Jerzy Plucinski

Theoretical foundations for noninvasive measurement of variations in the width of the subarachnoid space.

Numerical modeling was used for the theoretical analysis of the propagation of optical radiation in the tissues of the human head, generated by a single source placed on the surface of the scalp. Of special interest and importance is the propagation of radiation within the layer of cerebrospinal fluid contained in the subarachnoid space (SAS), which is the only low absorption/high transmittance medium whose width can vary rapidly. Qualitative and quantitative assessment of changes in propagation of radiation within the SAS could become a source of information on changes in the geometry of this anatomical compartment playing a crucial role in cranio-spinal physiology and pathology. Essential for the idea of the possible noninvasive assessment of changes in width of the SAS by an optical method is the dependence of intensity of radiation reaching a photodetector located at a certain distance from the source on changes in the width of this fluid layer, which acts like a biological optical waveguide. Monte Carlo modeling and numerical analysis confirmed the feasibility of assessing changes in the width of the subarachnoid space optically. Presented here are details of the Monte Carlo simulation of light propagation in the tissues of human head and the results of such simulation as a function of the width of the subarachnoid space, calculated for different distances between the source and detector and for a few selected values of bone thickness. Results of numerical modeling were then compared with those of experiments on a mechanical-optical model.

Fiber optic quasi-distributed temperature sensor

The subject of this paper is an optical fiber temperature sensor using the techniques of optical time domain reflectometry. The sensor uses the dependence between the refractive index of epoxy resins and temperature and allows us to develop sensors working in transmission as well as in reflective mode.

Fiber optic sensor based on optical frequency domain reflectometry

In the paper, the analysis of the application of a tunable semiconductor laser working in 1550 nm band in a C-OFDR construction is presented. The laser was tuned in narrow 0.24 nm range by a PZT element and in wide 70 nm range by a stepping motor. The narrow range was used for signal separation from measurement points laying along optical fiber. The wide range can be used in to separate signals from branches of a fiber optic sensor network. The reflectometer was used for signal detection from quasi-distributed sensors network. Measurements were carried out for different distances of point fiber optic sensors from the reflectometer. As the models of point sensors air cavities were used. The influence of tuning range of the laser on measurement errors is discussed.

Optical refractometer for complex refractive index measurement in UV-NIR range

An optical system for measuring the spectrum of the complex refractive index of liquids in the UV-NIR range is described. The presented optical fiber measurement method allows remote control of the index. The developed refractometer has been tested with samples from different sections of paper mill and chemical pulp mill production processes. The obtained accuracy of the real part refractive index measurements was 10-5 with resolution 2 (DOT) 10-6 (for the wavelength in range 300 - 920 nm with spectral resolution better than 0.5 nm). The absorption corresponding to the imaginary part of the refractive index is measured in 0 divided by 20 dB/cm range with 0.01 dB/cm resolution.

Optical Fibre Refractometer For Liquid Refractive Index Measurement

The construction and principle of operation of optical fibre refractometer is given in the paper. The refractometer operates on attenuation changing measurement. The attenuation changing is a function of mode radiation from specially bent optical fibre. A quartz step index, optical fibre with polymer coat and 130 um core in diameter was used to develop the model of the sensor. At the place of bending the coat was removed. The sensors with a different diameter of bending were examined in liquids with known refractive indexes. In the transmitter was used LED while receiver was made with pin fotodiode.

Interferometric optical fiber sensors with active stabilization of the operating point using a tunable semiconductor laser

Optical fiber force sensors using Michelson interferometer and a tunable external cavity semiconductor lase rsource are investigated in order to develop a sensor whose operating point is actively stabilized by the change of the source wavelength. Two configurations of such sensros are briefly discussed, and their advantages are compared. Based on presented results a sensor was built and tested. The sensor employs an indirect force transducer in which the force acting on it is converted into hydrostatic pressure which is subsequently measured. The sensor exhibits good linearity. Its bandwidth is currently limited by the tuning speed of the laser and can be extended by increasing the tuning speed of the laser.

Application of computer-assisted modified coupled-mode method for the design of polarimetric sensors

A method for modeling of multiply purturbed fibers was developed as an extension to the modified coupled-mode method. Being based on numerical solution of coupled mode equations, the method is not limited in the scope of its applications to the cases in which coupling coefficients are constant along the fiber. Short computation time was achieved as a result of modification to the solved coupled-mode equations. Presented method was developed as a design tool for polarimetric optical fiber sensors. The use of the method is demonstrated on an example of a twisted single-mode elliptic-core fiber subjected to pure bending. Moreover, it was shown that the presented method can be also applied to visibility calculation in polarimetric sensors using polychromatic sources.

System for time-resolved spectroscopy using a semiconductor picosecond laser

Optical time-resolved spectroscopy using optical fibers opens up new possibilities for research on highly scattering materials. We present a system that measures the time of fligh distribution of light propagating through such materials. The system employs a picosecond semiconductor laser, a photon counter using an avalanche photodiode working in Geiger mode and standard, gradient index profile, multimode fibers. We present the results of measurements obtained using this system and conclusions regarding the further improvement of the system.

Quasi-distributed fiber optic temperature sensor working in transmission mode

In the paper, a quasi-distributed fiber optic temperature sensor working in transmission mode is presented. This sensor is based on partial reflection from silicone resin layers placed between ends of adjoining optical fiber segments. For signal detection. an optical time domain reflectometer was used. The transmission mode of operation allows temperature to be measured in up to tens points whose spacing along the fiber can range from few centimeters to few kilometers. A complex calibration procedure of the sensor is also presented.

Optical setup for the measurement of instant velocity of samples subjected to breaking test

In the paper a setup for the measurement of instant velocity of samples subjected to breaking test is described. It was estimated that the maximum speed of deformation is 50 m/s and maximum strain is 5 mm. An optical method has been selected and a measurement setup was built. We discuss the setup performance and the measurement results.