RESUMEN
This paper is a continuation of previous work and shows the enhancement of the surface plasmon resonance effect in a tapered optical fiber device. The study investigated liquid crystal cells containing a tapered optical fiber covered with a silver nanolayer, surrounded by a low refractive index liquid crystal in terms of the properties of light propagation in the taper structure. Silver films with a thickness of d = 10 nm were deposited on the tapered waist area. Measurements were performed at room temperature; liquid crystal steering voltage U from 0 to 200 V, with and without any amplitude modulation with a frequency of f = 5 Hz, and the wavelength λ ranged from 550 to 1200 nm. A significant influence of the initial arrangement of liquid crystals molecules on light propagation was observed. Three types of liquid crystal cells-orthogonal, parallel, and twist-were considered. During the measurements, resonant peaks were obtained-the position of which can also be controlled by the type of liquid crystal cells and the steering voltage. Based on the obtained results, the best parameters, such as highest peak's width reduction, and the highest SNR value were received for twisted cells. In addition, the present work was compared with the previous work and showed the possibility of improving properties of the manufactured probes, and consequently, the surface plasmon resonance effect. In the presented paper, the novelty is mainly focused on the used materials as well as suitable changes in applied technological parameters. In contrast to gold, silver is characterized by different optic and dielectric properties, e.g., refractive index, extension coefficient, and permittivity, which results in changes in the light propagation and the SPR wavelengths.
RESUMEN
This paper presents the influence of a thin metal layer deposition on the surface of a tapered optical fiber surrounded by a low liquid crystal, on light propagation inside the taper structure. In this research, three types of liquid crystal cells were under investigation: orthogonal, parallel, and twist. They differed by the rubbing direction of the electrodes in relation to the fiber axis determining the initial molecule arrangement inside the cell. Gold films with thickness d = 30 nm were deposited on the tapered fiber surface in the tapered waist area. Cells including a tapered optical fiber with no metallic layer were also examined and presented as a reference. All measurements were performed at room temperature for a different steering voltage U from 0 to 200 V, with and without any amplitude modulation with a frequency f = 5 Hz, and the wavelength λ range from 550 to 1200 nm. As a result, the resonant peaks were obtained, which depends on a liquid crystal cell type and steering voltage, as well. This paper shows the possibility of sensing the change of applied voltage by the constructed system. During measurements, additional effects as signal overlapping and intermodal interference were observed reducing measured voltage value. In the future, the improved, similar systems that will have a better response could be used as a sensor of factors to which liquid crystal (LC) will be sensitive, especially temperature and electric field.
RESUMEN
We propose an electrically tunable phase shifter for terahertz frequencies. The device is based on a polymer stabilized liquid crystal which allows for a simple device geometry. The polymer stabilized liquid crystal enables continuous tuning of the introduced phase shift with only one pair of electrodes. By characterizing the device with terahertz time-domain spectroscopy we demonstrate a phase shift up to 2.5 terahertz, only slightly changed properties of the neat liquid crystal and significantly reduced response times.
