Enhanced Optical Modulation in AZO-Based Engineered Hybrid Plasmonic Waveguide: High Extinction Ratio and Low Voltage Operation

In this study, we propose a high-extinction-ratio, low-voltage optical modulator with wide optical bandwidth operation in an engineered Hybrid Plasmonic Waveguide (HPW) utilizing Aluminum-doped Zinc Oxide (AZO). Incorporating a thin AZO layer into the HPW enables vertical and lateral plasmonic mode confinement. By inducing carrier changes electrically in AZO, we achieve the epsilon-near-zero (ENZ) state, facilitating efficient intensity and phase modulation across a wavelength range of 1500 nm to 1650nm. Optimized device geometry ensures proficient electro-optic coupling between the dielectric waveguide mode and the surface plasmon mode, resulting in lower losses compared to conventional HPWs. The extinction ratio (ER) ranges from 13 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m to 45 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m at a low voltage of 1 V, with modulation efficiency spanning from 2.75 V-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m to 2.90 V-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m for wavelengths between 1500 nm and 1650 nm. We conduct a comparative analysis with another popular ENZ material, Indium Tin Oxide (ITO), demonstrating that the AZO-based modulator, with its high carrier mobility, outperforms the ITO-based modulator. AZO, as an ENZ material, holds transformative potential for optical modulation due to its unique electro-optical properties and compatibility with HPWs, offering significant advantages for high-speed, efficient, and compact optical modulators. Our proposed modulation scheme is poised to play a crucial role in advancing optical communication, quantum computing, and quantum sensing technologies.