We modified the optical properties of organic semiconductor distributed feedback lasers by introducing a high refractive index layer consisting of tantalum pentoxide between the substrate and the active material layer. A thin film of tris-(8-hydroxyquinoline) aluminium doped with the laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran was used as the active layer. By varying the intermediate layer thickness we could change the effective refractive index of the guided laser mode and thus the laser wavelength. With this technique we were able to tune the laser emission range between 613 nm and 667 nm. For high index layer thicknesses higher than 40 nm the laser operated on the TE(1)-mode rather than the fundamental TE(0)-mode.

We modified the photonic band structure of organic distributed feedback lasers by introducing a patterned high index intermediate layer of tantalum pentoxide. This layer was oblique angle evaporated onto one dimensional surface gratings with a periodicity of 400 nm. The dielectric broadened the stopband due to its high refractive index compared to both the substrate and the active layer. By tuning the layer thickness we could increase the stopband from 3 to 16 nm