All-optical THz-wave modulation for satellite telecommunication

B. Nafradi, E. Horvath, L. Forro
École polytechnique fédérale de Lausanne (EPFL), VD, Switzerland

Keywords: magnetic photoconductor, terrahertz telecomunication, radar

Broadband optical communication, used in most of the present day telecommunication, is based on sending information-carrying light pulses. This become feasible by the development of efficient phase- and amplitude modulators. Whereas active modulation in the optical regime is well established, THz-wave manipulation and modulation is lagging behind limiting is performance. In high-speed telecommunication, the missing key component is the spatial light modulator, i.e., a component to actively control spatial transmission or reflection. We present a novel all-optical approach to actively modulate waves from 0.1 THz up to 0.5 THz in microcrystalline magnetic photoconductors. Via optical melting of the ferromagnetism, we control the THz-wave absorption of the material. Using low-fluence (up to 20 μW/cm2) red light (λ=633 nm) illumination, we demonstrate amplitude modulation of the THz-waves up to 30%. The THz-modulation amplitude remains tunable using light intensity as a control parameter. The modulation speed is found to be above ~100 kHz. Our method provides a very simple and energy-efficient technique for amplitude modulation, and it opens the way for a new family of spatial light modulator components. It offers several advantages in broadban tenability and speed compared to competing technologies proposed around metamaterials, phase-transition materials or superconductors.