Influence of the organic film thickness on the second order distributed feedback resonator properties of an organic semiconductor laser

We report on the cavity numerical characterization of a second order one-dimensional distributed feedback organic laser. The gain medium containing 6 wt. % of 4,4′-bis[(N-carbazole)styryl]biphenyl) in a 4,4′-bis[9-dicarbazolyl]-2,2′-biphenyl) host is vacuum deposited to form an organic thin film on a SiO₂ grating. The influence of the organic film thickness on the properties of the resonant cavity is investigated through numerical calculations of both the confinement factor Γ and the Q-factor. The Q-factor is obtained using two methods, one by calculating the eigenmodes of the resonant cavity and the other by calculating the reflection spectrum. It was found that while the Γ increases with the organic film thickness, the Q-factor shows a non-monotonic function with a maximum value for a thickness of 200 nm.