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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. [Copyright &y& Elsevier]

Abstract: We have experimentally demonstrated the optical diode performance in a two-layered device consisting of a cholesteric liquid crystal (CLC) film with a right-handed helical structure and a nematic liquid crystal (NLC) layer as a phase retarder of a half wave. Right-circularly polarized (RCP) light of the wavelength the same as the optical pitch of the helix is totally reflected by the CLC film when the light is incident from the CLC film side. On the other hand, if the incidence is made from the NLC side, RCP is transformed to left-circularly polarized (LCP) light and is then passed through the CLC film. Not only such an optical diode performance, i.e., unidirectional propagation (non-reciprocal transmission), but also its electro-tunability was also shown. The transmittance can be essentially tuned between 0% and 100%. [Copyright &y& Elsevier]