Evaluation of Electro-Optic Behaviour of Chiral Smetic Liquid Crystals Dispalys with V-shaped response

In the last years, chiral smectic liquid crystals with V-shaped electro-optic response have been reported as one of the most promising technologies for display applications. In this work,some experiments have been made in order to check electrooptical performance of this kind of materials. Particularly, frequency dependence of optical response and memory effect in transmission have been analyzed. Microscopic observations of intermediate transmission levels and measurements of apparent tilt angle and response time have been also carried out

Modal liquid crystal microaxicon array

A novel tunable liquid crystal microaxicon array is proposed and experimentally demonstrated. The proposed structure is capable of generating tunable axicons (thousands of elements) of micrometric size, with simple control (four control voltages) and low voltage, and is totally reconfigurable. Depending on the applied voltages, control over the diameter, as well as the effective wedge angle, can be achieved. Controls over the diameter ranging from 107 to 77 μm have been demonstrated. In addition, a control over the phase profile tunability, from 12π to 24π radians, has been demonstrated. This result modifies the effective cone angle. The diameter tunability, as well the effective cone angle, results in a control over the nondiffractive Bessel beam distance. The RMS wavefront deviation from the ideal axicon is only λ∕3. The proposed device has several advantages over the existing microaxicon arrays, including being simple having a low cost. The device could contribute to developing new applications and to reducing the fabrication costs of current devices

Recent Advances in Adaptive Liquid Crystal Lenses

An adaptive-focus lens is a device that is capable of tuning its focal length by means of an external stimulus. Numerous techniques for the demonstration of such devices have been reported thus far. Moving beyond traditional solutions, several new approaches have been proposed in recent years based on the use of liquid crystals, which can have a great impact in emerging applications. This work focuses on the recent advances in liquid crystal lenses with diameters larger than 1 mm. Recent demonstrations and their performance characteristics are reviewed, discussing the advantages and disadvantages of the reported technologies and identifying the challenges and future prospects in the active research field of adaptive-focus liquid crystal (LC) lenses.This work was supported by Comunidad de Madrid and FEDER Program under grant S2018/NMT-4326 and the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R)

A novel liquid crystal temperature sensor based on modal control principle

[Poster of]: 12th European Conference on Liquid Crystals (ECLC 2013), 22-27 September, 2013, Rhodes, Greece.The well-known electrically-controlled anisotropic properties of liquid crystals not only have been valued in displays applications, but also have led to the conception of innovative approaches for a wide and diversified field of applications, such as optical communications, imaging, metamaterials, microwaves, biomedical, etc. Also, the fact that liquid crystals parameters have a strong dependence with temperature, has allowed researchers to extend the design of liquid crystal devices into the field of sensors. The simultaneous effect of both dependences, on voltage and temperature, has been recently exploited in a novel frequency-temperature liquid crystal transducer [1]...Financial support of Spanish Ministerio de Economía y Competitividad (grant no.TEC2009-13991-C02-01) and Comunidad de Madrid (grant no. FACTOTEM2 S2009/ESP-1781) is acknowledged.No publicad

Liquid crystal temperature sensor based on a micrometric structure and a metallic nanometric layer

This letter presents a novel temperature sensor, which consists of an interdigitated comb electrode structure with a micrometric-scale size, nanometric metallic layer, and nematic liquid crystal (NLC) film. This sensor exploits the permittivity dependence of the NLC with temperature and principle of electrical conductivity above the percolation threshold in thin film metallic layers. The latter has been demonstrated to increase the temperature sensitivity considerably. The high impedance input reduces the power dissipation, and the high enough voltage output makes it easy to measure the output signal with high precision. The operation principle and fabrication process as well as the characterization of the temperature sensor are presented. Experimental results show that the device offers a sensitivity of 9 mV/°C and is dependent on the applied voltage. This is six times greater than the same structure without the use of a nanometric layer

Using an analytical model to design liquid crystal microlenses

We have developed new analytical expressions for designing liquid crystal (LC) microlenses. These equations are based on a novel equivalent electric circuit and can be used to create an optimum design for the LC lenses in which the lens diameter ranges from a few micrometers to several millimeters. Thus far, only experimental studies have been conducted on the LC lenses. The analytical expressions developed in this letter depend on various manufacturing parameters and can be used to design lenses with specific focal lengths and a parabolic phase profile. The required driving scheme (modal or hole-patterned) can be predicted. The LC microlenses were manufactured and electrooptically characterized: the measurements were compared using an analytical approach

Note: Electrical modeling and characterization of voltage gradient in liquid crystal microlenses

Copyright 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments (2013), 84 (11). and may be found at http://dx.doi.org/10.1063/1.4832419In this work, a novel equivalent electric circuit for modeling liquid crystal microlenses is proposed. This model is focused on explaining a lens behavior at the micrometric scale, using its manufacturing parameters. It suggests an approach to predict the solution of the voltage gradient distribution across a microlens. An interesting feature of the model is that it provides an analytical solution for microlenses with modal and hole-patterned electrode schemes, by a simple software tool. The model flexibility allows lens designers to apply complex waveform signals with different harmonics. The voltage distribution has been tested. The simulated and measured voltage profiles are fairly in agreement.Spanish Ministerio de Economia y Competitividad (Grant No. TEC2009-13991-C02-01) and Comunidad de Madrid (Grant No. FACTOTEM S2009/ESP/1781).Publicad

High-Sensitivity Fabry-Perot Temperature Sensor Based on Liquid Crystal Doped With Nanoparticles

The response of a Fabry-Perot interferometer filled with a nematic liquid crystal doped with silver nanoparticles is theoretically studied as a temperature sensor. It has been observed that the high dependence of the extraordinary refractive index of a liquid crystal along with the influence of the plasmonic resonances of nanoparticles produce useful phenomena for temperature sensing. Accordingly, we theoretically demonstrated the optical response of this device as a function of the temperature and the nanoparticles radius. The application of different technologies as optical sources was investigated through a simulation program. The latter enabled us to estimate the sensitivity and predict interesting parameters of the device, such as optimum wavelength ranges, for the optical sources or optimum sizes of the nanoparticles. Maximum sensitivities of 24 . 10(-2) dB/degrees C are obtained.This work was supported in part by the Ministerio de Ciencia e Innovación of Spain (grant no. TEC2013-47342-C2-2-R) and the Comunidad de Madrid (grant no. FACTOTEM2 S2009/ESP-1781).Publicad

Modal liquid crystal temperature sensor

Proceeding of: 2014 IEEE SENSORS proceedings: Valencia, Spain, November 2-5, 2014.In this work, a novel liquid crystal temperature sensor is proposed. This sensor is composed by only two electrodes. A simple and easily scalable structure uses the temperature dependence of the liquid crystal permittivity as the sensing magnitude. The sensor has a high sensitivity, low voltage control, low power consumption and high linearity. The analytical modelling allows an optimization of the structure, in terms of sensitivity. Several liquid crystal has been investigated. The response improves the characteristics of previous LC sensors and even some commercial sensors (e.g. 60 mV/°C for 10 V rms of applied voltage, six times more than of most silicon temperature sensors).This work was supported in part by the Ministerio de Ciencia e Innovación of Spain (grant no.TEC2009-13991-C02-01) and the Comunidad de Madrid (grant no. FACTOTEM2 S2009/ESP-1781)

An analytical approach to the design of liquid crystal microlenses

[Poster of]: 40th Topical Meeting on Liquid Crystals, Paderborn from March 20th-22nd, 2013.New analytical expressions for designing liquid crystal microlenses have been proposed. Equations involved, based on a novel equivalent electric circuit, lead to optimum designs of liquid crystal lenses which lens diameter ranges from few micrometers to one millimeter. A particular mathematical relationship between the microlens thickness and diameter is the key parameter to achieving a quasi-parabolic phase distribution across the microlens diameter. Frank-Oseen equations have been used for modeling and solving the problem. A solution for the elastic constants of a hypothetic liquid crystal, proper for a microlens device, is proposed. Manufacturing parameters of the lenses have been designed for fulfilling focal length and diameter requirements. Some of them are the thickness, the electrode configuration, and the driving scheme (modal or hole patterned). A set of liquid crystal microlenses has been manufactured and an electrooptic characterization has been carried out in order to compare the measurements with the analytical approach.This work was supported in part by the “Ministerio de Ciencia e Innovación” of Spain (grant no.TEC2009-13991-C02-01) and Comunidad de Madrid (grant no. FACTOTEM2 S2009/ESP-1781).No publicad