Influence of chelating agents on the photopolymerization of hybrid Ti-based waveguides

Sol-gel derived inorganic -organic hybrid materials (HYBRIMERs) have shown a great potential for planar and channel waveguides due to their high photosensitivity, low-cost processing and good suitability for doping. These materials have been synthesized with a high content of titanium (40%) and with three different chelating agents: acetylacetone, methacrylic acid and trifluoroacetic acid. The degree of photopolymerization of the methacrylate part changes with the nature of the chelating agent. Trifluoroacetic acid and methacrylic acid are the chelating agents showing the highest photopolymerization conversion. All coatings were crack free (thickness similar to 1 mm), transparent in the visible spectra range with refractive indexes from 1.54 to 1.58. Simple confined structures based on trifluoroacetic acid with well-defined shapes, smooth surfaces (RMS = 0.28 nm) and good optical properties were synthesized. Straight and bent channel waveguides and beam splitters were patterned by UV exposure and wet etching, and light confinement effects into the different channel waveguides were shown.