Liquid Crystal Photonic Devices Research Articles

Photonic Devices with Multi-Domain Liquid Crystal Structures

Photoalignment by azo dye nanolayers can provide high alignment quality for large-area liquid crystal devices. Application of this technology to active optical elements for signal processing and communications is a hot topic of photonics research. In this article, we review recent demonstrations and performance of liquid crystal photonic devices, discuss the advantages of the proposed technology, and identify challenges and future prospects in the research field of photoaligned multi-domain liquid crystal structures. We believe that the developments discussed here can provide directions for future research and potential opportunities for applications of liquid crystal devices based on multi-domain photoalignment.

Plasmonic‐Enhanced Polymer‐Stabilized Liquid Crystals Switching for Integrated Optical Attenuation

AbstractLiquid crystals are widely used in photonics because of their profound electro–optic properties. However, the slow switching speeds (milliseconds) and the fluid nature of liquid crystals restrict their potential use in integrated photonics. In this work, polymer‐stabilized liquid crystals are utilized as the functional material to improve the response time with a polymer network that helps pre‐orientate the liquid crystal. Additionally, plasmonic slot structures are simultaneously employed to minimize the switch voltage by confining the optical field within the electrode spacing at subwavelength scales. Thanks to the large overlap of the optical and electric fields, the scattering states of the polymer‐stabilized liquid crystal can be effectively manipulated to modulate the loss of the propagating wave, resulting in strong optical attenuation in the integrated photonic platform. Specifically, a plasmonic enhanced polymer‐stabilized liquid crystal photonic device for operation at 1550 nm, which has a length of only 10 µm and shows an extinction ratio of 0.38 dB µm−1, with a power consumption of less than 6 µW and a response time ≈20 µs, resulting in a figure‐of‐merit of 0.012 mW.

Highly efficient nonuniform finite difference method for three-dimensional electrically stimulated liquid crystal photonic devices

Liquid crystal (LC) photonic devices have attracted intensive attention in recent decades, due to the merits of tunability, cost-effectiveness, and high efficiency. However, the precise and efficient simulation of large-scale three-dimensional electrically stimulated LC photonic devices remains challenging and resource consuming. Here we report a straightforward nonuniform finite difference method (NFDM) for efficiently simulating large-scale LC photonic devices by employing a spatially nonuniform mesh grid. We show that the NFDM can be further accelerated by approximately 504 times by using the improved successive over-relaxation method (by 12 times), the symmetric boundary (by 4 times), the momentum gradient descent algorithm (by 3.5 times), and the multigrid (by 3 times). We experimentally fabricated the large-scale electrically stimulated LC photonic device, and the measured results demonstrate the effectiveness and validity of the proposed NFDM. The NFDM allocates more grids to the core area with steep electric field gradient, thus reducing the distortion of electric field and the truncation error of calculation, rendering it more precise than the finite element method and traditional finite difference method with similar computing resources. This study demonstrates an efficient and highly reliable method to simulate the large-scale electrically stimulated LC photonic device, and paves the way for customizing a large-scale LC photonic device with designable functionalities.

Active terahertz beam deflection based on a phase gradient metasurface with liquid crystal-enhanced cavity mode conversion.

Active manipulation of terahertz (THz) beam deflection and intensity is highly desired for possible applications in wireless communication, radar, and remote sensing. Here, by integrating the phase-gradient metasurfaces and tunable liquid crystal materials, we demonstrate an active THz beam deflection device based on polarization mode conversion. The resonant modes in the photonic cavity formed by the double-layer metasurface and the tunable anisotropic liquid crystal material in the cavity not only improve the polarization conversion efficiency of the device, but also actively regulate the resonance matching conditions. As a consequence, a beam deflection of 47.5° with 50% diffraction intensity at 0.69 THz is achieved in the x-to-y polarization conversion mode, and this beam can be actively modulated with an ultrahigh modulation depth of 99.6% by rotating the anisotropic optical axis of liquid crystals. Moreover, the proposed device can also work as the deflection of 32.5° in the y-to-x polarization conversion mode at 0.94 THz with a maximum diffraction intensity of 38% and an intensity modulation depth of 97.8%. This work provides a new approach based on liquid crystal photonic devices for wavefront manipulation and active modulation for THz waves.

Photopatterned azo poly(amide imide) layers as aligning substrates of holographic liquid crystal diffraction gratings for beam steering applications

Custom synthesized “T-type” azobenzene-functionalized poly(amide imide) allows for effective fabrication of a tunable liquid crystal photonic device for light beam steering.

Novel liquid crystal photonic devices enabled by two-photon polymerization [Invited

In addition to displays, liquid crystals (LCs) have also found widespread applications in photonic devices, such as adaptive lens, adaptive optics, and sensors, because of their responses to electric field, temperature, and light. As the fabrication technique advances, more sophisticated devices can be designed and created. In this review, we report recent advances of two-photon polymerization-based direct-laser writing enabled LC devices. Firstly, we describe the basic working principle of two-photon polymerization. With this powerful fabrication technique, we can generate anchoring energy by surface morphology to align LC directors on different form factors. To prove this concept, we demonstrate LC alignment on planar, curvilinear surfaces as well as in three-dimensional volumes. Based on the results, we further propose a novel, ultra-broadband, twisted-nematic diffractive waveplate that can potentially be fulfilled by this technique. Next, we briefly discuss the current status of direct-laser writing on LC reactive mesogens and its potential applications. Finally, we present two design challenges: fabrication yield and polymer relaxation/deformation, remaining to be overcome.

An optical system via liquid crystal photonic devices for photobiomodulation

Photobiomodulation or low-level light therapy (LLLT) has extensive applications based on light-induced effects in biological systems. Photobiomodulation remains controversial because of a poorly understood biochemical mechanism limited by the well-known biphasic dose response or Arndt-Schulz curve. The Arndt-Schulz curve states that an optimal dose of light is a key factor for realizing a therapeutic effect. In this report, we demonstrate a tunable optical system for photobiomodulation to aid physicians in overcoming the constraints of light due to biphasic dose response. The tunable optical system is based on a white light-emitting diode and four liquid crystal (LC) photonic devices: three LC phase retarders, and one LC lens. The output light of the tunable optical system exhibits electrical tunability for the wavelength, energy density and beam size. The operating principle is introduced, and the experimental results are presented. The proposed concept can be further extended to other electrically tunable photonic devices for different clinical purposes for photobiomodulation.

Beam shaping via photopatterned liquid crystals

ABSTRACTDue to the fantastic properties and diverse applications of specific beams, optical beam shaping has attracted intensive attentions recently. Generally, these beams can be converted from Gaussian beams via particular spatial amplitude or phase control. In this work, we present a liquid crystal photopatterning technique based on dynamic microlithography with a polarisation-sensitive photoalignment agent. This technique enables the accurate, arbitrary and reconfigurable azimuthal angle control of liquid crystals, thus providing a powerful approach for the manipulation of light. By this means, the tailoring of arbitrary fine microstructures with binary or continuously space-variant liquid crystal azimuthal orientations are demonstrated. We briefly review our recent work on some specially designed patterns and corresponding specific optical fields. High-quality vortex beams, vector beams and Airy beams are generated with unprecedented flexibility in the design and control of light wavefront. Besides high efficiency, good electrical switchability and broad wavelength tolerance, the proposed devices also exhibit merits of compact size, low cost, dynamic mode conversion and polarisation controllable energy distribution, and are available for short pulse and intense light modulation. This work may pave a bright way towards beam shaping and bring new possibilities for the design of novel advanced liquid crystal photonic devices.

Synthesis and the effect of 2,3-difluoro substitution on the properties of diarylacetylene terminated by an allyloxy group

A series of 2,3-difluoro tolane allyloxy-based liquid crystals (LCs), which are composed of the tolane unit, lateral fluoro substituents, alkoxy and allyloxy terminal groups, were synthesised with 4-bromo-2,3-difluorophenol as the starting material via a five-step reaction. Their structures were confirmed by infrared spectroscopy (IR), mass spectroscopy (MS) and nuclear magnetic resonance (NMR). The mesomorphic properties were investigated by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). The dielectric measurement was performed using an independent analyser EC-1 and the birefringence was determined using an Abbe refractometer. The results reveal that LCs have large negative dielectric anisotropy and high birefringence, which are potentially important for the fast response displays and liquid crystal photonic devices (LCDs).

Versatile alignment layer method for new types of liquid crystal photonic devices

Liquid crystal photonic devices are becoming increasingly popular. These devices often present a challenge when it comes to creating a robust alignment layer in pre-assembled cells. In this paper, we describe a method of infusing a dye into a microcavity to produce an effective photo-definable alignment layer. However, previous research on such alignment layers has shown that they have limited stability, particularly against subsequent light exposure. As such, we further describe a method of utilizing a pre-polymer, infused into the microcavity along with the liquid crystal, to provide photostability. We demonstrate that the polymer layer, formed under ultraviolet irradiation of liquid crystal cells, has been effectively localized to a thin region near the substrate surface and provides a significant improvement in the photostability of the liquid crystal alignment. This versatile alignment layer method, capable of being utilized in devices from the described microcavities to displays, offers significant promise for new photonics applications.

Reconfigurable fabrication of scattering-free polymer network liquid crystal prism/grating/lens

We report a simple reconfigurable printing method for fabricating submillisecond-response and scattering-free polymer network liquid crystal photonic devices, such as prism, grating, and lens. To suppress light scattering in the visible region, we reduce the domain sizes by controlling polymer concentration, selecting a high viscosity liquid crystal (LC) host, and performing UV curing at a low temperature. To demonstrate the configurability, we printed a LC micro-prism array with ∼300-μm feature size and a circular lens with 1.3-mm radius without any pre-patterned templates. This reconfigurable printing technique enables fast design iterations and should have widespread applications for fabricating display and photonic devices.

Neural network controller for Tunable Liquid Crystal Photonic Device work as Laser Beam Steering Device

In this paper, artificial neural network controller (NNC) was designed and used to adjust and control the work of the laser beam steering device consist of liquid crystals cell and other optical components. The target of the neurocontroller is to guarantee smooth deliver and exactly control the laser beam to a required location via control the liquid crystals cell and the optical components. Back propagation method is used to build up the neurocontroller, main artificial neurocontroller software is consists of three sub programs according to the three functions it proposed to administer. Trial results obtained after the execution of the neurocontroller affirmed the optimum performs in administrating, controlling and standardize the device while the value of the errors reached its minima, which coincidence with the approaches of the paper goals. Keyword Neural network; neurocontroller; Laser beam steering.