Optically Transparent Beam-Steering Reflectarray Antennas Based on Liquid Crystal for Millimeter-Wave Applications

This study presents a method to realize an optically transparent beam-steering antenna. The RF and optical features of Liquid Crystal (LC) technology are used in combination with transparent metal mesh to realize the first optically transparent reconfigurable reflectarray (RA). Since the electric field of bias and Radio Frequency (RF) signals are highly non-uniform, the LC permittivity is both anisotropic and inhomogeneous thus the behavior of LC molecules needs to be obtained for accurate modeling prior to antenna design. A unit cell consisting of metallic mesh and LC is analyzed and LC director distribution is obtained. The director data are transformed into permittivity tensors in the entire LC volume and the LC is discretized in electromagnetic simulation software to perform full-wave periodic boundary simulation to model the anisotropy and inhomogeneity. The discretized model is approximated by a single dielectric block with a new permittivity range for GT7 LC material. A 10×10 RA is fabricated and measured in terms of optical and RF performance. The measured phase shift of the unit cell is 260˚ when the voltage is increased from 0 V to 40 V. The measured beam scans from -10˚ to 50˚ in the E-plane and from -50 to +50 in the H-plane with a 14.35 dBi maximum gain. The prototype optical performance is also measured. The benefits and drawbacks of current RF LC mixtures are discussed. It shows that with an appropriate LC mixture optimized for both RF and optical transmission, the LC-based optically transparent antennas are a viable solution for various new applications

Thermally tunable polarization by nanoparticle plasmonic resonance in photonic crystal fibers

A photonic crystal fiber selectively filled with silver nanoparticles dispersed in polydimethylsiloxane has been numerically studied via finite elements analysis. These nanoparticles possess a localized surface plasmon resonance in the visible region which depends on the refractive index of the surrounding medium. The refractive index of polydimethylsiloxane can be thermally tuned leading to the design of polarization tunable filters. Filters found with this setup show anisotropic attenuation of the x-polarization fundamental mode around ?x = 1200dB/cm remarkably higher than the y-polarization mode. Moreover, high fiber birefringence and birefringence reversal is observed in the spectral region of the plasmon

Liquid crystal modulators on photonic integrated circuits

A photonic integrated circuit (PIC) or integrated optical circuit is a device that integrates multiple (at least two) photonic functions, being as such similar to electronic integrated circuits. The connections between components are made of light waveguides; these can be active themselves -i.e., light paths can be externally controlled- by using electrooptic (EO) materials within or onto the light path. The likelihood of liquid crystals to become EO materials for active waveguides in PICs has been explored. A number of multimode interference coupler (MMI), Mach-Zehnder interferometers (MZI) and rings resonators (RRs) have been simulated, designed and manufactured [1]. PICs have been fabricated on silicon and glass. Waveguides have been arranged in the same wafer having widths 1.5-2 μm and lengths of active regions of 8-700 μm. In all cases, waveguides are made of SiO 2 (substrate) and SU8 (film), the cover being SiO 2 , so that an LC structure can be eventually adapted onto the waveguide set. Several LCs materials are being tested, with and without 3D-stabilization by a reactive mesogen. Reorientation of the LC mixture modifies the evanescent field of the guided light, effectively affecting the underneath light path. As a result, the MMI pattern, the MZI transfer function, and the RR resonant wavelength can be externally controlled

Polarization dependent photonic liquid crystal fiber tunable interferometer

The Polarization Maintaing Photonic Crystal Fiber PM-1550-01 has been employed to create intermodal interferometers by splicing short (cm) portions of PCF between two single mode fiber (SMF) pigtails and PANDA fibers. It has been shown that this setup generates a intermodal interferometer. The interferometers have been made tunable by the inclusion of liquid crystal inside the PCF portion

Photonic crystal fibers infiltrated with metallic nanoparticles dispersed in polydimethylsiloxane

An experimental results on birefringent photonic crystal fiber (PCF) selectively infiltrated with metallic nanoparticles (NPs) dispersed in polydimethylsiloxane (PDMS) are presented. In general, PCFs are structures consisting of periodic matrix of microholes surrounding core region, that can be either solid or hollow

Light coupling and performance of LC modulated photonic integrated circuits

Coupling light into a photonic integrated circuit (PIC) is usually the most challenging task to characterize these circuits. PIC connections between components are made of light waveguides whose section is often of the same order as light wavelength, i.e., 1-5 ?m or even less. Waveguides may become active by inserting additional layers of electrooptic materials [1], either as a component within the light path, or deposited onto the waveguide affecting the evanescent field of the guided light. Testing the light behavior inside the PIC and comparing the experimental results with those predicted in modeled circuits may be hampered by the tiny cross-section of the waveguides ?especially monomode guides? and the arduous light coupling from external sources

Active photonic integrated circuits modulated by LCs

A photonic integrated circuit (PIC) or integrated optical circuit is a device that integrates multiple (at least two) photonic functions, being as such similar to electronic integrated circuits. The connections between components are made of light waveguides; these can be active themselves ?i.e., light paths can be externally controlled? by using electrooptic (EO) materials within or onto the light path. The likelihood of liquid crystals to become EO materials for active waveguides in PICs has been explored

Manufacturing arbitrarily-shaped active waveguides with liquid crystal cladding

Many photonic devices are based on waveguides (WG) whose optical properties can be externally modified. These active WGs are usually obtained with electrooptic materials in either the propagating film (core) or the substrate (cladding). In the second case, the WG tunability is based on the interaction of the active material with the evanescent field of the propagating beam.Liquid crystals (LCs) are an excellent choice as electrooptic active materials since they feature high birefringence, low switching voltage, and relatively simple manufacturing. In this work, we have explored alternative ways to prepare WGs of arbitrary shapes avoiding photolithographic steps. To do this, we have employed a UV laser unit (Spectra Physics)attached to an xyzCNC system mounted on an optical bench. The laser power is 300mW, the spot size can be reduced slightly below 1 µm, and the electromechanicalpositioning is well below that number.Different photoresinshave been evaluated for curing time and uniformity; the results have been compared to equivalent WGs realized by standard photolithographic procedures. Best results have been obtained with several kinds of NOA adhesives (Norland Products Inc.) and SU8 (Microchem). NOA81 optical adhesive has been employed by several groups for the preparation ofmicrochannels [1] and microfluidic systems[2]. In our case, several NOAs having different refractive indices have been tested in order to optimize light coupling and guiding. The adhesive is spinnedonto a substrate, and a number of segmented WGs are written with the laser system. The laser power is attenuated 20 dB. Then the laser spot is swept a number of times (from 1 to 900) on every segment. It has been found that, for example, the optimum number of sweeps for NOA81 is 30-70 times (center of the figure) under these conditions. The WG dimensions obtained with this procedure are about 7 µm high and 12 µm wide

Detection of microbes using flowing lyotropic liquid crystals

Microbial contamination of food, water and even air supply is a permanent threat against the health of humans and livestock. This threat is particularly serious in contexts such as hospitals (Legionella contamination of air-conditioning) and in extreme situations, such as those met in the third world and in natural crisis situations where water contamination is one of the most serious risks to human wellbeing