Mid-infrared tunable metamaterials
View Patent ↗A mid-infrared tunable metamaterial comprises an array of resonators on a semiconductor substrate having a large dependence of dielectric function on carrier concentration and a semiconductor plasma resonance that lies below the operating range, such as indium antimonide. Voltage biasing of the substrate generates a resonance shift in the metamaterial response that is tunable over a broad operating range. The mid-infrared tunable metamaterials have the potential to become the building blocks of chip based active optical devices in mid-infrared ranges, which can be used for many applications, such as thermal imaging, remote sensing, and environmental monitoring.
1. An optical device, comprising a metamaterial and a circuit adapted to apply a bias voltage to the metamaterial, wherein:
the metamaterial comprises a doped semiconductor substrate and an array of resonators overlying the substrate;
the array of resonators comprises a two-dimensional repeating pattern of electrically interconnected resonator units;
each said unit is dimensioned to have at least one resonant frequency responsive to stimulation by at least one frequency of electromagnetic radiation in a range of operating frequencies at least 15 THz;
the bias circuit is adapted to apply the bias voltage between the substrate and the array of resonators;
the substrate has a semiconductor plasma resonance lying below the operating frequency range; and
the array of resonators is electromagnetically coupled at least at one said resonant frequency to the substrate; and
each resonator unit is conformed as two or more electromagnetically coupled resonator arms having different resonant frequencies.
2. The optical device of claim 1 , wherein each resonator unit comprises a ring split into two unequal arcs.
3. The optical device of claim 1 , wherein at least one of the arms is conductively coupled to the bias circuit and at least one of the arms is not conductively coupled to the bias circuit.
4. The optical device of claim 1 , wherein the array is underlain by a resistive barrier layer.
5. The optical device of claim 4 , wherein the resistive barrier layer is composed of a semiconductor material having a greater bandgap than the substrate.
6. The optical device of claim 5 , wherein the substrate comprises GaAs, the resistive barrier layer comprises Al x Ga 1-x As, and x is greater than 0 but less than 1.
7. The optical device of claim 1 , wherein:
the array has relatively low transmissivity for electromagnetic radiation at the respective resonant frequencies; and
the respective resonant frequencies are selected such that the array has relatively high transmissivity for electromagnetic radiation in a range of frequencies lying between the resonant frequencies.
8. The optical device of claim 1 , wherein:
one set of resonator arms having a common resonant frequency is electrically interconnected by direct electrical contact;
at least one further set of resonator arms having a different common resonant frequency is electrically interconnected by direct electrical contact; and
the bias circuit is switchable between at least the one set of resonator arms and the further set of resonator arms.