PFI:AIR - TT: BaTiO3 Photonic Crystal Electro-optic Devices for 50 GHz Applications

Northwestern University, Evanston IL

Investigators

Abstract

This PFI Accelerating Innovation Technology Project focuses on the development of a prototype Photonic crystal (PhC) electro-optic modulator for ultra-high bandwidth optical systems. This is important because in the future, communication and cyber systems will require optical subsystems with ultra-high transmission rates due to the connectivity requirements of data centers, residential systems, mobile smartphones, and smart network communications. The optical modulator is a key piece of optical systems and at present is the component that limits the data transmission rates. This project focuses on developing a working, packaged prototype optical modulator based on barium titanate (BaTiO3) ferroelectric oxide thin films with a bandwidth of 50 GHz, which is 25% higher than the current state of the art technology based on Lithium niobate (LiNbO3). Lithium niobate (LiNbO3) has been established as the electro-optic material of choice for optical modulators due to its relatively high electro-optic (EO) coefficient. However, it has a high dielectric constant at microwave frequencies, which limits the bandwidth of conventional modulators to 40 gigahertz (GHz) or less. Approaches based on silicon, indium phosphide and polymeric materials have been widely investigated to solve this major challenge and although progress has been made, a number of significant challenges in speed and power required remain. This project takes an alternative approach by using BaTiO3 ferroelectric oxide thin films with experimentally demonstrated electro-optic (EO) coefficients more than an order of magnitude higher than that of LiNbO3. In this project, packaged EO modulators with photonic crystal waveguide structure will be developed. Devices will be fabricated using vapor phase epitaxial deposition, and both conventional photolithography and focused ion beam milling. The BaTiO3 thin film platform has numerous competitive advantages over other platforms for optical modulator applications such as (1) Large EO coefficient, ten times higher compared to those of LiNbO3 devices dominating optical modulator markets; (2) Low driving voltage thus low power consumption; (3) Ultrahigh bandwidth higher than 50 GHz demonstrated with potential reaching sub-THz regime; (4) potential for integration with Si electronics leading to ultrahigh compact electro-optical components at low cost. By using a BaTiO3 thin film platform with non-linear photonic crystals, significant improvements in bandwidth, operating voltage, and size are expected compared to conventional devices. A working packaged, prototype 50 GHz bandwidth modulator, 1mm long, will be demonstrated. The project will involve training of graduate students and postdoctoral scholars in photonic crystal design as well as offering experiences with technology transfer through the development and demonstration of the prototype.