Creating dynamic poling of ferroelectric thin films for chip-scale reconfigurable optical systems

Ohio State University, The, Columbus OH

Investigators

Abstract

The integrated photonics concept is the application of thin-film technology to optical circuits and devices for the purpose of achieving efficient, high-performance, and economical optical systems. One can view the field as the optical equivalent of microelectronics for integrated circuits. The interest in integrated photonics is driven by the need for miniature, portable, and efficient optical communications, computing, and sensing platforms that are not limited by large scale bulk optics, discrete components, and long distance optical fiber. Applications include the generation of light of different colors for precision measurements, the control of short optical pulses for high speed signal processing, and the modification of light color for low noise secure communications. To create functional optical devices in thin films, voltages in the kilovolt range are required for a process referred to as poling. Consequently, devices are static once fabricated by an external high voltage power supply. The research program aims to reduce the required voltage to only a few volts. Due to the low voltage requirements, static devices can become dynamic. Optical systems once thought of as fixed and inflexible become reconfigurable and programmable. Dynamic functionalities enable the realization of systems that utilize the properties of light to overcome the physical limitations imposed by electrons, impacting information technology, telecommunications, health care, the life sciences, and national defense. The integrated educational plan responds to the challenge of linking science and engineering to problems of public interest by developing a classical and modern optics seminar series, creating new classroom modules for integrated optics curriculum that engenders integrative research thinking, and involving graduate and undergraduate students, underrepresented groups, and minorities in the research program. A comprehensive research program is proposed involving theory, design, modeling, fabrication, and test to create dynamic poling of ferroelectric thin films for reconfigurable optical systems on a chip for the first time. The objectives are to create microscale planar optical waveguides in wafer scale thin films of magnesium oxide doped lithium niobate with optically transparent poling electrodes and low coercive field, allowing for on-chip poling and programming of the spontaneous polarization waveform. The design and modeling approach is based on numerical solutions to nonlinear coupled amplitude equations based on Maxwell's equations. The chip will be fabricated at Ohio State University using nanoscale fabrication techniques. A host of nonlinear optical phenomena with tunable center frequency and tunable bandwidth will be demonstrated. New broadband and compact optical system architectures involving the convergence of photonics with electronics in integrated circuits are envisioned. The research addresses the lack of second order susceptibility in silicon which is a major obstacle to achieving chip-scale nonlinear optics. The program exploits the low coercive field of sub-micrometer thin films of magnesium oxide doped lithium niobate, strip loaded optical waveguides with micrometer scale mode field diameter, transparent optical electrodes, and on-chip heaters to reduce the voltage required for poling to less than five volts. New horizons immediately become apparent when exploiting the capability of dynamic poling of the ferroelectric domains directly on-chip. Instead of being static, the poling period becomes tunable and poling electrodes can now be considered as programmable. Tuning the poling period results in the dynamic variation of the phase matching frequency. Programming the poling into a linear chirp produces dynamic control of the phase matching bandwidth. These concepts provide a new method of attack to achieve dynamically tunable nonlinear optical systems on a chip. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.