Researchers are making significant strides in the application of magneto-optic effects, which involve the manipulation of light polarization when photons interact with magnetic fields. A recent study introduces a novel thermally induced switching mechanism to control Faraday and Kerr rotations at terahertz (THz) frequencies, leveraging the unique properties of Vanadium dioxide (VO2) and graphene layers.
This innovative design features layered architecture, consisting of VO2, graphene, and magnesium oxide (MgO) defect layers, all integrated through dual Bragg reflectors. By modulating temperature, this system can switch between states of substantial optical transmission and reflection, providing promising applications for advanced optoelectronic devices.
The research team employed the transfer matrix method to analyze the structure using terahertz light, discovering distinctive magneto-optical properties. At room temperature (300 K), the experimental setup demonstrated significant transmission with an impressive Faraday rotation angle nearing 15.26 degrees, accompanied by minimal reflective response. When temperatures escalated to 350 K, the optical characteristics transitioned; the system shifted to a reflective condition where transmission was reduced, increasing the Kerr rotation angle to approximately 44.18 degrees.
This interplay between thermal conditions and magneto-optical effects showcases the process's efficiency, with the switching mechanism fundamentally dependent on the precise thickness of the MgO defect layer. The study reveals the temperature-sensitive nature of VO2, which transitions from semiconductor to metal at about 340 K, enhancing the system's functionality as it alters the electrical conductivities of the various materials involved. Specifically, VO2 conductivity at 300 K is around 2x10² S/m, jumping to 2x10⁵ S/m as temperatures rise.
The significance of the findings was underlined by the researchers, who emphasized the switching mechanism's versatility across both s- and p-polarizations, maintaining high stability even at near-normal incidence angles.
External magnetic fields (Bext) also play a pivotal role. Notably, as Bext increases, both transmission (Tr) and reflection (R) intensities decrease, overshadowed by rising values of the Faraday and Kerr rotation angles. These observations highlight the device's adaptability to varying external conditions.
The study explains the structure’s underlying operational dynamics through experimental data and computational modeling. For example, at lower incidence angles, especially below 15°, the system retains its switching capabilities, effectively preserving the resonance for both transmission and reflection modes.
Interestingly, the thickness of the MgO layer directly impacts the switching frequencies. Altering the dMgO led to noticeable shifts – increasing the thickness tends to lower the frequency, and optimizing the thickness allows for enhanced optical effects. Nevertheless, exceeding specific thickness thresholds can diminish the effectiveness of the magneto-optical responses, indicating the necessity for careful optimization during device design.
Conclusively, this innovative thermally controlled switching system stands poised to advance the design and enhancement of multifunctional optoelectronic devices. The comprehensive results reflect invaluable insights for future applications, spanning fields from telecommunications to complex data storage solutions. The authors of the article foresee this research catalyzing significant advancements, providing both foundational knowledge and practical pathways for improving optoelectronic functionalities.
