Voltage and temperature tuning of laser properties using liquid crystals

Liquid crystals are materials that have excellent electro-optic properties: moderate voltages are able to induce large refractive index changes. This refractive index tunability can be used to actively control laser emission by incorporating liquid crystal material inside the laser cavity. In the first example we have combined Vertical Cavity Surface Emitting Lasers (VCSELs) with a liquid crystal layer in an external cavity. Both chiral and non-chiral nematic liquid crystals have been used. The chiral liquid crystals act as a tunable mirror for the laser emission while the non-chiral liquid crystal is used to tune the external cavity length. Experimental and numerical results show the effect of the liquid crystal layer on the laser threshold and on the wavelength, polarization state and transverse profile of the emitted light. In a second example, laser dye is incorporated inside the liquid crystal material itself to form an optically pumped liquid crystal laser. By inserting this material between two weak reflectors we have obtained voltage tunable Fabry-Perot lasing with high slope efficiency and a tuning range up to 10 nm. In this configuration the laser light is emitted perpendicular to the liquid crystal layer. In a third example we look at numerical simulations of in-plane liquid crystal lasers. Here the laser light is emitted parallel to the surfaces containing the liquid crystal. The accurate modeling of the light generation in such systems is complex because the materials are optically anisotropic and the configuration is two-dimensional with fully two-dimensional variations of the liquid crystal orientation. Therefore we use advanced optical methods based on finite-element calculations of the optical modes in periodic two-dimensional structures. The optical modes in a lying helix configuration are calculated as a proof-of-principle for this simulation method. Interesting observations can be made when looking at the optical modes in these structures. Applying a voltage over the liquid crystal layer results in a shift of the laser emission.

ISBN:9789939671000

Jaar van publicatie:2014

Toegankelijkheid:Closed