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A series of phenylbithiophene stilbenes and phenyltetraenes were synthesized and their first-order molecular hyperpolarizabilities determined. Optical nonlinearities up to μβo=9300×10−69 C m5/V were measured at 1907 nm. We show that intermolecular interactions have a large influence on the optical nonlinearity of the molecules in solution and in guest-host polymers with polymethylmethacrylate and polyquinoline as the host. We propose the use of a bulky donor group and a side chain perpendicular to the molecule’s conjugate bridge to reduce aggregation. Electro-optic coefficients as high as r33=30 pm/V at 1.55 μm in polymethylmethacrylate with 25 wt % chromophore loading were measured.

We discuss the critical trade-off between the spectral dispersion in the second order nonlinearity d(2) and the linear absorption coefficient for second harmonic generation (SHG) by the mixing of copropagating or counterpropagating fundamental beams in poled polymers. The 4-dimethylamino–4′-nitrostilbene side-chain polymer is used as a specific example. The predictive power of the classical two-level model for SHG is also assessed.

First-order quasi-phase matched LiNbO 3 waveguide periodically poled by applying an external field for efficient blue second-harmonic generation Applied Physics Letters 62, 435 (1993);

We report on detailed investigations of ytterbium (Yb) and aluminum (Al) doped silica fiber and preform samples co-doped with cerium (Ce). The prevention of pump-induced photodarkening (PD) by temporary oxidation of Ce³⁺ to Ce⁴⁺ (or rather Ce³⁺⁺) was proved by observed modifications in the ultraviolet (UV) spectra of transient absorption during near-infrared (NIR) pumping of thin preform slices. Only a small part of available Ce³⁺ ions (< 4%) was found to be involved in this process despite Yb inversions of up to 0.28. The modifications in the UV absorption spectra disappeared completely when the pump power was switched-off. From these observations we conclude that the recombination to Ce³⁺ takes place very fast thereby enabling these ions to capture liberated holes h⁺ perpetually during further pumping. We found a concentration ratio of Ce/Yb ≈0.5 to be sufficient to reduce PD loss to 10% in comparison to Ce-free fibers. Thus, the thermal load caused by absorption of PD color centers at pump (and laser) wavelength is expected to be also reduced. Unfortunately, new heat sources arise with the presence of Ce which cannot be explained by the absorption of Ce ions at the pump wavelength but must be attributed to the interaction with excited Yb ions. Fiber temperature increase of more than 200 K was observed if both, Yb₂O₃ and Ce₂O₃ concentration exceed 0.4 mol%.

Organic thin films with non-centrosymmetric ordering of dipoles are very attractive as waveguides for nonlinear optic and electro-optic applications. [1,2] High electric field poling or self-assembly has been widely used to align dipolar molecules perpendicular to the film surface. [2] However, only a few examples of in-plane alignment of dipolar molecules have been described, including epitaxy on a lattice-matched organic substrate surface, [3,4] in-plane poling, [5] and Langmuir±Blodgett film deposition. [6,7] Based on a new type of nonlinear optical material, we have demonstrated, to our knowledge for the first time, that the dipolar molecules in an organic thin film can be in-situ aligned in any desired direction within the film plane by organic molecular beam deposition (OMBD) at oblique incidence. [8] This one-component, relatively fast (5 nm min ±1 ), OMBD based, and easily controlled thin film growth technique provides a new tool for the production of organic thin films with an in-plane directional order for second-order nonlinear optics (NLO) and electro-optics.Growth of organic thin films by OMBD (Fig. 1A) in ultrahigh vacuum (UHV) has many advantages over solution-based techniques, [9,10] such as greatly reduced contamination in the UHV environment, in-situ growth monitoring, high density of chromophores, and reasonably high growth rate. In addition, mask-defined microstructures such as strip waveguides, and integrated hetero-layer structures, like light emitting diode (LED) devices, [8,11] can be fabricated by OMBD. Despite these advantages, OMBD is still much less developed as compared to solution-based techniques for the preparation of second-order NLO films. The main obstacle lies within the materials.

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