Light source having an outsource device
The invention relates to a light source ( 1 ) comprising a light generating unit ( 2 ) like an organic light emitting diode and an outcoupling device ( 3 ) for coupling light out of the light generating unit in an outcoupling direction ( 4 ). The outcoupling device comprises a first region ( 5 ) for facing the light generating unit, a second region ( 7 ) having a refractive index being smaller than the refractive index of the first region, and a structured intermediate region ( 6 ) between the first region and the second region. The first region is optically homogenous and has a thickness in the outcoupling direction being larger than a coherence length of the light, thereby reducing generally possible wavelength dependent interference effects and, thus, a corresponding degradation of the outcoupling efficiency. The outcoupling efficiency can therefore be increased.
1. A light source comprising: a light generating unit for generating light, and an outcoupling device for coupling light out of the light generating unit in an outcoupling direction, wherein the outcoupling device comprises: a first region for facing the light generating unit, the first region being optically homogenous and having a thickness in the outcoupling direction being larger than 10 pm, a second region having a refractive index being smaller than the refractive index of the first region, and an intermediate region between the first region and the second region, the intermediate region being structured, wherein the intermediate region comprises particles for structuring the intermediate region, the particles having a refractive index being equal to or smaller than the refractive index of the second region or larger than the refractive index of the first region; and wherein the particles are distributed on and attached to the surface of the second region.
2. The light source as defined in claim 1 , wherein the light generating unit is a white light emitting organic light emitting diode comprising a cathode layer, an anode layer and several intermediate layers between the cathode layer and the anode layer.
3. The light source as defined in claim 1 , wherein the refractive index of the first region is equal to or larger than 1.7.
4. The light source as defined in claim 1 , wherein the first region comprises a first layer being a SiO x N y layer.
5. The light source as defined in claim 1 , wherein the outcoupling device is producible by depositing a first material on structures on a surface of a substrate, wherein after the deposition the first region comprises an optically homogenous first layer of the first material having a thickness in the outcoupling direction being larger than 10 μm and having a refractive index larger than the refractive index of the substrate, the second region comprises a second layer of the substrate and the intermediate region comprises an intermediate layer comprising the structures and the first material, the structures comprising particles having a refractive index being equal to or smaller than the refractive index of the second region or larger than the refractive index of the first region; and wherein the particles are distributed on and attached to the surface of the second region.
6. The light source as defined in claim 2 wherein the refractive index of the first region matches the average of the refractive indices of the intermediate layers of the light generating unit.
7. The light source as defined in claim 1 where the second region is a second layer and the particles of the intermediate region are homogenously distributed on the surface of the second layer and covered by the first region.
8. The light source as defined in claim 1 where the material in the optically homogenous first region is an inorganic material that is transparent to the generated light.
9. The light source as defined in claim 1 wherein the second region comprises glass.