In this work, a novel technique to create adaptive liquid crystal lenses and other optical components is proposed and demonstrated. This proposal avoid all of the previous techniques disadvantages, a simple fabrication process and low voltage control is required, and thin lenses can be obtained. The novelty of the proposal, resides in a micro-structured indium tin oxide, designed to transmit the voltage homogeneously across the entire surface of the active area. This design is composed of two main elements, a transmission line that generates a voltage gradient, and a series of combs that distribute the voltage across the entire active area. Two different apertures are designed. One of this designs is fabricated and measured to demonstrate the viability of the idea. This novel structure open new venues of research in phase-only LC optical devices.
Many optical applications requires often totally polarized light. However there are an other applications, such as optical spectrum analyzer, in which incident polarized light is undesirable. Insertion of depolarizer in such devices may stabilize the optical signal of the measured light, in order to reduce offsets in measurements. Liquid crystal are functional materials possessing anisotropies originating from their inner molecular alignment. A vertically aligned nematic liquid crystal with zero pretilts in the off state is isotropic for light impinging at normal incidence. However, the liquid crystal orientation upon electric switching is undefined; therefore the cell usually generates disordered birefringent medium related to undefined switching direction of molecules which produce random polarization of the transmitted light by liquid crystal cell, therefore depolarization effect is produced. In this work, the treatment of problems involving depolarization of incident polarized light beam passing through a depolarizing medium and general physical phenomena associated with it, will be investigated at the speckle scale. A suitable tool for this treatment will be real time Young’s interferometer constructed with a new principle including the possibility to control the fringe pattern in real time with objective to study the dynamics of speckle fluctuation. Modulation of depolarization control with an applied voltage are reported, also.
In the paper a concept of an optical vortex application for the secure optical system was presented. The proposed system uses a spatial multiplexing of optical signals performed by creating two separate communication channels in one optical fiber in which the important data can be encrypted. The optical secure system consists of three parts, i.e.: light beam generator, optical fiber link and demodulation unit. Light from a single source is split into two types of light beams. One of them remains unchanged and preserves its Gaussian shape. The other one is transformed to an optical vortex by passing through the liquid crystal spiral phase plate. This liquid crystal cell requires spatially distributed electrodes which can be supplied independently to introduce spatially distributed phase shifts what changes this Gaussian beam into optical vortex. It was applied as a perdeuterated liquid crystal D5CB which has a small absorption in telecommunications’ spectral region. Both beams are coupled together to the specially designed photonic crystal fiber which supports propagation of fundamental and vortex modes launched to it. The cross section of the optical fiber has a honey comb lattice with two types of air-holes rings. External one with four rings confines all propagating modes and internal single ring which spatially separates the fundamental mode and the first group of higher order modes. Both types of spatially separated modes can be used for transmitting important data. The fiber link output requires a second spatial demodulator to decouple both modes and decrypt transmitted data. At this stage of the project a light beam generator is developed, fiber link and demodulation unit are under testing.
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.