Bulletin of the Polish Academy of Sciences Technical Sciences

The paper presents a modification of capillary optical fibers fabrication method from an assembled glass preform. A change of dimensional proportions in the capillary optical fiber drawn from a single preform is allowed on-line via the control of overpressure and thermal conditions in the outflow meniscus which essentially lowers the manufacturing costs. These conditions are among the solutions (velocity fields) of the Navier-Stokes equations adapted to the capillary optical fiber pulling geometry and temperature distribution in the oven. The velocity fields give solutions to other quantities of interest such as flow rate, pulling force and fiber geometry. The calculation and experimental results for capillary optical fibers were shown in the following dimensional range: internal diameters 2-200 µm, external diameters 30-350 µm, within the assumed dimensional stability (including ellipticity) better than 1%. The parameters of fabricated capillary optical fibers of high-quality low-loss optical multicomponent glasses were: losses 100 dB/km, mechanical strength above 1GPa with Weibull coeffcient in the range 3-7, internal numerical aperture 0.1-0.3, external numerical aperture 0.1-0.3, core index 1.5-1.8, transparency 0.4-2 µm, thermally and/or chemically conditioned internal surface, double polyimide protection layer, soft or hard jacketed, connectorized. The capillary optical fibers were applied in our own and several external laboratories in spectroscopy, refractometry, micro-fluidics and functional microoptic components. The paper summarizes a design, technological and application work on capillary optical fibers performed during a recent national research program devoted to optoelectronic components and modules.

The paper presents the result of investigations of aluminosilicate (low silica - 25 mol%) and phosphate optical fibres. The methods of glass preparation and their properties are showed. A set of physical measurements including: DTA, DSC, DL analysis, absorption spectroscopy, visible and infrared absorption edges and thermo-physical properties were determined. The stable glass compositions were doped with rare earth elements. Selected properties of obtained glasses are: high transmission, refractive index 1.53-1.68, high solubility of RE ions (up to 10 wt%). Double-crucible and rod-in-tube drawing techniques were applied to obtain aluminosilicate and phosphate double clad optical fibres doped with neodymium and ytterbium ions. Luminescence spectra of manufactured glasses and fibres are presented.

The paper deals with the basic set-up of single-frequency microchip laser - so called Lyot filter configuration. Description of its operation and practical realization is given. Some results obtained for Nd:YAG/KTP microchip laser are presented. The evidences of single-frequency operation and its limits are emphasized. Described construction constitutes the base for building the frequency stabilization of green 532 nm microchip laser.

Lighting sources with a cold cathode are widely used in electronics. The lamps with a cold cathode are used primarily as sources of white light in optical scanners, digital indicators, display panels and signalling devices. In the paper the advantages of carbonaceous materials as emitters of cold electrons and the possibilities of using them to create a cathode in an electron lamp are discussed.

Polarimetric optical fiber sensors based on highly birefringent (HB) polarization-maintaining fibers have focused great interest for last decades. The paper presents a novel modular fiber optic sensing system of potential industrial applications to measure temperature, hydrostatic pressure, and strain that is based on classical HB and photonic crystal fibers and can operate at visible and infrared wavelengths. The main idea of the system is a novel and replaceable fiber-optic head, which allows adjusting the measuring system both to the required range and type (strain, pressure or temperature) of the external measurand. We propose also a new configuration of the fiber optic strain gauge with a free cylinder and an all-fiber built-in analyzer based on the photonic crystal fiber filled with a liquid crystal. Additionally, strain sensitivities of various HB fibers operating at visible and infrared wavelengths range have been measured.

A layered sensor structure of metal-free phthalocyanine H2Pc (~160 nm) with a very thin film of palladium (Pd ~20 nm) on the top, has been studied for hydrogen gas-sensing application at relatively low temperatures of about 30°C and about 40°C. The layered structure was obtained by vacuum deposition (first the phthalocyanine Pc and than the Pd film) onto a LiNbO3Y- cut Z-propagating substrate, making use of the Surface Acoustic Wave method, and additionally (in this same technological processes) onto a glass substrate with a planar microelectrode array for simultaneous monitoring of the planar resistance of the layered structure. In such a layered structure we can detect hydrogen in a medium concentration range (from 0.5 to 3% in air) even at about 30°C. At elevated temperature up to about 40°C the differential frequency increases proportionally (almost linearly) to the hydrogen concentration and the response reaches its steady state very quickly. The response times are about 18 s at the lowest 0.5% hydrogen concentration to about 42 s at 4% (defined as reaching 100% of the steady state). In the case of the investigated layered structure a very good correlation has been observed between the two utilized methods - the frequency changes in the SAW method correlate quite well with the decreases of the layered structure resistance.

In this contribution an optical method of controlling the state of soft biological tissues in real time, exposed to laser radiation is discussed. The method is based on the assumption that the change dynamics of the amplitude of the scattered diagnostic radiation (λ = 635 nm) is compatible with the change dynamics of the tissue inner structure exposed to the Nd:YAG laser radiation (λ = 1064 nm). In this method the measurement of the tissue temperature is omitted. Exemplary results of the laboratory research on this method and an interpretation of the results are presented.

The paper presents selected results of studies connected with modeling of a biological object which could be used for simulation and measurements of the selected human tissues optical transmittance. The studies were performed for transilluminated homogeneous tissue layers as well as for objects consisted of different tissues. During simulations the software built with LabVIEW environment was used. Experimental verification of the model structure was made with spectrophotometry. The presented examples of modeling concern the transmittance spectra for two selected specific objects: the venous blood and muscle tissue analyzed in the wavelength range extending from 360 nm to 900 nm. The implemented model could be used in estimating the content and thickness of particular layers distinguished in a complex object and prediction of their transillumination efficiency.

Optical low-coherence interferometry is one of the most rapidly advancing measurement techniques. This technique is capable of performing non-contact and non-destructive measurement and can be used not only to measure several quantities, such as temperature, pressure, refractive index, but also for investigation of inner structure of a broad range of technical materials. We present theoretical description of low-coherence interferometry and discuss its unique properties. We describe an OCT system developed in our Department for investigation of the structure of technical materials. In order to provide a better insight into the structure of investigated objects, our system was enhanced to include polarization state analysis capability. Measurement results of highly scattering materials e.g. PLZT ceramics and polymer composites are presented. Moreover, we present measurement setups for temperature, displacement and refractive index measurement using low coherence interferometry. Finally, some advanced detection setups, providing unique benefits, such as noise reduction or extended measurement range, are discussed.

The paper presents a construction of a system for measurements of pH, concentration of calcium ions and concentration of heavy metal ions in water. Three fiber optic sensors in flow configuration were designed and tested. The system is fully automatic and can be used for water quality monitoring.

In this work problems associated with requirements related to pollution emissions in compliance with more restrictive standards, low-emission combustion technology, technical realization of the monitoring system as well as algorithms allowing combustion process diagnostics are discussed. Results of semi-industrial laboratory facility and industrial (power station) research are presented as well as the possibility of application of information obtained from the optical fibre monitoring system for combustion process control. Moreover, directions of further research aimed to limit combustion process environmental negative effects are presented.