Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal dis... more Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal displays and photonic applications. A ternary mixture formed from three different nematic compounds shows peculiar behavior such as tunable electro-optical properties dependent on the frequency of the driving voltage. The paper presents an analysis of the response time and phase retardation of a frequency tunable nematic liquid crystal mixture (under code name 5005). This material possesses high birefringence (Δn = 0.32 at 633 nm) as well as high dielectric anisotropy (Δε = 6.3 at 100 Hz). The unique property of the 5005 mixture is frequency-controlled phase modulation, as in a dual frequency liquid crystal, while dielectric anisotropy goes to zero instead of being negative at high frequencies. For each component of the mixture, details on mesomorphic properties and their role in the formulation of the mixture are reported. The 5005 mixture was characterized by multiple investigation techni...
In this work, a technique to generate aspherical liquid crystal lenses with positive and negative... more In this work, a technique to generate aspherical liquid crystal lenses with positive and negative optical power is experimentally demonstrated. The main enabling element is a micro-metric electrode with variable spatial size. This produces a decreasing resistance towards the lens centre that generates the desired voltage/phase profiles. Then, the voltage is homogeneously distributed across the active area of the lens by micro-metric concentric electrodes. As it is demonstrated, the phase shift can be controlled with voltages from 0 to 4.5 VRMS. As a result, parabolic profiles are obtained both for negative and positive optical powers. Furthermore, this approach avoids some disadvantages of previous techniques; parabolic profiles can be obtained with only one lithographic step and one or two voltage sources. Other complex aspherical profiles could be fabricated using the same technique, such as elliptical or hyperbolic ones.
Novel Optical Systems, Methods, and Applications XXII, 2019
In this work, a novel technique to create adaptive liquid crystal lenses and other optical compon... more 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.
Liquid crystals act on the amplitude and the phase of a wave front under applied electric fields.... more Liquid crystals act on the amplitude and the phase of a wave front under applied electric fields. Ordinary LCs are known as field induced birefringence, thus both phase and amplitude modulation strongly depend on the voltage controllable molecular tilt. In this work we present electrooptical properties of novel liquid crystal (LC) mixture with frequency tunable capabilities from 100Hz to 10 KHz at constant applied voltage. The frequency tunability of presented mixtures shown here came from composition of three different families of rodlike liquid crystals. Dielectric measurements are reported for the compounds constituting frequency-controlled birefringence liquid crystal. Characterization protocols allowing the optimum classification of different components of this mixture, paying attention to all relevant parameters such as anisotropic polarizability, dielectric anisotropy, and dipole moment are presented.
Nematic liquid crystal (LC)-based beam steering has been reported for wide applications. However,... more Nematic liquid crystal (LC)-based beam steering has been reported for wide applications. However, for conventional nematic LC beam steering the thickness is of several microns in order to have a wider deflection angle. The response time is relatively slow and the diffraction efficiency is low. In this work, novel beam steering based on polymer stabilized blue phase liquid crystal (PS-BPLC) has been designed and theoretically analyzed. This special mesophase of the chiral doped nematic LC has several advantageous characteristics, for example no need for alignment layers, microsecond response time and an isotropic voltage-off state. The results reveal control over phase retardation. The direction of the steered beam can be tuned by voltage. Depending on voltage configuration, either diffractive beam steering (0.5deg deviation for 1st order) or a tunable continuous phase (tunable deviation of 0.002deg) can be obtained. In the first case, the deflection angle could be tuned by stacks of...
ABSTRACT New compounds (S)-4ʹ-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[3-(2,2,3,3,4,4,5,5,5-no... more ABSTRACT New compounds (S)-4ʹ-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[3-(2,2,3,3,4,4,5,5,5-nonafluoropentyloxy)prop-1-oxy]benzoates were synthesised and characterised. Their mesomorphic properties were tested by means of polarising optical microscopy and differential scanning calorimetry. The multicomponent antiferroelectric high tilt mixture with long pitch has been also formulated and characterised. The helical pitch of prepared mixture was estimated with selective reflection method. GRAPHICAL ABSTRACT
An experimental setup to measure the pretilt angle and cell gap in reflective VAN (vertically ali... more An experimental setup to measure the pretilt angle and cell gap in reflective VAN (vertically aligned nematic liquid crystals) has been developed. This setup, based on the rotation method, has been modified in order to measure simultaneously high pretilt angles in reflective cells along with the cell gap. The determination of the pretilt angle is achieved by finding the rotation
Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal dis... more Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal displays and photonic applications. A ternary mixture formed from three different nematic compounds shows peculiar behavior such as tunable electro-optical properties dependent on the frequency of the driving voltage. The paper presents an analysis of the response time and phase retardation of a frequency tunable nematic liquid crystal mixture (under code name 5005). This material possesses high birefringence (Δn = 0.32 at 633 nm) as well as high dielectric anisotropy (Δε = 6.3 at 100 Hz). The unique property of the 5005 mixture is frequency-controlled phase modulation, as in a dual frequency liquid crystal, while dielectric anisotropy goes to zero instead of being negative at high frequencies. For each component of the mixture, details on mesomorphic properties and their role in the formulation of the mixture are reported. The 5005 mixture was characterized by multiple investigation techni...
In this work, a technique to generate aspherical liquid crystal lenses with positive and negative... more In this work, a technique to generate aspherical liquid crystal lenses with positive and negative optical power is experimentally demonstrated. The main enabling element is a micro-metric electrode with variable spatial size. This produces a decreasing resistance towards the lens centre that generates the desired voltage/phase profiles. Then, the voltage is homogeneously distributed across the active area of the lens by micro-metric concentric electrodes. As it is demonstrated, the phase shift can be controlled with voltages from 0 to 4.5 VRMS. As a result, parabolic profiles are obtained both for negative and positive optical powers. Furthermore, this approach avoids some disadvantages of previous techniques; parabolic profiles can be obtained with only one lithographic step and one or two voltage sources. Other complex aspherical profiles could be fabricated using the same technique, such as elliptical or hyperbolic ones.
Novel Optical Systems, Methods, and Applications XXII, 2019
In this work, a novel technique to create adaptive liquid crystal lenses and other optical compon... more 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.
Liquid crystals act on the amplitude and the phase of a wave front under applied electric fields.... more Liquid crystals act on the amplitude and the phase of a wave front under applied electric fields. Ordinary LCs are known as field induced birefringence, thus both phase and amplitude modulation strongly depend on the voltage controllable molecular tilt. In this work we present electrooptical properties of novel liquid crystal (LC) mixture with frequency tunable capabilities from 100Hz to 10 KHz at constant applied voltage. The frequency tunability of presented mixtures shown here came from composition of three different families of rodlike liquid crystals. Dielectric measurements are reported for the compounds constituting frequency-controlled birefringence liquid crystal. Characterization protocols allowing the optimum classification of different components of this mixture, paying attention to all relevant parameters such as anisotropic polarizability, dielectric anisotropy, and dipole moment are presented.
Nematic liquid crystal (LC)-based beam steering has been reported for wide applications. However,... more Nematic liquid crystal (LC)-based beam steering has been reported for wide applications. However, for conventional nematic LC beam steering the thickness is of several microns in order to have a wider deflection angle. The response time is relatively slow and the diffraction efficiency is low. In this work, novel beam steering based on polymer stabilized blue phase liquid crystal (PS-BPLC) has been designed and theoretically analyzed. This special mesophase of the chiral doped nematic LC has several advantageous characteristics, for example no need for alignment layers, microsecond response time and an isotropic voltage-off state. The results reveal control over phase retardation. The direction of the steered beam can be tuned by voltage. Depending on voltage configuration, either diffractive beam steering (0.5deg deviation for 1st order) or a tunable continuous phase (tunable deviation of 0.002deg) can be obtained. In the first case, the deflection angle could be tuned by stacks of...
ABSTRACT New compounds (S)-4ʹ-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[3-(2,2,3,3,4,4,5,5,5-no... more ABSTRACT New compounds (S)-4ʹ-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[3-(2,2,3,3,4,4,5,5,5-nonafluoropentyloxy)prop-1-oxy]benzoates were synthesised and characterised. Their mesomorphic properties were tested by means of polarising optical microscopy and differential scanning calorimetry. The multicomponent antiferroelectric high tilt mixture with long pitch has been also formulated and characterised. The helical pitch of prepared mixture was estimated with selective reflection method. GRAPHICAL ABSTRACT
An experimental setup to measure the pretilt angle and cell gap in reflective VAN (vertically ali... more An experimental setup to measure the pretilt angle and cell gap in reflective VAN (vertically aligned nematic liquid crystals) has been developed. This setup, based on the rotation method, has been modified in order to measure simultaneously high pretilt angles in reflective cells along with the cell gap. The determination of the pretilt angle is achieved by finding the rotation
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