Electrically Tunable Printed Bifocal Liquid Crystal Microlens Arrays

Kamal, Waqas; Lin, James T.; Elston, Steve J.; Ali, Taimoor; Castrejón‐Pita, Alfonso A.; Morris, Stephen M.

doi:10.1002/admi.202000578

Cited by 16 publications

(21 citation statements)

References 29 publications

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“…For example, in 2020, S. M. Morris et al reported LCMs by using a DoD inkjet printing system. [ 48 ] As shown in Figure 6b. I, the high‐precision needle controlled by pulse signal can extricate LC droplets with an accuracy of ±5 µm.…”

Section: Fabricationsmentioning

confidence: 96%

Section: Design Principlesmentioning

confidence: 99%

“…A large quantity of methods has been proposed to regulate the tilt angle of GRIN lens, including patterning electrodes (Figure 1d,e), [ 46 ] drop‐on‐demand (DoD) system (Figure 1f,g), [ 47 ] and polymer mold (Figure 1h). [ 48 ] The principles underlying these seminal works can be concluded as employing external stimuli to steer the tilt angle of the director orientations, create the GRIN accordingly, and finally obtain the desired GRIN microlens. The resulting microlenses usually have adjustable focal lengths.…”

Section: Design Principlesmentioning

confidence: 99%

“…Generally, polymer molding can be fabricated via direct light molding [ 98,99 ] or mechanic‐assisted molding. [ 48,100 ]…”

Section: Fabricationsmentioning

confidence: 99%

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Design, Fabrication, and Applications of Liquid Crystal Microlenses

Chen

Hou

Shu-qing

et al. 2021

Advanced Optical Materials

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Microlenses and microlens arrays are one of the indispensable components in modern optical systems ranging from imaging and beam shaping to polarization control and switchable 2D/3D displays. Among them, the liquid crystal microlenses (LCMs) with size below 1 mm have attracted more and more attention due to their stimuli‐responsiveness and tunability in focal length and polarization. Compared with microlenses based on inorganic binary optics, diffractive optical elements, or metasurface, LCMs are more cost‐effective and can be easily tuned. In this paper, an in‐depth review of the design principles, fabrication techniques, emerging applications, and recent advances of LCMs and arrays is presented, aiming to clarify the characteristics, limitations, and challenges in LCMs design and fabrication. This review may provide directions for solving those challenges, and expand the applications of LCMs.

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Section: Fabricationsmentioning

confidence: 96%

Section: Design Principlesmentioning

confidence: 99%

Section: Design Principlesmentioning

confidence: 99%

“…Generally, polymer molding can be fabricated via direct light molding [ 98,99 ] or mechanic‐assisted molding. [ 48,100 ]…”

Section: Fabricationsmentioning

confidence: 99%

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Design, Fabrication, and Applications of Liquid Crystal Microlenses

Chen

Hou

Shu-qing

et al. 2021

Advanced Optical Materials

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“…For example, printing has already been employed with LC materials to develop monodisperse LC solutions, and optically-pumped thin-film lasers, as well as electrically and thermally tunable microlenses. [36][37][38][39] Due to its versatility, DoD inkjet printing offers a unique platform for the manufacture of PDLC films. By printing an LC and UV-curable polymer ink, PDLC films with spatially patterned emblems and logos can be successfully manufactured.…”

Section: Introductionmentioning

confidence: 99%

Spatially Patterned Polymer Dispersed Liquid Crystals for Image‐Integrated Smart Windows

Kamal

Lin

et al. 2021

Advanced Optical Materials

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be switched between an opaque and transparent state with the application of a voltage. Furthermore, their compatibility with cost-effective production processes such as roll-to-roll processing has ensured their successful deployment as a "smart window" technology. In contrast to multilayered electrochromic devices, PDLC technology is typically based upon a single-layered film that consists of liquid crystal (LC) droplets suspended in a polymer matrix. [6][7][8] The most common process employed to manufacture PDLC films involves the phase separation of a homogeneous mixture of LC and prepolymer, typically through a photopolymerization-induced phase separation technique (PIPS). This process can be used to form large area PDLCs films, which typically allows for a wide degree of control over droplet size and shape when compared to emulsification or thermal/solvent-induced phase separation techniques. [9][10][11][12] For smart glass and window applications, the size of the LC droplet after phase separation is generally within the range of 1-20 µm. [13,14] These LC droplets lack any preferential macroscopic orientation between LC domains. By matching the refractive index of the polymer matrix to one of the refractive indices of the LC, typically the ordinary refractive index, then a transparent state can be obtained by reorienting the LC director with an applied electric field so that the refractive indices of the LC droplets and the polymer binder match. [11,15] Even though the PIPS technique provides flexibility in terms of the phase separation process, a drawback lies in the inherent homogeneity that results from the mixing and coating procedures, which produces films consisting of a single LC and polymer formulation. To obtain PDLC films with spatially varying properties, the photopolymerization process has to be performed with the aid of a photomask or hologram to create patterns or variations in the film morphology. [16,17] Patterned PDLCs have attracted interest in recent years and several attempts have been made to manufacture them. Among the fabrication processes reported, irradiation of the material with coherent light allows for the use of holographic masks, which enables light with a structured intensity to be applied to the films. [17][18][19][20] Additionally, if the LC host is doped with an azo dye the use of a linearly polarized light source during the photopolymerization process can cause the LC director to adopt a preferential microscopic orientation following phase separation and the formation of a polymer binder. [21,22] Another method Conventional polymer dispersed liquid crystal (PDLC) films have been successful as electrically-switchable screens for privacy applications. However, spatial patterning of the films so as to generate a visually appealing design, logo, or image typically requires intricate fabrication processes, such as the use of prefabricated photomasks that do not allow for on-demand designs. Herein is reported on the fabrication and characterization of spatially patterned PDLC "pix...

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Drop‐on‐Demand Electrohydrodynamic Printing of Nematic Liquid Crystals

Kamal,

Li,

Sykes

et al. 2024

Adv Eng Mater

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In this paper, electrohydrodynamic (EHD) printing of nematic liquid crystals (LCs) is demonstrated. Miniscule LC droplets, as small as 1 micron, are generated with the EHD printing system and deposited with high precision onto a glass substrate. Herein, we investigate how the voltage waveform and pulse frequency applied to the print nozzle influences the dynamics of the deposition process and the final landed footprint diameter of the printed spherical‐cap‐shaped LC droplets at the glass substrate. To complement results from high‐speed shadowgraphy imaging, simulations were employed to model the jetting process and the formation of the Taylor Cone. Using EHD printing, we show results for two different printing modes: cone‐jetting and micro‐dripping. We highlight the benefits and drawbacks of each mode and conclude with the demonstration of a printed alphanumeric pattern that showcases the capability of EHD printing to deposit very small volumes of nematic LC in order to form well‐defined spatial patterns.This article is protected by copyright. All rights reserved.

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Electrically Tunable Printed Bifocal Liquid Crystal Microlens Arrays

Cited by 16 publications

References 29 publications

Design, Fabrication, and Applications of Liquid Crystal Microlenses

Design, Fabrication, and Applications of Liquid Crystal Microlenses

Spatially Patterned Polymer Dispersed Liquid Crystals for Image‐Integrated Smart Windows

Drop‐on‐Demand Electrohydrodynamic Printing of Nematic Liquid Crystals

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