Active terahertz metamaterial devices

An apparatus for modulating terahertz radiation, comprising:

• a substrate comprising a thin and lightly-doped semiconductor material;
• wherein said substrate comprises a sufficiently thin layer semiconductor material to allow the passage of a substantial portion of the terahertz radiation during portions of resonant cycles within said split-ring resonators;
• an array of multi-loop split-ring resonators on said substrate;
• said multi-loop split ring resonators of a size less that the wavelength of the incident terahertz radiation;
• at least one gap in said split-ring resonators, said gaps configured to modulate the circulation of current flow in said split-ring resonator;
• wherein said at least one gap is configured for generating a resonant response with alternating charge accumulation in response to the presence of said at least one gap;
• and
• wherein said at least one gap in said split-ring resonators drives the capacitance toward zero, and thus dampens resonant response, of said split-ring resonators in response to the presence of electrons in said gap;
• wherein said the capacitance of at least one gap in said split-ring resonators increases, and thus increases resonant response, of said split-ring resonators in response to the depletion of electrons from said gap;
• electrical contacts coupled to said array of multi-loop split-ring resonators for exciting electrons in said substrate to control their position in relation to said at least gap in said split-ring resonators and thus modulate the resonance of said array of multi-loop split-ring resonators for controlling the transmissive ratio of said apparatus.

A surface emitting (SE) quantum cascade laser (QCL), comprising:

• a substrate comprising a doped semiconductor material;
• a first electrode on the surface of said substrate;
• an active region upon said first electrode;
• a second electrode comprising an array of multi-loop split-ring resonators on the surface of said active region;
• said multi-loop split ring resonators of a size less that the wavelength of the characteristic terahertz radiation;
• at least one gap in said split-ring resonators, said gap configured to modulate the circulation of current flow in said split-ring resonator;
• wherein said at least one gap is configured for generating a resonant response with alternating charge accumulation in response to the presence of said at least one gap;
• and
• contacts on said first electrode and said second electrode through which a modulation signal is received for exciting electrons in said active region for modulating the resonance of said array of multi-loop split-ring resonators to control the surface emission from said transmissive ratio of said quantum cascade laser.

A method of modulating transmissivity of a metamaterial structure at terahertz frequencies, comprising:

• establishing a periodic array of metamaterial elements upon a semiconductor device layer;
• configuring each metamaterial element to have multiple loops with at least one gap;
• receiving an electrical modulation signal for controlling the transmissivity of said metamaterial structure;
• depleting the number of electrons near said at least one gap of said periodic array of metamaterial structures to provide a first level of transmissivity in response to a first level of electrical modulation;
• enhancing the number of electrons near said at least one gap of said periodic array of metamaterial structures to provide a second level of transmissivity in response to a second level of electrical modulation;
• and
• generating a resonant response with alternating charge accumulation near said at least one gap in each said metamaterial element in said periodic array in response to the presence of electrons near said at least one gap in each said metamaterial element toward changing transmissivity.