High-Frequency 40 GB/s MWIR and LWIR Metamaterials-based Electro-Optical Modulators for Free-Space Optical Communications

The research objective is to develop and demonstrate a metamaterial-based Electro-Optic Modulator (EOM) operating at Mid-Wave and Long-Wave Infrared (MWIR/LWIR) wavelength radiation for Free-Space Optical (FSO) communication links. Our approach will follow an iterative process of design, numerical analysis, fabrication, and laboratory testing. The EOM will provide low-latency, high-speed modulation (10-40 GHz), using a layer of Electro-Optic (EO) material within Fabry-Perot cavities of thin-film metamaterials with specially designed doping concentrations. We will implement an array of metamaterial structures to concentrate a high volume of incident light into the tuning layer with low insertion loss, so a low level of index modulation (~0.03) at low threshold voltages (< 5-10 V) can induce significant modulation. EO materials such as Lithium Niobate (LiNbO3) or Barium Titanate (BaTiO3) can reach speeds greater than 40 GHz to meet demands of modulation for optical communication. Individual elements of the metamaterial array will act as single pixels, capable of achieving either high-extinction or full 2?  phase modulation. Each element will be controlled by a field-programmable gate array or read-out integrated circuit. We will develop and fabricate an on-chip control circuit using graphene electrodes to control elements individually or uniformly. This precise level of control provides modulation over the phase or amplitude of light from a laser transmitter. Doped silicon and common EO materials are compatible with standard foundry processes, providing a path to scalable manufacturing for Department of Defense (DoD) or commercial applications. We will develop and optimize the EOM in Phase I using numerical analysis and machine learning. Finite-difference time-domain and finite element method simulations will be used to evaluate bounding limitations of a given EOM design. Machine learning through particle swarm optimization based on rigorous coupled-wave analysis will be used to optimize the EOM design. We will identify the optimal EOM design for a specific set of output properties or applications by varying design parameters such as specific doping concentrations, layer thicknesses, or applied voltages. Bounding conditions for optimization will be set based on practical constraints including fabrication tolerances and use-case restrictions. A prototype will be fabricated and tested during the Phase I Option to demonstrate basic performance of the EOM including modulation speed, coupling efficiency, and standard optical properties. Initial demonstration will be performed for a single EOM element to validate the design and optimization approach. The design, fabrication recipe, and performance of this prototype will serve as the foundation for further development of a full prototype in Phase II. The full EOM will be implemented in laboratory and field tests to demonstrate the potential for integration in communication systems for Naval applications.