Special projects between Bavaria and Florida

The aim of the project is to further develop the quasi-phase-matching (QPM) technique of integrated optical waveguides by the development of a destruction free measuring technique of the non-uniformity and quality of micro-structured QPM gratings. QPM-poled waveguides are used in optical communication systems for wavelength conversion and all-optical ultrafast signal processing. Based on an interferometric measurement of amplitude and phase of the generated second-harmonic (SH) versus phase-mismatch the QPM profile along the waveguide can be calculated. A non-linear optical interferometer for the waveguide-generated SH has to be developed with a compensation for reflection induced fringes. A phase-stable reference SH generator has to be developed. The expected result of the project is a compact measurement set-up for QPM-waveguide characterisation.

In cooperation with the University of Central Florida gratings for quasi phase-matching (QPM) in lithium niobate were destruction-free measured. Samples were produced at the University of Paderborn. Special gratings with non-uniformly distributed domain periods were developed. In bulk crystals and film waveguides local phase-matching measurements in non-co-linear second harmonic generation (SHG) yielded information on the local QPM period. The QPM grating could be characterized with a resolution of ca. 2 mm in 5-cm long crystals. Very good agreement between measured and grating specification was found. In waveguide arrays SHG in diffraction-free propagating beams yielded similar good results in 7-cm long samples. For the measurement of non-uniformities in channel waveguides an extensive characterization of the samples were performed. QPM specific phase effects were found. A phase-stable reference SH generator was built. Based on an interferometric measurement of amplitude and phase of the generated second-harmonic (SH) versus phase-mismatch the QPM profile along the waveguide shall be calculated in a next step. The work and exchange between the University of Central Florida, the Friedrich Schiller Universität Jena and the Universität Paderborn continue and the final results of the non-uniformity measurements shall be presented in several publications.