Inorganic alternating current electroluminescent devices (AC-ELs) are known for their ruggedness and extreme long-term reliability, which is why they can often been found in industrial and medical equipment as well as in applications in the military sector. In contrast to the inorganic phosphors used in AC-ELs, organic materials offer a number of advantages, in particular a significantly higher efficiency, easier processibility, and a wide selection of emitter materials spanning the entire visible spectrum. Several efforts towards alternating current driven organic light-emitting devices have recently been made, however, important operating mechanism are still not well understood. In the first part of this theses, alternating current driven, capacitively coupled, pin-based organic light-emitting devices are investigated with respect to the influence of the thickness of the insulating layer and the intrinsic organic layer on the driving voltage. A three-capacitor model is employed to predict the basic behavior of the devices and good agreement with the experimental values is found. The proposed charge regeneration mechanism based on Zener tunneling is studied in terms of field strength across the intrinsic organic layers. A remarkable consistency between the measured field strength at the onset point of light emission (3–3.1 MV/cm) and the theoretically predicted breakdown field strength of around 3 MV/cm is obtained. The latter value represents the field required for Zener tunneling in wide band gap organic materials according to Fowler-Nordheim theory. In a second step, asymmetric driving of capacitively coupled OLEDs is investigated. It is found that different voltages and/or pulse lengths for positive and negative half-cycle lead to significant improvements in terms of brightness and device efficiency. Part two of this work demonstrates a device concept for highly efficient organic light-emitting devices whose emission color can be easily adjusted from, e.g., deep-blue through cold-white and warm-white to saturated yellow. The presented approach exploits the different polarities of the positive and negative half-cycles of an alternating current driving signal to independently address a fluorescent blue emission unit and a phosphorescent yellow emission unit vertically stacked on top of each other. The electrode design is optimized for simple fabrication and driving and allows for two-terminal operation by a single source. The presented approach for color-tunable OLEDs is versatile in terms of emitter combinations and meets application requirements by providing a high device efficiency of 36.2 lm/W, a color rendering index of 82 at application relevant brightness levels of 1000 cd/m², and warm-white emission color coordinates. The final part demonstrates an approach for full-color OLED pixels that are fabricated by vertical stacking of a red-, green-, and blue-emitting unit. Each unit can be addressed separately which allows to efficiently generate every color that is a superposition of spectra of the individual emission units. The device is built in a top-emission geometrywhich is highly desirable for display fabrication as the pixel can be directly deposited onto the back-plane electronics. Furthermore, the presented device design requires only three independently addressable electrodes which simplifies fabrication and electrical driving. The electrical performance of each individual unit is on par with standard pin single emission unit OLEDs, showing very low leakage currents and achieving high brightness levels at moderate voltages of around 3–4 V.

Im Rahmen der vorliegenden Arbeit ist es erstmals gelungen, mit einem ps-Pumplaser (10 ps) Weißlicht mit einer spektralen Breite von mehr als einer optischen Oktave in einer mikrostrukturierten Faser (MSF) bei einer Pumpwellenlänge von 1064 nm zu generieren. Es ließ sich, abgesehen von nichtkonvertierten Resten der Pumpstrahlung, ein unstrukturiertes und zeitlich stabiles Weißlichtspektrum von 700 nm bis 1650 nm generieren. Die maximale Ausgangsleistung dieser Weißlichtstrahlung betrug 3,1 W. Es konnten sehr gute Einkoppeleffizienzen von maximal 62 % erzielt werden. Die an der Weißlichterzeugung beteiligten dispersiven und nichtlinear optischen Effekte, wie z.B. Selbstphasenmodulation, Vierwellenmischung, Modulationsinstabilitäten oder Solitoneneffekte, werden detailliert theoretisch untersucht und erläutert. Die Arbeit beinhaltet ebenfalls eine umfangreiche Beschreibung der Wirkungsweise und Eigenschaften von mikrostrukturierten Fasern mit einem festen Faserkern. Aufgrund der großen Variationsvielfalt des mikrostrukturierten Fasermantels und der damit verbundenen Wellenleitereigenschaften ergeben sich, insbesondere für die Anwendung in der nichtlinearen Optik, eine Reihe von interessanten Eigenschaften. Es wurden insgesamt vier verschiedene mikrostrukturierte Fasern experimentell untersucht. Für die Interpretation der experimentellen Ergebnisse ist die Pulsausbreitung der ps-Pumppulse in einer dispersiven, nichtlinear optischen Faser anhand der verallgemeinerten nichtlinearen Schrödinger-Gleichung berechnet worden. Durch einen Vergleich der Berechnungen mit den Messdaten ließen sich verstärkte Modulationsinstabilitäten und verschiedene Solitoneneffekte als hauptsächlich für die Weißlichterzeugung bei ps-Anregungspulsen verantwortlich identifizieren. Auf der Basis der durchgeführten Untersuchungen wurde in Kooperation mit der Fa. Jenoptik Laser, Optik, Systeme GmbH eine kompakte und leistungsstarke Weißlichtquelle entwickelt. Diese wurde erfolgreich in einer Kohärenztomographiemessung (Optical Coherence Tomography - OCT) getestet: Es konnte in ex vivo-Untersuchungen gezeigt werden, dass sich mit dieser ps-Weißlichtquelle eine hohe Eindringtiefe von ca. 400 µm in die Netzhaut eines Affen erreichen lässt. / With the present work it succeeded for the first time to generate white-light with a spectral width of more than an optical octave in a microstructured fiber (MSF) with a pump wavelength of 1064 nm and ps-pump pulses (10 ps). Apart from non-converted remainders of the pumping radiation, an unstructured and temporally stable white-light spectrum from 700 nm to 1650 nm could be generated. The maximum output power of this white-light radiation amounted to 3.1 W. Very good coupling efficiencies of max. 62 % could be obtained. At the white light generation different dispersive and nonlinear optical effects took part, e.g. self-phase modulation, four-wave mixing, modulation instabilities and soliton effects. These processes are theoretically examined and described in detail. Likewise the work contained an extensive description of the principle of operation and characteristics of microstructured fibers with a solid fiber core. Due to the large variation variety of the microstructured fiber cladding and the associated wave-guiding characteristics arise, in particular for application in the nonlinear optics, a set of interesting properties. Altogether four different microstructured fibers were experimentally examined. For the interpretation of the experimental results the pulse propagation of ps-pump pulses in a dispersive, nonlinear optical fiber was computed on the basis of the generalized nonlinear Schroedinger equation. By a comparison of the calculation results with the measuring data amplified modulation instabilities and different soliton effects could be identified as main responsible for the white light generation with ps-pump pulses. With respect to the accomplished experimental and theoretical investigations in co-operation with the company Jenoptik laser, optics, systems GmbH a compact and high-performance white-light source was developed. This broadband light source was tested successfully in an optical coherence tomography measurement (OCT): It could be shown in ex vivo investigations that with this white-light source high penetration depths of approx. 400 µm into the retina of a monkey could be achieved.

Inorganic alternating current electroluminescent devices (AC-ELs) are known for their ruggedness and extreme long-term reliability, which is why they can often been found in industrial and medical equipment as well as in applications in the military sector. In contrast to the inorganic phosphors used in AC-ELs, organic materials offer a number of advantages, in particular a significantly higher efficiency, easier processibility, and a wide selection of emitter materials spanning the entire visible spectrum. Several efforts towards alternating current driven organic light-emitting devices have recently been made, however, important operating mechanism are still not well understood. In the first part of this theses, alternating current driven, capacitively coupled, pin-based organic light-emitting devices are investigated with respect to the influence of the thickness of the insulating layer and the intrinsic organic layer on the driving voltage. A three-capacitor model is employed to predict the basic behavior of the devices and good agreement with the experimental values is found. The proposed charge regeneration mechanism based on Zener tunneling is studied in terms of field strength across the intrinsic organic layers. A remarkable consistency between the measured field strength at the onset point of light emission (3–3.1 MV/cm) and the theoretically predicted breakdown field strength of around 3 MV/cm is obtained. The latter value represents the field required for Zener tunneling in wide band gap organic materials according to Fowler-Nordheim theory. In a second step, asymmetric driving of capacitively coupled OLEDs is investigated. It is found that different voltages and/or pulse lengths for positive and negative half-cycle lead to significant improvements in terms of brightness and device efficiency. Part two of this work demonstrates a device concept for highly efficient organic light-emitting devices whose emission color can be easily adjusted from, e.g., deep-blue through cold-white and warm-white to saturated yellow. The presented approach exploits the different polarities of the positive and negative half-cycles of an alternating current driving signal to independently address a fluorescent blue emission unit and a phosphorescent yellow emission unit vertically stacked on top of each other. The electrode design is optimized for simple fabrication and driving and allows for two-terminal operation by a single source. The presented approach for color-tunable OLEDs is versatile in terms of emitter combinations and meets application requirements by providing a high device efficiency of 36.2 lm/W, a color rendering index of 82 at application relevant brightness levels of 1000 cd/m², and warm-white emission color coordinates. The final part demonstrates an approach for full-color OLED pixels that are fabricated by vertical stacking of a red-, green-, and blue-emitting unit. Each unit can be addressed separately which allows to efficiently generate every color that is a superposition of spectra of the individual emission units. The device is built in a top-emission geometrywhich is highly desirable for display fabrication as the pixel can be directly deposited onto the back-plane electronics. Furthermore, the presented device design requires only three independently addressable electrodes which simplifies fabrication and electrical driving. The electrical performance of each individual unit is on par with standard pin single emission unit OLEDs, showing very low leakage currents and achieving high brightness levels at moderate voltages of around 3–4 V.