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Development of photonic crystal fibers (PCFs) technology has created new research fields for optical sensors and telecommunication. The cross section geometry modifications of this type of fibers allow to influence their optical parameters. These modifications are not limited to change sizes and arrangements of an air holes’ lattice, but also replacing air with another material. In the paper we have shown how to change thermo-optical properties of a large mode area commercially available LMA-10 PCF by filling it with different chemical substances. Our previous research has led us to develop a class of optical fiber temperature threshold sensor transducers based on a partially filled PCF with higher alkanes. The principle of work of such a sensor transducer is to use a temperature bi-stability of a filling material because when the higher alkane is in the solid state light cannot pass through the transducer, and when it is in the liquid state light can be transmitted. One of the most important advantages of higher alkanes we used in the experiments are their different melting points, but the most important disadvantage is discrepancy between melting and crystallization temperatures and the sensor switches on and off for different temperatures. This effect called supercoiling appears due to the lack of nucleation centers. To reduce this effect the gold nanoparticels (NPs) in hexane colloid were used. We have prepared samples with three higher alkanes doped with 1% of Au NPs and we have shown their temperature and time responses. The proper selection of melting points of higher alkanes allows to design the multilevel temperature threshold sensor which can cover the temperature range from -20°C up to 70°C, and can be applied in chemical, oil, gas and energy industry.
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