The paper presents the results of design, manufacturing and characterization of an hybrid broad band in-line device using a nematic liquid crystal as an active medium which influences light propagating in a biconical optical fibre taper. A liquid crystal mixture denoted 6CHBT*and E7 is designed for electric, as well as temperature control of electromagnetic wave propagation in a broad wavelength range. The main reason of using the taper structure with a waist of 10± 0.5 μm and losses lower than 0.5 dB is possibility of using a liquid crystalline medium as cladding. Such approach enables effective control of its refractive index. Two kinds of initial liquid crustal molecules’ orientation (parallel and orthogonal) in relation to the light beam propagating in a taper were applied. Performance of a tuned cladding was studied at electric field of the range of 0V – 160V in the room temperature equal to 20°C. Influence of induced reorientation of liquid crystal molecules was measured at a broad wavelength range [500-1700 nm].
Optical fiber vibration sensors are an appropriate alternative for piezoelectric devices, which are electromagnetic sensitive to the external conditions. Most of the vibration sensors demonstrated in previous publications resist to different interferometers or Bragg’s gratings. Such sensors require a long time of stabilization of an optical signal, because they are vulnerable to undesirable disturbance. In majority, time response of an optical sensor should be instantaneous, therefore we have proposed an in- line vibration sensing passive element based on a tapered fiber. Micrometer sized optical fiber tapers are attractive for many optical areas due to changes process of boundary conditions. Such phenomena allow for a sensitive detection of the modulation phase. Our experiment shows that a singlemode, adiabatic tapered fiber enables detecting an acoustic vibration. In this study, we report on Mach- Zehnder (MZ) interferometer as a vibration sensor which was composed of two 50/50 couplers at 1550 nm. In the reference arm we used a 4 meter singlemode optical fiber (SMF28), while in the arm under test we placed tapered optical fibers attached to a metal plate, put directly on speaker. Researches carried out on different tapered fibers which diameter of a taper waist was in the range from 5 μm to 25 μm, and each taper was characterized by optical losses less than 0,5 dB. The measured phase changes were over a frequency from 100 Hz to 1 kHz and an amplitude in the range from 100 mVpp to 1 Vpp. Although on account of a limited space we have showed only the results for 100 Hz. Nevertheless, experimental results show that this sensing system has a wide frequency response range from a few hertz to one of kilohertz, however for some conditions, a standard optical fiber showed better result.
The present work has been centered in the design, fabrication and characterization of a new in-line tunable nematic liquid crystal (TNLC) optical fiber device. The main reason of using a biconical optical fibre taper as a core surrounded by liquid crystals molecules is the possibility to change the losses by the electrically induced reorientation of liquid crystal molecules. A taper is made from a standard fiber SMF28®, whereas the clad uses the nematic mixture 1550C1 type. A supercontinuum source with a bandwidth of [500-700 nm] and laser with wavelength 532 nm were used as light sources.
Propagation of a light beam in optical fiber tapers depends on few parameters like diameter of a taper waist region, adiabatic or non-adiabatic shape of a whole, as well as boundary condition connected with refractive index surrounding the taper. As external materials many mixtures can be used allowing to manufacture different applications [1-3]. In this work we applied liquid crystals’ medium due to its optical properties - anisotropic as a cladding for the manufactured taper. Properties of liquid crystals can be modified by electric or magnetic fields, as well as by temperature change. These features make liquid crystal fibers very important for optical applications. In this work we have built an optical cell which consists of a liquid crystals’ mixture of 1550C1 . The applied taper can be described by the following parameters: diameters of 10+/- 0.5 μm, losses lower than 0.5 dB in visible range, manufactured on FOTET. The tapered fiber was put in a liquid-crystal cell made of two tin oxide coated glass plates separated by spacers. The value of the used electric field was contained in the range of 0V - 160V. This experiment demonstrates ability of changing optical transmission in a tapered fiber immersed in a liquid-crystal medium. The range of optical transmission observation was between 500-700 nm which was connected with an LC transmission. Also, were performed measurements of influence of temperature in the range of 20-80°C on the proposed device. For temperature higher than 50°C, increased optical power propagating in the tapered fiber was observed.