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Organic Liquid Crystal Optoelectronic Materials and Devices
Published in Sam-Shajing Sun, Larry R. Dalton, Introduction to Organic Electronic and Optoelectronic Materials and Devices, 2016
The most common and well-recognized applications of liquid crystals nowadays are displays. It is the most natural way to utilize extraordinary electro-optical properties of liquid crystals together with its liquid-like behavior. All the other applications are known as nondisplay applications of liquid crystals. Nondisplay applications are based on the liquid crystals molecular order sensitivity to the external incentive. This can be an external electric and magnetic field, temperature, chemical agents, mechanical stress, pressure, irradiation by different electromagnetic waves, or radioactive agents. Liquid crystals sensitivity for such wide spectrum of factors results in tremendous diversity of nondisplay applications. The most known are spatial light modulators (SLMs) for laser beam steering, adaptive optics, light shutters and attenuators for telecommunication, cholesteric LC filters, LC thermometers, stress meters, dose meters, crystals paints, and cosmetics. Another field of interest employing lyotropic liquid crystals is biomedicine, where the LC plays an important role as a basic unit of the living organisms by means of plasma membranes of the living cells. More about existing nondisplay applications can be found in preferred reading materials [19].
Metasurfaces, Then and Now
Published in Costantino De Angelis, Giuseppe Leo, Dragomir N. Neshev, Nonlinear Meta-Optics, 2020
Sébastien Héron, Patrice Genevet
The general function of most optical devices can be described as the modification of the wavefront of light by altering its phase, amplitude, and polarization in a desired manner. Conventional optical elements, such as lenses, liquid crystal, planar phased arrays, and vortex elements fabricated using grayscale lithography, are modifying the phase of the wavefront using “propagation effect,” φ = kr. This limits the longitudinal dimension of the optical elements to be several orders thicker than the wavelength, l > λ. The class of optical components that alter the phase of light waves includes lenses, prisms, spiral phase plates, axicons, and more generally spatial light modulators (SLMs), which are able to behave such many of these components by means of a dynamically tunable spatial phase response. A second class of optical components such as waveplates utilizes bulk birefringent crystals with optical anisotropy to change the polarization of light. A third class of optical components such as gratings and holograms is based on diffractive optics, where diffracted in-phase spherical waves departing from different parts of the components interfere in the far-field to produce the desired optical patterns. All of these components shape optical wavefronts using the propagation effect: the change in phase and polarization is gradually accumulated during light propagation. This approach is generalized in transformation optics [1] which utilizes metamaterials to engineer the spatial distribution of refractive indices and therefore bend light in unusual ways, achieving remarkable phenomena such as negative refraction, subwavelength-focusing, and cloaking [2–7].
Smart structures and materials
Published in Jun Ohta, Smart CMOS Image Sensors and Applications, 2020
The pattern is spatially fixed in coded aperture cameras but some types of coded apertures introduced programmable apertures [353–355]. SLMs (spatial light modulators) are used as programmable coded apertures, where transparency can be controlled in each pixel independently. By introducing programmable coded apertures, instantaneous field of view change, split field of view and optical computation during image formation can be achieved [353]. As an example of a camera being used as a computational sensor, an optical correlation processing can be executed to display a correlation template image on the programmable coded apertures.
Colour 3D holographic display based on a quantum-dot-doped liquid crystal
Published in Liquid Crystals, 2019
Pengcheng Zhou, Yan Li, Shuxin Liu, Yikai Su
Holographic display is one of the most promising three-dimensional (3D) display techniques. By reconstructing light wavefront, it could produce 3D imagery as if it comes from a nature scene [1–3]. A spatial light modulator (SLM), which modulates the phase or amplitude of light, is a key component of a holographic display. However, due to the limited bandwidth of conventional electrically addressed SLMs, it is difficult to realise a wide-view and full-colour holographic display [4–7]. On the other hand, optical holography based on photorefractive (PR) materials is an alternative to produce a vivid 3D display [8]. Those materials are of high resolution, low cost, high scalability and easy fabrication [1,9]. Therefore, extensive research has been carried out for new photorefractive materials for holographic displays such as photorefractive polymers [1,9–12], photorefractive liquid crystals (LCs) [13–17], etc. Among them, photorefractive polymers usually exhibit high spatial resolution and high diffraction efficiency but require a relatively high external-electrical field to achieve sufficient index change. And the response of photorefractive polymers is too slow to enable a real-time video-rate display.
Some features of magneto-optics of cholesteric liquid crystals
Published in Journal of Modern Optics, 2021
A. H. Gevorgyan, S. S. Golik, N. A. Vanyushkin, A. V. Borovsky, H. Gharagulyan, T. M. Sarukhanyan, M. Z. Harutyunyan, G. K. Matinyan
Thus, the CLC layer can be used as a practically ideal monochromator, just changing the azimuth at a fixed ellipticity or changing the ellipticity for a fixed azimuth of the incident light. And a high-speed, power-efficient light modulation is in high demand for a variety of photonic devices used as building blocks of displays and optical information processors. These include tunable lenses, focusers, wave-front correctors, and correlators [38–44]. Liquid crystal spatial light modulators are widely used as devices to modulate the amplitude, the phase, or polarization of light waves in space and time [45].
Rapid phase calibration of a spatial light modulator using novel phase masks and optimization of its efficiency using an iterative algorithm
Published in Journal of Modern Optics, 2020
Amar Deo Chandra, Ayan Banerjee
Spatial Light Modulators (SLMs) are dynamic optical elements which can be used to modulate the amplitude or the phase of an incident light beam. They have given rise to a plethora of applications by leveraging their modulation characteristics in the field of beam shaping [1], optical trapping [1–3], super-resolution imaging [4] and wavefront-correction [5,6]. Applications such as beam shaping and optical trapping entail static modification of the phase distribution of a light beam falling on the SLM. On the other hand, applications such as wavefront-correction require dynamic changes in the phase distribution of the incident light beam. It is necessary to measure the phase response of the SLM in ambient laboratory conditions because the phase response of an SLM varies with parameters such as incident laser power [7], operating temperature [8] and wavelength of incident light [9]. Thus, use of SLMs in any phase modulation settings with high fidelity necessitates precise knowledge of the phase response of the device. The efficacy of SLMs in many applications such as beam shaping and holographic optical trapping depend on the diffraction efficiency of the device which is dependent on criteria such as the fill factor [10], pixel size, input polarisation, maximum phase modulation and nonlinear profile of the actual phase vs intended phase of the SLM [11,12]. There are a variety of SLMs currently available in the market having phase modulation depths ranging anywhere from about π radians to about radians and higher. Phase limited SLMs () are economical compared to the high-end ones but exhibit limited diffraction efficiency. However, recent studies [11,12] have shown that it is possible to improve the efficiency of phase limited SLMs by changing their phase response by modifying the global look-up table (LUT) of these devices. Applications such as beam shaping and optical trapping often require splitting the input beam into an array of spots. An interesting study [13] has demonstrated that non-iterative algorithms perform poorly in efficiency compared to iterative algorithms such as the Gerchberg-Saxton (GS) algorithm [14] and other modified iterative algortihms [15–18] while generating an array of symmetric spots.