Nonlinear optical metasurfaces for terahertz difference-frequency generation

• Applicant: Professor Mikhail Belkin, Ph.D.
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 506515587

The goal of the project is to investigate nonlinear optical metasurfaces for broadly-tunable continuous-wave terahertz generation that would overcome the high-frequency limitations of terahertz photomixers. The operating principle of the proposed metasurfaces is based on coupling of electromagnetic modes in nanoresonators with intersubband transitions in multi-quantum-well semiconductor heterostructures engineered for giant nonlinear response. We have recently demonstrated very large nonlinear response in similar structures for second harmonic and difference-frequency generation in the mid-infrared spectral range. Our calculations show, that we can create approximately 1-micron-thick metasurfaces for terahertz difference-frequency generation with the second-order nonlinear susceptibilities in the range 10^6-10^7 pm/V, up to 4 orders of magnitude larger than that of the state-of-the-art nonlinear crystals that are currently used for terahertz difference-frequency generation. Such optically-thin highly-nonlinear metasurfaces would be able to produce terahertz radiation through efficient difference-frequency mixing without phase-matching constrains and resultant bandwidth limitations associated with bulk nonlinear crystals. Experimentally, the metasurfaces will operate in a configuration similar to that used by photomixers with two commercially-available semiconductor lasers (in our case, mid-infrared quantum cascade lasers) used as optical pumps for frequency mixing. However, unlike photomixers that perform poorly at frequencies above ~2.5 THz due to time-of-flight and resistance-capacitance time constant constrains, the proposed metasurfaces are expected to generate continuous-wave terahertz powers in the range 0.1-1 mW in the 2-6 THz spectral range. The results of this project may lead to the realization of compact broadly-tunable or frequency comb terahertz sources with performance exceeding that of photomixers by several orders of magnitude in the 2-6 THz spectral range.

• DFG Programme: Research Grants