Pawel Wierzba

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.

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.

Interferometric optical fiber sensor for weigh-in motion of road vehicles

An interferometric optical fiber sensor intended for use in Weigh-in-Motion systems is presented. The sensor uses a modified Michelson interferometer configuration with two sensing arms. To avoid polarization induced fading the force acting on the sensor is measured indirectly, using modulators which convert it to pressure. Operation of such modulators was verified by experiment and based on its results a laboratory model of a sensor was built and tested.

Distributed polarimetric optical fiber sensor using a tunable semiconductor laser

The widespread migration to the Wavelength Division Multiplexing telecommunication systems stimulates the demand for tunable external cavity semiconductor lasers used for production testing and maintenance purposes. As these lasers have a coherence length of hundreds meters and their prices are continually decreasing, it can be predicted that these lasers will soon be commonly used as a source in interferometric and polarimetric sensors. In this paper we present the theoretical description of a distribution optical fiber sensor using polarization mode coupling in a polarization maintaining optical fiber. The performance of the sensor using a tunable semiconductor laser is analyzed and the possible applications of this type of sensor are discussed.

Noise measurement of micromachined bolometers

The full characterization of a detector requires the calculation of the detectivity (D*), based on responsivity and noise equivalent power measurement. In this paper we present a system, developed for noise measurements of micromachined bolometers designed and produced at the VTT Electronics. Measurement results are presented and some ideas for improvement of the developed measuring system, are discussed.

Polarimetric optical fiber sensor for weight-in-motion applications

Stress sensors dedicated for Weigh-in-Motion of road vehicles should exhibit high dynamic range, good accuracy and repeatability, as well as long service life. One of the most promising group of sensors for this application are polarimetric sensors, due to their simplicity and high sensitivity. Preliminary measurements of the optical fiber properties in this application resulted in significant hysteresis being observed even for relatively low stress, which is probably caused by the cladding properties or by the construction of the modulator used in the measurement.

System for measuring thickness of opaque dielectric layers

The subject of this paper is a system for measuring thickness of opaque dielectric layers using the change of the coefficient of the magnetic coupling of two coils. This circuit was designed for measurements of thickness of elements in boats made from epoxy-glass laminates. It can, however, be used everywhere, where the need occurs to make non-destructive thickness measurements of dielectric layers in the range from 5 to 30 mm with an accuracy of 0,5 mm.