, 1W laser diode operating at 808nm was used for Nd:YAG microchip pumping. The laser pumping was directly coupled into the microchip laser using free-space lens optics. Slope efficiency up to 70% was obtained in stable, high-quality, 1064nm laser beam with CW power up to 350mW. The system was successfully used for scanning of super-Gaussian laser mirrors reflectivity profile.

An all-fibre optical sensor of an angular velocity (fibre-optic gyroscope) based on the Sagnac interferometer and using a loop-back phase shift compensation is presented. The sensing loop consists of 760 metres of an ordinary single-mode fibre, which makes this setup cost-effective. To ensure principles of beams reciprocity, randomly induced changes of polarization in the fibre are reduced by using an unpolarized light. This is achieved by a fibre Lyot depolarizer and a super fluorescent fibre source consisting of an erbium-doped fibre pumped by a laser diode. Unlike common approaches to the unpolarized fibre-optic gyroscope with a single-mode fibre, whose output is naturally nonlinear, we use a loop-back compensation of a rotation-induced phase shift to achieve a linear response. In most cases, this technique requires fast electro-optical modulator, which is compatible only with an expensive polarization-maintaining fibre. We use a novel loop-back modulation scheme utilizing only harmonic signals and thus compatible with a piezoelectric fibre stretcher, which can be used with any kind of optical fibre. As result of the closed-loop operation, the range of the gyroscope's linearity is greatly increased and a sensitivity to source power changes is suppressed. We describe the gyroscope setup with proposed modulation method and provide a comparison to the common open-loop setup.

Interference of light provides a high precision, non-contact and fast method for measurement method for distances. Therefore this technology dominates in high precision systems. However, in the field of compact sensors capacitive, resistive or inductive methods dominates. The reason is, that the interferometric system has to be precise adjusted and needs a high mechanical stability. As a result, we have usual high-priced complex systems not suitable in the field of compact sensors. To overcome these we developed a new concept for a very small interferometric sensing setup. We combine a miniaturized laser unit, a low cost pixel detector and machine vision routines to realize a demonstrator for a Michelson type micro interferometer. We demonstrate a low cost sensor smaller 1cm³ including all electronics and demonstrate distance sensing up to 30 cm and resolution in nm range.

The increasing demand for the efficiency in the fabrication of jewelry stones pushes producers to look for new and fast methods of the quality control. One possible way, how to reach satisfactory results, is to use the camera-based system and appropriate methods of image post-processing. Since the glass stones are very small, this task is quite challenging. This paper focuses on methods of quality assessment of the glass jewelry stones and proposes semi-automatic method of their classification based on stone feature detection and distance transform. This algorithm includes rough stone classification, which achieves 93.97% hits in our experiment, and classification based on the evaluation of single stone facets with 96.67% hits.

Recently, a digital holographic method called Frequency Sweeping Digital Holography (FSDH) for high precision measurements of surface topography of mechanical parts has been introduced. The greatest advantage of the presented FSDH is the fact that the measurement is absolute. i.e. optical path difference is independently retrieved in every single pixel. This approach can therefore be used also for measurement of large displacements and deformation. FSDH is particularly suitable in cases where the common digital holographic methods fail due to e.g. 2π unambiguity problem or speckle decorrelation. Measurement method principles, setup details, an some features of the method are discussed.

Structured Illumination Microscopy (SIM) is a powerful super-resolution technique, which is able to enhance the resolution of optical microscope beyond the Abbe diffraction limit. In the last decade, numerous SIM methods that achieve the resolution of 100 nm in the lateral dimension have been developed. The SIM setups with new high-speed cameras and illumination pattern generators allow rapid acquisition of the live specimen. Therefore, SIM is widely used for investigation of the live structures in molecular and live cell biology.

Quantitative evaluation of resolution enhancement in a real sample is essential to describe the efficiency of super-resolution microscopy technique. However, measuring the resolution of a live cell sample is a challenging task. Based on our experimental findings, the widely used Fourier ring correlation (FRC) method does not seem to be well suited for measuring the resolution of SIM live cell video sequences. Therefore, the resolution assessing methods based on Fourier spectrum analysis are often used. We introduce a measure based on circular average power spectral density (PSD_ca) estimated from a single SIM image (one video frame). PSD_ca describes the distribution of the power of a signal with respect to its spatial frequency. Spatial resolution corresponds to the cut-off frequency in Fourier space. In order to estimate the cut-off frequency from a noisy signal, we use a spectral subtraction method for noise suppression. In the future, this resolution assessment approach might prove useful also for single-molecule localization microscopy (SMLM) live cell imaging.

Biotechnology applications are nowadays increasing in many areas, from agriculture to biochemistry, or even biomedicine. Knowledge on biological processes is becoming essential in order to be able to adequately estimate and control the production of these elements.
Cyanobacteria present the capability of producing oxygen and biomass, from CO2 and light irradiation. Therefore, they could be fundamental for human subsistence in adverse environments, as basic needs of breathing and food would be guaranteed. Cyanobacteria cultivation, as other microorganisms, is carried out in photo-bioreactors. The adequate design of photobioreactors greatly influences elements production throughput. This design includes optical illumination and optical measurement of cyanobacteria growth. In this work an analysis of optical measurement of cyanobacteria growth in a photobioreactor is made. As cyanobacteria are inhomogeneous elements, the influence of light scattering is significant. Several types of cyanobacteria are considered, as long as several spatial profiles and irradiances of the incident light. Depending on cyanobacteria optical properties, optical distribution of transmitted light can be estimated. These results allow an appropriate consideration, in the optical design, of the relationship between detected light and cyanobacteria growth. As a consequence, the most adequate conditions of elements production from cyanobacteria could be estimated.

The previously developed full-atomistic approach to the thin film growth simulation is applied for the investigation of the dependence of silicon dioxide films properties on deposition conditions. It is shown that the surface roughness and porosity are essentially reduced with the growth of energy of deposited silicon atoms. The growth of energy from 0.1 eV to 10 eV results in the increase of the film density for 0.2 - 0.4 g/cm³ and of the refractive index for 0.04-0.08. The compressive stress in films structures is observed for all deposition conditions. Absolute values of the stress tensor components increase with the growth of e energy of deposited atoms. The increase of the substrate temperature results in smoothing of the density profiles of the deposited films.

In this work we report on the determination of the cross-relaxation energy-transfer coefficients from the measurements of the fluorescence lifetimes of the ³F₄ and ³H₄ energy levels of Tm³⁺ ions in the experimentally prepared optical fibers. Optical fiber preforms were prepared by solution-doping of Tm³⁺ ions with either Al³⁺ ions or dispersed alumina nanoparticles. Optical fibers were characterized by means of Tm, Al and Ge concentrations, refractive index profiles, optical spectral attenuations, luminescence spectra and fluorescence lifetimes. Highly aluminium-codoped optical fibers exhibited fluorescence lifetimes of up to 756 μs.

This paper reports on the design of the surface enhanced Raman spectroscopy (SERS) structures that were optimized through computation and simulation to obtain the best enhancement of the surface plasmon-polariton (SPP) response on these structures. The structure of the silver nano-grating was designed, fabricated, optimized and measured. The enhancement factor and the increase in the absorption capabilities associated with SPP were evaluated. The rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) computational/simulation methods were utilized. The comparison between the computation simulation outputs and the measured outputs of the fabricated samples was performed.

The paper presents an example of an optical RRH (Remote Radio Head) design, which is equipped with photonic components for direct connection to an all-optical network. The features that can be fulfilled by an all-optical network are indicated to support future 5G mobile networks. The demand for optical bandwidth in fronthaul/midhaul distribution network links, working in D-RoF and A-RoF formats was performed. The increase in demand is due to the very large traffic generated by the Optical Massive-MIMO RRH/RRU will work in format of an Active-Distributed Antenna System (A-DAS). An exemplary next-generation mobile network that will utilize O-RRH and an all-optical backbone is presented. All components of presented network will work in the Centralized/Cloud Radio Access Network (C-RAN) architecture, which is achievable by control with the use of the OpenFlow (OF).

We numerically investigated the properties of diffraction gratings designated for fabrication on the facet of an optical fiber. The gratings are intended to be used in high-power fiber lasers as mirrors either with a low or high reflectivity. The modal reflectance of low reflectivity polarizing grating has a value close to 3% for TE mode while it is significantly suppressed for TM mode. Such a grating can be fabricated on laser output fiber facet. The polarizing grating with high modal reflectance is designed as a leaky-mode resonant diffraction grating. The grating can be etched in a thin layer of high index dielectric which is sputtered on fiber facet. We used refractive index of Ta₂O₅ for such a layer. We found that modal reflectance can be close to 0.95 for TE polarization and polarization extinction ratio achieves 18 dB. Rigorous coupled wave analysis was used for fast optimization of grating parameters while aperiodic rigorous coupled wave analysis, Fourier modal method and finite difference time domain method were compared and used to compute modal reflectance of designed gratings.

In this work a theoretical model of the holographic formation of the polarization diffractive optical elements for the transformation of Gaussian light beams into Bessel-like ones in polymer-dispersed liquid crystals (PDLC) is developed. The model is based on solving the equations of photo-induced Fredericks transition processes for polarization diffractive elements formation by orthogonally polarized light beams with inhomogeneous amplitude and phase profiles. The results of numerical simulation of the material’s dielectric tensor changing due to the structure’s formation process are presented for various recording beams’ polarization states. Based on the results of numerical simulation, the ability to form the diffractive optical elements for light beams transformation by the polarization holography methods is shown.

In this contribution we report and discuss the results of laser characterizations of experimental thulium-doped optical fibers. These active fibers were fabricated in house and were tested in two laser systems to verify their characteristics. The first one, a monolithic fiber laser, was of great interest to us due to its potentially lower overall resonator losses, improved laser lifetime and better robustness. The compact laser cavities with a Bragg gratings inscribed directly into the active optical fiber differs to the second laser system where the Bragg gratings were inscribed into a passive fiber which had to be spliced to the active fiber. The tested fibers were manufactured by the modified chemical vapor deposition method and a solution-doping of thulium ions with Al₂O₃ or alumina nanoparticles, respectively. We focused on comparison of laser output powers, slope efficiencies, and laser thresholds for particular thulium-doped fiber in different laser configurations.

Chalcogenide materials due to high refractive indices, transparency in the mid-IR spectral region, nonlinear refractive indices, etc, have been employed as fibers and films in different photonic devices such as light amplifiers, optical regenerators, broadband radiation sources. Chalcogenide films can be prepared by physical methods as well as by solution-based techniques in which solutions of chalcogenides in amines are used. This paper presents results on the solution-based fabrication and optical characterization of single arsenic sulfide layers and multilayer stacks containing As₂S₃ layers together with porous silica layers coated on planar and fiber-optic substrates.
Input As₂S₃ solutions for the layer fabrications were prepared by dissolving As₂S₃ powder in n-propylamine in a concentration of 0.50 mol/l. These solutions were applied on glass slides by dip-coating method and obtained layers were thermally treated in vacuum at temperatures up to 180 °C. Similar procedure was used for As₂S₃ layers in multilayer stacks. Such stacks were fabricated by repeating the application of one porous silica layer prepared by the sol-gel method and one As₂S₃ layer onto glass slides or silica fibers (a diameter of 0.3 mm) by using the dip-coating method. It has been found that the curing process of the applied layers has to be carefully controlled in order to obtain stacks with three pairs of such layers.
Single arsenic and porous silica layers were characterized by optical microscopy, and by measuring their transmission spectra in a range of 200-2500 nm. Thicknesses and refractive indices were estimated from the spectra. Transmission spectra of planar multilayer stacks were measured, too. Interference bands have been determined from optical measurements on the multilayer stacks with a minimum transmittance of about 50% which indicates the possibility of using such stacks as reflecting mirrors.

SiON is a suitable material for the implementation of photonic integrated circuits with a middle refractive index contrast for the visible and near infrared region. The paper presents the design, fabrication and characterization of SiON/SiO2/Si structures for passive optical waveguides realization with designed refractive index contrast 0.13. This refractive index contrast allows fabrication of strip SiOx/SiON/SiO2/Si waveguides with waveguide band losses bellow 0.01dB/cm at 150um waveguide radius. SiON and SiOx layers were fabricated by plasma-enhanced chemical vapor deposition techniques. The plasma-enhanced chemical vapor deposition technological parameters were tuned and optimized for designed refractive index contrast 0.13 and designed waveguide thickness 2.5 m. The refractive index of fabricated SiON layers were measured by optical ellipsometry.

Channel optical waveguides with spatial optical modulation of their parameters and one-dimensional phase diffraction gratings are generated by laser radiation with wavelengths of 450 and 532 nm within lithium niobate surface layers doped with iron, copper, and their combinations. The characteristics of induced elements are studied by diffraction of light with wavelengths 532 and 633 nm. Formation of photorefractive channel waveguides along forbidden by photorefractive properties of lithium niobate direction using point-by-point exposure of its photorefractive surface is experimentally demonstrated. It is shown that phase diffraction gratings are optically induced only within the crystal surface part doped with photorefractive impurities in studied crystal samples. The dependence of diffraction grating thickness on wavelength of writing light is also demonstrated and explained by distinction of optical absorption within doped layer for light waves of different wavelengths.

This paper summarizes the results of the gain transmission characteristics measurement carried out on the new ion exchange Ag⁺ - Na⁺ optical Er³⁺ and Yb³⁺ doped active planar waveguides realized on a silica based glass substrates. The results were used for optimization of the precursor concentration in the glass substrates. The gain measurements were performed by the time domain method using a pulse generator, as well as broadband measurement method using supercontinuum optical source in the wavelength domain. Both methods were compared and the results were graphically processed. It has been confirmed that pulse method is useful as it provides a very accurate measurement of the gain - pumping power characteristics for one wavelength. In the case of radiation spectral characteristics, our measurement exactly determined the maximum gain wavelength bandwidth of the active waveguide. The spectral characteristics of the pumped and unpumped waveguides were compared. The gain parameters of the reported silica-based glasses can be compared with the phosphate-based parameters, typically used for optical active devices application.

In this contribution a new method for determination of transmission characteristics and mechanism of optical radiation propagation in Bragg fibers is described. The investigated Bragg fibers are designed for high-power laser radiation delivery. Attenuation coefficient and coupling efficiency are usually measured using simple cutback method for optimum mode matching of the incident radiation to the fiber mode. Our current approach is based on the cut-back technique but we also investigate the dependence of the mentioned parameters on radial position of the excitation mode from the fiber axis. In addition, using the imaging of the measured fiber output face on a CCD camera, the spatial profile of the propagated beam can be obtained. For this reason this method is suitable for delivered laser mode control.

The investigated Bragg fiber consisted of the 26um diameter silica core surrounded by three pairs of circular Bragg layers. Each pair is composed of one layer with a high and one layer with a low refractive index being characterized by a refractive-index contrast up to ~0.03. The 1064nm laser beam was focused by a telescope onto the fiber input face. The beam radius in the focal plane was 5um. The Bragg fiber output face was imaged by a 1:6 optical telescope on the CCD camera. The transmitted power and spatial beam profile were registered simultaneously for various offset from the fiber axis. After the fiber shortening, the measurement was repeated and the cut-back was performed. The lowest attenuation coefficient of 0.17dB/m corresponded to a core mode of the delivered laser radiation. In general, the attenuation was higher with a shift from the radial axis of the fiber symmetry. In the case of cladding mode excitation, the attenuation parameter shows a local minimum. This phenomenon was consistent with the refractive index profile of the tested Bragg fiber.

Layers based on TiO₂-SiO₂ systems fabricated by sol-gel method have been investigated for the preparation of planar waveguides, antireflective coatings, Bragg mirrors, etc. However, at high titania contents such materials exhibit high viscosities and tendency to phase separation. In this paper we present optical properties of films containing TiO₂ which are prepared via a novel approach sol-gel on the basis of ternary Na₂O-TiO₂-SiO₂ glasses and which can exhibit lower viscosities.
Films of Na₂O-TiO₂-SiO₂ systems were prepared from input sols mixed of silica, titania and sodium oxide sols. The silica sol was prepared from tetraethyl orthosilicate (TEOS), ethanol, hydrochloric acid and water, with a TEOS c= 2 mol/l and water/alkoxide ratio 1.75. The titania sol was mixed from titanium tetraisopropoxide (TiPr), propan-2-ol, nitric acid and water, c= 0.5 mol/l, RW= 0.42. The sodium oxide sols with c= 0.474 mol/l were prepared from sodium ethoxide and ethanol. Input sols were prepared by mixing the silica and titania sols first and then the sodium sol was added. The input sols were aged for one hour. Stable input sols were obtained. The input sols were deposited on glass and silica slides by dip-coating technique at a withdrawing speeds of 200 mm/min. Applied gel layers were thermally treated at temperatures of 450 and 900°C. Layers containing sodium oxide and titania in concentration ranges of 0-20 mol.% and 0-30 mol.% respectively have been fabricated. Optical properties of layers were determined by UV-VIS-NIR transmission and reflection spectrophotometry. Refractive indices of layers were determined by spectral ellipsometry and from transmission spectra. Optical properties were correlated with results of XRD spectroscopy, optical microscopy, and atomic force microscopy. Transparent homogenous films with a maximum refractive index of 1.61 at a wavelength of 600 nm have been obtained.

TThe paper discuss about aging of the passive optical couplers in their burdened high temperature. The article focuses on applied research and experimental development of resources for safety operation of optical networks in environment with higher temperature. It addresses issues of accelerated aging of optical fiber components in their burdened with high temperature. How does temperature influence on optical network elements? It is necessary to specify the changes in the optical coupler and find out why these changes occur. This article is devoted experimental measurement of the impact of temperature loading on the geometrical parameters of optical beam of SM optical FBT couplers. In the paper there are compared couplers of different manufacturers and same dividing ratios of output power 1:8. Optical passive component were continuously exposed to temperature 95°C for long time period. Measurements are focused on the parameters of geometry of optical beam. Graphical and mathematical detect changes in the dissemination of energy coupler after long lasting dose of temperature loading are useful to understand the phenomenon of accelerated aging elements of optical networks in environments with an higher temperature.

The influence of incoherent background illumination produced by light-emitting diodes (LED´s) of different average wavelengths and laser diode emitting in blue region of visible on diffraction characteristics of narrow coherent light beams of He-Ne laser due to refractive index changes of Fe-doped lithium niobate sample are studied. It has been experimentally demonstrated that nonlinear diffraction of red beams with wavelength 633 nm and diameters on full width of half maximum (FWHM) near to 15 μm may be totally compensated using background light with average wavelengths 450 – 465 nm. To provide the necessary intensity of incoherent background, the combinations of spherical and cylindrical concave lenses with blue LED and laser diode module without focusing its beam have been used.

We fabricated an infrared wire-grid polarizer with the high transverse magnetic (TM) polarization transmittance and high extinction ratio by soft imprint lithography, sol-gel method, and Al shadow coating processes. A zilconia film was coated on Si substrate by using sol-gel method and spin coating method. Then, sol-gel zirconia grating was formed on the back side using imprinting using a silicone mold. The polarizer was produced by depositing Al obliquely on the grating. The TM transmittance of the fabricated element was greater than 80% at a wavelength of 4.8 μm. The sol-gel zilconia films acted as antireflection films. The extinction ratio exceeded 26 dB at its wavelength.

We present preparation and characterization of thulium-doped silica-based optical fibers for fiber lasers. The fibers were prepared by modified chemical vapor deposition process and doped with alumina and thulium ions. Alumina co-doping was achieved through two different methods – solution doping and nanoparticle doping method. Prepared preforms were characterized in terms of refractive index profiles and dopants distribution. For the drawn fibers, their spectral attenuation, fluorescence lifetime and laser performance were measured. In the case of nanoparticle doping, better laser characteristics were observed. Discussion and explanation of the trends for laser efficiency improvement is given.

Today ultrashort pulse (USP) fiber lasers are in great demand in a frequency metrology field, THz pulse spectroscopy, optical communication, quantum optics application, etc. Therefore mode-locked (ML) fiber lasers have been extensively investigated over the last decade due the number of scientific, medical and industrial applications. It should be noted, that USP fiber lasers can be treated as an ideal platform to expand future applications due to the complex ML nonlinear dynamics in a laser resonator. Up to now a series of novel ML regimes have been investigated e.g. self-similar pulses, noise-like pulses, multi-bound solitons and soliton rain generation. Recently, we have used a highly nonlinear germanosilicate fiber (with germanium oxides concentration in the core ~ 50 mol. %) inside the resonator for more reliable and robust launching of passive mode-locking based on the nonlinear polarization evolution effect in fibers. In this work we have measured promising and stable ML regimes such as stretched pulses, soliton rain and multi-bound solitons formed in a highly-nonlinear ring laser and obtained by intracavity group velocity dispersion (GVD) variation in slightly negative region. As a result, we have obtained the low noise ultrashort pulse generation with duration < 250 fs (more than 20 bound pulses when obtained multi-bound soliton generation with intertemporal width ~ 5 ps) at a repetition rate ~ 11.3 MHz (with signal-to-noise ratio at fundamental frequency > 59 dB) and relative intensity noise <-101 dBc / Hz.

Structural, electronic and optical properties of four organic molecules named L1, L2, L3 and L4 were studied theoretically using DFT methodology. The UV-vis absorption spectra were investigated also experimentally when the molecules were dissolved in dicholoromethane. The calculations prove that for chosen molecules better results are obtained applying the LC-BLYP methodology due to the extended charge distribution and polarity of the molecules. The molecules L3 and L4 are characterised by the relatively high dipole moment and the low HOMO-LUMO energy gap splitting. It allows to suppose that these molecules may be useful for the nonlinear optical (NLO) applications. The solvent effect on the optical properties of the molecules was checked. The calculations were performed using polarisable continuum model and the data were compared to the experimental results.

A lot of attention is currently focused on synchronously pumped, extra-cavity crystalline Raman lasers generating one or two Stokes Raman components in KGW or diamond Raman-active crystals, and also generating additional components of stimulated polariton scattering in lithium niobate crystal having both cubic and quadratic nonlinearities.
In this contribution we report on generation of more than two Stokes components of stimulated Raman scattering with different Raman shifts in the all-solid-state, synchronously pumped, extra-cavity Raman laser based on the Raman-active a-cut BaWO₄ crystal excited by a mode-locked, 220 nJ, 36 ps, 150 MHz diode sidepumped Nd:GdVO₄ laser generating at the wavelength of 1063 nm. Excitation by the pumping radiation polarized along the BaWO₄ crystal optical axis resulted in the Raman generation with not only usual (925cm ^{– 1}), but also additional (332cm ^{– 1}) Raman shift. Besides the 1180-nm first and 1323 nm second Stokes components with the Raman shift of 925cm ^{– 1} from the 1063nm fundamental laser wavelength, we have achieved generation of the additional 1227 nm Raman component with different Raman shift of 332cm ^{– 1} from the 1180nm component. At the 1227 nm component the strongest 12-times pulse shortening from 36ps down to 3ps was obtained due to shorter dephasing time of this additional Raman line (3ps for the 332-cm ^{– 1} line instead of 6.5ps for the 925cm ^{– 1} line). It has to be also noted that the 1225 nm generation is intracavity pumped by the 1179 nm first Stokes component resulting in the strongest pulse shortening close to the 332cm ^-1 line dephasing time (3ps). Slope efficiency of three Stokes components generation exceeded 20%.

A novel, all-solid-state, self-mode-locked, collinearly phase-matched, parametric Raman Nd:YAG/CaCO₃ laser at 1168 nm anti-Stokes wavelength is reported. We have achieved parametric Raman conversion into the 1565 nm Stokes and 1168 nm anti-Stokes components and self-mode-locking using single Kerr-lens and Raman-active CaCO₃ nonlinear crystal inside the cavity of the diode side-pumped Nd:YAG laser generating at 1338 nm. Collinear phase matching of equally polarized Stokes-anti-Stokes coupling was self-organized due to zero dispersion of the CaCO₃ crystal at the fundamental laser wavelength of 1338 nm. We demonstrate possibilities of the Stokes and anti-Stokes picosecond pulse shortening and separation of few and even only one 120 ps ultra-short 1168 nm anti-Stokes pulse from the self-modelocked laser pulse train because of fast and spatially uniform depletion of pumping of intracavity Raman conversion without using any electro-optical device. We have obtained high energy output of up to 1.1 μJ in the single intensive anti-Stokes 120 ps ultra-short pulse which was up to 6.8 % from overall output radiation pulse train energy.

Although Fiber Bragg gratings (FBGs) are well known devices, their using as all-optical switching elements has been still examined. Current research is focused on optimization of their properties for their using in future all-optical networks. The main problem are high switching intensities needed for achieving the changes of the transmission state. Over several years switching intensities have been reduced from hundreds of GW/cm² to tens of MW/cm² by selecting appropriate gratings and signal parameters or using suitable materials. Two principal nonlinear effects with similar power requirements can result in the bistable transmission/reflection of an input optical pulse. In the self-phase modulation (SPM) regime switching is achieved by the intense probe pulse itself. Using cross-phase modulation (XPM) a strong pump alters the FBG refractive index experienced by a weak probe pulse. As a result of this the detuning of the probe pulse from the center of the photonic band gap occurs. Using of XPM the effect of modulation instability is reduced. Modulation instability which is the main SPM degradation mechanism. We focused on nonlinear FBGs based on chalcogenide glasses which are very often used in various applications. Thanks to high nonlinear parameters chalcogenide glasses are suitable candidates for reducing switching intensities of nonlinear FBGs.

With growing demands of Internet Protocol services for transmission capacity and speed, the Optical Burst Switching presents the solution for future high-speed optical networks. Optical Burst Switching is a technology for transmitting large amounts of data bursts through a transparent optical switching network. To successfully transmit bursts over OBS network and reach the destination node, resource reservation schemes have to be implemented to allocate resources and configure optical switches for that burst at each node. The one-way resource reservation schemes and the performance evaluation of reservation schemes are presented. The OBS network model is performed using OMNeT++ simulation environment. During the reservation of network resources, the optical cross-connect based on semiconductor optical amplifier is used as the core node. Optical switches based on semiconductor optical amplifiers are a promising technology for high-speed optical communication networks.

Chromium ions Cr²⁺ are known to have good fluorescence properties in the mid-infrared spectral region around the wavelength of 2.5 μm. The aim of this study was the investigation of new laser crystal materials – Zn_0.95Mn_0.05Se, Zn_0.70Mn 0_.30Se, and Zn_0.75Mg_0.25Se doped by Cr²⁺ ions and comparison of their spectral and laser characteristics. The spectroscopic parameters as absorption and fluorescence spectra as well as lifetimes were measured. As optical pumping the laser diode generating radiation at the wavelength of 1.69 μm (pulse repetition rate 10 Hz, pulse width 2 ms) was used. The longitudinal-pumped resonator was hemispherical with an output coupler radius of curvature 150 mm. The laser emission spectra were investigated and the highest intensity of emitted radiation was achieved at wavelengths 2451 nm, 2469 nm, and 2470 nm from the Cr:Zn_0.95Mn_0.05Se, Cr:Zn_0.70Mn_0.30Se, and Cr:Zn_0.75Mg_0.25Se laser systems, respectively. The input-output characteristics of laser systems were measured; the maximum output peak power 177 mW was obtained for Cr:Zn_0.95Mn_0.05Se laser system with slope efficiency of 6.3 % with respect to absorbed peak power. The output peak power as well as output beam spatial structure were stable during measurements. For the selection of the lasing wavelength, the single 1.5 mm thick quartz plate was placed at the Brewster angle inside the optical resonator between the output coupler and laser active medium. This element provided the tuning in the wavelength range 2290–2578 nm, 2353–2543 nm, and 2420–2551 nm for Cr:Zn_0.95Mn_0.05Se, Cr:Zn_0.70Mn_0.30Se, and Cr:Zn_0.75Mg_0.25Se, respectively. The obtained spectral FWHM linewidth of the individual output radiation was ~ 10 nm. A comparison with previously measured Cr:ZnSe laser system was added in the end

This article summarizes a measurement of gallium arsenide (GaAs) solar cells during their thermal processing. These solar cells compared to standard silicon cells have better efficiency and high thermal stability. However, their use is partly limited due to high acquisition costs. For these reasons, GaAs cells are deployed only in the most demanding applications where their features are needed, such as space applications. In this work, GaAs solar cells were studied in a high temperature range within 30-650 °C where their functionality and changes in surface topology were monitored. These changes were recorded using an electron microscope which determined the position of the defects; using an atomic force microscope we determined the roughness of the surface and an infrared camera that showed us the thermal radiated places of the defected parts of the cell. The electrical characteristics of the cells during processing were determined by its current-voltage characteristics. Despite the occurrence of subtle changes on the solar cell with newly created surface features after 300 °C thermal processing, its current-voltage characteristic remained without a significant change.

HID, LED and laser-based high resolution automotive headlamps, as of late known as ‘pixel light systems’, are at the forefront of the developing technologies paving the way for autonomous driving. In addition to light distribution capabilities that outperform Adaptive Front Lighting and Matrix Beam systems, pixel light systems provide the possibility of image projection directly onto the street. The underlying objective is to improve the driving experience, in any given scenario, in terms of safety, comfort and interaction for all road users. The focus of this work is to conduct a short survey on this state-of-the-art image projection functionality.

A holistic research regarding the image projection functionality can be divided into three major categories: scenario selection, technological development and evaluation design. Consequently, the work presented in this paper is divided into three short studies. Section 1 provides a brief introduction to pixel light systems and a justification for the approach adopted for this study. Section 2 deals with the selection of scenarios (and driving maneuvers) where image projection can play a critical role. Section 3 discusses high power LED and LED array based prototypes that are currently under development. Section 4 demonstrates results from an experiment conducted to evaluate the illuminance of an image space projected using a pixel light system prototype developed at the Institute of Product Development (IPeG).

Findings from this work can help to identify and advance future research work relating to: further development of pixel light systems, scenario planning, examination of optimal light sources, behavioral response studies etc.

High-resolution vehicle headlamps represent a future-oriented technology that can be used to increase traffic safety and driving comfort. As a further development to the current Matrix Beam headlamps, LED-based pixel light systems enable ideal lighting functions (e.g. projection of navigation information onto the road) to be activated in any given driving scenario. Moreover, compared to other light-modulating elements such as DMDs and LCDs, instantaneous LED on-off toggling provides a decisive advantage in efficiency.

To generate highly individualized light distributions for automotive applications, a number of approaches using an LED array may be pursued. One approach is to vary the LED density in the array so as to output the desired light distribution. Another notable approach makes use of an equidistant arrangement of the individual LEDs together with distortion optics to formulate the desired light distribution. The optical system adjusts the light distribution in a manner that improves resolution and increases luminous intensity of the desired area.

An efficient setup for pixel generation calls for one lens per LED. Taking into consideration the limited space requirements of the system, this implies that the luminous flux, efficiency and resolution image parameters are primarily controlled by the lens dimensions.

In this paper a concept for an equidistant LED array arrangement utilizing distortion optics is presented. The paper is divided into two parts. The first part discusses the influence of lens geometry on the system efficiency whereas the second part investigates the correlation between resolution and luminous flux based on the lens dimensions.

An imperfections or defects may appear in fabricated monocrystalline solar cells. These microstructural imperfections could have impact on the parameters of whole solar cell. The research is divided into two parts, firstly, the detection and localization defects by using several techniques including current-voltage measurement, scanning probe microscopy (SPM), scanning electron microscope (SEM) and electroluminescence. Secondly, the defects isolation by a focused ion beam (FIB) milling and impact of a milling process on solar cells. The defect detection is realized by I-V measurement under reverse biased sample. For purpose of localization, advantage of the fact that defects or imperfections in silicon solar cells emit the visible and near infrared electroluminescence under reverse biased voltage is taken, and CCD camera measurement for macroscopic localization of these spots is applied. After rough macroscopic localization, microscopic localization by scanning probe microscopy combined with a photomultiplier (shadow mapping) is performed. Defect isolation is performed by a SEM equipped with the FIB instrument. FIB uses a beam of gallium ions which modifies crystal structure of a material and may affect parameters of solar cell. As a result, it is interesting that current in reverse biased sample with isolated defect is smaller approximately by 2 orders than current before isolation process.

The aim of this research is to detect and localize microstructural defects by using an electrically excited light emission from a forward/reverse-bias stressed pn-junction in thin-film Cu(In; Ga)Se₂ solar cells with metal wrap through architecture. A different origin of the local light emission from intrinsic/extrinsic imperfections in these chalcopyrite-based solar cells can be distinguished by a spectrally-filtered electroluminescence mapping. After a light emission mapping and localization of the defects in a macro scale is performed a micro scale exploration of the solar cell surface by a scanning electron microscope which follows the particular defects obtained by an electroluminescence. In particular, these macroscopic/microscopic examinations are performed independently, then the searching of the corresponding defects in the micro scale is rather difficult due to a diffused light emission obtained from the macro scale localization. Some of the defects accompanied by a highly intense light emission very often lead to a strong local overheating. Therefore, the lock-in infrared thermography is also performed along with an electroluminescence mapping.

The development of laser-based lighting systems has been the latest step towards a revolution in illumination technology brought about by solid-state lighting. Laser-activated remote phosphor systems produce white light sources with significantly higher luminance than LEDs. The weak point of such systems is often considered to be the conversion element. The high-intensity exciting laser beam in combination with the limited thermal conductivity of ceramic phosphor materials leads to thermal quenching, the phenomenon in which the emission efficiency decreases as temperature rises. For this reason, the aim of the presented study is the modeling of remote phosphor systems in order to investigate their thermal limitations and to calculate the parameters for optimizing the efficiency of such systems. The common approach to simulate remote phosphor systems utilizes a combination of different tools such as ray tracing algorithms and wave optics tools for describing the incident and converted light, whereas the modeling of the conversion process itself, i.e. photoluminescence, in most cases is circumvented by using the absorption and emission spectra of the phosphor material. In this study, we describe the processes involved in luminescence quantum-mechanically using the single-configurational-coordinate diagram as well as the Franck-Condon principle and propose a simulation model that incorporates the temperature dependence of these processes. Following an increasing awareness of climate change and environmental issues, the development of ecologically friendly lighting systems featuring low power consumption and high luminous efficiency is imperative more than ever. The better understanding of laser-based lighting systems is an important step towards that aim as they may improve on LEDs in the near future.

Application of photonic crystal structures (PhC) can be attractive for overall and local enhancement of light from patterned areas of the light emitting diode (LED) surface. We used interference and near-field scanning optical microscope lithography for patterning of the surface of GaAs/AlGaAs based LEDs emitted at 840 nm. Also new approach with patterned polydimethylsiloxane (PDMS) membrane applied directly on the surface of red emitting LED was investigated. The overall emission properties of prepared LED with patterned structure show enhanced light extraction efficiency, what was documented from near- and far-field measurements.

Photonic crystals have been extensively studied for their unique optical properties that promise interesting novel devices. Our contribution is focused on a 2D photonic crystal structure formed by Al2O3 layer on silicon substrate, patterned with periodic hexagonal lattice of deep air holes. Azimuthal angle dependences of the specular light reflection were recorded photo-electrically at various angles of icidence and wavelengths. Data obtained were processed via mapping in reciprocal k-space. The method promises a possibility to visualize the equi-frequency contours and get more detailed information about the properties of the sample used.

In this work we study optical properties of nanostructured layers formed on silicon surface. Nanostructured layers on Si are formed in order to reach high suppression of the light reflectance. Low spectral reflectance is important for improvement of the conversion efficiency of solar cells and for other optoelectronic applications. Effective method of forming nanostructured layers with ultralow reflectance in a broad interval of wavelengths is in our approach based on metal assisted etching of Si. Si surface immersed in HF and H2O2 solution is etched in contact with the Pt mesh roller and the structure of the mesh is transferred on the etched surface. During this etching procedure the layer density evolves gradually and the spectral reflectance decreases exponentially with the depth in porous layer. We analyzed properties of the layer porosity by incorporating the porosity gradient into construction of the layer spectral reflectance theoretical model. Analyzed layer is splitted into 20 sublayers in our approach. Complex dielectric function in each sublayer is computed by using Bruggeman effective media theory and the theoretical spectral reflectance of modelled multilayer system is computed by using Abeles matrix formalism. Porosity gradient is extracted from the theoretical reflectance model optimized in comparison to the experimental values. Resulting values of the structure porosity development provide important information for optimization of the technological treatment operations.

A new generation of the WILLIAM (WIde-field aLL-sky Image Analyzing Monitoring system) camera includes new features such as monitoring of rain and storm clouds during the day observation. Development of the new generation of weather monitoring cameras responds to the demand for monitoring of sudden weather changes. However, new WILLIAM cameras are ready to process acquired image data immediately, release warning against sudden torrential rains, and send it to user's cell phone and email. Actual weather conditions are determined from image data, and results of image processing are complemented by data from sensors of temperature, humidity, and atmospheric pressure. In this paper, we present the architecture, image data processing algorithms of mentioned monitoring camera and spatially-variant model of imaging system aberrations based on Zernike polynomials.

Education in the field of photonics is usually somehow complex due to the fact that most of the programs include just a few subjects on the field, apart from specific Master programs in Photonics. There are also specific doctorate programs dealing with photonics. Apart from the problems shared with photonics in education in general, biophotonics specifically needs an interdisciplinary approach between biomedical and technical or scientific fields. In this work, we present our education experience in teaching the subject Fundamentals of Biophotonics, intended preferentially to engineering Bachelor and Master degrees students, but also to science and medicine students. First it was necessary to join a teaching group coming from the scientific technical and medical fields, working together in the subject. This task was easier as our research group, the Applied Optical Techniques group, had previous contacts and experience in working with medicine professors and medical doctors at hospitals. The orientation of the subject, intended for both technical and medical students, has to be carefully selected. All this information could be employed by other education institutions willing to implement studies on biomedical optics.