Low-power optical technique using semiconductors modulates terahertz radiation

Lying in the spectral range between microwaves and infrared light, radiation at terahertz frequencies is able to safely penetrate nonconducting materials. Few compact solid-state methods for controlling the properties of these waves exist, and only bulky macroscopic modulators are proposed. Recent efforts to modulate radiation at these frequencies using semiconductors, however, shed light on how this little-understood, nonionizing region of the electromagnetic spectrum might be modulated in low-power, optically controlled terahertz devices.

Researchers demonstrated a new way to induce a broadband modulation of terahertz absorption by optically exciting a semi-insulating gallium arsenide (GaAs) crystal within the spectral range of crystal’s impurity transitions. In the findings they report in AIP Advances, the team used pulsed terahertz transmission spectroscopy to study how factors including temperature, power and spectrum of photon excitation, and the makeup of the GaAs crystal affect the terahertz waveform they induced.

Because the frequency characteristics of the modulators are limited by the relaxation rates of the electrons, adjusting for impurity type and density within a crystal allows one to control modulation frequency. Changes in temperature were also found to have affected terahertz absorption. The group reports their device achieves a modulation factor of 80 percent.

The findings potentially pave the way for other forms of manipulating terahertz waves, including beam steering and parallel data transmission. The use of this spectral range in low-power devices might lead to applications ranging from medical and security imaging to high-speed wireless data transfer.

Source: “Impurity-induced modulation of terahertz waves in optically excited GaAs,” by A. S. Kurdyubov, A. V. Trifonov, I. Ya. Gerlovin, I. V. Ignatiev, and A. V. Kavokin, AIP Advances (2017). The article can be accessed at https://doi.org/10.1063/1.4995358 .