Surface plasmon resonance (SPR) is widely applied for bio/ chemical sensing. The main problem for all sensors is accuracy and sensitivity enhancement. For SPR sensors the accuracy depends on the characteristics of the plasmon resonance. In this work, we study SPR excitation assisted by liquid crystal layer. We consider Kretshmann configuration where a liquid crystal is sandwiched between a prism and glass plate, while the gold layer is evaporated over the glass plate. We show that the Bragg reflection of cholesteric liquid crystals modifies the plasmon resonance in a way increasing the accuracy of its location. Also, features of plasmon resonance excitation are studied for chiral liquid crystals.
In this paper we derive interference equations and present theoretical models for a variety of cases of interfering mode pairs: non-degenerate and non-degenerate; non-degenerate and degenerate as well as degenerate and degenerate even/odd LP modes assuming a Gaussian approximation and an identical polarization. For 2x2 fiber
couplers of different coupling ratios and single mode at 1310/1550nm, we measure the coupling ratio in a few mode regime of operation at 650nm and record the pattern distributions. We find a very good correspondence between theoretical and experimental results which will be used for optimizing a CCD array used for the analysis of the
external disturbances along an optical fiber intrusion sensor.
In this work we present an analysis of the response of a compact, simple and inexpensive optoelectronic
sensor system intended to detect spectral shifts of a long-period fiber grating (LPG). The system makes use of a
diffraction grating and a couple of receiving optical fibers that pick up signals at two different wavelengths. This
differential detection system provides the same useful information from an LPG-based sensor as with a conventional
laboratory system using optical spectrum analyzers for monitoring the minimum offset of LPG. The design of the
fiber detection pair as a function of the parameters of the dispersion grating, the pick-up fiber and the LPG
parameters, is presented in detail. Simulation of the detection system responses is presented using real from spectral
shifts in nano-coated LPGs caused by the evaporation of various liquids such as water, ethanol and acetone, which
are examples of corrosive, flammable and hazardous substances. Fiber optic sensors with similar detection can find
applications in structural health monitoring for moisture detection, monitoring the spillage of toxic and flammable
substances in industry etc.
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