(502c) Improving Integrated Photonics With Sol Gel Chemistry

Silica-based materials have found numerous important applications in the chemical and materials industries as well as in electronics and optics.  To further benefit these applications, development and characterization of new silica materials with improved properties is crucial.   However, tuning the properties of silica materials can be difficult.  One approach is to add dopants, although integrating them uniformly within silica is challenging.  Alternatively, polymers may have favorable properties for some applications, although they are not as thermally robust as oxides and not compatible with all fabrication processes.

Sol gel chemistry offers a unique and efficient means to develop custom oxide materials while overcoming these challenges.   To produce sol gel silica, a liquid precursor (typically a silicon alkoxide) is combined with solvent and water. Any additional materials, such as dopants, can be easily and uniformly added to the liquid precursor solution as well.  Then, the precursor undergoes acid- or base-catalyzed hydrolysis and condensation reactions to form a gel-like oxide matrix.  Afterward, the sol gel materials are baked to remove the solvent and subsequently annealed at high temperatures to form densified oxides.  Using this sol gel approach, we have developed several customized silica materials with unique optical properties.  By combining these novel glass materials with integrated photonic devices, we are able to create devices with previously unachievable behaviors. 

This presentation will focus on two advances in sol-gel chemistry which have enabled the development of new devices.  The first is the development of high index films for manipulating the location of the optical field within integrated photonic devices and the second is the incorporation of rare earth metals to enable the fabrication of ultra-low threshold lasers.  The integrated device platform which is combined with the sol-gel materials is an optical resonant microcavity. 

By adding small amounts of titanium butoxide to silica made from methyl triethoxysilane (MTES) and tetraethyl orthosilicate (TEOS) precursors, the refractive index can be tuned from 1.44 to 1.62, as measured by spectroscopic ellipsometry.   When this high index material is conformally coated on an integrated device, the optical field is confined within the high index material, and the optical field intensity is increased.  In addition, we have added rare earth dopants (eg Er, Yb, Nd) to sol gel silica to synthesize glasses which are capable of fluorescence and lasing at various wavelengths from the visible through the near-IR.  Since these materials are made primarily of silica, we also confirm that they retain many of silica’s important properties, including its robustness and high transparency.  Photonic devices are fabricated directly from these materials, and integrated microlasers are demonstrated.