Albert D. Grine

Single-quantum-well grating-gated terahertz plasmon detectors

A grating-gated field-effect transistor fabricated from a single-quantum well in a high-mobility GaAs–AlGaAs heterostructure is shown to function as a continuously electrically tunable photodetector of terahertz radiation via excitation of resonant plasmon modes in the well. Different harmonics of the plasmon wave vector are mapped, showing different branches of the dispersion relation. As a function of temperature, the resonant response magnitude peaks at around 30K. Both photovoltaic and photoconductive responses have been observed under different incident power and bias conditions.

Enhanced performance of resonant sub-terahertz detection in a plasmonic cavity

A multi-gate high electron mobility transistor coupled to a log-periodic antenna was engineered to detect sub-terahertz radiation through resonant excitation of plasmon modes in the channel. The device was integrated with a silicon hyper-hemispherical lens in order to enhance radiation collection and eliminate parasitic substrate modes. The continuous detector response spectrum from 185 GHz to 380 GHz indicates the presence of distinct collective plasmonic cavity modes resulting from the quantization of the plasmon wavevector. In a bolometric detection mode, a noise equivalent power of less than 50 pW/Hz1/2 and a responsivity exceeding 100 kV/W have been measured at 11.5 K.

Enhanced responsivity in membrane isolated split-grating-gate plasmonic terahertz detectors

A 50-fold increase in responsivity of plasmon resonant detectors is achieved by thermally isolating the detector on a thin membrane. Terahertz radiation is resonantly absorbed in the grating-gated channel while temperature modulation is sensed by the resistance of a narrow center region biased to pinch off. Thermal isolation enhances the temperature rise on absorption. Detectors with and without the additional thermal isolation demonstrate a linear power dependence.

Far-Infrared Spectrum Analysis Using Plasmon Modes in a Quantum-Well Transistor

Excitation of resonant plasmon modes by far-infrared (FIR) radiation in a quantum-well transistor is used to analyze the spectral content of FIR illumination at frequencies between 0.58 and 0.99 THz. A split grating gate design that allows localized pinch-off of the transistor channel greatly enhances FIR response and allows completely electrical tuning of the plasmon resonance, enabling broadband FIR spectrum analysis without moving parts. A voltage ramp applied to the gate can generate a spectrum at video rate

Heterodyne Mixing of Terahertz Quantum Cascade Lasers Using a Planar Schottky Diode

Terahertz quantum cascade lasers (QCLs) have been used together with a monolithic planar Schottky diode receiver to study the heterodyne mixing between dual internal modes of a QCL and between a single mode of a QCL and a known molecular line from a molecular gas laser. Dual-mode mixing shows that the intrinsic linewidth of a free-running QCL is les30 kHz . Mixing against a molecular laser line gives a high precision measurement of a QCLs absolute frequency and can show transient turn-on behavior in a pulsed QCL.

Heterogeneous metasurface for high temperature selective emission

We demonstrate selective emission from a heterogeneous metasurface that can survive repeated temperature cycling at 1300 K. Simulations, fabrication, and characterization were performed for a cross-over-a-backplane metasurface consisting of platinum and alumina layers on a sapphire substrate. The structure was stabilized for high temperature operation by an encapsulating alumina layer. The geometry was optimized for integration into a thermophotovoltaic (TPV) system, and was designed to have its emissivity matched to the external quantum efficiency spectrum of 0.6 eV InGaAs TPV material. We present spectral measurements of the metasurface that result in a predicted 22% optical-to-electrical power conversion efficiency in a simplified model at 1300 K. Furthermore, this broadly adaptable selective emitter design can be easily integrated into full-scale TPV systems.

Design, fabrication, and characterization of metal micromachined rectangular waveguides at 3 THz

Single-mode 75 mum x 37 mum rectangular waveguide components, including horn antennas, couplers, and bends, for operation at 3 THz have been designed and fabricated using thick gold micromachining. THz transmission through these waveguides has been quasi-optically measured at 2.92 THz. This technology offers the potential for realizing miniature integrated systems operating in the 3 THz frequency range.

Properties of Surface Metal Micromachined Rectangular Waveguide Operating Near 3 THz

Single-mode TE10 rectangular waveguides operating near 3 THz have been demonstrated. The waveguides have internal dimensions of 75 μm × 37 μm (WR-0.3) and are fabricated using an additive gold electroplating process on a silicon substrate. The impact of photoresist removal holes was minimized by full-wave design of the hole and matching structures. Waveguides were measured at three frequencies from 2.56 to 3.11 THz and demonstrated loss as low as 1.3 dB/mm at 3.11 THz, corresponding to a loss per wavelength of 0.12 dB/λ. This paper summarizes the design, fabrication, and measurement of these micromachined waveguides operating near 3 THz.

Terahertz quantum cascade laser integration with on-chip micromachined rectangular waveguides

Integration of THz quantum cascade lasers (QCLs) with single-mode 75 μm x 37 μm rectangular waveguide components, including horn antennas, couplers, and bends, for operation at 3 THz has been designed and fabricated using thick gold micromachining. Measurements on the isolated waveguide components exhibit fairly low loss and integration with THz QCLs has been demonstrated. This technology offers the potential for realizing miniature integrated systems operating in the 3 THz frequency range.

Integrated chip-scale THz technology

The quantum cascade laser (QCL) is currently the only solid-state source of coherent THz radiation capable of delivering more than 1 mW of average power at frequencies above ~ 2 THz. This power level combined with very good intrinsic frequency definition characteristics make QCLs an extremely appealing solid-state solution as compact sources for THz applications. I will present results on integrating QCLs with passive rectangular waveguides for guiding and controlling the radiation emitted by the QCLs and on the performance of a THz integrated circuit combining a THz QCL with a Schottky diode mixer to form a heterodyne receiver/transceiver.