In the last decade, the processing of the waveguide structures on various substrates under mild conditions has been an appealing aim. The lithographic patterning of organic-inorganic hybrid materials processed by means of sol-gel technology allows the production of waveguides and other optical components.
We describe the synthesis of a new, photo-patternable, organically modified material with an improved ageing stability. Synthesis step does not involve widely used zirconia precursors, but it retains the same possibility of altering the refractive index by tailoring of the material composition. Refractive index values varied from 1.4700 to 1.5100. Measured birefringence values meet the requirements of most integrated planar optic applications. The synthesized material is compatible with silicon, glass and plastic substrates.
Material was analyzed using <sup>29</sup>Si NMR techniques. The processed slab waveguides were characterized by using the prism coupling technique at various wavelengths. The attenuation in the waveguide was determined by the cut-back method, and it was found to be less than 0.5dB/cm at the wavelength of 830 nm. The morphology of the microstructures was measured by using the interferometer equipment. Slab waveguides rms values were in order of only 2 nm.
The scalability to mass production and low cost are two driving forces towards multimode waveguide technologies. Organic-inorganic hybrid materials realized by sol-gel technology are promising choices for the fabrication of integrated optical circuits. This paper describes fabrication and characterization of the photo-patternable materials that are based on the sol-gel technology. The materials can be processed directly, using UV lithographic processing. Tailored polymeric materials are achieved, avoiding the use of the previously developed pre-hydrolyzed zirconium sol-gel precursors, which exhibit a lack of environmental stability. Films, which behave as a negative tone photoresist under UV-exposure, are fabricated by the spin-coating method on various substrates. The procedure shows the possibility for tailoring the refractive index and birefringence of the materials by varying the composition concentrations of the hybrid polymer system. Refractive indices vary from 1.4770 to 1.4950. The synthesized material also exhibits the possibility for birefringence optimization depending on the composition concentrations. The direct lithography process was demonstrated on various substrate materials (i.e., silicon wafer, glass, quartz, as well as flexible plastics, LTCC and semiconductor materials). The film waveguides are characterized by using of prism coupling technique at various wavelengths. The morphology of the optical structures is measured with a white-light interferometer.
Lithographic patterning of organic-inorganic hybrid materials processed by the use of sol-gel technology allows for the generation of waveguide structures at low temperatures onto polymer or ceramic substrates. In addition, sol-gel technology provides the possibility to process precision structures, such as, grooves and cavities, which are applicable for the passive alignment of photonic devices. This provides the possibility for the realization of mass-producible photonic circuits onto large-area substrates. At the moment, the most potential applications are systems based on then use of multimode waveguide structures. Actually, when utilizing sol-gel technology, the challenge is how to process homogenous, low-loss and high-aspect-ratio structures. In addition, when aiming to highly mass-producible multimode modules, the key issue is the alignment of photonic devices preferably by the use of passive precision structures. In the future, when the systems need to be more complicated, the modeling of systems requires sophisticated 3D modeling tools. In this paper, the processing of multimode structures with sol-gel technologies is described, and the characterization results of prototype devices are reported. In addition, molding and cofiring technologies potentially applicable for the hybrid integration of photonic modules are reviewed. Finally, the future research aims for the commercialization of photonic modules based on the use of sol-gel technologies are envisioned.