Title: Electro-Optic Modulation Based on Lossy Mode Resonance
Research proposal No: 1.1.1.9/LZP/1/24/117
Duration: 01.06.2025.-31.05.2028.
Project Leader: Ph.D. Edvīns Ļetko, Institute of Solid State Physics University of Latvia (ISSP UL)
Total budget: 184 140 EUR
European Regional Development Fund (ERDF) funding: 156 519 EUR
State budget funding: 18 414 EUR
ISSP UL budget: 9 207 EUR
Project description:
This interdisciplinary postdoctoral project introduces a novel mechanism for integrated modulation of wavelength, intensity, and polarization in photonic chips with the goal of surpassing current technologies. By leveraging the previously unexplored application of the lossy mode resonance phenomenon in photonics modulation, the project focuses on three main innovations: broad-spectrum signal modulation enabled by electrically tunable lossy mode resonance, ultra-fast modulation achieved through short-range electron migration at the lossy coating interface, and the expansion of lossy mode resonance applications beyond sensing to include optical modulation. The approach combines expertise from materials science, physics, chemistry, microfabrication, photonics, and optical computing, promising new functionalities and improved performance in integrated photonic systems.
PROJECT PROGRESS
Time period: 01.05.2025. – 30.09.2025.
Project implementation began with device modeling in the COMSOL Multiphysics environment. Since the operation of the proposed device is based on electro-optical effects arising from the redistribution of free charge carriers, it was necessary to master new built-in modules of this simulation tool. I already had prior experience with the Optic Wave module, so it was clear how to use it for modeling optical effects within the device. However, to understand the kinetics of free carriers, it was necessary to learn the Semiconductor module from the ground up. Mastering this module made it possible to determine which materials would be most suitable for the device design.
First, it was found that the LMR signal shift under the influence of an external electric field can be observed only in the near-infrared spectral range. This phenomenon can be explained by the Drude oscillator model, which describes the variation of optical properties depending on the concentration of free charge carriers specifically within this range. Based on the obtained results, the commercially available photoresist OrmoCore was selected as the waveguide material, characterized by losses of 0.2 dB/cm at a wavelength of 1310 nm, which are lower than those of other photoresists of a similar class.
Secondly, the analysis showed that the optimal waveguide dimensions for the designed device are 40 × 40 µm. The device follows an electrode–insulator–semiconductor–insulator–electrode architectural principle. The insulating material chosen was Al₂O₃ due to its excellent dielectric properties and widespread use in optoelectronics. The analysis also indicated that the insulating layer should be as thin as possible to minimize its impact on the LMR signal. Such thin films can be deposited using an Atomic Layer Deposition system available at ISSP UL, confirming the material’s suitability.
The electrode material selected was indium tin oxide (ITO), as it combines optical transparency with electrical conductivity, thereby preventing light losses that would occur if metallic electrodes were used. The modulating material chosen was TiO₂, whose ability to generate the LMR effect is confirmed by literature data. Moreover, the analysis showed that this material possesses a high dielectric permittivity, which increases the Debye length and thus enhances the effectiveness of the external electric field.
During the same project phase, alongside the theoretical development of the device, experimental studies were carried out to optimize thin-film deposition processes. All films were successfully deposited using atomic layer deposition and magnetron sputtering, and their optical properties were characterized to provide data for further device simulations.