A group led by Mona Jarrahi, UCLA associate professor of electrical engineering, has developed an electrically operated modulator that performs across a wide range of the terahertz band with high efficiency and signal clarity. The modulator operates at room temperature and without the need for special light sources.
The modulator is based on an innovative artificial metamaterial surface — a type of surface with unique properties that is defined by the geometry of its individual building blocks, and their arrangement. The metasurface developed by Jarrahi's team is composed of an array of MEMS units that can be opened and closed using electric voltage. Opening or closing the metasurface encodes the incoming terahertz wave into a corresponding series of zeroes or ones, which are then transformed into images.
The MEMS are made from an array of vertically oriented gold membranes suspended above a Si substrate. Depending on the voltage difference between the Au membranes and the Si substrate, the Au membranes can be suspended above the Si substrate or be in contact with an array of horizontally-oriented Au patches on the substrate.
"Our new metasurface broadens the realm of metamaterials to broadband operation for the first time, and it diminishes many of the fundamental physical constraints in routing and manipulating terahertz waves, especially in terahertz imaging and spectroscopy systems," said Jarrahi, in a statement. "Our device geometry can switch from an array of microscale metallic islands to an array of interconnected metallic loops, altering its electromagnetic properties from a transparent surface to a reflecting surface, which manipulates the intensity of terahertz waves passing through over a broad range of frequencies."
The terahertz band lies between the infrared and microwave parts of the electromagnetic spectrum and can penetrate plastics and fabrics allowing the waves to be used for security. It can also be used to characterize certain materials for certain security and medical applications.
The research was published July 16 in the