Electro-optic technology relies on the operation of systems/devices through the propagation and interaction of light with various tailored/optically active materials. Typical electro-optical devices are designed to modulate the properties of a light wave (e.g., phase, polarization, amplitude, frequency, direction of propagation) and include photodetectors, laser diodes, flat-screen displays, and photonic IC. A waveguide is an electro-optical device component designed to guide electromagnetic waves in the optical spectrum, with a variety of waveguides available for use including planar, strip, or fiber types depending on application. Major concerns that currently limit the functionality of electro-optic systems include less than desirable operational/transmission speed and high operational power consumption.
In order to address speed/power consumption issues, various solutions have been investigated and/or developed, including use of high performance electro-optic materials/polymers, and use of improved phase/polarizing/amplitude modulators, and waveguides. The ferroelectric material, barium titanate, BaTiO3 (BTO), has excellent electrical properties, and electro-optic coefficients (Pockels coefficients) which shows promise for use in electro-optic modulators and switches. Use of BTO in waveguides has to date been limited due to the processing requirement to etch the BTO, which results in the developed waveguide designs having less than desirable performance/power consumption characteristics. In light of this, it is clear that the development of a technology that allowed the integration of BTO into waveguides without the drawbacks of lower performance or increased power consumption associated with etching could pave the way for their use to greatly improve many electro-optic devices.
Researchers at UT Austin have developed a proof-of-concept design and process for construction of a monolithic, unetched, BTO strip waveguide. The key aspect of this process is the ability to realize the benefits of BTO as an electro-optic material, while at the same time not compromising its performance by use of other materials (e.g., Si/Si-nitride) in waveguide construction which would usually be required to guide the light. The waveguides produced by this technology are entirely fabricated from BTO, rather than the other materials used in hybrid BTO waveguides, and has been accomplished without the requirement for BTO etching and its resulting material damage and decreases in device performance. The developed process includes growing an epitaxial SrTiO3 (STO) template on Si, and then oxidizing the underlying Si through the STO via elevated temperature (800°C) O2 annealing. Initial testing on two different BTO layers of varying thickness (100 nm, 200 nm) resulted in better optical performance as well as lower power requirements than hybrid BTO construction. The developed strip waveguide has potential for use in a range of photonic devices including modulators, switches, interferometers, and filters.