We provide insight into the driving mechanisms and requirements to create an electro-optic spatial light modulator based on a Barium Titanate waveguide and an optically transparent electrode cladding layer. We have developed a generic framework of electric field simulations and non-linear optics to create any desired modulation in an area of interest, applicable for liquid crystals, Pockels and Kerr cells. Targeting our device structure, we have evaluated several design parameters of the arbitrarily reprogrammable SLM, capable of optical beamforming and high-quality holograms.
The authors present experimental results on mechanically stacked organic solar modules and their advantage over standard tandem architectures. A four-terminal configuration of two single junction modules with complementary absorbing active layers uses the more efficient energy conversion of a tandem structure without the necessity of matching currents or voltages of electrically connected subcells. The presented combination of semitransparent and opaque solar cells consists of solution processed polymer-fullerene blends as active materials. A cost-effective mechanical scribing process is applied for the patterning of the deposited layers. The best devices have an efficiency of over 6.5% on an aperture area of 16 cm2 which equals a gain of 30% over the best single junction module fabricated by the same process. Optical simulations demonstrate a 32% increased annual energy output of a mechanically stacked device in comparison to a monolithic tandem structure using an equivalent geometry.
Organic light-emitting diodes (OLEDs) usually exhibit a low light-outcoupling efficiency of only 20%. Typically, more than 30% of the available power is lost to surface plasmons (SPs). Consequently, the overall efficiency could be strongly enhanced by recovering SP losses. Therefore, three suitable techniques for extracting SPs-index coupling, prism coupling, and grating coupling-are discussed from a theoretical point of view and investigated experimentally in simplified OLED-like structures. The basic physical processes are clarified by systematic variations of the involved layer thicknesses and by excited state lifetime measurements. In addition, the analysis of the results is supported by optical simulations based on a dipole model. Finally, the advantages and disadvantages of each method, their potential efficiency for recovering SP losses, as well as the applicability in OLEDs are compared.
We report on three-dimensional numerical optical simulations of the emission extraction efficiency in light emitting
devices with field effect carrier transport. The finite difference time domain (FDTD) method is applied for
organic thin film structures on silicon substrates with metal and metal oxide electrodes. Simulations are performed
for Au, Ag and indium tin oxide electrodes in bottom gate, bottom contact geometries. Special attention
is paid on the dependence on electrode thickness and contact shape. It is demonstrated that in unipolar driven
devices with Si gate, silicon dioxide insulator and 40 nm-thick organic films the maximum out-coupling efficiency
is below 10 %. This value can be doubled by an implementation of metal reflecting layers on the Si substrate.
Furthermore, the emission efficiency in the ambipolar regime is investigated. The results present the dependence
of light extraction on the distance between light source and electrode. Additionally, the influence of the contact
edge shape is investigated for two different designs with rectangular and wedge electrodes. Interference effects cause an oscillation in the distance dependence.
We present a study of time-resolved transmission and emission properties of optically anisotropic planar microcavity
structures. The structures consist of λ/4-layers of SiO2 and TiO2 for the dielectric mirrors and a cavity
layer of either SiO2 or the organic dye composite AlQ3/DCM. For the SiO2 cavity, we observe a polarization
splitting at normal incidence leading to terahertz oscillations of transmitted coherent light. The polarization
splitting is explained by an optical anisotropy of the dielectric layers caused by the fabrication process. We
apply an up-conversion setup for temporally and spectrally resolved transmission measurements and obtain a
corresponding beating of 1.25 THz. Time resolved measurements yield a Q-value of 1600, corresponding to a
cavity photon lifetime of 0.65 ps. We explain our observations with a transfer-matrix model and introduce a
Fourier-transform based analytical algorithm. The cavity filled with the organic dye composite can act as an
organic microcavity laser. The birefringence of the distributed Bragg reflectors leads to lasing in two perpendicularly
polarized modes. Investigations of the ultrafast dynamics of this laser system show a phase coupling
of the two laser modes leading to the generation of a terahertz optical beat. The oscillation frequency can be
widely tuned by variations in the fabrication process.
We report on the experimental observation of polarization splitting and terahertz oscillations in transmission and laser emission from optically anisotropic microcavities. A guest-host composite of tris-(8-hydroxyquinoline) aluminium (Alq3) and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) serves as active laser material. The anisotropy is attributed to oblique columnar structures in the distributed Bragg reflector mirrors of our microcavity, resulting from sample fabrication. A splitting of 0.2 nm occurs in the laser emission from an organic vertical cavity surface emitting laser at a wavelength of 612.6 nm, and a splitting of 2.5nm is obtained from a sample for Ti-Sapphire laser transmission at 781 nm. Split modes are perpendicularly polarized.
An upconversion setup allows temporally resolved studies of transmission and emission behavior, showing an oscillation at a frequency of 1.25THz in transmission, and 0.18THz in emission, respectively. The temporal behavior of laser emission is modelled by a set of rate-equations and extended to account for the resulting oscillations. Our observations suggest that a phase-coupling mechanism between both occuring modes is present in the laser emission from our microcavity.