Terahertz Radiation Detection by Field Effect Transistor in Magnetic Field

We report on terahertz radiation detection with InGaAs/InAlAs Field Effect Transistors in quantizing magnetic field. The photovoltaic detection signal is investigated at 4.2 K as a function of the gate voltage and magnetic field. Oscillations analogous to the Shubnikov-de Haas oscillations, as well as their strong enhancement at the cyclotron resonance, are observed. The results are quantitatively described by a recent theory, showing that the detection is due to rectification of the terahertz radiation by plasma waves related nonlinearities in the gated part of the channel.Comment: 4 pages, 3 figure

A Test Vector Generation Method Based on Symbol Error Probabilities for Low-Complexity Chase Soft-Decision Reed-Solomon Decoding

© 2019 IEEE. Personal use of this material is permitted. Permissíon from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertisíng or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] This paper presents a low-complexity chase (LCC) decoder for Reed-Solomon (RS) codes, which uses a novel method for the selection of test vectors that is based on the analysis of the symbol error probabilities derived from simulations. Our results show that the same performance as the classical LCC is achieved with a lower number of test vectors. For example, the amount of test vectors is reduced by half and by 1/16 for the RS(255,239) and RS(255,129) codes, respectively. We provide an evidence that the proposed method is suitable for RS codes with different rates and Galois fields. In order to demonstrate that the proposed method results in a reduction of the complexity of the decoder, we also present a hardware architecture for an RS(255,239) decoder that uses 16 test vectors. This decoder achieves a coding gain of 0.56 dB at the frame error rate that is equal to 10(-6) compared with hard-decision decoding, which is higher than that of an eta = 5 LCC. The implementation results in ASIC show that a throughput of 3.6 Gb/s can be reached in a 90-nm process and 29.1XORs are required. The implementation results in Virtex-7 FPGA devices show that the decoder reaches 2.5 Gb/s and requires 5085 LUTs.This work was supported by the Spanish Ministerio de Economia y Competitividad and FEDER under Grant TEC2015-70858-C2-2-R. This paper was recommended by Associate Editor M. Boukadoum.Valls Coquillat, J.; Torres Carot, V.; Canet Subiela, MJ.; García-Herrero, FM. (2019). A Test Vector Generation Method Based on Symbol Error Probabilities for Low-Complexity Chase Soft-Decision Reed-Solomon Decoding. IEEE Transactions on Circuits and Systems I Regular Papers. 66(6):2198-2207. https://doi.org/10.1109/TCSI.2018.2882876S2198220766

Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses

Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens

Plasmonic terahertz detection by a double-grating-gate field-effect transistor structure with an asymmetric unit cell

Plasmonic terahertz detection by a double-grating gate field-effect transistor structure with an asymmetric unit cell is studied theoretically. Detection responsivity exceeding 8 kV/W at room temperature in the photovoltaic response mode is predicted for strong asymmetry of the structure unit cell. This value of the responsivity is an order of magnitude greater than reported previously for the other types of uncooled plasmonic terahertz detectors. Such enormous responsivity can be obtained without using any supplementary antenna elements because the double-grating gate acts as an aerial matched antenna that effectively couples the incoming terahertz radiation to plasma oscillations in the structure channel.Comment: Submitted to APL, 8 pages, 2 figure

Graphene field-effect transistors as room-temperature terahertz detectors.

The unique optoelectronic properties of graphene make it an ideal platform for a variety of photonic applications, including fast photodetectors, transparent electrodes in displays and photovoltaic modules, optical modulators, plasmonic devices, microcavities, and ultra-fast lasers. Owing to its high carrier mobility, gapless spectrum and frequency-independent absorption, graphene is a very promising material for the development of detectors and modulators operating in the terahertz region of the electromagnetic spectrum (wavelengths in the hundreds of micrometres), still severely lacking in terms of solid-state devices. Here we demonstrate terahertz detectors based on antenna-coupled graphene field-effect transistors. These exploit the nonlinear response to the oscillating radiation field at the gate electrode, with contributions of thermoelectric and photoconductive origin. We demonstrate room temperature operation at 0.3 THz, showing that our devices can already be used in realistic settings, enabling large-area, fast imaging of macroscopic samples

Room Temperature Coherent and Voltage Tunable Terahertz Emission from Nanometer-Sized Field Effect Transistors

We report on reflective electro-optic sampling measurements of TeraHertz emission from nanometer-gate-length InGaAs-based high electron mobility transistors. The room temperature coherent gate-voltage tunable emission is demonstrated. We establish that the physical mechanism of the coherent TeraHertz emission is related to the plasma waves driven by simultaneous current and optical excitation. A significant shift of the plasma frequency and the narrowing of the emission with increasing channel's current are observed and explained as due to the increase of the carriers density and drift velocity.Comment: 3 figure

High performance bilayer-graphene Terahertz detectors

We report bilayer-graphene field effect transistors operating as THz broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity $\sim 1.2V/W (1.3 mA/W)$ and a noise equivalent power $\sim 2\times 10^{-9} W/Hz^{-1/2}$ in the 0.29-0.38 THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems