Photonic defect modes of cholesteric liquid crystals

Yang, Youngoo; Kee, Chul‐Sik; Kim, Jae Eun; Park, Hae Yong; Lee, Jong-Cheon; Jeon, Yong Jin

doi:10.1103/physreve.60.6852

Cited by 167 publications

(98 citation statements)

References 13 publications

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“…However, the proper understanding some of its basic features has appeared much later, when the interest in lasing in LC systems has been renovated [2][3][4][5][6][7][8][9][10][11]. The current interpretation of the effect is based on the photonic band-gap concept [2].…”

Section: Introductionmentioning

confidence: 99%

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General properties of lasing effect in chiral liquid crystals

Palto

Shtykov

Umansky

et al. 2006

Opto-Electronics Review

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Section: Introductionmentioning

confidence: 99%

“…Because the density of photon states achieves maxima just at the spectral boundaries of the band, namely these spectral regions are treated as most favourable for appearance of the low-threshold lasing effect. The lasing inside the photonic band-gap is forbidden unless defects are introduced into CLC layers [4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

General properties of lasing effect in chiral liquid crystals

Palto

Shtykov

Umansky

et al. 2006

Opto-Electronics Review

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“…It was in dyedoped CLCs that suppression of the density of states in a stop band and lasing in long-lived modes at the band edge were first demonstrated [10]. In analogy with isotropic periodic structures, a defect can be produced in a helical structure by adding an isotropic layer in the middle of a CLC [11,12]. The reflection and transmission of radiation with opposite senses of circular polarization were shown to be equal at resonance [12].…”

mentioning

confidence: 99%

“…In analogy with isotropic periodic structures, a defect can be produced in a helical structure by adding an isotropic layer in the middle of a CLC [11,12]. The reflection and transmission of radiation with opposite senses of circular polarization were shown to be equal at resonance [12]. In addition, a "chiral twist" defect created by rotating one part of the sample about its helical axis without separating the two parts was proposed (Fig.…”

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confidence: 99%

Twist Defect in Chiral Photonic Structures

2002

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We demonstrate that twisting one part of a chiral photonic structure about its helical axis produces a single circularly polarized localized mode that gives rise to an anomalous crossover in propagation. Up to a crossover thickness, this defect results in a peak in transmission and exponential scaling of the linewidth for a circularly polarized wave with the same handedness as structure. Above the crossover, however, the linewidth saturates and the defect mode can be excited only by the oppositely polarized wave, resulting in a peak in reflection instead of transmission.PACS numbers: 42.70. Qs, 42.70.Df Localized modes produced by regular defects in periodic structures can serve as low threshold lasers [1], low loss waveguides, and narrow band filters in an expanding array of photonic devices [2,3]. When defects are randomly positioned, localized states are produced within the photonic band gap (PBG) by multiple scattering [4,5]. The photon dwell time at resonance with a defect state generally increases exponentially with the structure thickness L. This suppresses the lasing threshold in an active structure without the use of external feedback. In 3D PBGs, thresholdless lasing has been predicted when the band gap exceeds the emission bandwidth since emission can then couple only to the single defect mode [1]. Exceptionally low lasing thresholds have been achieved in vertical cavity surface emitting lasers (VCSELs), in which an amplifying defect layer is sandwiched between stacks of layers with periodically alternating refractive index [6]. A rich variety of physical effects have been observed when point, line and planar defects are introduced into periodic dielectric structures by the modifying refractive index or thickness of isotropic material. We consider here the unusual photonic properties of a defect created by twisting one part of an anisotropic structure relative to the rest of the sample. This "chiral twist" provides an additional degree of freedom for the design of photonic structures.Periodic chiral media appear in nature and can be synthesized as self-organized cholesteric liquid crystals (CLCs) [7] or fabricated by a variety of techniques, for example, by glancing-angle deposition on a rotating substrate [8]. In CLCs, the director, which is the average orientation of molecules in a plane, rotates with pitch P as shown in Fig. 1a. A reflection band forms for circularly polarized light with the same handedness as the structure itself. Light with opposite circular polarization is transmitted through the structure without attenuation. The edges of the band are defined by two sharp optical modes peaked at a wavelength inside the medium equal to P. These correspond to circularly polarized standing waves, in which the electric field in the bulk of the sample is aligned along either the ordinary or the extraordinary molecular axes [9]. It was in dyedoped CLCs that suppression of the density of states in a stop band and lasing in long-lived modes at the band edge were first demonstrated [10]. In analogy w...

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“…The use of defect modes has also been proposed for lasing at low threshold [12,13]. Generally, two kinds of configurations for generating defect modes in CLCs are suggested theoretically: introduction of an isotropic spacing layer in the middle of CLCs [14] and creation of a phase jump without any spacing in CLC structures [15 -17]. Recently, Schmidtke et al [18] experimentally demonstrated the defect mode lasing caused by a phase jump in CLCs and described its polarization characteristics.…”

Section: Introductionmentioning

confidence: 99%

Polarization characteristics of phase retardation defect mode lasing in polymeric cholesteric liquid crystals

Song

Shin

Park

et al. 2004

Science and Technology of Advanced Materials

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We have studied the lasing characteristics of a dye-doped nematic layer sandwiched by two polymeric cholesteric liquid crystal (CLC) films as photonic band gap (PBG) materials. The nematic layer acts as a defect layer, the anisotropy of which brings about the following remarkable optical characteristics: (1) reflectance in the PBG region exceeds 50% due to the retardation effect, being unpredictable from a single CLC film; (2) efficient lasing occurs either at the defect mode wavelength or at the photonic band edge; and (3) the lasing emission due to both the defect mode and the photonic band edge mode contains both right-and left-circular polarizations, while the lasing emission from a dye-doped single CLC layer with a left-handed helix is left-circularly polarized. q

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Photonic defect modes of cholesteric liquid crystals

Cited by 167 publications

References 13 publications

General properties of lasing effect in chiral liquid crystals

General properties of lasing effect in chiral liquid crystals

Twist Defect in Chiral Photonic Structures

Polarization characteristics of phase retardation defect mode lasing in polymeric cholesteric liquid crystals

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