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Liquid-crystal-based resonant cavities as a strategy to design low-threshold electrically-tunable lasers

ABSTRACT We present an experimental study of an electrically tunable laser based on liquid-crystal elements and analyse theoretically its main working principles. The laser structure includes two polymer-stabilised cholesteric-liquid-crystal slabs that act as polarisation-sensitive reflectors, and a dye-doped nematic layer sandwiched between them. The wavelength of lasing can be changed by modifying the optical retardation of the nematic layer by means of a low-amplitude square wave. For all wavelengths the laser light is circularly polarised with opposite handedness to that of the cholesteric mirrors. Good laser performance has been achieved, with low thresholds and quasi-continuous tuning ranges. The laser threshold varies with the wavelength, and was found to be highly dependent on the spatial location of the indium-tin-oxide (ITO) electrodes, inside or outside the laser resonator. A theoretical account for this effect is given using simulations based on the Berreman 4 × 4 matrix method. Graphical abstract