This paper presents an experimental study on influence of input light polarization on the spectral characteristics of a fibre twist sensor based on Tilted Fiber Bragg Grating (TFBG) with simultaneous application of bending to an optical fibre. The application of proposed measurement stand could provide the ability of transforming the bending to a displacement. The twist measurement was performed by tuning of the sensor illuminating light polarization angle. The spectral parameters of selected cladding mode which are sensitive to the rotation of input light polarization angle have been shown. This paper shows the characteristics of transmittivity and wavelength shift for an incident high-order cladding mode measured with different curvatures of fibre. The dependency of selected cladding mode spectral parameters related with the twist measurement on the influence of temporary bending has been shown. The measurements were performed for two positions of sensing structure refractive index perturbations in relation to the bending direction plane. The experimental results show that the direction of TFBG structure bending has a small influence on the stability of spectral parameters characteristic for twist measurement, assuming that the bending direction is fixed while measurement.
Detection of explosives vapors is an extremely difficult task. The sensitivity of currently constructed detectors is often insufficient. The paper presents a description of an explosive vapors concentrator that improves the detection limit of some explosives detectors. These detectors have been developed at the Institute of Optoelectronics. The concentrator is especially dedicated to operate with nitrogen oxide detectors. Preliminary measurements show that using the concentrator, the recorded amount of nitrogen dioxide released from a 0.5 ng sample of TNT increases by a factor of approx. 20. In the concentrator an induction heater is applied. Thanks to this and because of the miniaturization of the container with an adsorbing material (approx. 1 cm3), an extremely high rate of temperature growth is achieved (up to 500 °C within approx. 25 s). The concentration process is controlled by a microcontroller. Compact construction and battery power supply provide a possibility of using the concentrator as a portable device.