1 May 2014 Threshold reduction by multidimensional photonic confinement in metal-organic microcavities
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Abstract
Due to their geometry, optical microcavities allow strong confinement of light between the mirrors and promise single mode operation at lowest possible lasing thresholds. Nevertheless, such devices suffer from losses not only due to parasitic absorption of the active or mirror layers, but especially via outcoupling of leaky and waveguided modes within the active layer. In this work, we present an organic microcavity sandwiched between high quality dielectric distributed Bragg reflectors. A highly conductive silver layer of 40nm thickness is added next to the active layer, leading to the formation of Tamm-Plasmon-Polaritons (TPP), one replacing the original cavity mode and shifting its resonance to the red, another one emerging from the long-wavelength sideband and moving to the blue. To avoid parasitic absorption introduced by such contacts, the silver layer is structured on the micrometer-scale using photolithography, yielding separated areas supporting either original cavity mode or red shifted TPP-resonances. This separation leads to a strong spatial trapping of the modes to only their resonant regions on the sample and can in turn be exploited to achieve complete three-dimensional confinement of photons. In elliptic holes produced in the metal layer, we observe the formation of Mathieu-Modes, leading to a reduction of the lasing threshold by six times. Facilitating triangular cuts in the silver layer, highly confined standing modes develop in the system, allowing a precise optimization of the spatial mode extension and reducing the threshold even further down to one order of magnitude below the threshold of an unstructured organic cavity. These results show that the introduction of absorptive metals, needed for the realization of an electrically driven laser, can in turn be harnessed to improve the characteristics of the device.
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Andreas Mischok, Robert Brückner, Christoph Reinhardt, Markas Sudzius, Vadim G. Lyssenko, Hartmut Fröb, Karl Leo, "Threshold reduction by multidimensional photonic confinement in metal-organic microcavities", Proc. SPIE 9137, Organic Photonics VI, 91370D (1 May 2014); doi: 10.1117/12.2051491; https://doi.org/10.1117/12.2051491
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