Electrical tuning of the wavelength of the defect mode lasing in a one-dimensional photonic crystal has been demonstrated using a conducting polymer as an active emission layer and a nematic liquid crystal as an electrically tunable defect layer in the periodic structure. Lasing wavelength is widely tuned upon applying the electric field, which follows a defect mode shift due to the refractive index change in the nematic liquid crystal defect layer caused by field-induced realignment of the liquid crystal molecules.
Laser action in a one-dimensional photonic crystal (PC) with dye-doped cholesteric liquid crystals as a defect layer has been investigated. A single-mode lasing has been achieved in the PC with a helical structure, which is based on the defect mode of the PC with a defect and the band edge effect of the cholesteric helix. The contribution of the interaction between the defect mode and band edge effects to the laser action was confirmed on the basis of the helix pitch dependence of lasing characteristics. The threshold of the laser action in the PC with the helical structure was lower than that in the helical structure without a PC. It has also been found that lasing wavelength shifts as a function of temperature corresponding to the band edge shift of the cholesteric liquid crystal.
Position sensitive lasing with continuous wavelength tunability and emission in the cell-plane direction is demonstrated from a photopolymerized cholesteric liquid crystal film. The device has a gradually dilating helix lying in the cell-plane direction and is fabricated by applying a vertical electric field in a conventionally rubbed wedge cell while cooling the sample from the isotropic phase. Tuning range of ∼100nm is achieved by translating the device with respect to the pump beam. Photopolymerizable materials are especially useful in this configuration since a freestanding film, not requiring any external voltage to maintain the molecular ordering, can be prepared.
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