Theoretical and experimental analysis of a new fibre-optic ellipsometer in polarimetric configuration is presented. The main idea of a system operation is based on controlled birefringence introducing on a piece standard single-mode fibre. Estimation of a real-time changes in polarisation state parameter, and the ellipsometer measurement have been done for the known induced birefringence. In the paper, research of the constructed in-line system as a new ellipsometer detection system for the fibre-optic sensor application is also presented.
The idea of the polarimetric detection system presented in this paper is a new approach to problem of state of polarisation measurements. The system controlled by computer consists of tunable retarder, analyzer, and detector. Theoretical considerations have been confirmed by an experiment, where twisted single-mode fiber has been used.
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The construction of the in-line fiber-optic polarizer is presented. This element based on the biconical taper structure is positioned on a metal layer. the four-layer planar structure has been used for theoretical investigation of polarizer action. The theoretical results have been compared with experimental investigation of manufactured elements. The technological set-up for the polarizer preparation is also shown. The polarizers have been made for 0.33 and 1.300 mm wavelenghths. The first of them has a typical extinction ratio of 25dB with an attenuation of guided mode of 3dB. The second one has typical extinction ratio of 30 dB or more, with an attenuation of the desired polarisation of about 2 dB.
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The various possible applications of the fiber-optic Sagnac interferometer as a sensor of physical fields are presented. The use of the Segnac interferometer as an optical gyroscope for an investigation of show-speed rotational platforms and a construction of distributed security system are described. The possibility of applying a modified system for measurement of nanometer vibrations and parameters of the in-ine fiber-optic polarizer, phase and polarisation modular are also presented. Finally, the usability of the Sagnac interferometer as a fiber-optic ellipsometer is described.
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The construction of the fibre-optic sensor of external perturbations and results of the relevant studies are presented. As a sensor head, the sample of two-mode optical fiber is used. Changes of intermodal interference condition, caused by external perturbation, generated changes of output speckle pattern. This output has been considered as an intensity image and diffraction method has been applied for its recognition. For this reason, the ring-wedge photodetector has been placed in the Fourier plane of the image studied. The digital signal generated by this detector has been processed by software neural network. As a result of a suitable process of network training, a possibility o recognizing the perturbation has emerged, which made it possible to avoid troublesome analysis of intermode interactions.
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