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All-optical signal processing is becoming a key issue with the
steady increase of bandwith demand in telecommunication and IT industries.
Significantly higher channel rates require new concepts and device
structures. In this context organic semiconductor devices offer
some advantages with respect to traditional materials and devices.
In particular, they feature easy processing, low cost and flexibility.
If successful, lasers and ultrafast all-optical switches based on
organic semiconductors could become important due to their integration
potential on arbitrary substrates and the tunability of the lasing
emission.
Organic lasers are improved by incorporating a photonic crystal
that consists of a thin layer of TiO2. The TiO2 increases the index
contrast and the confinement in the waveguide. Thus the mode coupling
is increased, which results in larger feedback given to the lasing
modes. The larger feedback leads to smaller devices as the interaction
length is decreased to achieve the lasing threshold. To employ a
photonic crystal consisting of a high-index material in this way
gives rise to new design criteria. These criteria are investigated
and employed to design an optimum organic photonic crystal laser.
Devices have been fabricated according to optimum parameters and
characterized. The measured spectral features of the laser agree
very well with the predictions obtained from simulations.
Furthermore, Fabry-Perot cavities are fabricated by incorporating
an organic nonlinear Kerr material between two dielectric mirrors.
Using femto-second pump and probe measurements we characterize these
hybrid 1-D photonic band gap structures for various organic materials.
Promising organic materials are C60 and MEH-PPV. By varying the
pump beam wavelength across the cavity resonance we are able to
delineate the various underlying nonlinear processes. It turns out
that, in the spectral region from 780 to 880 nm, nonlinear absorption
dominates the signal. However, for larger wavelengths of around
1300 to 1500 nm, refractive nonlinear effects dominate the signal.
Comparing these measurements with computations, we are able to quantify
both the refractive and absorptive nonlinear coefficients of various
organic materials.
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