Active Optically Controlled Broadband Terahertz Modulator Based on Fe3O4 Nanoparticles

Abstract

We report an active broadband terahertz (THz) modulator based on a Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanoparticle/silicon (Si) structure, where the interface effects were measured in a homemade THz time-domain spectroscopy system. An approximately 100-nm Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanoparticle thin film on the high-resistance Si substrate was easily attained by spin-coating ferrofluids. In our experiment, a modulation depth as high as 92% was achieved at an external laser irradiance of 3.6 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This result can be explained by the accumulation of carriers at the interface of the hybrid structure, which induces intense absorption of the terahertz transmission. In addition, the limit modulated frequency of the device is ~12 kHz. The superior performance of this device for THz wave modulation in comparison to other nano-material-based terahertz modulators, and the ease of fabrication both illustrate that this is a promising method in the modulation of THz transmission. Furthermore, this modulator could also potentially provide an essential component in a wide variety of technologies, such as terahertz communications and terahertz imaging, etc.