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SUMMARY:Liquid Crystal Photonic Devices - Myoung Hoon Song
DTSTART:20061018T103000Z
DTEND:20061018T111500Z
UID:TALK5547@talks.cam.ac.uk
CONTACT:Chris McNeill
DESCRIPTION:In this presentation\, I will adress the liquid crystal photon
 ic devices. For this purpose\, we studied mainly two different kinds of ph
 otonic effect\, i.e.\, (1) lasing and (2) electro-tunable optical diode ef
 fect in a sophisticated structure containing an anisotropic nematic layer 
 and cholesteric liquid crystal films.\nSection 1 described the overview of
  the photonic effect particularly in cholesteric liquid crystals. The foll
 owing 5 sections are devoted to describe major topics studied in this thes
 is. \nIn section 2\, we demonstrated the characteristic of new type of def
 ect mode lasing from a dye-doped 2-micrometre thick anisotropic nematic la
 yer sandwiched by two polymeric cholesteric liquid crystal (CLC) films as 
 photonic band gap materials. The nematic layer acts as an anisotropic defe
 ct layer\, the anisotropy of which brings about the following remarkable o
 ptical characteristics\; (1) reflectance in the photonic band gap region e
 xceeds 50 % due to the retardation effect\, being unpredictable from a sin
 gle CLC film\, (2) efficient lasing occurs either at the defect mode wavel
 ength or at the photonic band edge\, and (3) the lasing emission both from
  the defect mode and the photonic band edge mode contains both right- and 
 left-circular polarizations\, while the lasing emission from a dye-doped s
 ingle CLC layer with a left-handed helix is left-circularly polarized. We 
 also demonstrated the electro-tunable lasing of the anisotropic NLC layer 
 introduced between photopolymerized CLC films. Field-induced tunable lasin
 g could be achieved by increasing applied voltage due to the decrease of o
 ptical path length of an anisotropic NLC layer caused by the reorientation
  of NLC molecules.\nIn section 3\, we found the optical characteristics of
  a thick anisotropic NLC layer introduced between PCLC layers such as anis
 otropic mode spacing. The transmittance spectra of a 100-micrometre-thick 
 anisotropic NLC layer displayed several dips within PBG\, that is differen
 t form that of a 100-micrometre-thick isotropic layer. We also found that 
 the LCP (opposite to the helix handedness) component shows a very large mo
 dulation within the PBG. Multi-mode lasing without any particular polariza
 tions occurs within the PBG at the wavelength corresponding to the transmi
 ttance maxima due to the new structure.\nIn section 4\, we introduce exper
 imental results toward CW lasing\, which are desirable in view of practica
 l application\, using defect mode or Fabry-Perot cavity realized by the st
 ructures that include both a spacing layer defect and a phase effect.\nIn 
 section 5\, we studied another type of defect modes by introducing differe
 nt optical pitch and handedness of CLC between two PCLC layers\, giving ri
 se to additional resonant modes by the results of transmittance\, polariza
 tion of lasing\, and threshold. To confirm that this is a new type of defe
 ct mode\, we introduce 3 types of cell configuration and compare them\; i.
 e.\, (a) R-helical PCLC/ polymeric dye-doped L-helical CLC/ R-helical PCLC
 \, (b) R-helical PCLC/ polymeric dye-doped L-helical CLC\, and (c) polymer
 ic dye-doped L-helical CLC. Introducing different optical pitch and handed
 ness of CLC between two PCLC layers produces high-Q laser cavities\, and i
 t shows efficient lasing emission with low threshold value. The lasing cha
 racteristics were discussed based on transmission\, DOS\, and threshold be
 havior. From these results\, it was demonstrated that the configuration of
  L-helical CLC sandwiched by polymer-dye doped R-helical PCLC layers is ve
 ry attractive and efficient for lasing\, suggesting that it can be a candi
 date of CW lasing.\nIn section 6\, we investigated the optical properties 
 of an OHAS\, composed of a nematic liquid crystal anisotropic layer sandwi
 ched by two cholesteric liquid crystal layers possessing heterogeneous pho
 tonic bandgaps. We showed experimentally the electro-tunable optical diode
  (OD) performance (non-reciprocal transmission property) in transmittance 
 and lasing when a half-wave phase retarder is incorporated as the anisotro
 pic layer.\nIn section 7\, we concluded them. \n
LOCATION:IRC Superconductivity Seminar Room\, Cavendish Laboratory\, Depar
 tment of Physics
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