Wide-band reflective polarizers from cholesteric polymer networks with a pitch gradient

Broer, Dirk J.; Lub, Johan; Mol, G.N.

doi:10.1038/378467a0

Cited by 684 publications

(440 citation statements)

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“…On the basis of these concepts, three-dimensional (3D) chiral structures such as helices may be used to realize circular polarizers 1,2 . Similarly, cholesteric liquid crystals are composed of chiral molecules with a helical pitch that may be used to selectively filter one circular polarization based on Bragg reflection [3][4][5][6] . Conventional circular polarizers based on these concepts typically operate over narrow frequency bands 4 , which may be broadened by stacking multiple polarizers or introducing a gradient in the helical pitch 3,6 .…”

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confidence: 99%

“…Similarly, cholesteric liquid crystals are composed of chiral molecules with a helical pitch that may be used to selectively filter one circular polarization based on Bragg reflection [3][4][5][6] . Conventional circular polarizers based on these concepts typically operate over narrow frequency bands 4 , which may be broadened by stacking multiple polarizers or introducing a gradient in the helical pitch 3,6 . However, modest bandwidth increases are usually achieved at the price of much bulkier devices, which are difficult to integrate within today's nanophotonic systems.…”

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confidence: 99%

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Twisted optical metamaterials for planarized ultrathin broadband circular polarizers

2012

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optical metamaterials are usually based on planarized, complex-shaped, resonant nanoinclusions. Three-dimensional geometries may provide a wider set of functionalities, including broadband chirality to manipulate circular polarization at the nanoscale, but their fabrication becomes challenging as their dimensions get smaller. Here we introduce a new paradigm for the realization of optical metamaterials, showing that three-dimensional effects may be obtained without complicated inclusions, but instead by tailoring the relative orientation within the lattice. We apply this concept to realize planarized, broadband bianisotropic metamaterials as stacked nanorod arrays with a tailored rotational twist. Because of the coupling among closely spaced twisted plasmonic metasurfaces, metamaterials realized with conventional lithography may effectively operate as three-dimensional helical structures with broadband bianisotropic optical response. The proposed concept is also shown to relax alignment requirements common in three-dimensional metamaterial designs. The realized sample constitutes an ultrathin, broadband circular polarizer that may be directly integrated within nanophotonic systems.

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Twisted optical metamaterials for planarized ultrathin broadband circular polarizers

2012

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“…In that case, special procedures are necessary. 16,17 The ability of the chiral molecules to induce a molecular helix is quantified by the so-called helical twisting power (HTP), which is defined as HTP = (pc) −1 where c is the concentration of chiral dopant and assuming that the dopant consists of one enantiomer. Some HTP values can be found in Figure 4.…”

Section: ■ Liquid Crystal Monomersmentioning

confidence: 99%

Liquid Crystal Polymer Networks: Preparation, Properties, and Applications of Films with Patterned Molecular Alignment

2014

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Monolithically ordered liquid crystal polymer networks are formed by the photoinitiated polymerization of multifunctional liquid crystal monomers. This paper describes the relevant principles and methods, the basic structure− property relationships in terms of mesogenic properties of the monomers, and the mechanical and optical properties of the polymers. Strategies are discussed to control the molecular orientation by various means and in all three dimensions. The versatility of the process is demonstrated by two examples of films with a patterned molecular order. It is shown that patterned retarders can be made by a two-step polymerization process which is successfully employed in a transflective display principle. A transflective display is a liquid crystal display that operates in both a reflective mode using ambient light and a transmissive mode with light coming from a backlight system. Furthermore, a method is discussed to create a patterned film in a single polymerization process. This film has alternating planar chiral nematic areas next to perpendicularly oriented (so-called homeotropic) areas. When applied as a coating to a substrate, the film changes its surface texture. During exposure to UV light, it switches from a flat to a corrugated state.

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“…CLCs may be applied that cover a broader range of wavelengths, if desired, which would enhance the OPV performance but at the cost of the loss of some transparency. 10 In conclusion, the use of solution-processable organic wavelength dependent reflectors of chiral nematic ͑choles-teric͒ liquid crystals with transparent organic solar cells is demonstrated. Their ease of application is a distinct advantage over multilayer inorganic Bragg-type reflectors, which are much more difficult to apply and are much more expensive.…”

Section: -2mentioning

confidence: 99%

Semitransparent organic solar cells with organic wavelength dependent reflectors

Galagan

Debije

Blom

2011

Applied Physics Letters

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Semitransparent organic solar cells employing solution-processable organic wavelength dependent reflectors of chiral nematic (cholesteric) liquid crystals are demonstrated. The cholesteric liquid crystal (CLC) reflects only in a narrow band of the solar spectrum and remains transparent for the remaining wavelengths. The reflective band is matched to the absorption spectrum of the organic solar cell such that only unabsorbed photons that can contribute to the photocurrent are reflected to pass through the active layer a second time. In this way, the efficiency of semitransparent organic solar cells can be enhanced without significant transparency losses. An efficiency increase of 6% was observed when a CLC reflector with a reflection band of 540–620 nm was used, whereas the transparency of the organic solar cells is only suppressed in the 80 nm narrow bandwidth.

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Wide-band reflective polarizers from cholesteric polymer networks with a pitch gradient

Cited by 684 publications

References 3 publications

Twisted optical metamaterials for planarized ultrathin broadband circular polarizers

Twisted optical metamaterials for planarized ultrathin broadband circular polarizers

Liquid Crystal Polymer Networks: Preparation, Properties, and Applications of Films with Patterned Molecular Alignment

Semitransparent organic solar cells with organic wavelength dependent reflectors

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